Address ANI and icon review feedback

src/ImageSharp/Formats/Ani/AniDecoderCore.cs

@@ -310,7 +310,7 @@ internal sealed class AniDecoderCore : ImageDecoderCore, IDisposable
         ReadExactly(stream, data, "ANI header");
         this.header = AniHeader.Parse(data);
 
-        if (this.header.BytesInHeader < AniHeader.Size)
+        if (this.header.BytesInHeader < AniHeader.Size || this.header.BytesInHeader > chunkSize)
         {
             throw new InvalidImageContentException("The ANI animation header declares an invalid size.");
         }
@@ -412,6 +412,12 @@ internal sealed class AniDecoderCore : ImageDecoderCore, IDisposable
         }
 
         int count = (int)Math.Min(chunkSize / sizeof(uint), this.Options.MaxFrames);
+        if (count is 0)
+        {
+            this.ThrowOrIgnoreNonStrictSegmentError($"The ANI {description} chunk does not contain any values.");
+            return;
+        }
+
         IMemoryOwner<uint> valuesOwner;
         bool replaceOwner;
 
@@ -532,71 +538,102 @@ internal sealed class AniDecoderCore : ImageDecoderCore, IDisposable
         bool hasSequence = this.sequence is not null;
         int decodedResourceCount = 0;
         int maxDecodedResources = (int)this.Options.MaxFrames;
-        uint lastRequiredResource = 0;
+        IMemoryOwner<uint>? sortedSequenceOwner = null;
 
-        if (hasSequence)
+        try
         {
-            if (sequence.IsEmpty)
+            ReadOnlySpan<uint> requiredResources = sequence;
+            if (hasSequence)
             {
-                return;
-            }
+                bool isSorted = true;
+                for (int i = 1; i < sequence.Length; i++)
+                {
+                    if (sequence[i] < sequence[i - 1])
+                    {
+                        isSorted = false;
+                        break;
+                    }
+                }
 
-            // Only resources referenced by the retained sequence steps can contribute to the bounded output frame set.
-            for (int i = 0; i < sequence.Length; i++)
-            {
-                lastRequiredResource = Math.Max(lastRequiredResource, sequence[i]);
+                if (!isSorted)
+                {
+                    // Playback order can reference resources arbitrarily. A sorted allocator-owned copy turns the physical
+                    // resource scan into a linear merge instead of searching the complete sequence for every icon chunk.
+                    sortedSequenceOwner = this.Options.Configuration.MemoryAllocator.Allocate<uint>(sequence.Length);
+                    Span<uint> sortedSequence = sortedSequenceOwner.GetSpan();
+                    sequence.CopyTo(sortedSequence);
+                    sortedSequence.Sort();
+                    requiredResources = sortedSequence;
+                }
             }
-        }
 
-        foreach ((long start, long end) in this.frameLists)
-        {
-            stream.Position = start;
+            int requiredResourceIndex = 0;
+            uint lastRequiredResource = hasSequence ? requiredResources[^1] : 0;
 
-            while (stream.Position + AniConstants.ChunkHeaderSize <= end)
+            foreach ((long start, long end) in this.frameLists)
             {
-                AniRiffChunkHeader chunk = this.ReadChunkHeader(stream);
-                long dataStart = stream.Position;
-                long dataEnd = GetChunkDataEnd(stream, chunk.Size, end);
+                stream.Position = start;
 
-                if ((AniFrameChunkType)chunk.FourCc is AniFrameChunkType.Icon)
+                while (stream.Position + AniConstants.ChunkHeaderSize <= end)
                 {
-                    int resourceIndex = resources.Count;
+                    AniRiffChunkHeader chunk = this.ReadChunkHeader(stream);
+                    long dataStart = stream.Position;
+                    long dataEnd = GetChunkDataEnd(stream, chunk.Size, end);
 
