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Apply ICC Profile / Color Conversion when decoding PNG #3028

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e965d3f
Apply color conversion when decoding PNG
Socolin Dec 5, 2025
bd532d6
Add tests to check if PngDecoder apply ICC profile
Socolin Dec 19, 2025
15d1151
Fix concurrency problem with MemoryAllocatorValidator
Socolin Dec 19, 2025
f8c8174
Rework ApplyIccProfile to use ProcessPixelRowsAsVector4
Socolin Dec 19, 2025
472089a
Use bulk overload to convert the pixel row from Vector4 to Rgb in App…
Socolin Dec 19, 2025
e6d62d0
Make sure pixel values are float between 0 and 1 during processing of…
Socolin Dec 19, 2025
7d06e6d
Use the same MemoryAllocator as the one of the image when decoding ic…
Socolin Dec 19, 2025
33aa0c8
Apply ICC profile when decoding InterlacedRgba PNG
Socolin Dec 20, 2025
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11 changes: 11 additions & 0 deletions src/ImageSharp/ColorProfiles/Rgb.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,17 @@ public static Rgb FromScaledVector4(Vector4 source)
public Vector4 ToScaledVector4()
=> new(this.AsVector3Unsafe(), 1F);

/// <summary>
/// Expands the color into a generic ("scaled") <see cref="Vector4"/> representation
/// with values scaled and usually clamped between <value>0</value> and <value>1</value>.
/// The vector components are typically expanded in least to greatest significance order.
/// </summary>
/// <param name="alpha">The alpha component.</param>
/// <returns>The <see cref="Vector4"/>.</returns>
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public Vector4 ToScaledVector4(float alpha)
=> new(this.AsVector3Unsafe(), 1F);

/// <inheritdoc/>
public static void ToScaledVector4(ReadOnlySpan<Rgb> source, Span<Vector4> destination)
{
Expand Down
109 changes: 95 additions & 14 deletions src/ImageSharp/Formats/Png/PngDecoderCore.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -7,9 +7,12 @@
using System.Globalization;
using System.IO.Compression;
using System.IO.Hashing;
using System.Numerics;
using System.Runtime.CompilerServices;
using System.Runtime.InteropServices;
using System.Text;
using SixLabors.ImageSharp.ColorProfiles;
using SixLabors.ImageSharp.ColorProfiles.Icc;
using SixLabors.ImageSharp.Common.Helpers;
using SixLabors.ImageSharp.Compression.Zlib;
using SixLabors.ImageSharp.Formats.Png.Chunks;
Expand All @@ -23,6 +26,7 @@
using SixLabors.ImageSharp.Metadata.Profiles.Icc;
using SixLabors.ImageSharp.Metadata.Profiles.Xmp;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;

namespace SixLabors.ImageSharp.Formats.Png;

Expand Down Expand Up @@ -212,6 +216,7 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
currentFrameControl = this.ReadFrameControlChunk(chunk.Data.GetSpan());
break;
case PngChunkType.FrameData:
{
if (frameCount >= this.maxFrames)
{
goto EOF;
Expand All @@ -229,13 +234,19 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance

this.InitializeFrame(previousFrameControl, currentFrameControl.Value, image, previousFrame, out currentFrame);

if (this.Options.TryGetIccProfileForColorConversion(metadata.IccProfile, out IccProfile? iccProfile))
{
metadata.IccProfile = null;
}

this.currentStream.Position += 4;
this.ReadScanlines(
chunk.Length - 4,
currentFrame,
pngMetadata,
this.ReadNextFrameDataChunk,
currentFrameControl.Value,
iccProfile,
cancellationToken);

