You're welcome and let me expand on my short answer above! (I had to wrangle my kids earlier and couldn't take the time).
We discussed Levels here.
To begin this discussion, I used the color picker to sample a purple flower in your photo. Here is the color without any change. We'll call this, "Our Purple" in this discussion.
Here is Our Purple:
This is a good time to explain that all colors on your computer are represented by a blend of only 3: Red, Green and Blue. By mixing various amounts of each, all colors can be created...or at least approximated! To make this the same as our previous discussion on levels, we'll use the same scale. 0 to 255. 0 means that color is not present and 255 means there could not possibly be more of that color.
Techie note: This is called 8-bit color because your computer stores this in 8 bits of data. 2^8 = 256, which covers the range 0 to 255.
You can see the mix of Our Purple in the yellow highlighted section of the picture above. Our
Our Purple = 128
Red + 64
Green + 101
Blue.
We talked about levels as a way to increase or reduce contrast. Let's talk about brightness. Brightening something adds white. Making it darker adds black (or subtracts white, if you prefer to think of it that way). Let's look at a brightness adjustment highlighted in yellow:
What I want you to notice is the vertical slider next to the highlight. The ends of it range from a very dark purple to a very light purple. That's because brightness keeps the ratio the same as it darkens or lightens them. Let's make an adjustment to brightness....here's an example:
Here is Bright Purple:
Bright Purple = 200 Red + 100 Green + 158 Blue
Notice something interesting. Bright Purple is the same "mix" ratio as Our Purple! Let me repeat the two so you can see what I mean:
Our Purple = 128 Red + 64 Green + 101 Blue
Bright Purple = 200 Red + 100 Green + 158 Blue
In Our Purple, there is twice as much Red as Green. The same is true for Bright Purple! All brightness did was bump the values of everything up by a fixed ratio. Without dragging you through it, lowering brightness has the same effect. A "Dark Purple" would have lower numbers, but there would still be twice as much Red as Green.
Now let's talk a bit about saturation. (Finally!)
Saturation attempts to push a color toward a "pure" version of that same color. Does Our Purple look purple to you? It should. But ask yourself, "How is Purple made from primary colors?" And you'll answer, "Red and Blue!" But wait a minute...Our Purple has GREEN in it!
Saturation attempts to "fix" that little "problem" by pushing Our Purple toward a "true" purple. Here is a look at saturation:
Again, note the slider. This time, the purple scale ranges from a grey to a "true" purple! Let's make an adjustment and see the result:
Here is Real Purple:
Real Purple = 128 Red + 26 Green + 85 Blue
Notice that the ratio has changed. There is now 5 times as much Red as Green. If we kept pushing the saturation higher, there would eventually be 0 Green in the purple. Hopefully it's obvious that as saturation is lowered, everything moves toward grey because the ratios get flat. 128 of each Red, Green and Blue is grey...it's not purple at all!
Quick Summary
So, brightness adds or subtracts white. Saturation pushes all colors toward "true" colors or toward shades of grey. They're very different things!
Effects of Levels in CS3
