Well, I'm just glad you guys aren't debating or anything.
Seriously though, I think this dialogue is useful, not for determining which method is "best", but to help folks understand the differences and think about what tool they want to use for a particular task.
I also think this points out some of the difficulty that software developers like Adobe have when addressing these things. I have read through several threads on other forums where members of the Adobe team have talked about why they made certain decisions like, for example, how the tone curve reacts in ACR and Lightroom. Their comments are usually similar to "well, we tried a pure luminosity change but it produced a result that we knew would not be acceptable to the majority of Photoshop users." In the case of ACR/LR, I believe they ended up with a hybrid solution that now opens them up to attacks from both camps. And luminosity vs. saturation is only ONE of the controversial areas. If you really want some fun, go find a thread where a bunch of color management gurus have gotten together to discuss the pros and cons of "hue twists".
Why am I mentioning this related to THIS thread? Because even though doing adjustments on a Luminosity layer (or perhaps on the L layer of LAB) SOUNDS like the right way to do things (adjusting brightness or contrast without changing saturation), the result sometimes looks, well, WRONG. As an example I look at the strip of adjustments to the girls face that Peano posted and I bet if you asked a group of people which adjustment was the most PLEASING, the majority would say the multiply one.
Another example, going back to ACR and Lightroom, is the different ways that those programs process a "lens" vignette vs. a "post-crop" vignette. The "lens" vignette applies a multiply-like adjustment to form the vignette and the "post-crop" applies a luminosity-like adjustment. Which effect do many people prefer? The multiply-like adjustment of the lens vignette. In fact, I have seen tips from PS gurus recommending that users wanting a decent post-crop vignette bring the image into PS and apply the vignette there USING THE MULTIPLY BLEND MODE. I also believe I read a rumor somewhere that Adobe may be changing the behavior of the post-crop vignette tool in the new versions of LR and ACR because of this preference by the majority of users.
I am certainly not saying that doing adjustments in Luminosity mode is "BAD" either. Sometimes it is very useful to make those adjustments separate from hue and saturation. The important thing is to learn how the various tools work and when to use them to produce the results we are after.
Eyeball wrote:
even though doing adjustments on a Luminosity layer (or perhaps on the L layer of LAB) SOUNDS like the right way to do things (adjusting brightness or contrast without changing saturation), the result sometimes looks, well, WRONG. As an example I look at the strip of adjustments to the girls face that Peano posted and I bet if you asked a group of people which adjustment was the most PLEASING, the majority would say the multiply one.
My purpose in that illustration wasn't to render a pleasing result. Nor was it to suggest that one method is "better" than the other. It was to show, by exaggeration, the difference between darkening via luminance mode and darkening via multiply mode.
When using these blend modes to (for instance) deepen shadows on a model's face, in neither case would you apply the effect at 100%. You'd paint it on with a low-opacity brush, and only where you wanted deeper shadows.
In some cases you might want the increased saturation that multiply causes. In others you might want to decrease brightness without increasing saturation. It depends, as always on the image and on what result you're after.
