Merge branch 'main' into heic-support

src/ImageSharp/Formats/Jpeg/Components/Decoder/JpegBitReader.cs

@@ -22,6 +22,9 @@ internal struct JpegBitReader
     // Whether there is no more good data to pull from the stream for the current mcu.
     private bool badData;
 
+    // How many times have we hit the eof.
+    private int eofHitCount;
+
     public JpegBitReader(BufferedReadStream stream)
     {
         this.stream = stream;
@@ -31,6 +34,7 @@ internal struct JpegBitReader
         this.MarkerPosition = 0;
         this.badData = false;
         this.NoData = false;
+        this.eofHitCount = 0;
     }
 
     /// <summary>
@@ -219,11 +223,16 @@ internal struct JpegBitReader
         // we know we have hit the EOI and completed decoding the scan buffer.
         if (value == -1 || (this.badData && this.data == 0 && this.stream.Position >= this.stream.Length))
         {
-            // We've encountered the end of the file stream which means there's no EOI marker
+            // We've hit the end of the file stream more times than allowed which means there's no EOI marker
             // in the image or the SOS marker has the wrong dimensions set.
-            this.badData = true;
-            this.NoData = true;
-            value = 0;
+            if (this.eofHitCount > JpegConstants.Huffman.FetchLoop)
+            {
+                this.badData = true;
+                this.NoData = true;
+                value = 0;
+            }
+
+            this.eofHitCount++;
         }
 
         return value;

src/ImageSharp/Formats/Jpeg/Components/Decoder/SpectralConverter{TPixel}.cs

@@ -201,7 +201,8 @@ internal class SpectralConverter<TPixel> : SpectralConverter, IDisposable
         this.pixelBuffer = allocator.Allocate2D<TPixel>(
             pixelSize.Width,
             pixelSize.Height,
-            this.Configuration.PreferContiguousImageBuffers);
+            this.Configuration.PreferContiguousImageBuffers,
+            AllocationOptions.Clean);
         this.paddedProxyPixelRow = allocator.Allocate<TPixel>(pixelSize.Width + 3);
 
         // Component processors from spectral to RGB

src/ImageSharp/Formats/Png/PngDecoderCore.cs

@@ -234,8 +234,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                                 PngThrowHelper.ThrowMissingFrameControl();
                             }
 
-                            previousFrameControl ??= new((uint)this.header.Width, (uint)this.header.Height);
-                            this.InitializeFrame(previousFrameControl.Value, currentFrameControl.Value, image, previousFrame, out currentFrame);
+                            this.InitializeFrame(previousFrameControl, currentFrameControl.Value, image, previousFrame, out currentFrame);
 
                             this.currentStream.Position += 4;
                             this.ReadScanlines(
@@ -246,11 +245,16 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                                 currentFrameControl.Value,
                                 cancellationToken);
 
-                            previousFrame = currentFrame;
-                            previousFrameControl = currentFrameControl;
+                            // if current frame dispose is restore to previous, then from future frame's perspective, it never happened
+                            if (currentFrameControl.Value.DisposeOperation != PngDisposalMethod.RestoreToPrevious)
+                            {
+                                previousFrame = currentFrame;
+                                previousFrameControl = currentFrameControl;
+                            }
+
                             break;
                         case PngChunkType.Data:
-
+                            pngMetadata.AnimateRootFrame = currentFrameControl != null;
                             currentFrameControl ??= new((uint)this.header.Width, (uint)this.header.Height);
                             if (image is null)
                             {
@@ -267,9 +271,12 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
                                 this.ReadNextDataChunk,
                                 currentFrameControl.Value,
                                 cancellationToken);
+                            if (pngMetadata.AnimateRootFrame)
+                            {
+                                previousFrame = currentFrame;
+                                previousFrameControl = currentFrameControl;
+                            }
 
-                            previousFrame = currentFrame;
-                            previousFrameControl = currentFrameControl;
                             break;
                         case PngChunkType.Palette:
                             this.palette = chunk.Data.GetSpan().ToArray();
@@ -638,7 +645,7 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
     /// <param name="previousFrame">The previous frame.</param>
     /// <param name="frame">The created frame</param>
     private void InitializeFrame<TPixel>(
-        FrameControl previousFrameControl,
+        FrameControl? previousFrameControl,
         FrameControl currentFrameControl,
         Image<TPixel> image,
         ImageFrame<TPixel>? previousFrame,
@@ -651,12 +658,16 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
         frame = image.Frames.AddFrame(previousFrame ?? image.Frames.RootFrame);
 
         // If the first `fcTL` chunk uses a `dispose_op` of APNG_DISPOSE_OP_PREVIOUS it should be treated as APNG_DISPOSE_OP_BACKGROUND.
-        if (previousFrameControl.DisposeOperation == PngDisposalMethod.RestoreToBackground
-            || (previousFrame is null && previousFrameControl.DisposeOperation == PngDisposalMethod.RestoreToPrevious))
+        // So, if restoring to before first frame, clear entire area. Same if first frame (previousFrameControl null).
+        if (previousFrameControl == null || (previousFrame is null && previousFrameControl.Value.DisposeOperation == PngDisposalMethod.RestoreToPrevious))
+        {
+            Buffer2DRegion<TPixel> pixelRegion = frame.PixelBuffer.GetRegion();
+            pixelRegion.Clear();
+        }
+        else if (previousFrameControl.Value.DisposeOperation == PngDisposalMethod.RestoreToBackground)
         {
-            Rectangle restoreArea = previousFrameControl.Bounds;
-            Rectangle interest = Rectangle.Intersect(frame.Bounds(), restoreArea);
-            Buffer2DRegion<TPixel> pixelRegion = frame.PixelBuffer.GetRegion(interest);
+            Rectangle restoreArea = previousFrameControl.Value.Bounds;
+            Buffer2DRegion<TPixel> pixelRegion = frame.PixelBuffer.GetRegion(restoreArea);
             pixelRegion.Clear();
         }
 
@@ -1972,6 +1983,9 @@ internal sealed class PngDecoderCore : IImageDecoderInternals
         }
 
         // We rent the buffer here to return it afterwards in Decode()
+        // We don't want to throw a degenerated memory exception here as we want to allow partial decoding
+        // so limit the length.
+        length = (int)Math.Min(length, this.currentStream.Length - this.currentStream.Position);
         IMemoryOwner<byte> buffer = this.configuration.MemoryAllocator.Allocate<byte>(length, AllocationOptions.Clean);
 
         this.currentStream.Read(buffer.GetSpan(), 0, length);

src/ImageSharp/Formats/Png/PngEncoderCore.cs

@@ -167,6 +167,7 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
 
         ImageFrame<TPixel>? clonedFrame = null;
         ImageFrame<TPixel> currentFrame = image.Frames.RootFrame;
+        int currentFrameIndex = 0;
 
         bool clearTransparency = this.encoder.TransparentColorMode is PngTransparentColorMode.Clear;
         if (clearTransparency)
@@ -195,29 +196,50 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
 
         if (image.Frames.Count > 1)
         {
-            this.WriteAnimationControlChunk(stream, (uint)image.Frames.Count, pngMetadata.RepeatCount);
+            this.WriteAnimationControlChunk(stream, (uint)(image.Frames.Count - (pngMetadata.AnimateRootFrame ? 0 : 1)), pngMetadata.RepeatCount);
+        }
+
+        // If the first frame isn't animated, write it as usual and skip it when writing animated frames
+        if (!pngMetadata.AnimateRootFrame || image.Frames.Count == 1)
+        {
+            FrameControl frameControl = new((uint)this.width, (uint)this.height);
+            this.WriteDataChunks(frameControl, currentFrame.PixelBuffer.GetRegion(), quantized, stream, false);
+            currentFrameIndex++;
+        }
 
-            // Write the first frame.
+        if (image.Frames.Count > 1)
+        {
+            // Write the first animated frame.
+            currentFrame = image.Frames[currentFrameIndex];
             PngFrameMetadata frameMetadata = GetPngFrameMetadata(currentFrame);
             PngDisposalMethod previousDisposal = frameMetadata.DisposalMethod;
             FrameControl frameControl = this.WriteFrameControlChunk(stream, frameMetadata, currentFrame.Bounds(), 0);
-            this.WriteDataChunks(frameControl, currentFrame.PixelBuffer.GetRegion(), quantized, stream, false);
+            uint sequenceNumber = 1;
+            if (pngMetadata.AnimateRootFrame)
+            {
+                this.WriteDataChunks(frameControl, currentFrame.PixelBuffer.GetRegion(), quantized, stream, false);
+            }
+            else
+            {
+                sequenceNumber += this.WriteDataChunks(frameControl, currentFrame.PixelBuffer.GetRegion(), quantized, stream, true);
+            }
+
+            currentFrameIndex++;
 
             // Capture the global palette for reuse on subsequent frames.
             ReadOnlyMemory<TPixel>? previousPalette = quantized?.Palette.ToArray();
 