// if current frame dispose is restore to previous, then from future frame's perspective, it never happened
Expand All @@ -246,7 +257,10 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
}

break;
}

case PngChunkType.Data:
{
pngMetadata.AnimateRootFrame = currentFrameControl != null;
currentFrameControl ??= new FrameControl((uint)this.header.Width, (uint)this.header.Height);
if (image is null)
Expand All @@ -257,12 +271,18 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
AssignColorPalette(this.palette, this.paletteAlpha, pngMetadata);
}

if (this.Options.TryGetIccProfileForColorConversion(metadata.IccProfile, out IccProfile? iccProfile))
{
metadata.IccProfile = null;
}

this.ReadScanlines(
chunk.Length,
image.Frames.RootFrame,
pngMetadata,
this.ReadNextDataChunk,
currentFrameControl.Value,
iccProfile,
cancellationToken);
if (pngMetadata.AnimateRootFrame)
{
Expand All @@ -276,6 +296,8 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
}

break;
}

case PngChunkType.Palette:
this.palette = chunk.Data.GetSpan().ToArray();
break;
Expand Down Expand Up @@ -323,6 +345,11 @@ protected override Image<TPixel> Decode<TPixel>(BufferedReadStream stream, Cance
PngThrowHelper.ThrowNoData();
}

if (this.Options.TryGetIccProfileForColorConversion(metadata.IccProfile, out IccProfile? iccProfileToApply))
{
ApplyRgbaCompatibleIccProfile(image, iccProfileToApply, CompactSrgbV4Profile.Profile);
}

return image;
}
catch
Expand Down Expand Up @@ -743,13 +770,15 @@ private int CalculateScanlineLength(int width)
/// <param name="pngMetadata">The png metadata</param>
/// <param name="getData">A delegate to get more data from the inner stream for <see cref="ZlibInflateStream"/>.</param>
/// <param name="frameControl">The frame control</param>
/// <param name="iccProfile">Optional ICC profile for color conversion.</param>
/// <param name="cancellationToken">The cancellation token.</param>
private void ReadScanlines<TPixel>(
int chunkLength,
ImageFrame<TPixel> image,
PngMetadata pngMetadata,
Func<int> getData,
in FrameControl frameControl,
IccProfile? iccProfile,
CancellationToken cancellationToken)
where TPixel : unmanaged, IPixel<TPixel>
{
Expand All @@ -763,11 +792,11 @@ private void ReadScanlines<TPixel>(

if (this.header.InterlaceMethod is PngInterlaceMode.Adam7)
{
this.DecodeInterlacedPixelData(frameControl, dataStream, image, pngMetadata, cancellationToken);
this.DecodeInterlacedPixelData(frameControl, dataStream, image, pngMetadata, iccProfile, cancellationToken);
}
else
{
this.DecodePixelData(frameControl, dataStream, image, pngMetadata, cancellationToken);
this.DecodePixelData(frameControl, dataStream, image, pngMetadata, iccProfile, cancellationToken);
}
}

Expand All @@ -779,12 +808,14 @@ private void ReadScanlines<TPixel>(
/// <param name="compressedStream">The compressed pixel data stream.</param>
/// <param name="imageFrame">The image frame to decode to.</param>
/// <param name="pngMetadata">The png metadata</param>
/// <param name="iccProfile">Optional ICC profile for color conversion.</param>
/// <param name="cancellationToken">The CancellationToken</param>
private void DecodePixelData<TPixel>(
FrameControl frameControl,
DeflateStream compressedStream,
ImageFrame<TPixel> imageFrame,
PngMetadata pngMetadata,
IccProfile? iccProfile,
CancellationToken cancellationToken)
where TPixel : unmanaged, IPixel<TPixel>
{
Expand Down Expand Up @@ -851,7 +882,7 @@ private void DecodePixelData<TPixel>(
break;
}