-                    // Sequence entries index the physical resource table, so ignored corrupt resources retain an empty slot.
-                    resources.Add(null);
-
-                    // Unsequenced resources are consumed in physical order; sequenced files need only the referenced indices.
-                    bool shouldDecode = !hasSequence || sequence.Contains((uint)resourceIndex);
-                    if (shouldDecode)
+                    if ((AniFrameChunkType)chunk.FourCc is AniFrameChunkType.Icon)
                     {
-                        this.ExecuteImageDataSegmentAction(() =>
+                        int resourceIndex = resources.Count;
+
+                        // Sequence entries index the physical resource table, so ignored corrupt resources retain an empty slot.
+                        resources.Add(null);
+
+                        if (hasSequence)
                         {
-                            // Child decoders may seek according to embedded offsets; the bounded view prevents crossing the icon chunk.
-                            frameStream.Reset(dataStart, chunk.Size);
-                            AniFrameFormat format = this.GetFrameFormat(frameStream);
+                            while (requiredResourceIndex < requiredResources.Length && requiredResources[requiredResourceIndex] < (uint)resourceIndex)
+                            {
+                                requiredResourceIndex++;
+                            }
+                        }
 
-                            // Format probing consumes the directory prefix, while the selected child decoder requires the complete resource.
-                            frameStream.Position = 0;
-                            resources[resourceIndex] = (format, action(format, frameStream));
-                        });
+                        // Unsequenced resources are consumed in physical order; sequenced files need only the referenced indices.
+                        bool shouldDecode = !hasSequence
+                            || (requiredResourceIndex < requiredResources.Length && requiredResources[requiredResourceIndex] == (uint)resourceIndex);
 
-                        if (resources[resourceIndex] is not null)
+                        if (shouldDecode)
                         {
-                            decodedResourceCount++;
+                            this.ExecuteImageDataSegmentAction(() =>
+                            {
+                                // Child decoders may seek according to embedded offsets; the bounded view prevents crossing the icon chunk.
+                                frameStream.Reset(dataStart, chunk.Size);
+                                AniFrameFormat format = this.GetFrameFormat(frameStream);
+
+                                // Format probing consumes the directory prefix, while the selected child decoder requires the complete resource.
+                                frameStream.Position = 0;
+                                resources[resourceIndex] = (format, action(format, frameStream));
+                            });
+
+                            if (resources[resourceIndex] is not null)
+                            {
+                                decodedResourceCount++;
+                            }
                         }
-                    }
 
-                    // Every decoded resource contributes at least one output frame, while a sequence cannot reference later indices.
-                    if ((!hasSequence && decodedResourceCount == maxDecodedResources)
-                        || (hasSequence && (uint)resourceIndex == lastRequiredResource))
-                    {
-                        return;
+                        // Every decoded resource contributes at least one output frame, while a sequence cannot reference later indices.
+                        if ((!hasSequence && decodedResourceCount == maxDecodedResources)
+                            || (hasSequence && (uint)resourceIndex == lastRequiredResource))
+                        {
+                            return;
+                        }
                     }
-                }
 
-                stream.Position = GetPaddedEnd(dataEnd, chunk.Size, end);
+                    stream.Position = GetPaddedEnd(dataEnd, chunk.Size, end);
+                }
             }
         }
+        finally
+        {
+            sortedSequenceOwner?.Dispose();
+        }
     }
 
     /// <summary>

src/ImageSharp/Formats/Ani/AniEncoderCore.cs

@@ -54,11 +54,22 @@ internal sealed class AniEncoderCore
         AniFrameMetadata firstMetadata = image.Frames.RootFrame.Metadata.GetAniMetadata();
         AniFrameFormat firstFormat = firstMetadata.FrameFormat;
         bool bitmapResources = firstFormat is AniFrameFormat.Bmp;
+        bool writeSequence = imageMetadata.Flags.HasFlag(AniHeaderFlags.ContainsSequence);
         uint displayRate = firstMetadata.FrameDelay is 0 ? imageMetadata.DisplayRate : firstMetadata.FrameDelay;
         bool hasVariableRates = false;
         int groupCount = 0;
         int maxGroupSize = 1;
 
+        if (bitmapResources && imageMetadata.BitCount is not (0 or 1 or 2 or 4 or 8 or 16 or 24 or 32))
+        {
+            throw new ImageFormatException("ANI bitmap resources require a supported bit depth.");
+        }
+
+        if (bitmapResources && imageMetadata.Planes is not (0 or 1))
+        {
+            throw new ImageFormatException("ANI bitmap resources require exactly one color plane.");
+        }
+
         // This validation pass derives the fixed ANI header and largest icon directory without allocating a grouping graph.
         // Encoding repeats the linear grouping scan below, trading a cheap pass for zero per-group collections.
         for (int frameIndex = 0; frameIndex < image.Frames.Count;)
@@ -66,6 +77,12 @@ internal sealed class AniEncoderCore
             AniFrameMetadata metadata = image.Frames[frameIndex].Metadata.GetAniMetadata();
             int groupSize = 1;
 
