sRGB to CMYK color conversion (Not Image) with icc profile using xc: and -format

[necessarylion]

Hi, I have a magick command that can convert sRGB color to CMYK color using icc profile.
I am looking for alternative solution using this magick-wasm library.

magick xc:"srgb(255,255,255,255)" -profile sRGB.icc -profile CoatedFOGRA39.icc -colorspace CMYK  -format '%[pixel:u]' info:

OUTPUT - cmyk(0,0.622568,0.0933852,0)

References

• https://stackoverflow.com/a/47023522/9773835
• https://stackoverflow.com/a/48191994/9773835

[dlemstra]

What have you tried so far and where are you stuck?

[necessarylion]

I haven't tried any solutions yet, as the package might not be designed for this purpose.

I'm looking for something like:

image.xc("srgb(255,255,255,255)")
image.format("%[pixel:u]", ":info") 

or perhaps a function to execute custom commands.
or perhaps color converter function in MagickColor class.

I try to use jsColorEngine, but the output doesn't quite match what I get with ImageMagick.

Currently, to convert colors, I rely on a backend service where ImageMagick is installed. I'm searching for a solution to perform this conversion directly in the browser using JavaScript.

[dlemstra]

xc:"srgb(255,255,255,255)" should be the name of the image e.g. : new MagickImage('xc:srgb(255,255,255,255)') but the format argument is not yet available in the api. I can add this for you.

[dlemstra]

This shouldn't be that difficult to add. I now also wonder if the transformColorSpace method should change the colorSpace of the image to the colorSpace of the target profile. I was creating a unit test and after setting the profile I also had to change the colorSpace before the correct value would be returned in the new formatExpression method. Your thoughts?

[necessarylion]

I'm not entirely sure how transformColorSpace works, but I believe it would be better to follow the standard approach of the parent ImageMagick command:

magick -profile input.icc -profile output.icc

For example, when transforming a color space, we typically use profiles twice and setting color space separately. Therefore, it should look like this:

image.profile(input);
image.profile(output);
image.colorSpace = ColorSpace.CMYK;

I use the gm npm package (https://www.npmjs.com/package/gm) on the server side for my app. And Its design also requires handling profile twice and setting the colorspace have to done separately.

const imgMagick = gm.subClass({ imageMagick: '7+' })
imgMagick(bytes)
  .profile(inputProfile)
  .profile(outputProfile)
  .colorspace('CMYK')
  .background('#FFFFFF')
  .flatten()
  .quality(100)
  .setFormat('jpg')
  .trim()
  .toBuffer((err, buffer) => {
    if (err) rejects(err)
    if (buffer) resolve(Uint8Array.from(buffer))
  })

[dlemstra]

I checked this with my Magick.NET library and I want it to behave in the same way.

I just pushed a patch to remove the name argument of ColorSpace constructor. Only icc will be used in the future. The transformColorSpace should change the colorSpace of an image using the specified color profile. In the next release you no longer need to do image.colorSpace = ColorSpace.CMYK;. You can still do this but you don't need to do it anymore.

[dlemstra]

I also pushed a patch to add formatExpression to MagickImage, this will become available in the next release.

[necessarylion]

Yeah. It Make scene. Thanks for the adding this feature.

[necessarylion]

Hi, @dlemstra
While I was testing newly added feature formatExpression. I found out that the result did not match exactly (but correct).

I convert this srgb(255,255,255,255)
and in CLI command got this cmyk(0,0.622568,0.0933852,0).
But in magick-wasm I got this cmyk(0,1,0,0).

So basically, in wasm version, values are parsed into integer.

So not sure if we can use -precision for it. I try to check if there is precision function, unfortunately there is not.

[necessarylion]

Seem like Q16.

Version: ImageMagick 7.1.1-38 Q16-HDRI aarch64 22398 https://imagemagick.org
Copyright: (C) 1999 ImageMagick Studio LLC
License: https://imagemagick.org/script/license.php
Features: Cipher DPC HDRI Modules OpenMP
Delegates (built-in): bzlib fontconfig freetype gslib heic jng jp2 jpeg jxl lcms lqr ltdl lzma openexr png ps raw tiff webp xml zlib zstd
Compiler: gcc (4.2)

Yeah. no need to add -precision for now.

[dlemstra]

This is indeed happening because of the Q8 depth. And I also though I did not need to add the ColorTransformMode but it turns out I need to do that to keep the results the same as the Magick.NET library. This will also become available in the next release.

[necessarylion]

Really appreciate your support. Looking forward for the release.

[dlemstra]

Just to clarify the next release will still show it as integers instead of floating point numbers because this wasm library has a quantum depth of 8 bit and not 16 bit.

[necessarylion]

It should be fine. Thanks.