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Posted

Can one explain why an HSL adjustment in a CYMK document does not affect K-Only / 100-K as colour swatch – while it slightly does affect 100 K in a CMYK raster image?

866160955_v1105HSL-adjust_cmyk-k.jpg.5cf126a73e31dfc217b91f9fc680c756.jpg

 

Whereas if copied into an RGB document the adjustment affects the K channel of every item – but in images quite different, differing with their colour spaces:

577630517_v1105HSL-adjust_rgb-k.jpg.280694926e8e7926235253bbc6892259.jpg

… and what happens to the CMYK.jpg which was set in the CMYK afpub to "K Only" before being copied to the RGB afpub – since the K-Only option does not exist in an RGB document?

1782944034_v1105K-OnlyimagecopiedinRGBafpub.thumb.jpg.b8e04f8c6a4eb7ac81b53b70ab9f4dfe.jpg

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

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Posted

Hi @thomaso,

This isn't something i'm aware of specifically, however I can raise this internally with the product experts/devs and see if they can provide some answers. The teams are currently busy so it may take some time to get a response back.

To provide as much detail as possible, could you provide us with your sample images/document along with a screen recording demonstration (if possible).

Many thanks 🙂

 

Posted
On 10/15/2022 at 2:38 PM, thomaso said:

Can one explain why an HSL adjustment in a CYMK document does not affect K-Only / 100-K as colour swatch – while it slightly does affect 100 K in a CMYK raster image?

 

In general, i would recommend to open the file in Photo, and use the channels panel to selectively choose one color channel.

you can emulate that function in other apps by adding a channel mixer adjustment with appropriate settings.

HSL adjustment normally convert to HSL or HSV mode, and then back into CMYK. This can give surprising results. It does not work “natively” with cmyk. Better not use it at all in cmyk documents.

The K channel gives multiple bad surprises when used with e.g. invert or other adjustments affecting all channels. 
As best practice, don't use such adjustments in CMYK documents unless you really understand how they work.

And this is pure mathematics (and no bug of Affinity): in contrast to all other formats, K is dependent to CMY. You don’t have 4 independent channels.

 

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Posted
3 hours ago, NotMyFault said:

best practice, don't use such adjustments in CMYK documents unless you really understand how they work.

… this is why I asked 🤓

3 hours ago, NotMyFault said:

K is dependent to CMY. You don’t have 4 independent channels.

I assumed something like this … similar to Black in UCR | GCR, plus the complexity of additive | subtractive differences. But it's not enough to really understand (being able to visualize or explain).

macOS 10.14.6 | MacBookPro Retina 15" | Eizo 27" | Affinity V1

Posted

 

On 10/15/2022 at 2:38 PM, thomaso said:

Can one explain why an HSL adjustment in a CYMK document does not affect K-Only / 100-K as colour swatch – while it slightly does affect 100 K in a CMYK raster image?

 Take 2 rectangles with gradient from black to white.

  • top: right black to white
  • bottom: K only black to white.
  • add HSL adjustment with saturation + 100

The rich black contains C as dominant color (see color panel, which shows black from gradient)

the K only black has no saturation.

Depending on color profile, rich black may have a different dominant color.

 

Inspect your rasterised image with Photo and info panel. you will see that it has at least a little color cast. Using HSL with big slider input amplifies all color casts.

 

It would help if you can upload the actual afphoto images instead of screenshots only.

Screenshot 2022-10-19 at 17.13.03.png

Mac mini M1 A2348 | Windows 10 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080

LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5

iPad Air Gen 5 (2022) A2589

Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps.

My posts focus on technical aspects and leave out most of social grease like „maybe“, „in my opinion“, „I might be wrong“ etc. just add copy/paste all these softeners from this signature to make reading more comfortable for you. Otherwise I’m a fine person which respects you and everyone and wants to be respected.

 

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