             // Write following frames.
-            uint increment = 0;
             ImageFrame<TPixel> previousFrame = image.Frames.RootFrame;
 
             // This frame is reused to store de-duplicated pixel buffers.
             using ImageFrame<TPixel> encodingFrame = new(image.Configuration, previousFrame.Size());
 
-            for (int i = 1; i < image.Frames.Count; i++)
+            for (; currentFrameIndex < image.Frames.Count; currentFrameIndex++)
             {
                 ImageFrame<TPixel>? prev = previousDisposal == PngDisposalMethod.RestoreToBackground ? null : previousFrame;
-                currentFrame = image.Frames[i];
-                ImageFrame<TPixel>? nextFrame = i < image.Frames.Count - 1 ? image.Frames[i + 1] : null;
+                currentFrame = image.Frames[currentFrameIndex];
+                ImageFrame<TPixel>? nextFrame = currentFrameIndex < image.Frames.Count - 1 ? image.Frames[currentFrameIndex + 1] : null;
 
                 frameMetadata = GetPngFrameMetadata(currentFrame);
                 bool blend = frameMetadata.BlendMethod == PngBlendMethod.Over;
@@ -238,22 +260,17 @@ internal sealed class PngEncoderCore : IImageEncoderInternals, IDisposable
                 }
 
                 // Each frame control sequence number must be incremented by the number of frame data chunks that follow.
-                frameControl = this.WriteFrameControlChunk(stream, frameMetadata, bounds, (uint)i + increment);
+                frameControl = this.WriteFrameControlChunk(stream, frameMetadata, bounds, sequenceNumber);
 
                 // Dispose of previous quantized frame and reassign.
                 quantized?.Dispose();
                 quantized = this.CreateQuantizedImageAndUpdateBitDepth(pngMetadata, encodingFrame, bounds, previousPalette);
-                increment += this.WriteDataChunks(frameControl, encodingFrame.PixelBuffer.GetRegion(bounds), quantized, stream, true);
+                sequenceNumber += this.WriteDataChunks(frameControl, encodingFrame.PixelBuffer.GetRegion(bounds), quantized, stream, true) + 1;
 
                 previousFrame = currentFrame;
                 previousDisposal = frameMetadata.DisposalMethod;
             }
         }
-        else
-        {
-            FrameControl frameControl = new((uint)this.width, (uint)this.height);
-            this.WriteDataChunks(frameControl, currentFrame.PixelBuffer.GetRegion(), quantized, stream, false);
-        }
 
         this.WriteEndChunk(stream);
 

src/ImageSharp/Formats/Png/PngMetadata.cs

@@ -29,6 +29,7 @@ public class PngMetadata : IDeepCloneable
         this.InterlaceMethod = other.InterlaceMethod;
         this.TransparentColor = other.TransparentColor;
         this.RepeatCount = other.RepeatCount;
+        this.AnimateRootFrame = other.AnimateRootFrame;
 
         if (other.ColorTable?.Length > 0)
         {
@@ -83,6 +84,11 @@ public class PngMetadata : IDeepCloneable
     /// </summary>
     public uint RepeatCount { get; set; } = 1;
 
+    /// <summary>
+    ///  Gets or sets a value indicating whether the root frame is shown as part of the animated sequence
+    /// </summary>
+    public bool AnimateRootFrame { get; set; } = true;
+
     /// <inheritdoc/>
     public IDeepCloneable DeepClone() => new PngMetadata(this);
 

src/ImageSharp/Formats/Png/PngScanlineProcessor.cs

@@ -180,11 +180,13 @@ internal static class PngScanlineProcessor
         ref byte scanlineSpanRef = ref MemoryMarshal.GetReference(scanlineSpan);
         ref TPixel rowSpanRef = ref MemoryMarshal.GetReference(rowSpan);
         ref Color paletteBase = ref MemoryMarshal.GetReference(palette.Value.Span);
+        uint offset = pixelOffset + frameControl.XOffset;
+        int maxIndex = palette.Value.Length - 1;
 
-        for (nuint x = pixelOffset, o = 0; x < frameControl.XMax; x += increment, o++)
+        for (nuint x = offset, o = 0; x < frameControl.XMax; x += increment, o++)
         {
             uint index = Unsafe.Add(ref scanlineSpanRef, o);
-            Unsafe.Add(ref rowSpanRef, x) = TPixel.FromRgba32(Unsafe.Add(ref paletteBase, index).ToPixel<Rgba32>());
+            Unsafe.Add(ref rowSpanRef, x) = TPixel.FromRgba32(Unsafe.Add(ref paletteBase, (int)Math.Min(index, maxIndex)).ToPixel<Rgba32>());
         }
     }
 

src/ImageSharp/Formats/Tga/TgaDecoderCore.cs

@@ -84,7 +84,7 @@ internal sealed class TgaDecoderCore : IImageDecoderInternals
                 throw new UnknownImageFormatException("Width or height cannot be 0");
             }
 
-            Image<TPixel> image = Image.CreateUninitialized<TPixel>(this.configuration, this.fileHeader.Width, this.fileHeader.Height, this.metadata);
+            Image<TPixel> image = new(this.configuration, this.fileHeader.Width, this.fileHeader.Height, this.metadata);
             Buffer2D<TPixel> pixels = image.GetRootFramePixelBuffer();
 
             if (this.fileHeader.ColorMapType == 1)

src/ImageSharp/Formats/Webp/BitWriter/BitWriterBase.cs

@@ -88,7 +88,8 @@ internal abstract class BitWriterBase
     /// <param name="iccProfile">The color profile.</param>
     /// <param name="hasAlpha">Flag indicating, if a alpha channel is present.</param>
     /// <param name="hasAnimation">Flag indicating, if an animation parameter is present.</param>
-    public static void WriteTrunksBeforeData(
+    /// <returns>A <see cref="WebpVp8X"/> or a default instance.</returns>
+    public static WebpVp8X WriteTrunksBeforeData(
         Stream stream,
         uint width,
         uint height,
@@ -102,16 +103,19 @@ internal abstract class BitWriterBase
         RiffHelper.BeginWriteRiffFile(stream, WebpConstants.WebpFourCc);
 
         // Write VP8X, header if necessary.
+        WebpVp8X vp8x = default;
         bool isVp8X = exifProfile != null || xmpProfile != null || iccProfile != null || hasAlpha || hasAnimation;
         if (isVp8X)
         {
-            WriteVp8XHeader(stream, exifProfile, xmpProfile, iccProfile, width, height, hasAlpha, hasAnimation);
+            vp8x = WriteVp8XHeader(stream, exifProfile, xmpProfile, iccProfile, width, height, hasAlpha, hasAnimation);
 
             if (iccProfile != null)
             {
                 RiffHelper.WriteChunk(stream, (uint)WebpChunkType.Iccp, iccProfile.ToByteArray());
             }
         }
+
+        return vp8x;
     }
 
     /// <summary>
@@ -124,10 +128,16 @@ internal abstract class BitWriterBase
     /// Write the trunks after data trunk.
     /// </summary>
     /// <param name="stream">The stream to write to.</param>
-    /// <param name="exifProfile">The exif profile.</param>
+    /// <param name="vp8x">The VP8X chunk.</param>
+    /// <param name="updateVp8x">Whether to update the chunk.</param>
+    /// <param name="initialPosition">The initial position of the stream before encoding.</param>
+    /// <param name="exifProfile">The EXIF profile.</param>
     /// <param name="xmpProfile">The XMP profile.</param>
     public static void WriteTrunksAfterData(
         Stream stream,
+        in WebpVp8X vp8x,
+        bool updateVp8x,
+        long initialPosition,
         ExifProfile? exifProfile,
         XmpProfile? xmpProfile)
     {
@@ -141,7 +151,7 @@ internal abstract class BitWriterBase
             RiffHelper.WriteChunk(stream, (uint)WebpChunkType.Xmp, xmpProfile.Data);
         }
 
-        RiffHelper.EndWriteRiffFile(stream, 4);
+        RiffHelper.EndWriteRiffFile(stream, in vp8x, updateVp8x, initialPosition);
     }
 
