This is a response to a question @vanessa asked in Landscape Critique regarding one of her images, histograms, and how color is reduced when an image is brightened. I replied here, because her post is no longer new and I thought it important that others could weigh in. Here’s my thoughts, please add your wisdom as well:
The answer to this is much of the time yes, but as with most rules of photography some very powerful images come from breaking the rules.
This gets a bit wonkish, but what you may be noting is a result of the way that that the rgb colorspace works. I’ll try to explain, but I’m no expert and so hopefully others on NPN more experienced than I can point out the parts that are complete hogwash .
In rgb, luminosity (brightness) is defined on a scale of 0 to 255. When all three of red, green, and blue have the same value there is no color, only shades of gray. For example, when red, green, and blue all equal zero you have pure black. When they all are 255, you have pure white. How dark or light the gray is, is determined by how high or low the numbers are; a medium gray is when all three colors are set to 128.
Color happens when the numbers are set to different levels. For example, the pure and brightest red that is possible in rgb is when the red is set to 255, and green and blue are set to zero.
Here’s the interesting part though. As you brighten you get closer and closer to white, which has no color. If we take that brightest pure red I defined above and we raise the green and blue values to say 128 (instead of zero) the color becomes brighter but not so red; the “redness” has now been diluted because the green and blue are stronger. If I take it even further and raise the green and blue to 244, the image becomes only a tiny bit red; it is now almost a pure white even though red still has a value of 255.
To illustrate this, take a look at these three images. I was bracketing, so each time I pushed the shutter the camera took three images: dark, medium, and bright. They were taken almost at the same time, so the color in the sky didn’t change, but notice how the richness of the color changes in each. In the darker version, the sky is very red, and in the lighter version it is almost washed out. Again, that’s because in rgb the brighter you get, the closer you get to white and white has no color.
Software that edits images takes this into account, and so it assumes that the brighter an image is the less color it should have. That’s another reason why the image loses color when you brighten it in post-processing.
To get around the dilemma, there are two options that I know of. One is to increase saturation when you brighten. That works against the assumption the software makes that brighter images should be less colorful. That can work as long as the color you are editing is not too bright, but it is limited as a color gets brighter because once the value hits 255 you can’t go any higher. (To have the color red, red’s value has to be a higher value than green and blue. If green and blue are close to 255, you just don’t have the room to make the image redder.) The second option is to not brighten as much. While that allows you to keep rich colors, you sometimes sacrifice the wonderful textures that come from luminosity contrast.
With processing software that lets you edit selectively, to a great extent you can have your cake and eat it too. In those images above, if you didn’t have the middle image you could brighten the ground in the first image, or darken the sky in the final image, to get something closer to the more pleasing middle image. In addition, you could selectively increase the contrast in the sky, which would let the brightest parts be very bright but hold the color in the parts that are darker and richer.
Again, hopefully others can add their wisdom and correct the error of my ways!