this.ProcessDefilteredScanline(frameControl, currentRow, scanSpan, imageFrame, pngMetadata, blendRowBuffer);
this.ProcessDefilteredScanline(frameControl, currentRow, scanSpan, imageFrame, pngMetadata, blendRowBuffer, iccProfile);
this.SwapScanlineBuffers();
currentRow++;
}
Expand All @@ -869,12 +900,14 @@ private void DecodePixelData<TPixel>(
/// <param name="compressedStream">The compressed pixel data stream.</param>
/// <param name="imageFrame">The current image frame.</param>
/// <param name="pngMetadata">The png metadata.</param>
/// <param name="iccProfile">Optional ICC profile for color conversion.</param>
/// <param name="cancellationToken">The cancellation token.</param>
private void DecodeInterlacedPixelData<TPixel>(
in FrameControl frameControl,
DeflateStream compressedStream,
ImageFrame<TPixel> imageFrame,
PngMetadata pngMetadata,
IccProfile? iccProfile,
CancellationToken cancellationToken)
where TPixel : unmanaged, IPixel<TPixel>
{
Expand Down Expand Up @@ -965,6 +998,7 @@ private void DecodeInterlacedPixelData<TPixel>(
rowSpan,
pngMetadata,
blendRowBuffer,
iccProfile,
pixelOffset: Adam7.FirstColumn[pass],
increment: Adam7.ColumnIncrement[pass]);

Expand Down Expand Up @@ -1003,13 +1037,15 @@ private void DecodeInterlacedPixelData<TPixel>(
/// <param name="pixels">The image</param>
/// <param name="pngMetadata">The png metadata.</param>
/// <param name="blendRowBuffer">A span used to temporarily hold the decoded row pixel data for alpha blending.</param>
/// <param name="iccProfile">Optional ICC profile for color conversion.</param>
private void ProcessDefilteredScanline<TPixel>(
in FrameControl frameControl,
int currentRow,
ReadOnlySpan<byte> scanline,
ImageFrame<TPixel> pixels,
PngMetadata pngMetadata,
Span<TPixel> blendRowBuffer)
Span<TPixel> blendRowBuffer,
IccProfile? iccProfile)
where TPixel : unmanaged, IPixel<TPixel>
{
Span<TPixel> destination = pixels.PixelBuffer.DangerousGetRowSpan(currentRow);
Expand Down Expand Up @@ -1043,7 +1079,8 @@ private void ProcessDefilteredScanline<TPixel>(
in frameControl,
scanlineSpan,
rowSpan,
pngMetadata.TransparentColor);
pngMetadata.TransparentColor,
iccProfile);

break;

Expand All @@ -1054,7 +1091,8 @@ private void ProcessDefilteredScanline<TPixel>(
scanlineSpan,
rowSpan,
(uint)this.bytesPerPixel,
(uint)this.bytesPerSample);
(uint)this.bytesPerSample,
iccProfile);

break;

Expand All @@ -1063,7 +1101,8 @@ private void ProcessDefilteredScanline<TPixel>(
in frameControl,
scanlineSpan,
rowSpan,
pngMetadata.ColorTable);
pngMetadata.ColorTable,
iccProfile);

break;

Expand All @@ -1076,7 +1115,8 @@ private void ProcessDefilteredScanline<TPixel>(
rowSpan,
this.bytesPerPixel,
this.bytesPerSample,
pngMetadata.TransparentColor);
pngMetadata.TransparentColor,
iccProfile);

break;

Expand All @@ -1088,7 +1128,8 @@ private void ProcessDefilteredScanline<TPixel>(
scanlineSpan,
rowSpan,
this.bytesPerPixel,
this.bytesPerSample);
this.bytesPerSample,
iccProfile);