     /// <summary>
@@ -186,19 +196,21 @@ internal abstract class BitWriterBase
     /// Writes a VP8X header to the stream.
     /// </summary>
     /// <param name="stream">The stream to write to.</param>
-    /// <param name="exifProfile">A exif profile or null, if it does not exist.</param>
-    /// <param name="xmpProfile">A XMP profile or null, if it does not exist.</param>
+    /// <param name="exifProfile">An EXIF profile or null, if it does not exist.</param>
+    /// <param name="xmpProfile">An XMP profile or null, if it does not exist.</param>
     /// <param name="iccProfile">The color profile.</param>
     /// <param name="width">The width of the image.</param>
     /// <param name="height">The height of the image.</param>
     /// <param name="hasAlpha">Flag indicating, if a alpha channel is present.</param>
     /// <param name="hasAnimation">Flag indicating, if an animation parameter is present.</param>
-    protected static void WriteVp8XHeader(Stream stream, ExifProfile? exifProfile, XmpProfile? xmpProfile, IccProfile? iccProfile, uint width, uint height, bool hasAlpha, bool hasAnimation)
+    protected static WebpVp8X WriteVp8XHeader(Stream stream, ExifProfile? exifProfile, XmpProfile? xmpProfile, IccProfile? iccProfile, uint width, uint height, bool hasAlpha, bool hasAnimation)
     {
         WebpVp8X chunk = new(hasAnimation, xmpProfile != null, exifProfile != null, hasAlpha, iccProfile != null, width, height);
 
         chunk.Validate(MaxDimension, MaxCanvasPixels);
 
         chunk.WriteTo(stream);
+
+        return chunk;
     }
 }

src/ImageSharp/Formats/Webp/Chunks/WebpVp8X.cs

@@ -3,7 +3,7 @@
 
 namespace SixLabors.ImageSharp.Formats.Webp.Chunks;
 
-internal readonly struct WebpVp8X
+internal readonly struct WebpVp8X : IEquatable<WebpVp8X>
 {
     public WebpVp8X(bool hasAnimation, bool hasXmp, bool hasExif, bool hasAlpha, bool hasIcc, uint width, uint height)
     {
@@ -51,6 +51,24 @@ internal readonly struct WebpVp8X
     /// </summary>
     public uint Height { get; }
 
+    public static bool operator ==(WebpVp8X left, WebpVp8X right) => left.Equals(right);
+
+    public static bool operator !=(WebpVp8X left, WebpVp8X right) => !(left == right);
+
+    public override bool Equals(object? obj) => obj is WebpVp8X x && this.Equals(x);
+
+    public bool Equals(WebpVp8X other)
+        => this.HasAnimation == other.HasAnimation
+        && this.HasXmp == other.HasXmp
+        && this.HasExif == other.HasExif
+        && this.HasAlpha == other.HasAlpha
+        && this.HasIcc == other.HasIcc
+        && this.Width == other.Width
+        && this.Height == other.Height;
+
+    public override int GetHashCode()
+        => HashCode.Combine(this.HasAnimation, this.HasXmp, this.HasExif, this.HasAlpha, this.HasIcc, this.Width, this.Height);
+
     public void Validate(uint maxDimension, ulong maxCanvasPixels)
     {
         if (this.Width > maxDimension || this.Height > maxDimension)
@@ -65,6 +83,9 @@ internal readonly struct WebpVp8X
         }
     }
 
+    public WebpVp8X WithAlpha(bool hasAlpha)
+        => new(this.HasAnimation, this.HasXmp, this.HasExif, hasAlpha, this.HasIcc, this.Width, this.Height);
+
     public void WriteTo(Stream stream)
     {
         byte flags = 0;

src/ImageSharp/Formats/Webp/Lossless/Vp8LEncoder.cs

@@ -236,7 +236,7 @@ internal class Vp8LEncoder : IDisposable
     /// </summary>
     public Vp8LHashChain HashChain { get; }
 
-    public void EncodeHeader<TPixel>(Image<TPixel> image, Stream stream, bool hasAnimation)
+    public WebpVp8X EncodeHeader<TPixel>(Image<TPixel> image, Stream stream, bool hasAnimation)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         // Write bytes from the bit-writer buffer to the stream.
@@ -246,7 +246,8 @@ internal class Vp8LEncoder : IDisposable
         ExifProfile exifProfile = this.skipMetadata ? null : metadata.ExifProfile;
         XmpProfile xmpProfile = this.skipMetadata ? null : metadata.XmpProfile;
 
-        BitWriterBase.WriteTrunksBeforeData(
+        // The alpha flag is updated following encoding.
+        WebpVp8X vp8x = BitWriterBase.WriteTrunksBeforeData(
             stream,
             (uint)image.Width,
             (uint)image.Height,
@@ -261,9 +262,11 @@ internal class Vp8LEncoder : IDisposable
             WebpMetadata webpMetadata = WebpCommonUtils.GetWebpMetadata(image);
             BitWriterBase.WriteAnimationParameter(stream, webpMetadata.BackgroundColor, webpMetadata.RepeatCount);
         }
+
+        return vp8x;
     }
 
-    public void EncodeFooter<TPixel>(Image<TPixel> image, Stream stream)
+    public void EncodeFooter<TPixel>(Image<TPixel> image, in WebpVp8X vp8x, bool hasAlpha, Stream stream, long initialPosition)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         // Write bytes from the bit-writer buffer to the stream.
@@ -272,7 +275,9 @@ internal class Vp8LEncoder : IDisposable
         ExifProfile exifProfile = this.skipMetadata ? null : metadata.ExifProfile;
         XmpProfile xmpProfile = this.skipMetadata ? null : metadata.XmpProfile;
 
-        BitWriterBase.WriteTrunksAfterData(stream, exifProfile, xmpProfile);
+        bool updateVp8x = hasAlpha && vp8x != default;
+        WebpVp8X updated = updateVp8x ? vp8x.WithAlpha(true) : vp8x;
+        BitWriterBase.WriteTrunksAfterData(stream, in updated, updateVp8x, initialPosition, exifProfile, xmpProfile);
     }
 
     /// <summary>
@@ -284,7 +289,8 @@ internal class Vp8LEncoder : IDisposable
     /// <param name="frameMetadata">The frame metadata.</param>
     /// <param name="stream">The <see cref="Stream"/> to encode the image data to.</param>
     /// <param name="hasAnimation">Flag indicating, if an animation parameter is present.</param>
-    public void Encode<TPixel>(ImageFrame<TPixel> frame, Rectangle bounds, WebpFrameMetadata frameMetadata, Stream stream, bool hasAnimation)
+    /// <returns>A <see cref="bool"/> indicating whether the frame contains an alpha channel.</returns>
+    public bool Encode<TPixel>(ImageFrame<TPixel> frame, Rectangle bounds, WebpFrameMetadata frameMetadata, Stream stream, bool hasAnimation)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         // Convert image pixels to bgra array.
@@ -323,6 +329,8 @@ internal class Vp8LEncoder : IDisposable
         {
             RiffHelper.EndWriteChunk(stream, prevPosition);
         }
+
+        return hasAlpha;
     }
 
     /// <summary>
@@ -501,7 +509,7 @@ internal class Vp8LEncoder : IDisposable
     /// <typeparam name="TPixel">The type of the pixels.</typeparam>
     /// <param name="pixels">The frame pixel buffer to convert.</param>
     /// <returns>true, if the image is non opaque.</returns>
-    private bool ConvertPixelsToBgra<TPixel>(Buffer2DRegion<TPixel> pixels)
+    public bool ConvertPixelsToBgra<TPixel>(Buffer2DRegion<TPixel> pixels)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         bool nonOpaque = false;

src/ImageSharp/Formats/Webp/Lossy/Vp8Encoder.cs

@@ -310,7 +310,7 @@ internal class Vp8Encoder : IDisposable
     /// </summary>
     private int MbHeaderLimit { get; }
 
-    public void EncodeHeader<TPixel>(Image<TPixel> image, Stream stream, bool hasAlpha, bool hasAnimation)
+    public WebpVp8X EncodeHeader<TPixel>(Image<TPixel> image, Stream stream, bool hasAlpha, bool hasAnimation)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         // Write bytes from the bitwriter buffer to the stream.
@@ -320,7 +320,7 @@ internal class Vp8Encoder : IDisposable
         ExifProfile exifProfile = this.skipMetadata ? null : metadata.ExifProfile;
         XmpProfile xmpProfile = this.skipMetadata ? null : metadata.XmpProfile;
 
-        BitWriterBase.WriteTrunksBeforeData(
+        WebpVp8X vp8x = BitWriterBase.WriteTrunksBeforeData(
             stream,
             (uint)image.Width,
             (uint)image.Height,
@@ -335,9 +335,11 @@ internal class Vp8Encoder : IDisposable
             WebpMetadata webpMetadata = WebpCommonUtils.GetWebpMetadata(image);
             BitWriterBase.WriteAnimationParameter(stream, webpMetadata.BackgroundColor, webpMetadata.RepeatCount);
         }
+
+        return vp8x;
     }
 
-    public void EncodeFooter<TPixel>(Image<TPixel> image, Stream stream)
+    public void EncodeFooter<TPixel>(Image<TPixel> image, in WebpVp8X vp8x, bool hasAlpha, Stream stream, long initialPosition)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         // Write bytes from the bitwriter buffer to the stream.
@@ -346,7 +348,9 @@ internal class Vp8Encoder : IDisposable
         ExifProfile exifProfile = this.skipMetadata ? null : metadata.ExifProfile;
         XmpProfile xmpProfile = this.skipMetadata ? null : metadata.XmpProfile;
 
