Sepia hue on desaturated CMYK image

[lj_bl]

Hi,

When using the Hue/Saturation adjustment layer on a CMYK image I am left with a slight sepia hue, any ideas on whats causing this?

[Mylenium]

Well, Hue/ Saturation is obviously based on an RGB color model, so deviations in other color spaces may occur naturally. Simply more adjustments on top or use a different approach from the start. That and of course working with CMYK requires your color management to be set up and work correctly.

Mylenium

[lj_bl]

Thanks for the answer, aside from changing mode to greyscale, what do you think would be the best approach to desaturate if I want to work with both colour and grey scale imagery on different layers within the same document.

[Mylenium]

Aside what D. Fosse alreeady said, for CMYK I tend to work only with Curves, Levels or Selective Color that are a) atuned to reflect specifics of the CMYK color model and b) per-channel control. due to how CMYK works the composite image is not necessarily an intuitive outcome of a global adjustment. That said, of course you can always use Hue/ Sat, you just need to make sure to have one of those otehr tweaks on top to get rid of color casts and washes plus meticulously inspect the individual channels in the palette before finalising your files.

Mylenium

[D Fosse]

Cyan ink is a little weaker than the others, so requires a higher percentage. A neutral CMYK color may have values like 40-30-30-0.

The profile reflects this, so a flat desaturation by numbers produces the opposite (red) color cast.