Multichannel color space

[Aardo]

Hi Everyone,

Is it possible to work in a multichannel color space in Affinity Photo, say CMYKOGV?

Can I convert an image to such a space in Affinity Photo (if I had an appropriate ICC output profile for CMYKOGV)?

[thomaso]

Nowadays working color spaces are limited to have either 1 (bitmap, grayscale) or 3 (RGB, Lab) or 4 color channels (CMYK). Therefore a 5, 6 or 7 channel profile can't be used as working profile but as output profile only. To achieve a multichannel working color space you would create its additional channels manually and assign their color content accordingly, as it is done for instance when using additionally (Pantone) spot colors in APub.

The limitation of usual max. 4 channels as working space makes it for instance also so tricky to create print files for Riso, a low-cost spot color print process used by RISO hardware, as noted e.g. in this article: http://en.duplo.press/exploriso/color/separations/using-multicolor-profiles/  (btw., a nice video introduction into risoprinting is given by this print provider https://www.youtube.com/watch?v=1rfwKuXIhcE )

It appears in Affinity I am not able to select a multichannel profile as output profile on PDF export but on print only. Maybe it's by design – or a bug?
Although I am able to print to PDF it doesn't help here because I can't choose a profile for this process, instead a default profile is used by my OS (macOS).

On 4/10/2020 at 10:32 AM, Aardo said:

(if I had an appropriate ICC output profile for CMYKOGV)

You can find some for download, e.g.:

https://www.fogra.org/en/fogra-research/prepress/research-projects-prepress/multicolor--2-766/fogra55-en/fogra55---the-ecg-7c-exchange-colour-space.html

https://www.pantone.com/pages/pantone/pantone.aspx?ca=12&pg=20338

 

If you want to experiment with custom color channels created in AP this video shows the detailed workflow – regardless that it 'just' converts RGB into 3 custom color channels only (which possibly could alternatively achieved with a profile).

I didn't discover yet if in AP the option "Spare channel" (right click an existing color channel) does add Alpha channels only (for masking, transparency) or even can be used to create an additional color channel. Their layers position let me assume they can't be used as color channels.