-        BitWriterBase.WriteTrunksAfterData(stream, exifProfile, xmpProfile);
+        bool updateVp8x = hasAlpha && vp8x != default;
+        WebpVp8X updated = updateVp8x ? vp8x.WithAlpha(true) : vp8x;
+        BitWriterBase.WriteTrunksAfterData(stream, in updated, updateVp8x, initialPosition, exifProfile, xmpProfile);
     }
 
     /// <summary>
@@ -357,9 +361,10 @@ internal class Vp8Encoder : IDisposable
     /// <param name="stream">The stream to encode the image data to.</param>
     /// <param name="bounds">The region of interest within the frame to encode.</param>
     /// <param name="frameMetadata">The frame metadata.</param>
-    public void EncodeAnimation<TPixel>(ImageFrame<TPixel> frame, Stream stream, Rectangle bounds, WebpFrameMetadata frameMetadata)
-        where TPixel : unmanaged, IPixel<TPixel> =>
-        this.Encode(stream, frame, bounds, frameMetadata, true, null);
+    /// <returns>A <see cref="bool"/> indicating whether the frame contains an alpha channel.</returns>
+    public bool EncodeAnimation<TPixel>(ImageFrame<TPixel> frame, Stream stream, Rectangle bounds, WebpFrameMetadata frameMetadata)
+        where TPixel : unmanaged, IPixel<TPixel>
+        => this.Encode(stream, frame, bounds, frameMetadata, true, null);
 
     /// <summary>
     /// Encodes the static image frame to the specified stream.
@@ -384,7 +389,8 @@ internal class Vp8Encoder : IDisposable
     /// <param name="frameMetadata">The frame metadata.</param>
     /// <param name="hasAnimation">Flag indicating, if an animation parameter is present.</param>
     /// <param name="image">The image to encode from.</param>
-    private void Encode<TPixel>(Stream stream, ImageFrame<TPixel> frame, Rectangle bounds, WebpFrameMetadata frameMetadata, bool hasAnimation, Image<TPixel> image)
+    /// <returns>A <see cref="bool"/> indicating whether the frame contains an alpha channel.</returns>
+    private bool Encode<TPixel>(Stream stream, ImageFrame<TPixel> frame, Rectangle bounds, WebpFrameMetadata frameMetadata, bool hasAnimation, Image<TPixel> image)
         where TPixel : unmanaged, IPixel<TPixel>
     {
         int width = bounds.Width;
@@ -514,6 +520,8 @@ internal class Vp8Encoder : IDisposable
         {
             encodedAlphaData?.Dispose();
         }
+
+        return hasAlpha;
     }
 
     /// <inheritdoc/>

src/ImageSharp/Formats/Webp/RiffHelper.cs

@@ -3,6 +3,7 @@
 
 using System.Buffers.Binary;
 using System.Text;
+using SixLabors.ImageSharp.Formats.Webp.Chunks;
 
 namespace SixLabors.ImageSharp.Formats.Webp;
 
@@ -107,6 +108,7 @@ internal static class RiffHelper
             position++;
         }
 
+        // Add the size of the encoded file to the Riff header.
         BinaryPrimitives.WriteUInt32LittleEndian(buffer, dataSize);
         stream.Position = sizePosition;
         stream.Write(buffer);
@@ -120,5 +122,18 @@ internal static class RiffHelper
         return sizePosition;
     }
 
-    public static void EndWriteRiffFile(Stream stream, long sizePosition) => EndWriteChunk(stream, sizePosition);
+    public static void EndWriteRiffFile(Stream stream, in WebpVp8X vp8x, bool updateVp8x, long sizePosition)
+    {
+        EndWriteChunk(stream, sizePosition + 4);
+
+        // Write the VP8X chunk if necessary.
+        if (updateVp8x)
+        {
+            long position = stream.Position;
+
+            stream.Position = sizePosition + 12;
+            vp8x.WriteTo(stream);
+            stream.Position = position;
+        }
+    }
 }

src/ImageSharp/Formats/Webp/WebpChunkParsingUtils.cs

@@ -2,7 +2,6 @@
 // Licensed under the Six Labors Split License.
 
 using System.Buffers.Binary;
-using System.Drawing;
 using SixLabors.ImageSharp.Formats.Webp.BitReader;
 using SixLabors.ImageSharp.Formats.Webp.Lossy;
 using SixLabors.ImageSharp.IO;

src/ImageSharp/Formats/Webp/WebpDecoderCore.cs

@@ -54,7 +54,7 @@ internal sealed class WebpDecoderCore : IImageDecoderInternals, IDisposable
     /// <summary>
     /// The flag to decide how to handle the background color in the Animation Chunk.
     /// </summary>
-    private BackgroundColorHandling backgroundColorHandling;
+    private readonly BackgroundColorHandling backgroundColorHandling;
 
     /// <summary>
     /// Initializes a new instance of the <see cref="WebpDecoderCore"/> class.

src/ImageSharp/Formats/Webp/WebpEncoderCore.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using SixLabors.ImageSharp.Formats.Webp.Chunks;
 using SixLabors.ImageSharp.Formats.Webp.Lossless;
 using SixLabors.ImageSharp.Formats.Webp.Lossy;
 using SixLabors.ImageSharp.Memory;
@@ -143,12 +144,14 @@ internal sealed class WebpEncoderCore : IImageEncoderInternals
                 this.nearLossless,
                 this.nearLosslessQuality);
 
-            encoder.EncodeHeader(image, stream, hasAnimation);
+            long initialPosition = stream.Position;
+            bool hasAlpha = false;
+            WebpVp8X vp8x = encoder.EncodeHeader(image, stream, hasAnimation);
 
             // Encode the first frame.
             ImageFrame<TPixel> previousFrame = image.Frames.RootFrame;
             WebpFrameMetadata frameMetadata = WebpCommonUtils.GetWebpFrameMetadata(previousFrame);
-            encoder.Encode(previousFrame, previousFrame.Bounds(), frameMetadata, stream, hasAnimation);
+            hasAlpha |= encoder.Encode(previousFrame, previousFrame.Bounds(), frameMetadata, stream, hasAnimation);
 
             if (hasAnimation)
             {
@@ -190,14 +193,14 @@ internal sealed class WebpEncoderCore : IImageEncoderInternals
                         this.nearLossless,
                         this.nearLosslessQuality);
 
-                    animatedEncoder.Encode(encodingFrame, bounds, frameMetadata, stream, hasAnimation);
+                    hasAlpha |= animatedEncoder.Encode(encodingFrame, bounds, frameMetadata, stream, hasAnimation);
 
                     previousFrame = currentFrame;
                     previousDisposal = frameMetadata.DisposalMethod;
                 }
             }
 
-            encoder.EncodeFooter(image, stream);
+            encoder.EncodeFooter(image, in vp8x, hasAlpha, stream, initialPosition);
         }
         else
         {
@@ -214,17 +217,20 @@ internal sealed class WebpEncoderCore : IImageEncoderInternals
                 this.spatialNoiseShaping,
                 this.alphaCompression);
 
+            long initialPosition = stream.Position;
+            bool hasAlpha = false;
+            WebpVp8X vp8x = default;
             if (image.Frames.Count > 1)
             {
-                // TODO: What about alpha here?
-                encoder.EncodeHeader(image, stream, false, true);
+                // The alpha flag is updated following encoding.
+                vp8x = encoder.EncodeHeader(image, stream, false, true);
 
                 // Encode the first frame.
                 ImageFrame<TPixel> previousFrame = image.Frames.RootFrame;
                 WebpFrameMetadata frameMetadata = WebpCommonUtils.GetWebpFrameMetadata(previousFrame);
                 WebpDisposalMethod previousDisposal = frameMetadata.DisposalMethod;
 
-                encoder.EncodeAnimation(previousFrame, stream, previousFrame.Bounds(), frameMetadata);
+                hasAlpha |= encoder.EncodeAnimation(previousFrame, stream, previousFrame.Bounds(), frameMetadata);
 
                 // Encode additional frames
                 // This frame is reused to store de-duplicated pixel buffers.
@@ -263,18 +269,19 @@ internal sealed class WebpEncoderCore : IImageEncoderInternals
                         this.spatialNoiseShaping,
                         this.alphaCompression);
 