+            if (metadata.FrameFormat is not (AniFrameFormat.Ico or AniFrameFormat.Cur or AniFrameFormat.Bmp))
+            {
+                // FrameFormat is public metadata and therefore must be validated before any container bytes are written.
+                throw new ImageFormatException("ANI contains an unsupported embedded frame format.");
+            }
+
             // Positive sequence numbers group adjacent resolution variants; non-positive values form independent steps.
             if (metadata.SequenceNumber > 0)
             {
@@ -118,9 +135,9 @@ internal sealed class AniEncoderCore
             Width = bitmapResources ? imageMetadata.Width is 0 ? (uint)image.Width : imageMetadata.Width : 0,
             Height = bitmapResources ? imageMetadata.Height is 0 ? (uint)image.Height : imageMetadata.Height : 0,
             BitCount = bitmapResources ? imageMetadata.BitCount is 0 ? 32U : imageMetadata.BitCount : 0,
-            Planes = bitmapResources ? imageMetadata.Planes is 0 ? 1U : imageMetadata.Planes : 0,
+            Planes = bitmapResources ? 1U : 0,
             DisplayRate = displayRate,
-            Flags = bitmapResources ? 0 : AniHeaderFlags.IsIcon
+            Flags = (bitmapResources ? 0 : AniHeaderFlags.IsIcon) | (writeSequence ? AniHeaderFlags.ContainsSequence : 0)
         };
 
         // One allocator-owned directory buffer is sliced and reused for every icon resource; its capacity is the largest group.
@@ -131,6 +148,11 @@ internal sealed class AniEncoderCore
         long riffSizePosition = this.BeginContainer(stream, AniConstants.RiffFourCc, AniConstants.AniFormTypeFourCc);
         this.WriteHeader(stream, header);
 
+        if (writeSequence)
+        {
+            this.WriteSequence(stream, groupCount);
+        }
+
         if (hasVariableRates)
         {
             this.WriteRates(stream, image, displayRate);
@@ -182,6 +204,27 @@ internal sealed class AniEncoderCore
         this.EndChunk(stream, sizePosition);
     }
 
+    /// <summary>
+    /// Writes an identity sequence table when the source metadata declares an explicit sequence.
+    /// </summary>
+    /// <param name="stream">The destination stream.</param>
+    /// <param name="stepCount">The number of animation steps.</param>
+    private void WriteSequence(Stream stream, int stepCount)
+    {
+        long sizePosition = this.BeginChunk(stream, "seq "u8);
+        Span<byte> value = this.buffer[..sizeof(uint)];
+
+        // Decoding expands source resource references into presentation order. Encoding writes those expanded steps as
+        // distinct resources, so an identity table preserves the explicit-sequence flag without changing playback.
+        for (uint i = 0; i < stepCount; i++)
+        {
+            BinaryPrimitives.WriteUInt32LittleEndian(value, i);
+            stream.Write(value);
+        }
+
+        this.EndChunk(stream, sizePosition);
+    }
+
     /// <summary>
     /// Writes per-step rates when they cannot be represented by one header value.
     /// </summary>
@@ -291,6 +334,7 @@ internal sealed class AniEncoderCore
                     {
                         PixelSamplingStrategy = this.encoder.PixelSamplingStrategy,
                         Quantizer = this.encoder.Quantizer,
+                        SkipMetadata = this.encoder.SkipMetadata,
                         TransparentColorMode = this.encoder.TransparentColorMode
                     });
 
@@ -302,6 +346,7 @@ internal sealed class AniEncoderCore
                     {
                         PixelSamplingStrategy = this.encoder.PixelSamplingStrategy,
                         Quantizer = this.encoder.Quantizer,
+                        SkipMetadata = this.encoder.SkipMetadata,
                         TransparentColorMode = this.encoder.TransparentColorMode
                     });
 
