Jpeg loaded with pink color blur

[teamnimbus]

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

2.1.2

Other ImageSharp packages and versions

2.1.3, 3.0.0-alpha.0.11, 3.0.0-alpha.0.21

Environment (Operating system, version and so on)

Windows 10 21H1 x64

.NET Framework version

.Net 6.0

Description

We stumbled on a Jpeg image that gets loaded with wrong colors on all versions after 2.1.1. Tested with 2.1.2, 2.1.3, 3.0.0-alpha.0.11 and 3.0.0-alpha.0.21.
This is very similar to issues #2133, #2141 and #2152. However we don't think it's a duplicate since it's not fixed in either 2.1.3 (like #2133) or 3.0.0-alpha.0.11 (like #2141 / #2152).

Steps to Reproduce

This NUnit test passes on 2.1.1 and fails on all later versions with "Expected: Rgba32(255, 255, 255, 255) But was: Rgba32(255, 128, 128, 255)".

[Test]
public async Task ImageShouldNotBePink()
{
	var response = await new HttpClient().GetAsync("https://www.mottafashionplace.com/media/catalog/product/1/0/10085001_11.jpg");
	await using var imageStream = await response.Content.ReadAsStreamAsync();

	var image = Image.Load<Rgba32>(imageStream);

	Assert.That(image[0, 0], Is.EqualTo(new Rgba32(255, 255, 255, 255)));
}

Images

We don't own the problematic image so we can't distribute it. You can download it and use it as a starting point to create another image with the same properties.

[brianpopow]

The image has 3 components with no subsampling, that's why ImageSharp deduces the colorspace to RGB. It seems it should be YCbCr instead, but I am not sure how we can come to this conclusion from the components info's. The component Id's are 0, 1 and 2.

I wish the jpeg spec would define the color space properly. This guessing the colorspace from the component info's really gets out of hand.

[br3aker]

The image has 3 components with no subsampling, that's why ImageSharp deduces the colorspace to RGB. It seems it should be YCbCr instead, but I am not sure how we can come to this conclusion from the components info's. The component Id's are 0, 1 and 2.

Actually it should be ycbcr regardless of the components' ids: 3 components without APP14 marker is YCbCr. RGB colorspace is defined by App14 marker with flag=0.

AFAIR we had this check did we change it some time ago?

P.S.
First time seeing [0, 1, 2] components' ids. It's usually [1, 2, 3] for ycbcr or [82,71,66] for rgb. Most likely we have some colorspace deduction based on ids.

[brianpopow]

Actually it should be ycbcr regardless of the components' ids: 3 components without APP14 marker is YCbCr. RGB colorspace is defined by App14 marker with flag=0.

@br3aker: The colorspace is determined as RGB, because it has 3 components and no subsampling, but it also has no APP14 marker. So this seems wrong then. It was introduced with #2124, with commit: 89668a6.

[br3aker]

So this seems wrong then. It was introduced with #2124, with commit: 89668a6.

I guess we just need to remove final if check here and return ycbcr as a fallback colorspace:

ImageSharp/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

Lines 534 to 540 in e7a10b0

	if (this.Components[2].Id == 3 && this.Components[1].Id == 2 && this.Components[0].Id == 1)
	{
	return JpegColorSpace.YCbCr;
	}
	JpegThrowHelper.ThrowNotSupportedColorSpace();
	}

[br3aker]

Oh wait, it's actually an app14 code path.

Colorspace deduction is done here:

ImageSharp/src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

Line 510 in e7a10b0

private JpegColorSpace DeduceJpegColorSpace(byte componentCount)

IMO we should remove any id-based deduction:

if(has App14)
{
    // current logic works fine
}
else
{
    // spec doesn't say anything about id-based color deduction
    // [1, 2, 3] == YCbCr worked before but image from this issue
    // has [0, 1, 2] ids and yet is completely valid according to the spec
    // AFAIR adobe spec about jpeg colorspace defines RGB colorspace
    // only if App14 is present
    return ColorSpace.YCbCr;
}

[JimBobSquarePants]

Was just reading through the decoder there as the condition looked incorrect. Agreed on the fix.

[br3aker]

I'll open PR today.