-                    animatedEncoder.EncodeAnimation(encodingFrame, stream, bounds, frameMetadata);
+                    hasAlpha |= animatedEncoder.EncodeAnimation(encodingFrame, stream, bounds, frameMetadata);
 
                     previousFrame = currentFrame;
                     previousDisposal = frameMetadata.DisposalMethod;
                 }
+
+                encoder.EncodeFooter(image, in vp8x, hasAlpha, stream, initialPosition);
             }
             else
             {
                 encoder.EncodeStatic(stream, image);
+                encoder.EncodeFooter(image, in vp8x, hasAlpha, stream, initialPosition);
             }
-
-            encoder.EncodeFooter(image, stream);
         }
     }
 }

src/ImageSharp/Memory/Allocators/Internals/UnmanagedMemoryHandle.cs

@@ -11,7 +11,7 @@ namespace SixLabors.ImageSharp.Memory.Internals;
 internal struct UnmanagedMemoryHandle : IEquatable<UnmanagedMemoryHandle>
 {
     // Number of allocation re-attempts when detecting OutOfMemoryException.
-    private const int MaxAllocationAttempts = 1000;
+    private const int MaxAllocationAttempts = 10;
 
     // Track allocations for testing purposes:
     private static int totalOutstandingHandles;

src/ImageSharp/Memory/Allocators/MemoryAllocator.cs

@@ -2,6 +2,7 @@
 // Licensed under the Six Labors Split License.
 
 using System.Buffers;
+using System.Runtime.CompilerServices;
 
 namespace SixLabors.ImageSharp.Memory;
 
@@ -10,6 +11,8 @@ namespace SixLabors.ImageSharp.Memory;
 /// </summary>
 public abstract class MemoryAllocator
 {
+    private const int OneGigabyte = 1 << 30;
+
     /// <summary>
     /// Gets the default platform-specific global <see cref="MemoryAllocator"/> instance that
     /// serves as the default value for <see cref="Configuration.MemoryAllocator"/>.
@@ -20,6 +23,10 @@ public abstract class MemoryAllocator
     /// </summary>
     public static MemoryAllocator Default { get; } = Create();
 
+    internal long MemoryGroupAllocationLimitBytes { get; private set; } = Environment.Is64BitProcess ? 4L * OneGigabyte : OneGigabyte;
+
+    internal int SingleBufferAllocationLimitBytes { get; private set; } = OneGigabyte;
+
     /// <summary>
     /// Gets the length of the largest contiguous buffer that can be handled by this allocator instance in bytes.
     /// </summary>
@@ -30,16 +37,24 @@ public abstract class MemoryAllocator
     /// Creates a default instance of a <see cref="MemoryAllocator"/> optimized for the executing platform.
     /// </summary>
     /// <returns>The <see cref="MemoryAllocator"/>.</returns>
-    public static MemoryAllocator Create() =>
-        new UniformUnmanagedMemoryPoolMemoryAllocator(null);
+    public static MemoryAllocator Create() => Create(default);
 
     /// <summary>
     /// Creates the default <see cref="MemoryAllocator"/> using the provided options.
     /// </summary>
     /// <param name="options">The <see cref="MemoryAllocatorOptions"/>.</param>
     /// <returns>The <see cref="MemoryAllocator"/>.</returns>
-    public static MemoryAllocator Create(MemoryAllocatorOptions options) =>
-        new UniformUnmanagedMemoryPoolMemoryAllocator(options.MaximumPoolSizeMegabytes);
+    public static MemoryAllocator Create(MemoryAllocatorOptions options)
+    {
+        UniformUnmanagedMemoryPoolMemoryAllocator allocator = new(options.MaximumPoolSizeMegabytes);
+        if (options.AllocationLimitMegabytes.HasValue)
+        {
+            allocator.MemoryGroupAllocationLimitBytes = options.AllocationLimitMegabytes.Value * 1024 * 1024;
+            allocator.SingleBufferAllocationLimitBytes = (int)Math.Min(allocator.SingleBufferAllocationLimitBytes, allocator.MemoryGroupAllocationLimitBytes);
+        }
+
+        return allocator;
+    }
 
     /// <summary>
     /// Allocates an <see cref="IMemoryOwner{T}" />, holding a <see cref="Memory{T}"/> of length <paramref name="length"/>.
@@ -64,15 +79,34 @@ public abstract class MemoryAllocator
     /// <summary>
     /// Allocates a <see cref="MemoryGroup{T}"/>.
     /// </summary>
+    /// <typeparam name="T">The type of element to allocate.</typeparam>
     /// <param name="totalLength">The total length of the buffer.</param>
     /// <param name="bufferAlignment">The expected alignment (eg. to make sure image rows fit into single buffers).</param>
     /// <param name="options">The <see cref="AllocationOptions"/>.</param>
     /// <returns>A new <see cref="MemoryGroup{T}"/>.</returns>
     /// <exception cref="InvalidMemoryOperationException">Thrown when 'blockAlignment' converted to bytes is greater than the buffer capacity of the allocator.</exception>
-    internal virtual MemoryGroup<T> AllocateGroup<T>(
+    internal MemoryGroup<T> AllocateGroup<T>(
         long totalLength,
         int bufferAlignment,
         AllocationOptions options = AllocationOptions.None)
         where T : struct
-        => MemoryGroup<T>.Allocate(this, totalLength, bufferAlignment, options);
+    {
+        if (totalLength < 0)
+        {
+            InvalidMemoryOperationException.ThrowNegativeAllocationException(totalLength);
+        }
+
+        ulong totalLengthInBytes = (ulong)totalLength * (ulong)Unsafe.SizeOf<T>();
+        if (totalLengthInBytes > (ulong)this.MemoryGroupAllocationLimitBytes)
+        {
+            InvalidMemoryOperationException.ThrowAllocationOverLimitException(totalLengthInBytes, this.MemoryGroupAllocationLimitBytes);
+        }
+
+        // Cast to long is safe because we already checked that the total length is within the limit.
+        return this.AllocateGroupCore<T>(totalLength, (long)totalLengthInBytes, bufferAlignment, options);
+    }
+
+    internal virtual MemoryGroup<T> AllocateGroupCore<T>(long totalLengthInElements, long totalLengthInBytes, int bufferAlignment, AllocationOptions options)
+        where T : struct
+        => MemoryGroup<T>.Allocate(this, totalLengthInElements, bufferAlignment, options);
 }

src/ImageSharp/Memory/Allocators/MemoryAllocatorOptions.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
 namespace SixLabors.ImageSharp.Memory;
@@ -9,6 +9,7 @@ namespace SixLabors.ImageSharp.Memory;
 public struct MemoryAllocatorOptions
 {
     private int? maximumPoolSizeMegabytes;
+    private int? allocationLimitMegabytes;
 
     /// <summary>
     /// Gets or sets a value defining the maximum size of the <see cref="MemoryAllocator"/>'s internal memory pool
@@ -27,4 +28,22 @@ public struct MemoryAllocatorOptions
             this.maximumPoolSizeMegabytes = value;
         }
     }
+
+    /// <summary>
+    /// Gets or sets a value defining the maximum (discontiguous) buffer size that can be allocated by the allocator in Megabytes.
+    /// <see langword="null"/> means platform default: 1GB on 32-bit processes, 4GB on 64-bit processes.
+    /// </summary>
+    public int? AllocationLimitMegabytes
+    {
+        get => this.allocationLimitMegabytes;
+        set
+        {
+            if (value.HasValue)
+            {
+                Guard.MustBeGreaterThan(value.Value, 0, nameof(this.AllocationLimitMegabytes));
+            }
+
+            this.allocationLimitMegabytes = value;
+        }
+    }
 }

src/ImageSharp/Memory/Allocators/SimpleGcMemoryAllocator.cs

@@ -1,7 +1,8 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
 using System.Buffers;
+using System.Runtime.CompilerServices;
 using SixLabors.ImageSharp.Memory.Internals;
 
 namespace SixLabors.ImageSharp.Memory;
@@ -17,7 +18,16 @@ public sealed class SimpleGcMemoryAllocator : MemoryAllocator
     /// <inheritdoc />
     public override IMemoryOwner<T> Allocate<T>(int length, AllocationOptions options = AllocationOptions.None)
     {
-        Guard.MustBeGreaterThanOrEqualTo(length, 0, nameof(length));
+        if (length < 0)
+        {
+            InvalidMemoryOperationException.ThrowNegativeAllocationException(length);
+        }
+
+        ulong lengthInBytes = (ulong)length * (ulong)Unsafe.SizeOf<T>();
+        if (lengthInBytes > (ulong)this.SingleBufferAllocationLimitBytes)
+        {
+            InvalidMemoryOperationException.ThrowAllocationOverLimitException(lengthInBytes, this.SingleBufferAllocationLimitBytes);
+        }
 
         return new BasicArrayBuffer<T>(new T[length]);
     }

src/ImageSharp/Memory/Allocators/UniformUnmanagedMemoryPoolMemoryAllocator.cs

@@ -83,10 +83,18 @@ internal sealed class UniformUnmanagedMemoryPoolMemoryAllocator : MemoryAllocato
         int length,
         AllocationOptions options = AllocationOptions.None)
     {
-        Guard.MustBeGreaterThanOrEqualTo(length, 0, nameof(length));
-        int lengthInBytes = length * Unsafe.SizeOf<T>();
+        if (length < 0)
+        {
+            InvalidMemoryOperationException.ThrowNegativeAllocationException(length);
+        }
+
+        ulong lengthInBytes = (ulong)length * (ulong)Unsafe.SizeOf<T>();
+        if (lengthInBytes > (ulong)this.SingleBufferAllocationLimitBytes)
+        {
+            InvalidMemoryOperationException.ThrowAllocationOverLimitException(lengthInBytes, this.SingleBufferAllocationLimitBytes);
+        }
 
