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ImageSharp 4.1.3 misclassifies linear RGB ICC profiles as sRGB

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csharp
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backend

Hướng nghiên cứu

The suspected cause is IsCanonicalSrgbMatrixTrc() in src/ImageSharp/Metadata/Profiles/ICC/IccProfile.SRGB.cs, which compares the red, green and blue curves but not whether they are the sRGB transfer function. Start with the reproduction ZIP linked in the issue and run it in both DEBUG and RELEASE to see the four failing assertions. Done means linear gamma=1 profiles are not classed as sRGB, Convert produces the expected pixel values, and Compact keeps the profile.

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Mô tả

needs triage
Prerequisites
  • I have written a descriptive issue title
  • I have verified that I am running the latest version of ImageSharp
  • I have verified if the problem exist in both DEBUG and RELEASE mode
  • I have searched open and closed issues to ensure it has not already been reported
ImageSharp version

4.1.3

Other ImageSharp packages and versions

None

Environment (Operating system, version and so on)

Ubuntu WSL2, Linux x64, .NET SDK 10.0.112

.NET Framework version

.NET 10.0.12

Description

ImageSharp 4.1.3 incorrectly classifies certain linear RGB ICC profiles as canonical sRGB.

When decoding JPEG or PNG images containing a linear RGB ICC profile with sRGB primaries and gamma=1, ColorProfileHandling.Convert removes the ICC profile without converting the pixel values to sRGB.

PNG:
Actual RGB: [32,64,128]
Expected sRGB: [99,137,188]

JPEG:
Actual RGB: [40,80,120]
Expected sRGB: [110,152,182]

The expected values were independently verified using Little CMS 2.17.

ColorProfileHandling.Compact also incorrectly removes the non-sRGB ICC profile while leaving the RGB values unchanged.

The defect occurs immediately after Image.Load returns, before orientation correction, metadata removal or output encoding.

The issue reproduces identically in both DEBUG and RELEASE configurations with .NET 10.

Suspected cause:
The IsCanonicalSrgbMatrixTrc() method checks that the red, green and blue tone reproduction curves match, but does not verify that they implement the actual sRGB transfer function. Therefore, identical linear gamma=1 curves may be incorrectly classified as canonical sRGB.

Source:
https://github.com/SixLabors/ImageSharp/blob/v4.1.3/src/ImageSharp/Metadata/Profiles/ICC/IccProfile.SRGB.cs

Impact:
This defect can cause incorrect photographic colors when an ICC profile is removed without performing the necessary color transformation.

Could the maintainers confirm this issue and advise whether a fix or officially supported workaround is available for ImageSharp 4.1.x?

Steps to Reproduce

Steps to reproduce:

  1. Use SixLabors.ImageSharp 4.1.3 with .NET 10 on Linux x64 (Ubuntu WSL2).

  2. Extract the attached reproduction ZIP into a clean directory and follow its README instructions. Use a valid Six Labors license stored outside the project.

  3. Restore the locked NuGet dependencies and compile the reproduction project.

  4. Run the reproduction in both DEBUG and RELEASE configurations.

  5. The supplied synthetic JPEG and PNG images contain an ICC v4.3 RGB profile with sRGB primaries and linear gamma=1 transfer curves.

  6. Load the images using Image.Load with ColorProfileHandling.Convert, Compact and Preserve.

  7. Inspect the RGB pixel values and ICC profile immediately after decoding.

  8. Compare the results against the expected sRGB values independently verified using Little CMS 2.17.

Expected versus actual results:

PNG Convert:
Expected RGB: [99,137,188]
Actual RGB: [32,64,128]
ICC: Absent in both cases.

JPEG Convert:
Expected RGB: [110,152,182]
Actual RGB: [40,80,120]
ICC: Absent in both cases.

PNG Compact:
Expected RGB: [32,64,128]
Actual RGB: [32,64,128]
Expected ICC: Present
Actual ICC: Absent

JPEG Compact:
Expected RGB: [40,80,120]
Actual RGB: [40,80,120]
Expected ICC: Present
Actual ICC: Absent

Verification:

The defect reproduces identically in DEBUG and RELEASE.

Two Preserve control assertions pass.
Four assertions fail.
Exit code 1 is intentional because the tests detect the defect.

The problem occurs immediately after Image.Load returns, before orientation correction, metadata removal or PNG encoding.

The attached ZIP contains the minimal .NET 10 project, synthetic JPEG/PNG/ICC fixtures, instructions, expected results and SHA-256 hashes.

No license credentials, customer images or proprietary code are included.

Images

imagesharp-4.1.3-linear-icc-repro.zip

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