@@ -318,6 +363,7 @@ internal sealed class AniEncoderCore
                         PixelSamplingStrategy = this.encoder.PixelSamplingStrategy,
                         Quantizer = this.encoder.Quantizer,
                         SkipFileHeader = true,
+                        SkipMetadata = this.encoder.SkipMetadata,
                         SupportTransparency = bitCount is 32,
                         TransparentColorMode = this.encoder.TransparentColorMode
                     };

src/ImageSharp/Formats/Ani/AniMetadata.cs

@@ -60,11 +60,11 @@ public class AniMetadata : IFormatMetadata<AniMetadata>
     public uint BitCount { get; set; }
 
     /// <summary>
-    /// Gets or sets the color-plane count declared by the ANI header.
+    /// Gets or sets the number of independently addressable color planes declared by the ANI header.
     /// </summary>
     /// <remarks>
-    /// Bitmap-based ANI files use one plane. Icon-based files commonly store zero because this header field is reserved
-    /// when the embedded resources are ICO or CUR data.
+    /// Bitmap-based ANI files use the Windows DIB plane value, which must be one. Icon-based ANI files use zero because
+    /// each embedded ICO or CUR entry describes its own pixel layout. No other values are defined by the format.
     /// </remarks>
     public uint Planes { get; set; }
 

src/ImageSharp/Formats/Bmp/BmpEncoderCore.cs

@@ -102,6 +102,11 @@ internal sealed class BmpEncoderCore
     /// <inheritdoc cref="BmpDecoderOptions.SkipFileHeader"/>
     private readonly bool skipFileHeader;
 
+    /// <summary>
+    /// Whether optional image metadata should be omitted.
+    /// </summary>
+    private readonly bool skipMetadata;
+
     /// <inheritdoc cref="BmpDecoderOptions.UseDoubleHeight"/>
     private readonly bool isDoubleHeight;
 
@@ -122,6 +127,7 @@ internal sealed class BmpEncoderCore
         this.infoHeaderType = encoder.SupportTransparency ? BmpInfoHeaderType.WinVersion4 : BmpInfoHeaderType.WinVersion3;
         this.processedAlphaMask = encoder.ProcessedAlphaMask;
         this.skipFileHeader = encoder.SkipFileHeader;
+        this.skipMetadata = encoder.SkipMetadata;
         this.isDoubleHeight = encoder.UseDoubleHeight;
     }
 
@@ -174,7 +180,7 @@ internal sealed class BmpEncoderCore
 
         byte[]? iccProfileData = null;
         int iccProfileSize = 0;
-        if (metadata.IccProfile != null)
+        if (!this.skipMetadata && metadata.IccProfile != null)
         {
             this.infoHeaderType = BmpInfoHeaderType.WinVersion5;
             iccProfileData = metadata.IccProfile.ToByteArray();
@@ -229,7 +235,8 @@ internal sealed class BmpEncoderCore
         int hResolution = 0;
         int vResolution = 0;
 
-        if (metadata.ResolutionUnits != PixelResolutionUnit.AspectRatio
+        if (!this.skipMetadata
+            && metadata.ResolutionUnits != PixelResolutionUnit.AspectRatio
             && metadata.HorizontalResolution > 0
             && metadata.VerticalResolution > 0)
         {

src/ImageSharp/Formats/Icon/IconDecoderCore.cs

@@ -78,7 +78,8 @@ internal abstract class IconDecoderCore : ImageDecoderCore
                 throw new InvalidImageContentException("The icon file does not contain any decodable image entries.");
             }
 
-            ImageMetadata metadata = new();
+            // General profiles belong to the icon result even though the first successfully decoded child image is temporary.
+            ImageMetadata metadata = decodedEntries[0].Image.Metadata.DeepClone();
             BmpMetadata? bmpMetadata = null;
             PngMetadata? pngMetadata = null;
             ImageFrame<TPixel>[] frames = new ImageFrame<TPixel>[decodedCount];
@@ -93,7 +94,7 @@ internal abstract class IconDecoderCore : ImageDecoderCore
                     Image<TPixel> decoded = decodedEntries[i].Image;
                     ref IconDirEntry entry = ref this.entries[decodedEntries[i].EntryIndex];
                     ImageFrame<TPixel> source = decoded.Frames.RootFrameUnsafe;
-                    ImageFrame<TPixel> target = new(this.Options.Configuration, this.Dimensions);
+                    ImageFrame<TPixel> target = new(this.Options.Configuration, this.Dimensions, source.Metadata.DeepClone());
                     frames[i] = target;
                     initializedFrameCount++;
 