-        if (lengthInBytes <= this.sharedArrayPoolThresholdInBytes)
+        if (lengthInBytes <= (ulong)this.sharedArrayPoolThresholdInBytes)
         {
             var buffer = new SharedArrayPoolBuffer<T>(length);
             if (options.Has(AllocationOptions.Clean))
@@ -97,7 +105,7 @@ internal sealed class UniformUnmanagedMemoryPoolMemoryAllocator : MemoryAllocato
             return buffer;
         }
 
-        if (lengthInBytes <= this.poolBufferSizeInBytes)
+        if (lengthInBytes <= (ulong)this.poolBufferSizeInBytes)
         {
             UnmanagedMemoryHandle mem = this.pool.Rent();
             if (mem.IsValid)
@@ -111,20 +119,15 @@ internal sealed class UniformUnmanagedMemoryPoolMemoryAllocator : MemoryAllocato
     }
 
     /// <inheritdoc />
-    internal override MemoryGroup<T> AllocateGroup<T>(
-        long totalLength,
+    internal override MemoryGroup<T> AllocateGroupCore<T>(
+        long totalLengthInElements,
+        long totalLengthInBytes,
         int bufferAlignment,
         AllocationOptions options = AllocationOptions.None)
     {
-        long totalLengthInBytes = totalLength * Unsafe.SizeOf<T>();
-        if (totalLengthInBytes < 0)
-        {
-            throw new InvalidMemoryOperationException("Attempted to allocate a MemoryGroup of a size that is not representable.");
-        }
-
         if (totalLengthInBytes <= this.sharedArrayPoolThresholdInBytes)
         {
-            var buffer = new SharedArrayPoolBuffer<T>((int)totalLength);
+            var buffer = new SharedArrayPoolBuffer<T>((int)totalLengthInElements);
             return MemoryGroup<T>.CreateContiguous(buffer, options.Has(AllocationOptions.Clean));
         }
 
@@ -134,18 +137,18 @@ internal sealed class UniformUnmanagedMemoryPoolMemoryAllocator : MemoryAllocato
             UnmanagedMemoryHandle mem = this.pool.Rent();
             if (mem.IsValid)
             {
-                UnmanagedBuffer<T> buffer = this.pool.CreateGuardedBuffer<T>(mem, (int)totalLength, options.Has(AllocationOptions.Clean));
+                UnmanagedBuffer<T> buffer = this.pool.CreateGuardedBuffer<T>(mem, (int)totalLengthInElements, options.Has(AllocationOptions.Clean));
                 return MemoryGroup<T>.CreateContiguous(buffer, options.Has(AllocationOptions.Clean));
             }
         }
 
         // Attempt to rent the whole group from the pool, allocate a group of unmanaged buffers if the attempt fails:
-        if (MemoryGroup<T>.TryAllocate(this.pool, totalLength, bufferAlignment, options, out MemoryGroup<T>? poolGroup))
+        if (MemoryGroup<T>.TryAllocate(this.pool, totalLengthInElements, bufferAlignment, options, out MemoryGroup<T>? poolGroup))
         {
             return poolGroup;
         }
 
-        return MemoryGroup<T>.Allocate(this.nonPoolAllocator, totalLength, bufferAlignment, options);
+        return MemoryGroup<T>.Allocate(this.nonPoolAllocator, totalLengthInElements, bufferAlignment, options);
     }
 
     public override void ReleaseRetainedResources() => this.pool.Release();

src/ImageSharp/Memory/DiscontiguousBuffers/MemoryGroup{T}.cs

@@ -83,15 +83,16 @@ internal abstract partial class MemoryGroup<T> : IMemoryGroup<T>, IDisposable
     {
         int bufferCapacityInBytes = allocator.GetBufferCapacityInBytes();
         Guard.NotNull(allocator, nameof(allocator));
-        Guard.MustBeGreaterThanOrEqualTo(totalLengthInElements, 0, nameof(totalLengthInElements));
-        Guard.MustBeGreaterThanOrEqualTo(bufferAlignmentInElements, 0, nameof(bufferAlignmentInElements));
 
-        int blockCapacityInElements = bufferCapacityInBytes / ElementSize;
+        if (totalLengthInElements < 0)
+        {
+            InvalidMemoryOperationException.ThrowNegativeAllocationException(totalLengthInElements);
+        }
 
-        if (bufferAlignmentInElements > blockCapacityInElements)
+        int blockCapacityInElements = bufferCapacityInBytes / ElementSize;
+        if (bufferAlignmentInElements < 0 || bufferAlignmentInElements > blockCapacityInElements)
         {
-            throw new InvalidMemoryOperationException(
-                $"The buffer capacity of the provided MemoryAllocator is insufficient for the requested buffer alignment: {bufferAlignmentInElements}.");
+            InvalidMemoryOperationException.ThrowInvalidAlignmentException(bufferAlignmentInElements);
         }
 
         if (totalLengthInElements == 0)

src/ImageSharp/Memory/InvalidMemoryOperationException.cs

@@ -1,6 +1,8 @@
 // Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
+using System.Diagnostics.CodeAnalysis;
+
 namespace SixLabors.ImageSharp.Memory;
 
 /// <summary>
@@ -24,4 +26,17 @@ public class InvalidMemoryOperationException : InvalidOperationException
     public InvalidMemoryOperationException()
     {
     }
+
+    [DoesNotReturn]
+    internal static void ThrowNegativeAllocationException(long length) =>
+        throw new InvalidMemoryOperationException($"Attempted to allocate a buffer of negative length={length}.");
+
+    [DoesNotReturn]
+    internal static void ThrowInvalidAlignmentException(long alignment) =>
+        throw new InvalidMemoryOperationException(
+                $"The buffer capacity of the provided MemoryAllocator is insufficient for the requested buffer alignment: {alignment}.");
+
+    [DoesNotReturn]
+    internal static void ThrowAllocationOverLimitException(ulong length, long limit) =>
+            throw new InvalidMemoryOperationException($"Attempted to allocate a buffer of length={length} that exceeded the limit {limit}.");
 }

tests/ImageSharp.Tests/Formats/Bmp/BmpDecoderTests.cs

@@ -558,4 +558,16 @@ public class BmpDecoderTests
         // Compare to reference output instead.
         image.CompareToReferenceOutput(provider, extension: "png");
     }
+
+    [Theory]
+    [WithFile(Issue2696, PixelTypes.Rgba32)]
+    public void BmpDecoder_ThrowsException_Issue2696<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        InvalidImageContentException ex = Assert.Throws<InvalidImageContentException>(() =>
+            {
+                using Image<TPixel> image = provider.GetImage(BmpDecoder.Instance);
+            });
+        Assert.IsType<InvalidMemoryOperationException>(ex.InnerException);
+    }
 }

tests/ImageSharp.Tests/Formats/Jpg/JpegDecoderTests.cs

@@ -338,21 +338,11 @@ public partial class JpegDecoderTests
     }
 
     [Theory]
-    [WithFile(TestImages.Jpeg.Issues.HangBadScan, PixelTypes.L8)]
-    public void DecodeHang<TPixel>(TestImageProvider<TPixel> provider)
+    [WithFile(TestImages.Jpeg.Issues.HangBadScan, PixelTypes.Rgb24)]
+    public void DecodeHang_ThrowsException<TPixel>(TestImageProvider<TPixel> provider)
         where TPixel : unmanaged, IPixel<TPixel>
-    {
-        if (TestEnvironment.IsWindows &&
-            TestEnvironment.RunsOnCI)
-        {
-            // Windows CI runs consistently fail with OOM.
-            return;
-        }
-
-        using Image<TPixel> image = provider.GetImage(JpegDecoder.Instance);
-        Assert.Equal(65503, image.Width);
-        Assert.Equal(65503, image.Height);
-    }
+        => Assert.Throws<InvalidImageContentException>(
+            () => { using Image<TPixel> image = provider.GetImage(JpegDecoder.Instance); });
 
