Photo – CMYK or RGB to greyscale

[tersmuse]

Sorry but I can't do it without comparison.

In Photoshop I change the colours of a photo with one click. Image > Mode > Greyscale, that's it! I get a photo that is completely in greyscale (0-100 % K, 0 % C, 0 % M, 0 % Y).

In Photo there is another way

Convert / Format ICC Profiles
? Generic Gray Gamma 2.2 Profile
? Generic Gray Profile
? Greyscale D50
Rendering Input
? Perceptual
? Relative Colourimetric
? Saturation
? Absolute Colourimetric

? Black Point Compensation

No matter which selection I do, I don't get what I need: 0 - 100 % K.

Example: I have a shade of green (20, 0, 100, 19) in a graphic.
My client receives the graphic in different formats, CMYK, RGB, greyscale and black/white. Black and white are not supported by the Affinity Apps, sad, but another topic.

After converting (colour format: grey/8) the CMYK file, I get in Photo the following "greyscales": 29, 22, 22, 6 (Hue). The right value should be around 40 % K, without cyan, yellow and magenta.

What am I doing wrong? Why do I not get a true greyscale result for offset printing when converting to grey/8?

[NathanC]

Hi @tersmuse,

To clarify, in your example are you converting from CMYK to Greyscale and them sampling for CMYK colour values on the greyscale image?

If I open the same RGB JPEG image in both AFPhoto and Photoshop, convert the documents to the same Generic Grey colour profile and then sample, I'm given a K only value for the greyscale sampler as expected but an equivalent 4C CMYK value in both apps, are you expecting the CMYK value to also read a K only value? If it is giving you a K only CMYK value in Photoshop, is there something you have done differently?

Example below is the Greyscale Generic Grey colour profile, left sampler is Greyscale which shows K only and right is CMYK.

If I then convert from Grey to CMYK, i'm left with the same 4C CMYK values in both apps. In Afphoto, If I wanted the image to be K only I would have to clear the CMY channels on the image layer via the channels panel, however this does result in a significant loss of detail, specifically in the highlights. I'm not aware of a method to convert to CMYK with K only values in this example.

If I have mis-interpreted, could you perhaps provide a little more detail along with some sample files?

Many thanks!