Bug in HSL development

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Chris Brandin

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I think I have found a bug in the HSL color function of the development section of Lightroom.

A color value that contains all three primaries (like R=5'% + G=5'% + B=5'%, for example), will stay at a mid-gray even if all color luminance sliders are set to -1''. It appears the sliders affect only spectral and synthetic color components and not natural grays. That means that if you try to stack virtual red, green, and blue filters in Lightroom the result will be different than it would be in the physical world. With real filters the result would be simply a darker image, with Lightroom the result is that colored components of the original image are darker but the components that started out as natural gray stay the same.

I tried an experiment. I created a spectrum with a neutral gray frame. Then I set all the color luminance sliders to -1''. The spectrum came out very dark whereas the neutral gray frame stayed the same. It seems to me that with all color luminance sliders set to -1'' the gray area should have come out dark too.

From a theoretical standpoint this looks like a bug. It poses some very interesting possibilities, though. If Adobe corrects this, I hope they provide an option to leave it the way it is.

Chris
 
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Chris

Could you show an example of what you mean. I kinda get what your saying, but not really. :lol:

Could you ellude what would be the interesting possibilities? From what i gather it would allow for more creative filtering?
 
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HSL test chart

Take the file I've attached and open it with Lightroom. Set all the color luminance sliders to -1'' (in any mode you like, color or grayscale). You'll notice that the colored part gets darker but the gray part stays the same, even if you set ALL the luminance sliders to -1''.

It seems that Lightroom's sliders only affect colors, and not grays. I think there are some interesting creative possibilities with this behavior - even though it is not "correct".

Chris
 
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I tried it in Photoshop - it behaves the same way. I also tried the Power Retouche B&W Studio plug-in - the same behavior.

I wonder if I've stumbled on the reason B&W conversions don't come out quite right in some cases. Do you suppose this might be a limitation of the LAB colorspace?

Chris
 
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I thought that color conversions largely take place in the LAB colorspace (they do in Photoshop) - is that incorrect?

Actually, I think I need to amend my statement that the behavior of luminance sliders is "incorrect". For their primary purpose - to bring out or tone down particular colors - they are completely correct and would not work otherwise. For B&W conversion, however, they behave differently than film and filters - so, they are only "not correct" in that you cannot accurately model the behavior of B&W films and filters.

I wonder if it would make sense for Adobe to offer the option where luminance sliders affect the overall tint of an image (before B&W conversion) instead of particular ranges of colors for the purpose of B&W conversions.

Chris
 
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