Understanding RGB and CMYK Color Spaces in short...

When we are introduced that all colors could be reproduced with the combination of only three colors, then there a lot of color space were developed on the basis of that X-Y-Z colors. It takes some time to evolve from the very first color space to C-M-Y-K color space. As we see it has four primary colors in CMY-K, so it should be the special. We will discuss that in a while.

R-G-B color space is the pre-ancestor of C-M-Y-K color space. RGB is the additive color space so it should be use where we need to add those primary colors (R-G-B) to make another new color and it should be any illuminative source (light source) and obviously we are following this thing, if you put a water drop (not recommended) on the monitor you will see some tiny dots of only R,G,B.

So, as its comes from illuminative source this is the source where all the primary colors add with each other and emits the resultant color as light, those reproduced colors are very bright in RGB color space. Hence it cover a wide range of brightness.

In RGB color space, there are 256 steps for each of the primary color, so it can cover 256 (R) x 256 (G) x 256 (B) colors. And why is the 256 threshold is there? :) Because, our eyes can only perceive 256 (0 to 255) brightness value of any single color. In full intensity this color space produce pure white and in nil value it produce black. It means when all the pigment of RGB were in full intensity it is producing white color and when all RGB pigment were in off state then its produce black obviously.

So, from the last paragraph we found if we want to print black with RGB color we can't be able to do this because in black state the value of R G B is just '0 (Zero)' so none of any color will be printed, what we will see then noly the paper color. So, in this condition we should take Black as paper color. But none of the color will be printed as bright in comprising with printed over a white paper, right!.....So it doesn't help.

Now, what we need is one color space that will act just opposite of RGB color space or we can say just the Inverse of RGB color space. So, developers' come to find this solution and they did as expected. They inverted the R-G-B colors. And after inversion we got Red > Cyan, Green > Magenta, Yellow > Blue i.e. C-M-Y color space.

In that way we found a new color space C-M-Y capable of the same brightness coverage and same number of color coverage. But in full intensity it produce Black and in nil condition white. A it is the inverse color space of RGB so its not additive color space any more, its now reflective or you can say substractive color space, light will come to the printed sheet first and then it will reflect to our eyes, so now we will see the substracted color as a rule of color reflection (CMY is substractive color space). Its clear as its not a illuminative source it couldn't cover that wide range of brightness.

Now the time to answer, where the "K" comes from, here K stand for Black. If full intensity of C,M and Y produce the black so what is the necessary to ad a Black color with that?? In full intensity C, M and Y doesn't produce the rich black at all in real life, what it produce is a dull dark brown tone. That is why black is separately introduced. In CMY color space the highest value of all the element colors are 100 as there is a guest (K) in color space so they had to distribute total color range among all of them. So it cover 100 (C) x 100 (M) x 100 (Y) x 100 (K) total color range.

But, it can't cover the range of RGB as it has a wide brightness coverage that CMYK doesn't.

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