If I understand correctly, chroma is how colorful the brain thinks something is inherently, which depends on both the perceived lighting conditions and the color of light reflected off the object. By contrast, saturation is just a property of reflected or emitted light, essentially the difference between the highest and lowest of the RGB channels, normalized to the highest RGB channel. Moving a red ball from bright to dark lighting conditions might affect the saturation but not the chroma. The phenomenon is illustrated by the pictures in this article, where figures 2 and 3 show the same shades of red against an even gray background vs. a gradient.
When it comes to actually editing a photo and playing with the sliders in darktable’s color balance rgb module, both the saturation and chroma sliders will make things more colorful, even though saturation affects brightness as well.
My question: what are the situations where it is better to edit one over the other? Other than playing with both and just seeing which looks better on a particular photo, are there principles that should guide the creative decision? Thanks.
I think this will be very difficult to talk about in the abstract. I’d encourage you to share some specific photos and share why you think one is better than the other.
Personally, I am not adjusting saturation much anymore, ususally chroma first, then vibrance. I don’t use saturation because I generally don’t want to affect the tonal balance of my image.
Just as you describe here I think its easy to see by just picking one color and taking both through the full range… Now imagine that you want to tweak red in your photo… see what would happen if you used one vs the other…
Yes, thanks. This is useful for understanding what is happening mechanically, but I’m asking a more subjective question about the kinds of situations where creatively you should use one rather than the other. For example, should you use saturation to make emissive sources more colorful and chroma to make reflective objects more colorful? Or in many of his videos, @s7habo reduces the saturation on highlights, but I’m wondering why not chroma? Because I’m just starting out with photo editing, even when I can tell that something looks better, I can’t always articulate why, so I’m really looking for some kind of artistic theory behind colorfulness, if that makes sense…
I think because reducing saturation shifts toward white, whereas chroma doesn’t have that brightness increase. White looks better in highlights, as opposed to grey ( to use an extreme example).
That’s my understanding of that particular bit, more than that I’m not sure!
I tend to use saturation if I’m interested in very bright colors. Very bright colors often can’t increase chroma at their brightness level without pushing out of gamut, which saturation addresses by lowering their brightness a little.
For shadows and midtones I don’t usually see a huge difference between saturation and chroma (for small-ish corrections). So I often just stick to saturation in general, or fine-tune the look with the tone-masked variants.
@123sg has already pointed in the right direction. Perceptive means “according to our perception” - we perceive saturated colors as darker. Thus, with perceptive saturation grading we have the possibility of an additional contrast control based on saturation.
In this flower, for example, you get more depth with perceptual saturation grading (left side):
In this example in turn, linear chroma grading works better. I wanted to increase the saturation in the yellow part of the flower while keeping the delicate transition between the saturated and unsaturated parts of the flower (right side):
And now back to your question, if I want to additionally increase contrast based on saturation in highlights, I use highlights slider in perceptual saturation grading, because that way I additionally brighten the highlights.
