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HSL-Blend Ranges luminosity conflict


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Start with a colour wheel image, add HSL adjustment, then turn saturation half-way down and luminosity half-way up.

Now add Blend Ranges and pull down left node of right-hand chart. Colours like yellow are strongly affected but blue and red are hardly affected at all.

Why is this happening? My guess is that lightness conversion in Blend Ranges uses luminosity perception, where yellow is seen as a brighter colour and blue a darker colour. However HSL luminosity is value-based and so shows the same amount of greyness.

Hence we have a conflict in the treatment of luminosity. I don't know if it is a bug, but it is certainly bugging me as it clogs an effect I was trying to create. At the very least it is a usability defect as it easily causes confusion.

Maybe one way to address it is with a checkbox on Blend Ranges that switches between perceptual (as current) and value-based luminosity variation.

Thank you for your kind consideration and have a nice day.

Dave Straker

Cameras: Sony A7R2, RX100V

Computers: Win10: Chillblast i9 Custom + Philips 40in 4K & Benq 23in; Surface Pro 4 i5; iPad Pro 11"

Favourite word: Aha. For me and for others.

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  • 2 weeks later...

I had a similar question watching your video (How the Graphs in Affinity Photo's Blend Ranges Really Work!) at 9:17 when you set Saturation to -100%. Why were the gray levels all the same? I think part of the answer lies in the HSL model. https://en.wikipedia.org/wiki/HSL_and_HSV#Saturation Saturation is chroma scaled to always fit between 0-1, looking at fig 14. The problem is discussed in the Saturation section, see purple boxes.

BTW your videos are a great help to understanding the fundamentals!

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  • 1 month later...
  • Staff


Thank you for reporting a problem using 1.7.x . It appears that a member of the Affinity QA team didn't get round to fully investigating this specific report posted in the bugs forums. We are very sorry for this oversight. Yours is one of a number of reports that I am posting this apology to, using an automated script.

Now we have released 1.8.3 on all platforms containing many hundreds of bug fixes, and we hope your problem has already been fully addressed. If you still have this problem in the 1.8.3 release build, then the QA team would really appreciate you reporting again it in the relevant Bugs forum.

Each of those links above contains instructions how best to report a bug to us. If that is what you already did in this thread just copy paste your original report into a new thread. We appreciate all the information that you have including sample files and screen shots to help us replicate your problem.

This thread has now been locked as the QA team are not following the threads to which this automatic reply is made, which is why we would appreciate a new bug report if you are still have this problem in the current 1.8.3 release build.

Patrick Connor
Serif Europe Ltd

"There is nothing noble in being superior to your fellow man. True nobility lies in being superior to your previous self."  W. L. Sheldon


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