CalculateJpegChannelSizes()

src/ImageSharp/Formats/Jpeg/Common/ComponentUtils.cs

@@ -81,18 +81,45 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Common
         public static bool IsChromaComponent(this IJpegComponent component) =>
             component.Index > 0 && component.Index < 3;
 
-        public static Size CalculateJpegChannelSize(this IJpegComponent component, SubsampleRatio ratio = SubsampleRatio.Undefined)
+        public static Size[] CalculateJpegChannelSizes(IEnumerable<IJpegComponent> components, SubsampleRatio ratio)
         {
-            Size size = new Size(component.WidthInBlocks, component.HeightInBlocks) * 8;
+            IJpegComponent[] c = components.ToArray();
+            Size[] sizes = new Size[c.Length];
 
-            if (component.IsChromaComponent())
+            Size s0 = new Size(c[0].WidthInBlocks, c[0].HeightInBlocks) * 8;
+            sizes[0] = s0;
+
+            if (c.Length > 1)
             {
-                return ratio.CalculateChrominanceSize(size.Width, size.Height);
+                Size chromaSize = ratio.CalculateChrominanceSize(s0.Width, s0.Height);
+                sizes[1] = chromaSize;
+
+                if (c.Length > 2)
+                {
+                    sizes[2] = chromaSize;
+                }
             }
-            else
+
+            if (c.Length > 3)
             {
-                return size;
+                sizes[3] = s0;
             }
+
+            return sizes;
         }
+
+        //public static Size CalculateJpegChannelSize(this IJpegComponent component, SubsampleRatio ratio = SubsampleRatio.Undefined)
+        //{
+        //    Size size = new Size(component.WidthInBlocks, component.HeightInBlocks) * 8;
+
+        //    if (component.IsChromaComponent())
+        //    {
+        //        return ratio.CalculateChrominanceSize(size.Width, size.Height);
+        //    }
+        //    else
+        //    {
+        //        return size;
+        //    }
+        //}
     }
 }

src/ImageSharp/Formats/Jpeg/GolangPort/Components/Decoder/OrigJpegPixelArea.cs

@@ -42,7 +42,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
             : this(Buffer2D<byte>.CreateClean(size))
         {
         }
-        
+
         /// <summary>
         /// Gets the pixels buffer.
         /// </summary>
@@ -83,12 +83,6 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort.Components.Decoder
             }
         }
 
-        public static OrigJpegPixelArea CreateForComponent(IJpegComponent component, SubsampleRatio ratio = SubsampleRatio.Undefined)
-        {
-            Size size = component.CalculateJpegChannelSize(ratio);
-            return new OrigJpegPixelArea(size);
-        }
-
         /// <summary>
         /// Gets the subarea that belongs to the Block8x8 defined by block indices
         /// </summary>

src/ImageSharp/Formats/Jpeg/GolangPort/OrigJpegDecoderCore.cs

@@ -782,19 +782,21 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.GolangPort
         /// </summary>
         private void InitJpegImageChannels()
         {
+            Size[] sizes = ComponentUtils.CalculateJpegChannelSizes(this.Components, this.SubsampleRatio);
+
             if (this.ComponentCount == 1)
             {
-                this.grayImage = OrigJpegPixelArea.CreateForComponent(this.Components[0]);
+                this.grayImage = new OrigJpegPixelArea(sizes[0]);
             }
             else
             {
-                Size size = this.Components[0].CalculateJpegChannelSize();
+                Size size = sizes[0];
 
                 this.ycbcrImage = new YCbCrImage(size.Width, size.Height, this.SubsampleRatio);
 
                 if (this.ComponentCount == 4)
                 {
-                    this.blackImage = OrigJpegPixelArea.CreateForComponent(this.Components[3]);
+                    this.blackImage = new OrigJpegPixelArea(sizes[3]);
                 }
             }
         }

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

@@ -69,15 +69,17 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
         }
 
         [Fact]
-        public void CalculateJpegChannelSize_Grayscale()
+        public void CalculateJpegChannelSizes_Grayscale()
         {
             using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(TestImages.Jpeg.Baseline.Jpeg400))
             {
-                Assert.Equal(1, decoder.ComponentCount);
+                Size[] sizes = ComponentUtils.CalculateJpegChannelSizes(decoder.Components, decoder.SubsampleRatio);
+
+                Assert.Equal(1, sizes.Length);
+
                 Size expected = decoder.Components[0].SizeInBlocks() * 8;
-                Size actual = decoder.Components[0].CalculateJpegChannelSize(decoder.SubsampleRatio);
 
-                Assert.Equal(expected, actual);
+                Assert.Equal(expected, sizes[0]);
             }
         }
 
@@ -85,38 +87,40 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
         [InlineData(TestImages.Jpeg.Baseline.Calliphora, 1)]
         [InlineData(TestImages.Jpeg.Baseline.Jpeg444, 1)]
         [InlineData(TestImages.Jpeg.Baseline.Jpeg420, 2)]
-        public void CalculateJpegChannelSize_YCbCr(
+        public void CalculateJpegChannelSizes_YCbCr(
             string imageFile,
             int chromaDiv)
         {
             using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(imageFile))
             {
-                Size ySize = decoder.Components[0].SizeInBlocks() * 8;
-                Size cSize = decoder.Components[1].SizeInBlocks() * 8 / chromaDiv;
+                Size[] s = ComponentUtils.CalculateJpegChannelSizes(decoder.Components, decoder.SubsampleRatio);
 
-                Size s0 = decoder.Components[0].CalculateJpegChannelSize(decoder.SubsampleRatio);
-                Size s1 = decoder.Components[1].CalculateJpegChannelSize(decoder.SubsampleRatio);
-                Size s2 = decoder.Components[2].CalculateJpegChannelSize(decoder.SubsampleRatio);
+                Assert.Equal(3, s.Length);
 
-                Assert.Equal(ySize, s0);
-                Assert.Equal(cSize, s1);
-                Assert.Equal(cSize, s2);
+                Size ySize = decoder.Components[0].SizeInBlocks() * 8;
+                Size cSize = ySize / chromaDiv;
+
+                Assert.Equal(ySize, s[0]);
+                Assert.Equal(cSize, s[1]);
+                Assert.Equal(cSize, s[2]);
             }
         }
 
         [Theory]
         [InlineData(TestImages.Jpeg.Baseline.Ycck)]
         [InlineData(TestImages.Jpeg.Baseline.Cmyk)]
-        public void CalculateJpegChannelSize_4Chan(string imageFile)
+        public void CalculateJpegChannelSizes_4Chan(string imageFile)
         {
             using (OrigJpegDecoderCore decoder = JpegFixture.ParseStream(imageFile))
             {
+                Size[] sizes = ComponentUtils.CalculateJpegChannelSizes(decoder.Components, decoder.SubsampleRatio);
+                Assert.Equal(4, sizes.Length);
+
                 Size expected = decoder.Components[0].SizeInBlocks() * 8;
 
-                foreach (OrigComponent component in decoder.Components)
+                foreach (Size s in sizes)
                 {
-                    Size actual = component.CalculateJpegChannelSize(decoder.SubsampleRatio);
-                    Assert.Equal(expected, actual);
+                    Assert.Equal(expected, s);
                 }
             }
         }