@@ -109,8 +110,6 @@ internal abstract class IconDecoderCore : ImageDecoderCore
                         {
                             pngMetadata = decoded.Metadata.GetPngMetadata();
                         }
-
-                        target.Metadata.SetFormatMetadata(PngFormat.Instance, source.Metadata.GetPngMetadata());
                     }
                     else
                     {
@@ -194,7 +193,21 @@ internal abstract class IconDecoderCore : ImageDecoderCore
 
                 bool isPng = flag.SequenceEqual(PngConstants.HeaderBytes);
                 ImageInfo frameInfo = this.GetDecoder(isPng).Identify(this.Options.Configuration, frameStream, cancellationToken);
-                ImageFrameMetadata frameMetadata = new();
+                ImageFrameMetadata frameMetadata = frameInfo.FrameMetadataCollection.Count is 0 ? new ImageFrameMetadata() : frameInfo.FrameMetadataCollection[0].DeepClone();
+
+                if (frameCount is 0)
+                {
+                    // The container has one image-level metadata object, so the first valid entry supplies general profiles and resolution.
+                    ImageMetadata sourceMetadata = frameInfo.Metadata;
+                    metadata.HorizontalResolution = sourceMetadata.HorizontalResolution;
+                    metadata.VerticalResolution = sourceMetadata.VerticalResolution;
+                    metadata.ResolutionUnits = sourceMetadata.ResolutionUnits;
+                    metadata.ExifProfile = sourceMetadata.ExifProfile?.DeepClone();
+                    metadata.IccProfile = sourceMetadata.IccProfile?.DeepClone();
+                    metadata.IptcProfile = sourceMetadata.IptcProfile?.DeepClone();
+                    metadata.XmpProfile = sourceMetadata.XmpProfile?.DeepClone();
+                    metadata.CicpProfile = sourceMetadata.CicpProfile?.DeepClone();
+                }
 
                 if (isPng)
                 {
@@ -202,8 +215,6 @@ internal abstract class IconDecoderCore : ImageDecoderCore
                     {
                         pngMetadata = frameInfo.Metadata.GetPngMetadata();
                     }
-
-                    frameMetadata.SetFormatMetadata(PngFormat.Instance, frameInfo.FrameMetadataCollection[0].GetPngMetadata());
                 }
                 else
                 {

src/ImageSharp/Formats/Icon/IconEncoderCore.cs

@@ -5,6 +5,7 @@ using System.Buffers;
 using SixLabors.ImageSharp.Formats.Bmp;
 using SixLabors.ImageSharp.Formats.Png;
 using SixLabors.ImageSharp.Memory;
+using SixLabors.ImageSharp.Metadata;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Processing.Processors.Quantization;
 
@@ -116,62 +117,90 @@ internal abstract class IconEncoderCore
                 height = frame.Height;
             }
 
-            long imageStart = stream.Position;
-            entries[i].Entry.ImageOffset = checked((uint)(imageStart - basePosition));
-
-            // ANI flattens variants onto a common canvas, while an icon entry can encode a smaller rectangle.
-            // Child encoders consume Image, so an isolated cropped image is required to prevent encoding the padded canvas.
-            using Image<TPixel> encodingFrame = new(image.Configuration, width, height);
-            for (int y = 0; y < height; y++)
+            if (width > frame.Width || height > frame.Height)
             {
-                frame.PixelBuffer.DangerousGetRowSpan(y)[..width].CopyTo(encodingFrame.GetRootFramePixelBuffer().DangerousGetRowSpan(y));
+                // EncodingWidth and EncodingHeight are public metadata, so reject a crop that exceeds the source frame here.
+                throw new ImageFormatException("The icon encoding dimensions exceed the source frame dimensions.");
             }
 
+            long imageStart = stream.Position;
+            entries[i].Entry.ImageOffset = checked((uint)(imageStart - basePosition));
             ref EncodingFrameMetadata encodingMetadata = ref entries[i];
+            Image<TPixel>? encodingImage = null;
 
