Fixed spectral block border pixel padding

src/ImageSharp/Formats/Jpeg/Components/Encoder/ComponentProcessor.cs

@@ -43,13 +43,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
         public void CopyColorBufferToBlocks(int spectralStep)
         {
             Buffer2D<Block8x8> spectralBuffer = this.component.SpectralBlocks;
-
-            // should be this.frame.MaxColorChannelValue
-            // but 12-bit jpegs are not supported currently
-            float normalizationValue = -128f;
-
             int destAreaStride = this.ColorBuffer.Width;
-
             int yBlockStart = spectralStep * this.component.SamplingFactors.Height;
 
             Block8x8F workspaceBlock = default;
@@ -77,7 +71,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
                         destAreaStride);
 
                     // level shift via -128f
-                    workspaceBlock.AddInPlace(normalizationValue);
+                    workspaceBlock.AddInPlace(-128f);
 
                     // FDCT
                     FastFloatingPointDCT.TransformFDCT(ref workspaceBlock);

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

@@ -98,9 +98,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
 
             int pixelBufferLastVerticalIndex = this.pixelBuffer.Height - 1;
 
+            // Pixel strides must be padded with the last pixel of the stride
+            int paddingStartIndex = this.pixelBuffer.Width;
+            int paddedPixelsCount = this.alignedPixelWidth - this.pixelBuffer.Width;
+
             Span<float> rLane = this.redLane.GetSpan();
             Span<float> gLane = this.greenLane.GetSpan();
             Span<float> bLane = this.blueLane.GetSpan();
+
             for (int yy = start; yy < end; yy++)
             {
                 int y = yy - this.pixelRowCounter;
@@ -110,6 +115,10 @@ namespace SixLabors.ImageSharp.Formats.Jpeg.Components.Encoder
                 Span<TPixel> sourceRow = this.pixelBuffer.DangerousGetRowSpan(srcIndex);
                 PixelOperations<TPixel>.Instance.UnpackIntoRgbPlanes(rLane, gLane, bLane, sourceRow);
 
+                rLane.Slice(paddingStartIndex).Fill(rLane[paddingStartIndex - 1]);
+                gLane.Slice(paddingStartIndex).Fill(gLane[paddingStartIndex - 1]);
+                bLane.Slice(paddingStartIndex).Fill(bLane[paddingStartIndex - 1]);
+
                 // Convert from rgb24 to target pixel type
                 var values = new JpegColorConverterBase.ComponentValues(this.componentProcessors, y);
                 this.colorConverter.ConvertFromRgb(values, rLane, gLane, bLane);

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

@@ -148,6 +148,7 @@ namespace SixLabors.ImageSharp.Tests.Formats.Jpg
         [WithTestPatternImages(nameof(BitsPerPixel_Quality), 48, 24, PixelTypes.Rgba32)]
         [WithTestPatternImages(nameof(BitsPerPixel_Quality), 46, 8, PixelTypes.Rgba32)]
         [WithTestPatternImages(nameof(BitsPerPixel_Quality), 51, 7, PixelTypes.Rgba32)]
+        [WithTestPatternImages(nameof(BitsPerPixel_Quality), 7, 5, PixelTypes.Rgba32)]
         public void EncodeBaseline_WithSmallImages_WorksWithDifferentSizes<TPixel>(TestImageProvider<TPixel> provider, JpegEncodingColor colorType, int quality)
             where TPixel : unmanaged, IPixel<TPixel> => TestJpegEncoderCore(provider, colorType, quality, comparer: ImageComparer.Tolerant(0.15f));