     // https://github.com/SixLabors/ImageSharp/issues/2517
     [Theory]
@@ -364,4 +354,15 @@ public partial class JpegDecoderTests
         image.DebugSave(provider);
         image.CompareToOriginal(provider);
     }
+
+    // https://github.com/SixLabors/ImageSharp/issues/2638
+    [Theory]
+    [WithFile(TestImages.Jpeg.Issues.Issue2638, PixelTypes.Rgba32)]
+    public void Issue2638_DecodeWorks<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(JpegDecoder.Instance);
+        image.DebugSave(provider);
+        image.CompareToOriginal(provider);
+    }
 }

tests/ImageSharp.Tests/Formats/Png/PngDecoderTests.cs

@@ -87,7 +87,9 @@ public partial class PngDecoderTests
         TestImages.Png.DisposeBackgroundRegion,
         TestImages.Png.DisposePreviousFirst,
         TestImages.Png.DisposeBackgroundBeforeRegion,
-        TestImages.Png.BlendOverMultiple
+        TestImages.Png.BlendOverMultiple,
+        TestImages.Png.FrameOffset,
+        TestImages.Png.DefaultNotAnimated
     };
 
     [Theory]
@@ -691,4 +693,12 @@ public partial class PngDecoderTests
         string path = Path.GetFullPath(Path.Combine(TestEnvironment.InputImagesDirectoryFullPath, file));
         _ = Image.Identify(path);
     }
+
+    [Theory]
+    [InlineData(TestImages.Png.Bad.Issue2714BadPalette)]
+    public void Decode_BadPalette(string file)
+    {
+        string path = Path.GetFullPath(Path.Combine(TestEnvironment.InputImagesDirectoryFullPath, file));
+        using Image image = Image.Load(path);
+    }
 }

tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.Chunks.cs

@@ -3,6 +3,7 @@
 
 using System.Buffers.Binary;
 using SixLabors.ImageSharp.Formats.Png;
+using SixLabors.ImageSharp.Formats.Png.Chunks;
 using SixLabors.ImageSharp.PixelFormats;
 
 // ReSharper disable InconsistentNaming
@@ -59,6 +60,38 @@ public partial class PngEncoderTests
         }
     }
 
+    [Theory]
+    [WithFile(TestImages.Png.DefaultNotAnimated, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Png.APng, PixelTypes.Rgba32)]
+    public void AcTL_CorrectlyWritten<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(PngDecoder.Instance);
+        PngMetadata metadata = image.Metadata.GetPngMetadata();
+        int correctFrameCount = image.Frames.Count - (metadata.AnimateRootFrame ? 0 : 1);
+        using MemoryStream memStream = new();
+        image.Save(memStream, PngEncoder);
+        memStream.Position = 0;
+        Span<byte> bytesSpan = memStream.ToArray().AsSpan(8); // Skip header.
+        bool foundAcTl = false;
+        while (bytesSpan.Length > 0 && !foundAcTl)
+        {
+            int length = BinaryPrimitives.ReadInt32BigEndian(bytesSpan[..4]);
+            PngChunkType type = (PngChunkType)BinaryPrimitives.ReadInt32BigEndian(bytesSpan.Slice(4, 4));
+            if (type == PngChunkType.AnimationControl)
+            {
+                AnimationControl control = AnimationControl.Parse(bytesSpan[8..]);
+                foundAcTl = true;
+                Assert.True(control.NumberFrames == correctFrameCount);
+                Assert.True(control.NumberPlays == metadata.RepeatCount);
+            }
+
+            bytesSpan = bytesSpan[(4 + 4 + length + 4)..];
+        }
+
+        Assert.True(foundAcTl);
+    }
+
     [Theory]
     [InlineData(PngChunkType.Gamma)]
     [InlineData(PngChunkType.Chroma)]

tests/ImageSharp.Tests/Formats/Png/PngEncoderTests.cs

@@ -448,6 +448,8 @@ public partial class PngEncoderTests
 
     [Theory]
     [WithFile(TestImages.Png.APng, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Png.DefaultNotAnimated, PixelTypes.Rgba32)]
+    [WithFile(TestImages.Png.FrameOffset, PixelTypes.Rgba32)]
     public void Encode_APng<TPixel>(TestImageProvider<TPixel> provider)
         where TPixel : unmanaged, IPixel<TPixel>
     {
@@ -459,15 +461,17 @@ public partial class PngEncoderTests
         image.DebugSave(provider: provider, encoder: PngEncoder, null, false);
 
         using Image<Rgba32> output = Image.Load<Rgba32>(memStream);
-        ImageComparer.Exact.VerifySimilarity(output, image);
 
-        Assert.Equal(5, image.Frames.Count);
+        // some loss from original, due to compositing
+        ImageComparer.TolerantPercentage(0.01f).VerifySimilarity(output, image);
+
         Assert.Equal(image.Frames.Count, output.Frames.Count);
 
         PngMetadata originalMetadata = image.Metadata.GetPngMetadata();
         PngMetadata outputMetadata = output.Metadata.GetPngMetadata();
 
         Assert.Equal(originalMetadata.RepeatCount, outputMetadata.RepeatCount);
+        Assert.Equal(originalMetadata.AnimateRootFrame, outputMetadata.AnimateRootFrame);
 
         for (int i = 0; i < image.Frames.Count; i++)
         {

tests/ImageSharp.Tests/Formats/Png/PngMetadataTests.cs

@@ -32,7 +32,8 @@ public class PngMetadataTests
             InterlaceMethod = PngInterlaceMode.Adam7,
             Gamma = 2,
             TextData = new List<PngTextData> { new PngTextData("name", "value", "foo", "bar") },
-            RepeatCount = 123
+            RepeatCount = 123,
+            AnimateRootFrame = false
         };
 
         PngMetadata clone = (PngMetadata)meta.DeepClone();
@@ -44,6 +45,7 @@ public class PngMetadataTests
         Assert.False(meta.TextData.Equals(clone.TextData));
         Assert.True(meta.TextData.SequenceEqual(clone.TextData));
         Assert.True(meta.RepeatCount == clone.RepeatCount);
+        Assert.True(meta.AnimateRootFrame == clone.AnimateRootFrame);
 
         clone.BitDepth = PngBitDepth.Bit2;
         clone.ColorType = PngColorType.Palette;
@@ -144,6 +146,26 @@ public class PngMetadataTests
         VerifyExifDataIsPresent(exif);
     }
 
+    [Theory]
+    [WithFile(TestImages.Png.DefaultNotAnimated, PixelTypes.Rgba32)]
+    public void Decode_IdentifiesDefaultFrameNotAnimated<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(PngDecoder.Instance);
+        PngMetadata meta = image.Metadata.GetFormatMetadata(PngFormat.Instance);
+        Assert.False(meta.AnimateRootFrame);
+    }
+
+    [Theory]
+    [WithFile(TestImages.Png.APng, PixelTypes.Rgba32)]
+    public void Decode_IdentifiesDefaultFrameAnimated<TPixel>(TestImageProvider<TPixel> provider)
+        where TPixel : unmanaged, IPixel<TPixel>
+    {
+        using Image<TPixel> image = provider.GetImage(PngDecoder.Instance);
+        PngMetadata meta = image.Metadata.GetFormatMetadata(PngFormat.Instance);
+        Assert.True(meta.AnimateRootFrame);
+    }
+
     [Theory]
     [WithFile(TestImages.Png.PngWithMetadata, PixelTypes.Rgba32)]
     public void Decode_IgnoresExifData_WhenIgnoreMetadataIsTrue<TPixel>(TestImageProvider<TPixel> provider)

tests/ImageSharp.Tests/Memory/Allocators/SimpleGcMemoryAllocatorTests.cs

@@ -19,13 +19,17 @@ public class SimpleGcMemoryAllocatorTests
 
     protected SimpleGcMemoryAllocator MemoryAllocator { get; } = new SimpleGcMemoryAllocator();
 
-    [Theory]
-    [InlineData(-1)]
-    public void Allocate_IncorrectAmount_ThrowsCorrect_ArgumentOutOfRangeException(int length)
+    public static TheoryData<int> InvalidLengths { get; set; } = new()
     {
-        ArgumentOutOfRangeException ex = Assert.Throws<ArgumentOutOfRangeException>(() => this.MemoryAllocator.Allocate<BigStruct>(length));
-        Assert.Equal("length", ex.ParamName);
-    }
+        { -1 },
+        { (1 << 30) + 1 }
+    };
+
+    [Theory]
+    [MemberData(nameof(InvalidLengths))]
+    public void Allocate_IncorrectAmount_ThrowsCorrect_InvalidMemoryOperationException(int length)
+        => Assert.Throws<InvalidMemoryOperationException>(
+            () => this.MemoryAllocator.Allocate<BigStruct>(length));
 
     [Fact]
     public unsafe void Allocate_MemoryIsPinnableMultipleTimes()

tests/ImageSharp.Tests/Memory/Allocators/UniformUnmanagedPoolMemoryAllocatorTests.cs

@@ -111,9 +111,20 @@ public class UniformUnmanagedPoolMemoryAllocatorTests
     public void AllocateGroup_SizeInBytesOverLongMaxValue_ThrowsInvalidMemoryOperationException()
     {
         var allocator = new UniformUnmanagedMemoryPoolMemoryAllocator(null);
-        Assert.Throws<InvalidMemoryOperationException>(() => allocator.AllocateGroup<S4>(int.MaxValue * (long)int.MaxValue, int.MaxValue));
+        Assert.Throws<InvalidMemoryOperationException>(() => allocator.AllocateGroup<byte>(int.MaxValue * (long)int.MaxValue, int.MaxValue));
     }
 
