What does it mean to change the color channel?

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Does it mean to control the combination between an image and a color overlay applied to it depending on the color space used (RGB, RGBA, CMYK, Lab, Grayscale, HSL, HSLA)? Or does it mean to change the color layer used in combination with other layers to form the final image? (if so, what could be changed in what regard?).

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Jason Sperske On

RGB are abbreviations for three color channels (red, green and blue). They represent specific frequencies of light. Inside each color channel is a range of intensity and a level of saturation. This model of colors is commonly taught in school and is how most people understand colors and mixing them. A different way to represent colors is HSL which stands for Hue, Saturation and Level. Here the Hue is the frequency of the color, while the Saturation can be like the contrast level, and Level is the amount of black. HSL (A stands for Alpha or transparency) is actually a much more programmer centric way of working with color (although most programmers seem to learn the RGB Hex values for colors). There is a great website called Mothereffing HSL which lets you play with HSL values to better understand them. CMYK is for pigments (which mix differently than light) and is found on printers. Same basic idea as RGB just with Cyan Magenta Yellow and Black. Now because light and pigments don't mix the same way there is a lot of work devoted to converting one color system to another (so you can see on your screen what will eventually come out of your printer). These systems are not perfectly aligned however so the goal is to get acceptability close.

Here is a comparison between RGB and CYMK

All of these colors when presented on a graph are called the color space.