Comments, docs, decoupling, removed redundant properties

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

@@ -106,13 +106,18 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
             this.SpectralBlocks = null;
         }
 
-        public void Init()
+        /// <summary>
+        /// Initializes component for future buffers initialization.
+        /// </summary>
+        /// <param name="maxSubFactorH">Maximal horizontal subsampling factor among all the components.</param>
+        /// <param name="maxSubFactorV">Maximal vertical subsampling factor among all the components.</param>
+        public void Init(int maxSubFactorH, int maxSubFactorV)
         {
             this.WidthInBlocks = (int)MathF.Ceiling(
-                MathF.Ceiling(this.Frame.PixelWidth / 8F) * this.HorizontalSamplingFactor / this.Frame.MaxHorizontalFactor);
+                MathF.Ceiling(this.Frame.PixelWidth / 8F) * this.HorizontalSamplingFactor / maxSubFactorH);
 
             this.HeightInBlocks = (int)MathF.Ceiling(
-                MathF.Ceiling(this.Frame.PixelHeight / 8F) * this.VerticalSamplingFactor / this.Frame.MaxVerticalFactor);
+                MathF.Ceiling(this.Frame.PixelHeight / 8F) * this.VerticalSamplingFactor / maxSubFactorV);
 
             int blocksPerLineForMcu = this.Frame.McusPerLine * this.HorizontalSamplingFactor;
             int blocksPerColumnForMcu = this.Frame.McusPerColumn * this.VerticalSamplingFactor;

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

@@ -69,16 +69,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// </summary>
         public JpegComponent[] Components { get; set; }
 
-        /// <summary>
-        /// Gets or sets the maximum horizontal sampling factor.
-        /// </summary>
-        public int MaxHorizontalFactor { get; set; }
-
-        /// <summary>
-        /// Gets or sets the maximum vertical sampling factor.
-        /// </summary>
-        public int MaxVerticalFactor { get; set; }
-
         /// <summary>
         /// Gets or sets the number of MCU's per line.
         /// </summary>
@@ -116,15 +106,17 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Decoder
         /// <summary>
         /// Allocates the frame component blocks.
         /// </summary>
-        public void InitComponents()
+        /// <param name="maxSubFactorH">Maximal horizontal subsampling factor among all the components.</param>
+        /// <param name="maxSubFactorV">Maximal vertical subsampling factor among all the components.</param>
+        public void Init(int maxSubFactorH, int maxSubFactorV)
         {
-            this.McusPerLine = (int)Numerics.DivideCeil((uint)this.PixelWidth, (uint)this.MaxHorizontalFactor * 8);
+            this.McusPerLine = (int)Numerics.DivideCeil((uint)this.PixelWidth, (uint)maxSubFactorH * 8);
-            this.McusPerColumn = (int)Numerics.DivideCeil((uint)this.PixelHeight, (uint)this.MaxVerticalFactor * 8);
+            this.McusPerColumn = (int)Numerics.DivideCeil((uint)this.PixelHeight, (uint)maxSubFactorV * 8);
 
             for (int i = 0; i < this.ComponentCount; i++)
             {
                 JpegComponent component = this.Components[i];
-                component.Init();
+                component.Init(maxSubFactorH, maxSubFactorV);
             }
         }
 

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -106,9 +106,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
         /// </summary>
         public JpegFrame Frame { get; private set; }
 
-        /// <inheritdoc/>
-        public Size ImageSizeInPixels { get; private set; }
-
         /// <inheritdoc/>
         Size IImageDecoderInternals.Dimensions => this.Frame.PixelSize;
 
@@ -845,12 +842,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             {
                 remaining -= length;
 
+                // Validity check: remaining part must be equal to components * 3
                 const int componentBytes = 3;
                 if (remaining != componentCount * componentBytes)
                 {
                     JpegThrowHelper.ThrowBadMarker("SOFn", remaining);
                 }
 
+                // components*3 bytes: component data
                 stream.Read(this.temp, 0, remaining);
 
                 // No need to pool this. They max out at 4
@@ -885,9 +884,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                     index += componentBytes;
                 }
 
-                this.Frame.MaxHorizontalFactor = maxH;
+                this.Frame.Init(maxH, maxV);
-                this.Frame.MaxVerticalFactor = maxV;
-                this.Frame.InitComponents();
 
                 this.scanDecoder.InjectFrameData(this.Frame, this);
             }

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

@@ -46,7 +46,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
                 Assert.Equal(1, decoder.Frame.ComponentCount);
                 Assert.Equal(1, decoder.Components.Length);
 
-                Size expectedSizeInBlocks = decoder.ImageSizeInPixels.DivideRoundUp(8);
+                Size expectedSizeInBlocks = decoder.Frame.PixelSize.DivideRoundUp(8);
 
                 Assert.Equal(expectedSizeInBlocks, decoder.Frame.McuSize);
 
@@ -70,7 +70,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
             using (JpegDecoderCore decoder = JpegFixture.ParseJpegStream(imageFile))
             {
                 sb.AppendLine(imageFile);
-                sb.AppendLine($"Size:{decoder.ImageSizeInPixels} MCU:{decoder.Frame.McuSize}");
+                sb.AppendLine($"Size:{decoder.Frame.PixelSize} MCU:{decoder.Frame.McuSize}");
                 JpegComponent c0 = decoder.Components[0];
                 JpegComponent c1 = decoder.Components[1];