Luminance and its relationship to color

- In Photoshop and other graphics programs,…brightness goes by many names including shade,…tone, and my favorite, luminants.…In your everyday average RGB image…which is far and away the most common kind of image…you'll encounter, luminants is measured…in steps known as levels.…A level of zero is black and a level of 255 is white.…The other levels, 1 through 254, represent the progressively…brighter shades of grey in between.…So where does color come in?…Again, assuming an RGB image, you have three…luminants-only versions of an image, called channels.…

The three channels are respectively colorized…red, green, and blue (hence RGB) and then blended…together to produce the full color composite.…In other words, color is the function of luminants.…Meanwhile, luminants in colors sometimes react…with each other in surprising ways.…Look at a strip of grey values and you see…a steady progression of neutral levels,…just as you would expect.…Throw a cool color like blue into the mix and the blues…go from light to dark as expected.…