[By Design] Affinity Photo - LAB colour mode

[Subclavius]

Affinity Photo 1.6.5.123/Windows 10 64 bit

This looks on the face of it like a bug but am not sure. A photo (pixel base layer) and a single curves adjustment in LAB mode working in 16 bit - if the AOpponent and BOpponent curves are set down to nothing i.e. desaturating the image, AF should according to me, produce a black and white image representing only the luminance.  However I get a monotone image in some shade of blue. It doesn't matter whether the document format is RGB or LAB, I get the same result.  Incidentally the behaviour is exactly the same in beta release 1.7.0.243.

Is this a bug? Any advice about what is going on would be appreciated.

Nigel

 

[Gabe]

Hi @Subclavius,

That's not really how it works. 

AOpponent: negative values indicate green while positive values indicate magenta

BOpponent: negative values indicate blue and positive values indicate yellow

So what you see is perfectly expected.

Have a look at this video for more info:

 

Thanks,

Gabe. 

[Subclavius]

Hello Gabe,

Thank you for the reply. I had already looked at the video tutorial but didn't find it really helpful in the context of this query. Your reply did however enable me to work out how to get a black and white image though. It seems that the 'meaning' of the axes changes from RGB to LAB. In RGB mode the vertical axis is dark to light whereas in LAB mode the vertical axis is blue to yellow or green to magenta.  Thus in LAB mode the neutral point of the axis is not at the bottom (as in RGB mode) but half way up.  If both the AOpponent and BOpponent curves are set to horizontal lines half way up (removing all colour information) the result is indeed a black and white image representing only Luminance.  Clearly when both curves are set to horizontal lines at the bottom of the graph the resultant colour is thus blue+green -> cyan

I would find it very helpful if the vertical axis could be coloured with a graded line from blue to yellow or green to magenta. Similarly on the RGB a graded line from dark to light would help. It's only a small wish in a great sea though!

Thank you,

Nigel

[Gabe]

I will move this to feature requests