-            // Compression and bitmap depth are per-entry, so the concrete encoder configuration must be selected per frame.
-            switch (encodingMetadata.Compression)
+            try
             {
-                case IconFrameCompression.Bmp:
+                bool requiresCrop = width != frame.Width || height != frame.Height;
+                bool requiresIsolatedImage = encodingMetadata.Compression is IconFrameCompression.Png && image.Frames.Count > 1;
+
+                if (requiresCrop || requiresIsolatedImage)
                 {
-                    BmpEncoder bmpEncoder = new()
+                    // PNG accepts Image rather than ImageFrame, and ANI variants may occupy only part of their common canvas.
+                    // Allocate only for those cases; full-sized BMP frames can be encoded directly from their existing storage.
+                    ImageMetadata? metadata = this.encoder.SkipMetadata || encodingMetadata.Compression is not IconFrameCompression.Png ? null : image.Metadata.DeepClone();
+                    encodingImage = new Image<TPixel>(image.Configuration, width, height, metadata);
+
+                    for (int y = 0; y < height; y++)
                     {
-                        Quantizer = this.GetQuantizer(encodingMetadata, colorTable),
-                        ProcessedAlphaMask = true,
-                        UseDoubleHeight = true,
-                        SkipFileHeader = true,
-                        SupportTransparency = false,
-                        TransparentColorMode = this.encoder.TransparentColorMode,
-                        PixelSamplingStrategy = this.encoder.PixelSamplingStrategy,
-                        BitsPerPixel = encodingMetadata.BmpBitsPerPixel,
-                        SkipMetadata = this.encoder.SkipMetadata
-                    };
-
-                    BmpEncoderCore bmpEncoderCore = new(bmpEncoder, image.Configuration.MemoryAllocator);
-                    bmpEncoderCore.Encode(encodingFrame, stream, cancellationToken);
-                    break;
+                        frame.PixelBuffer.DangerousGetRowSpan(y)[..width].CopyTo(encodingImage.GetRootFramePixelBuffer().DangerousGetRowSpan(y));
+                    }
+
+                    if (!this.encoder.SkipMetadata && encodingMetadata.Compression is IconFrameCompression.Png)
+                    {
+                        encodingImage.Frames.RootFrame.Metadata.SetFormatMetadata(PngFormat.Instance, frame.Metadata.GetPngMetadata().DeepClone());
+                    }
                 }
 
-                case IconFrameCompression.Png:
+                ImageFrame<TPixel> sourceFrame = encodingImage?.Frames.RootFrame ?? frame;
+
+                // Compression and bitmap depth are per-entry, so the concrete encoder configuration must be selected per frame.
+                switch (encodingMetadata.Compression)
                 {
-                    PngEncoder pngEncoder = new()
+                    case IconFrameCompression.Bmp:
+                    {
+                        BmpEncoder bmpEncoder = new()
+                        {
+                            Quantizer = this.GetQuantizer(encodingMetadata, colorTable),
+                            ProcessedAlphaMask = true,
+                            UseDoubleHeight = true,
+                            SkipFileHeader = true,
+                            SupportTransparency = false,
+                            TransparentColorMode = this.encoder.TransparentColorMode,
+                            PixelSamplingStrategy = this.encoder.PixelSamplingStrategy,
+                            BitsPerPixel = encodingMetadata.BmpBitsPerPixel,
+                            SkipMetadata = this.encoder.SkipMetadata
+                        };
+
+                        BmpEncoderCore bmpEncoderCore = new(bmpEncoder, image.Configuration.MemoryAllocator);
+                        bmpEncoderCore.Encode(sourceFrame, image.Metadata, stream, cancellationToken);
+                        break;
+                    }
+
+                    case IconFrameCompression.Png:
                     {
-                        // Only 32bit Png supported.
-                        // https://devblogs.microsoft.com/oldnewthing/20101022-00/?p=12473
-                        BitDepth = PngBitDepth.Bit8,
-                        ColorType = PngColorType.RgbWithAlpha,
-                        TransparentColorMode = this.encoder.TransparentColorMode,
-                        CompressionLevel = PngCompressionLevel.BestCompression,
-                        SkipMetadata = this.encoder.SkipMetadata
-                    };
-
-                    using PngEncoderCore pngEncoderCore = new(image.Configuration, pngEncoder);
-                    pngEncoderCore.Encode(encodingFrame, stream, cancellationToken);
-                    break;
+                        PngEncoder pngEncoder = new()
+                        {
+                            // Only 32bit Png supported.
+                            // https://devblogs.microsoft.com/oldnewthing/20101022-00/?p=12473
+                            BitDepth = PngBitDepth.Bit8,
+                            ColorType = PngColorType.RgbWithAlpha,
+                            TransparentColorMode = this.encoder.TransparentColorMode,
+                            CompressionLevel = PngCompressionLevel.BestCompression,
+                            SkipMetadata = this.encoder.SkipMetadata
+                        };
+
+                        using PngEncoderCore pngEncoderCore = new(image.Configuration, pngEncoder);
+                        pngEncoderCore.Encode(encodingImage ?? image, stream, cancellationToken);
+                        break;
+                    }
+
+                    default:
+                        throw new NotSupportedException();
                 }
-
-                default:
-                    throw new NotSupportedException();
+            }
+            finally
+            {
+                encodingImage?.Dispose();
             }
 