break;
}
Expand All @@ -1115,6 +1156,7 @@ private void ProcessDefilteredScanline<TPixel>(
/// <param name="destination">The current image row.</param>
/// <param name="pngMetadata">The png metadata.</param>
/// <param name="blendRowBuffer">A span used to temporarily hold the decoded row pixel data for alpha blending.</param>
/// <param name="iccProfile">Optional ICC profile for color conversion.</param>
/// <param name="pixelOffset">The column start index. Always 0 for none interlaced images.</param>
/// <param name="increment">The column increment. Always 1 for none interlaced images.</param>
private void ProcessInterlacedDefilteredScanline<TPixel>(
Expand All @@ -1123,6 +1165,7 @@ private void ProcessInterlacedDefilteredScanline<TPixel>(
Span<TPixel> destination,
PngMetadata pngMetadata,
Span<TPixel> blendRowBuffer,
IccProfile? iccProfile,
int pixelOffset = 0,
int increment = 1)
where TPixel : unmanaged, IPixel<TPixel>
Expand Down Expand Up @@ -1157,7 +1200,8 @@ private void ProcessInterlacedDefilteredScanline<TPixel>(
rowSpan,
(uint)pixelOffset,
(uint)increment,
pngMetadata.TransparentColor);
pngMetadata.TransparentColor,
iccProfile);

break;

Expand All @@ -1170,7 +1214,8 @@ private void ProcessInterlacedDefilteredScanline<TPixel>(
(uint)pixelOffset,
(uint)increment,
(uint)this.bytesPerPixel,
(uint)this.bytesPerSample);
(uint)this.bytesPerSample,
iccProfile);

break;

Expand All @@ -1181,7 +1226,8 @@ private void ProcessInterlacedDefilteredScanline<TPixel>(
rowSpan,
(uint)pixelOffset,
(uint)increment,
pngMetadata.ColorTable);
pngMetadata.ColorTable,
iccProfile);

break;

Expand All @@ -1196,7 +1242,8 @@ private void ProcessInterlacedDefilteredScanline<TPixel>(
(uint)increment,
this.bytesPerPixel,
this.bytesPerSample,
pngMetadata.TransparentColor);
pngMetadata.TransparentColor,
iccProfile);

break;

Expand All @@ -1210,7 +1257,8 @@ private void ProcessInterlacedDefilteredScanline<TPixel>(
(uint)pixelOffset,
(uint)increment,
this.bytesPerPixel,
this.bytesPerSample);
this.bytesPerSample,
iccProfile);

break;
}
Expand Down Expand Up @@ -2153,4 +2201,37 @@ private static bool IsXmpTextData(ReadOnlySpan<byte> keywordBytes)

private void SwapScanlineBuffers()
=> (this.scanline, this.previousScanline) = (this.previousScanline, this.scanline);

private static void ApplyRgbaCompatibleIccProfile<TPixel>(Image<TPixel> image, IccProfile sourceProfile, IccProfile destinationProfile)
where TPixel : unmanaged, IPixel<TPixel>
{
ColorConversionOptions options = new()
{
SourceIccProfile = sourceProfile,
TargetIccProfile = destinationProfile,
MemoryAllocator = image.Configuration.MemoryAllocator,
};

ColorProfileConverter converter = new(options);

image.Mutate(o => o.ProcessPixelRowsAsVector4(
(pixelsRow, _) =>
{
using IMemoryOwner<Rgb> rgbBuffer = image.Configuration.MemoryAllocator.Allocate<Rgb>(pixelsRow.Length);
Span<Rgb> rgbPacked = rgbBuffer.Memory.Span;

Rgb.FromScaledVector4(pixelsRow, rgbPacked);
converter.Convert<Rgb, Rgb>(rgbPacked, rgbPacked);

Span<float> pixelsRowAsFloats = MemoryMarshal.Cast<Vector4, float>(pixelsRow);
ref float pixelsRowAsFloatsRef = ref MemoryMarshal.GetReference(pixelsRowAsFloats);

int cIdx = 0;
for (int x = 0; x < pixelsRow.Length; x++, cIdx += 4)
{
Unsafe.As<float, Rgb>(ref Unsafe.Add(ref pixelsRowAsFloatsRef, cIdx)) = rgbPacked[x];
}
},
PixelConversionModifiers.Scale));
}
}
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