Enter red, green and blue color levels (0..255) and press the Convert button:
RGB to CMYK conversion formula
The R,G,B values are divided by 255 to change the range from 0..255 to 0..1:
R' = R/255
G' = G/255
B' = B/255
The black key (K) color is calculated from the red (R'), green (G') and blue (B') colors:
K = 1-max(R', G', B')
The cyan color (C) is calculated from the red (R') and black (K) colors:
C = (1-R'-K) / (1-K)
The magenta color (M) is calculated from the green (G') and black (K) colors:
M = (1-G'-K) / (1-K)
The yellow color (Y) is calculated from the blue (B') and black (K) colors:
Y = (1-B'-K) / (1-K)
RGB to CMYK table
RGB color space
A RGB color space is any additive color space based on the RGB color model. A particular RGB color space is defined by the three chromaticities of the red, green, and blue additive primaries, and can produce any chromaticity that is the triangle defined by those primary colors. The complete specification of an RGB color space also requires a white point chromaticity and a gamma correction curve. As of 2007, sRGB is by far the most commonly used RGB color space.
RGB is an abbreviation for red–green–blue.
A RGB color can be understood by thinking of it as all possible colors that can be made from three colored lights for red, green, and blue. Imagine, for example, shining three lights together onto a white wall in a dark room: one red light, one green light, and one blue light, each with dimmers. If only the red light is on, the wall will be red. If only the green light is on, the wall will look green. If the red and green lights are on together, the wall will look yellow. Dim the red light and the wall will become more of a yellow-green. Dim the green light instead, and the wall will become more orange. Bringing up the blue light a bit will cause the orange to become less saturated and more whitish. In all, each setting of the three dimmers will produce a different result, either in color or in brightness or both. The set of all possible results is the gamut defined by those particular color lamps. Swap the red lamp for one of a different brand that is slightly more orange, and there will be a slightly different gamut, since the set of all colors that can be produced with the three lights will be changed.
A computer LCD display can be thought of as a grid of millions of little red, green, and blue lamps, each with their own dimmers. The gamut of the display will depend on the three colors used for the red, green, and blue lights. A wide-gamut display will have very saturated, “pure” light colors, and thus be able to display very saturated, deep colors.
RGB is a convenient color model for computer graphics because the human visual system works in a way that is similar – though not quite identical – to an RGB color space. The most commonly used RGB color spaces are sRGB and Adobe RGB (which has a significantly larger gamut). Adobe has recently developed another color space called Adobe Wide Gamut RGB, which is even larger, in detriment to gamut density.
As of 2007, sRGB is by far the most commonly used RGB color space, particularly in consumer grade digital cameras, HD video cameras, and computer monitors. HDTVs use a similar space, commonly called Rec. 709, sharing the sRGB primaries. The sRGB space is considered adequate for most consumer applications. Having all devices use the same color space is convenient in that an image does not need to be converted from one color space to another before being displayed. However, sRGB’s limited gamut leaves out many highly saturated colors that can be produced by printers or in film, and thus is not ideal for some high quality applications. The wider gamut Adobe RGB is being built into more medium-grade digital cameras, and is favored by many professional graphic artists for its larger gamut.
RGB spaces are generally specified by defining three primary colors and a white point. In the table below the three primary colors and white points for various RGB spaces are given. The primary colors are specified in terms of their CIE 1931 color space chromaticity coordinates (x,y).
CMYK color space
The CMYK color model (also known as process color, or four color) is a subtractive color model, based on the CMY color model, used in color printing, and is also used to describe the printing process itself. CMYK refers to the four ink plates used in some color printing: cyan, magenta, yellow, and key (black).
The CMYK model works by partially or entirely masking colors on a lighter, usually white, background. The ink reduces the light that would otherwise be reflected. Such a model is called subtractive because inks "subtract" the colors red, green and blue from white light. White light minus red leaves cyan, white light minus green leaves magenta, and white light minus blue leaves yellow.
In additive color models, such as RGB, white is the "additive" combination of all primary colored lights, black is the absence of light. In the CMYK model, it is the opposite: white is the natural color of the paper or other background, black results from a full combination of colored inks. To save cost on ink, and to produce deeper black tones, unsaturated and dark colors are produced by using black ink instead of the combination of cyan, magenta, and yellow.
Different colors of inks are printed onto a surface in dots and then layered in order to produce the desired color. This is called ‘half-toning’, and conserves ink while creating the appearance of a solid color provided the dots are small enough.
The size and spacing of dots can be altered to produce the overall visible color. The dots are also printed at angles to each other in order to avoid creating unintentional patterns which could be visible to the user (called Moiré patterns).
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