             encodingMetadata.Entry.BytesInRes = checked((uint)(stream.Position - imageStart));

tests/ImageSharp.Tests/Formats/Ani/AniDecoderTests.cs

@@ -9,7 +9,7 @@ using static SixLabors.ImageSharp.Tests.TestImages.Ani;
 
 namespace SixLabors.ImageSharp.Tests.Formats.Ani;
 
-[Trait("format", "Ani")]
+[Trait("Format", "Ani")]
 [ValidateDisposedMemoryAllocations]
 public class AniDecoderTests
 {

tests/ImageSharp.Tests/Formats/Ani/AniEncoderTests.cs

@@ -3,8 +3,11 @@
 
 using System.Buffers.Binary;
 using SixLabors.ImageSharp.Formats.Ani;
+using SixLabors.ImageSharp.Formats.Bmp;
 using SixLabors.ImageSharp.Formats.Icon;
+using SixLabors.ImageSharp.Metadata.Profiles.Icc;
 using SixLabors.ImageSharp.PixelFormats;
+using SixLabors.ImageSharp.Tests.TestDataIcc;
 using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
 using static SixLabors.ImageSharp.Tests.TestImages.Ani;
 
@@ -133,6 +136,47 @@ public class AniEncoderTests
         Assert.Equal(frameFormat, decoded.Frames.RootFrame.Metadata.GetAniMetadata().FrameFormat);
     }
 