+    public static TheoryData<int> InvalidLengths { get; set; } = new()
+    {
+        { -1 },
+        { (1 << 30) + 1 }
+    };
+
+    [Theory]
+    [MemberData(nameof(InvalidLengths))]
+    public void Allocate_IncorrectAmount_ThrowsCorrect_InvalidMemoryOperationException(int length)
+        => Assert.Throws<InvalidMemoryOperationException>(() => new UniformUnmanagedMemoryPoolMemoryAllocator(null).Allocate<S512>(length));
+
     [Fact]
     public unsafe void Allocate_MemoryIsPinnableMultipleTimes()
     {
@@ -407,4 +418,28 @@ public class UniformUnmanagedPoolMemoryAllocatorTests
             _ = MemoryAllocator.Create();
         }
     }
+
+    [Fact]
+    public void Allocate_OverLimit_ThrowsInvalidMemoryOperationException()
+    {
+        MemoryAllocator allocator = MemoryAllocator.Create(new MemoryAllocatorOptions()
+        {
+            AllocationLimitMegabytes = 4
+        });
+        const int oneMb = 1 << 20;
+        allocator.Allocate<byte>(4 * oneMb).Dispose(); // Should work
+        Assert.Throws<InvalidMemoryOperationException>(() => allocator.Allocate<byte>(5 * oneMb));
+    }
+
+    [Fact]
+    public void AllocateGroup_OverLimit_ThrowsInvalidMemoryOperationException()
+    {
+        MemoryAllocator allocator = MemoryAllocator.Create(new MemoryAllocatorOptions()
+        {
+            AllocationLimitMegabytes = 4
+        });
+        const int oneMb = 1 << 20;
+        allocator.AllocateGroup<byte>(4 * oneMb, 1024).Dispose(); // Should work
+        Assert.Throws<InvalidMemoryOperationException>(() => allocator.AllocateGroup<byte>(5 * oneMb, 1024));
+    }
 }

tests/ImageSharp.Tests/Memory/Buffer2DTests.cs

@@ -4,6 +4,7 @@
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.PixelFormats;
 
 // ReSharper disable InconsistentNaming
 namespace SixLabors.ImageSharp.Tests.Memory;
@@ -337,4 +338,26 @@ public partial class Buffer2DTests
         Assert.False(mgBefore.IsValid);
         Assert.NotSame(mgBefore, buffer1.MemoryGroup);
     }
+
+    public static TheoryData<Size> InvalidLengths { get; set; } = new()
+    {
+        { new(-1, -1) },
+        { new(32768, 32769) },
+        { new(32769, 32768) }
+    };
+
+    [Theory]
+    [MemberData(nameof(InvalidLengths))]
+    public void Allocate_IncorrectAmount_ThrowsCorrect_InvalidMemoryOperationException(Size size)
+        => Assert.Throws<InvalidMemoryOperationException>(() => this.MemoryAllocator.Allocate2D<Rgba32>(size.Width, size.Height));
+
+    [Theory]
+    [MemberData(nameof(InvalidLengths))]
+    public void Allocate_IncorrectAmount_ThrowsCorrect_InvalidMemoryOperationException_Size(Size size)
+        => Assert.Throws<InvalidMemoryOperationException>(() => this.MemoryAllocator.Allocate2D<Rgba32>(new Size(size)));
+
+    [Theory]
+    [MemberData(nameof(InvalidLengths))]
+    public void Allocate_IncorrectAmount_ThrowsCorrect_InvalidMemoryOperationException_OverAligned(Size size)
+        => Assert.Throws<InvalidMemoryOperationException>(() => this.MemoryAllocator.Allocate2DOveraligned<Rgba32>(size.Width, size.Height, 1));
 }

tests/ImageSharp.Tests/Memory/DiscontiguousBuffers/MemoryGroupTests.Allocate.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Six Labors.
+// Copyright (c) Six Labors.
 // Licensed under the Six Labors Split License.
 
 using System.Runtime.CompilerServices;
@@ -219,11 +219,17 @@ public partial class MemoryGroupTests
 [StructLayout(LayoutKind.Sequential, Size = 5)]
 internal struct S5
 {
-    public override string ToString() => "S5";
+    public override readonly string ToString() => nameof(S5);
 }
 
 [StructLayout(LayoutKind.Sequential, Size = 4)]
 internal struct S4
 {
-    public override string ToString() => "S4";
+    public override readonly string ToString() => nameof(S4);
+}
+
+[StructLayout(LayoutKind.Explicit, Size = 512)]
+internal struct S512
+{
+    public override readonly string ToString() => nameof(S512);
 }

tests/ImageSharp.Tests/TestImages.cs

@@ -73,6 +73,8 @@ public static class TestImages
         public const string DisposeBackgroundRegion = "Png/animated/15-dispose-background-region.png";
         public const string DisposePreviousFirst = "Png/animated/12-dispose-prev-first.png";
         public const string BlendOverMultiple = "Png/animated/21-blend-over-multiple.png";
+        public const string FrameOffset = "Png/animated/frame-offset.png";
+        public const string DefaultNotAnimated = "Png/animated/default-not-animated.png";
         public const string Issue2666 = "Png/issues/Issue_2666.png";
 
         // Filtered test images from http://www.schaik.com/pngsuite/pngsuite_fil_png.html
@@ -190,6 +192,8 @@ public static class TestImages
 
             public const string BadZTXT = "Png/issues/bad-ztxt.png";
             public const string BadZTXT2 = "Png/issues/bad-ztxt2.png";
+
+            public const string Issue2714BadPalette = "Png/issues/Issue_2714.png";
         }
     }
 
@@ -316,6 +320,7 @@ public static class TestImages
             public const string HangBadScan = "Jpg/issues/Hang_C438A851.jpg";
             public const string Issue2517 = "Jpg/issues/issue2517-bad-d7.jpg";
             public const string Issue2067_CommentMarker = "Jpg/issues/issue-2067-comment.jpg";
+            public const string Issue2638 = "Jpg/issues/Issue2638.jpg";
 
             public static class Fuzz
             {
@@ -439,6 +444,8 @@ public static class TestImages
         public const string Rgba321010102 = "Bmp/rgba32-1010102.bmp";
         public const string RgbaAlphaBitfields = "Bmp/rgba32abf.bmp";
 
+        public const string Issue2696 = "Bmp/issue-2696.bmp";
+
         public const string BlackWhitePalletDataMatrix = "Bmp/bit1datamatrix.bmp";
 
         public static readonly string[] BitFields =

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_default-not-animated.png/00.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:8d4716e18655be53630d6d50daebe8c38e0eedb2432c7a73840b55d1473d5944
+size 1050

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_default-not-animated.png/01.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:9b5a6d3cf1a777f6b719c2a1cf79bffe2251355d75e6c0f7ce7a973b3d033419
+size 1177

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_frame-offset.png/00.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:b85aaf7153e0ca538856a58d7b069bcc13fadc468ea603c85f8782cc691f86c3
+size 387

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_frame-offset.png/01.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:fcb83d6893dcfd869b764ff9846c259eaa0caf26cec3f0fc2cbae2c26f2eeaa5
+size 660

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_frame-offset.png/02.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:562ec382f6d2af68e66092bf6949f66147d5f608d3c618eea5a7c1ea400737ff
+size 768

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_frame-offset.png/03.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:d12a7791b960072e32b78bd9aaf456dc99341eea1c66ea05050433d8c082c6ac
+size 579

tests/Images/External/ReferenceOutput/PngDecoderTests/Decode_VerifyAllFrames_Rgba32_frame-offset.png/04.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:2db38d7ffcc95c23a5c94a06f10c6cc67406ae581a955c99ede4af97b1a044f8
+size 628

tests/Images/Input/Bmp/issue-2696.bmp

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:bc42cda9bac8fc73351ad03bf55214069bb8d31ea5bdd806321a8cc8b56c282e
+size 126

tests/Images/Input/Jpg/issues/Issue2638.jpg

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:208d5b0b727bbef120a7e090e020a48f99c9e264c2d3939ba749f8620853c1fe
+size 70876

tests/Images/Input/Png/animated/default-not-animated.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:647d484c8f320b55824b9219270524df3edc434a4793e1627e0ee14af8d6e4f8
+size 1689

tests/Images/Input/Png/animated/frame-offset.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:3c019073841b48b02cb07c779fed8654c6052aee700e7620d07f5d775d97088f
+size 2156

tests/Images/Input/Png/issues/Issue_2714.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:9a4b6efc3090dbd70ae9efe97ea817464845263536beea4e80fd7c884dee6c5a
+size 128