Creating images for print using CMYK

[jimmyff]

Hi, I've created some tools using this library for generating print material, however I've realised I need to really be handling CMYK colours rather than RGB so the material will look brighter and will give more reliable results.

Is there a way to do this? I'm using functions such as like getPixelRgb / setPixelRgba for masking. The abstract Color class only mentions rgb.

Thanks

[brendan-duncan]

Hi, Unfortunately there isn't much in there to support CMYK. Images are centered around RGB(A). You could convert an image to CMYK by making it a 4 channel image (traditionally RGBA), convert it to CMYK yourself, and treating the 4 channels like CMYK. But none of the filter functions know about CMYK.

You could convert an image to CMYK using something like

import 'dart:math';
Image convertToCMYK(Image rgbImage) {
  final cmykImage = rgbImage.convert(numChannels: 4);
  for (final p in cmykImage) {
    final nr = p.rNormalized;
    final ng = p.gNormalized;
    final nb = p.bNormalized;
    
    final k = 1.0 - max(max(nr, ng), nb);
    final c = k == 0.0 ? 0.0 : (1.0 - nr - k) / (1.0 - k);
    final m =  k == 0.0 ? 0.0 : (1.0 - ng - k) / (1.0 - k);
    final y =  k == 0.0 ? 0.0 : (1.0 - nb - k) / (1.0 - k);
    
    p.rNormalized = c;
    p.gNormalized = m;
    p.bNormalized = y;
    p.aNormalized = k;
  }
  return cmykImage;
}

This is just theoretical, I haven't tested it.