+    /// <summary>
+    /// Verifies that metadata suppression is propagated to every embedded resource encoder.
+    /// </summary>
+    [Theory]
+    [InlineData(AniFrameFormat.Ico)]
+    [InlineData(AniFrameFormat.Cur)]
+    [InlineData(AniFrameFormat.Bmp)]
+    public void AniEncoder_SkipMetadataPropagatesToEmbeddedEncoder(AniFrameFormat frameFormat)
+    {
+        using Image<Rgba32> image = new(16, 16, Color.Red.ToPixel<Rgba32>());
+        image.Metadata.IccProfile = new IccProfile(IccTestDataProfiles.ProfileRandomArray);
+
+        AniMetadata imageMetadata = image.Metadata.GetAniMetadata();
+        imageMetadata.BitCount = 32;
+        imageMetadata.Planes = 1;
+
+        AniFrameMetadata frameMetadata = image.Frames.RootFrame.Metadata.GetAniMetadata();
+        frameMetadata.FrameFormat = frameFormat;
+        frameMetadata.Compression = IconFrameCompression.Bmp;
+        frameMetadata.BmpBitsPerPixel = BmpBitsPerPixel.Bit32;
+
+        using MemoryStream stream = new();
+        image.Save(stream, new AniEncoder { SkipMetadata = true });
+
+        ReadOnlySpan<byte> encoded = stream.GetBuffer().AsSpan(0, (int)stream.Length);
+        int frameChunkOffset = encoded.IndexOf("icon"u8);
+        Assert.True(frameChunkOffset >= 0);
+
+        ReadOnlySpan<byte> resource = encoded[(frameChunkOffset + AniConstants.ChunkHeaderSize)..];
+        int dibOffset = 0;
+
+        if (frameFormat is not AniFrameFormat.Bmp)
+        {
+            dibOffset = checked((int)BinaryPrimitives.ReadUInt32LittleEndian(resource[(IconDir.Size + IconDirEntry.Size - sizeof(uint))..]));
+        }
+
+        // Metadata-free ICO/CUR bitmaps use BITMAPINFOHEADER, while raw transparent ANI bitmaps require BITMAPV4HEADER.
+        int expectedHeaderSize = frameFormat is AniFrameFormat.Bmp ? BmpInfoHeader.SizeV4 : BmpInfoHeader.SizeV3;
+        Assert.Equal(expectedHeaderSize, BinaryPrimitives.ReadInt32LittleEndian(resource[dibOffset..]));
+    }
+
     /// <summary>
     /// Verifies that an independent frame cannot collide with an explicit sequence group.
     /// </summary>
@@ -153,4 +197,46 @@ public class AniEncoderTests
         Assert.Equal(1, decoded.Frames[0].Metadata.GetAniMetadata().SequenceNumber);
         Assert.Equal(2, decoded.Frames[1].Metadata.GetAniMetadata().SequenceNumber);
     }
+
+    /// <summary>
+    /// Verifies that an explicit source sequence is preserved as an identity table after playback-order expansion.
+    /// </summary>
+    [Fact]
+    public void AniEncoder_PreservesExplicitSequence()
+    {
+        using Image<Rgba32> image = new(16, 16, Color.Red.ToPixel<Rgba32>());
+        image.Frames.AddFrame(image.Frames.RootFrame);
+        image.Metadata.GetAniMetadata().Flags = AniHeaderFlags.IsIcon | AniHeaderFlags.ContainsSequence;
+
+        using MemoryStream stream = new();
+        image.Save(stream, new AniEncoder());
+
+        ReadOnlySpan<byte> data = stream.GetBuffer().AsSpan(0, (int)stream.Length);
+        int sequenceOffset = data.IndexOf("seq "u8);
+
+        Assert.True(sequenceOffset >= 0);
+        Assert.Equal((uint)(2 * sizeof(uint)), BinaryPrimitives.ReadUInt32LittleEndian(data[(sequenceOffset + sizeof(uint))..]));
+        Assert.Equal(0U, BinaryPrimitives.ReadUInt32LittleEndian(data[(sequenceOffset + AniConstants.ChunkHeaderSize)..]));
+        Assert.Equal(1U, BinaryPrimitives.ReadUInt32LittleEndian(data[(sequenceOffset + AniConstants.ChunkHeaderSize + sizeof(uint))..]));
+
+        stream.Position = 0;
+        using Image<Rgba32> decoded = Image.Load<Rgba32>(stream);
+
+        Assert.True(decoded.Metadata.GetAniMetadata().Flags.HasFlag(AniHeaderFlags.ContainsSequence));
+    }
+
+    /// <summary>
+    /// Verifies that unsupported public frame metadata is rejected before any container data is written.
+    /// </summary>
+    [Fact]
+    public void AniEncoder_UnsupportedFrameFormatThrowsBeforeWriting()
+    {
+        using Image<Rgba32> image = new(16, 16);
+        image.Frames.RootFrame.Metadata.GetAniMetadata().FrameFormat = (AniFrameFormat)byte.MaxValue;
+
+        using MemoryStream stream = new();
+
+        Assert.Throws<ImageFormatException>(() => image.Save(stream, new AniEncoder()));
+        Assert.Equal(0, stream.Length);
+    }
 }

tests/ImageSharp.Tests/Formats/Icon/Ico/IcoEncoderTests.cs

@@ -4,6 +4,8 @@
 using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Cur;
 using SixLabors.ImageSharp.Formats.Ico;
+using SixLabors.ImageSharp.Formats.Icon;
+using SixLabors.ImageSharp.Metadata.Profiles.Exif;
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Tests.TestUtilities.ImageComparison;
 using static SixLabors.ImageSharp.Tests.TestImages.Cur;
@@ -121,4 +123,22 @@ public class IcoEncoderTests
             }
         });
     }
+
+    [Fact]
+    public void PngEntry_PreservesExifProfile()
+    {
+        using Image<Rgba32> image = new(16, 16);
+        image.Metadata.ExifProfile = new ExifProfile();
+        image.Metadata.ExifProfile.SetValue(ExifTag.Software, "ImageSharp");
+        image.Frames.RootFrame.Metadata.GetIcoMetadata().Compression = IconFrameCompression.Png;
+
+        using MemoryStream stream = new();
+        image.Save(stream, Encoder);
+
+        stream.Position = 0;
+        using Image<Rgba32> decoded = Image.Load<Rgba32>(stream);
+
+        Assert.NotNull(decoded.Metadata.ExifProfile);
+        Assert.Equal(image.Metadata.ExifProfile.Values, decoded.Metadata.ExifProfile.Values);
+    }
 }