I have a formula for mixing a CMYK-OGV color that I want its C:0,M:16,Y:0,K:0,O:0,G:0,V:0. I got my formula from the Pantone CMYK Extended Gamut guide that was created to create Pantone shades using CMYKOGV as base colors instead of the usual 13 base shades that Pantone requires. I want a particular shade of magenta which is given in the Extended Gamut guide. Will this work if I mixed M (Magenta) at 16% with White at 84% ? If not then what is the right method to create a CMYK-OGV color using these formulas ?
There's no such thing as white cmyk color. It's nonexistent. White in cmyk system is the background that has got no color. It is visually as white as it happens to be. In computer screen it often is the same as the RGB white (R=G=B=255). Pro level software can show white like the forthcoming printing process will do. Or at least that is wanted.
You seem to use Paint.NET, which has no CMYK support. There's a plugin which makes CMYK color separations. Obviously it assumes a print process that has exactly the same available colors as the RGB screen that is in use.
Formula how to create CMYK values from RGB values:
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)
The preceding formula gives CMYK values as decimal from 0 to 1. Multiply them by 100 to get the percentages which are used in Photoshop and other common CMYK capable software.
There are also other formulas. The amount of K can vary. K is in theory unnecessary, but it's used to reduce the total amount of color. That's useful in printing, where exessive liquids are harmful. The less liquids, the faster is the drying and the sharper is the result. Here K is made as big as possible.
Practical printing processes are not as ideal as is assumed in the previous formula. This is because there's some free space between the printed raster dots. Thus the subjectively blackest black can well be other than CMYK=0,0,0,100.
From CMYK to RGB conversion one can use the following formula (taken from the same source as the preceding)
R = 255 × (1-C) × (1-K)
G = 255 × (1-M) × (1-K)
B = 255 × (1-Y) × (1-K)
Your color CMYK = 0, 16%, 0, 0 has thus RGB values R=255, G=214, B=255
In Photoshop one can easily spot a contradiction. The RGB values were typed in:
The color selection dialog shows 18% magenta, not 16%. The difference grows if the color is made stronger. That's not actually a contradiction. It comes from color management. The system generates the CMYK values for certain print process (=my default), not for ideal printing. In addition The CMYK values are forced to stay in actually printable range without clipping, so the color saturation is often drastically compressed.
Concept "MIX" is not simple and unique. I have not a slightest idea what you mean with that word. If you add cmyk colors, the result is darker except by adding nothing, which I think is the best meaning for adding white.
Before we can discuss about the mixing, we must have a common formula how the CMYK values depend on the CMYK values of the colors which we want to mix. I suggest the following:
Take any decimal number A between from 0 to 1. For the first color multiply the CMYK values with A. For the other color multiply the CMYK values with (1-A). Add the results of the multiplications for new C, M, Y and K. Round to the nearest available percentage from 0 to 100. A is the proportion of the first color.
In this formula the CMYK values are additive. Another person may want multiplicative formula due the nature of CMYK - its a partially transparent filter. There the result is not additive.
The third person might want to convert to RGB, add the RGB values in the wanted proportions and convert back to CMYK. He would have the following argument: I see mixing as summing the lights. It's also not additive method.
The answer is pretty simple. You do not. Process inks (CMYK describes processes inks) aren't mixed they are overlaid one another. Also process inks are not laid over with a diluted mixture but rather the ink is allays laid in full at 100%. The % refers to how the ink spatially interleaved alternating with ink and no ink. White comes form the substrate, paper in most cases.
Could you mix this way? Possibly, probably not but at least not with the inks in your printer. See for necessary reasons white has to be opaque, while the printer inks need to be transparent this make the interaction between these in a mixture slightly unpredictable
The difficulty you may be having is with the meaning of the word "MIX."
- Juxtapose. The process of creating the impression of a realistic image using only four different hues involves a perceptual "mix" (mental blend) of different amounts/percentages of area coverage by area.
A partial 50% area coverage of Cyan overlaid upon another partial 50% area coverage of Yellow creates the perception of a medium green. A magnified view of the area would reveal dots of each colour unaltered and interspersed. This is the way colour monitors, television, and process colour printing mix.
Blend. The process of creating a green can also use a physical combination of Cyan and Yellow pigments combined in equal parts by volume or weight. A medium green would be created by adding a neutral with enough volume to dilute the saturation to create a medium tint. A magnified view of the area would reveal a uniform medium green area. This is the way paint and inks mix.
Fusion. The phenomenon called persistence of vision gives us another way to experience a mix of different colours. Rapidly alternating overlay of different hues can produce the effect of mixing colours dynamically. Colour segments of a spinning wheel will produce a mental fusion into a mix of the segment colours. This is the way a spinning Newton colour wheel achieves a colour mix. When the wheel stops, however, the illusion is broken and the original colours are visible.
Having tubes of pigments and bottles of inks only allow a physical blend of the materials which is only one kind of mix. As you can see there are two other kinds. Perhaps this will help you with your understanding of the issue.
I know what you mean Hamish - just speak to the printer you are using. The additional high gamut colours are applied on spot plates OR the equivalent for digital press - and you specify which inks you require to be applied in these channels. Sound like you are trying to work out how an Indigo printer works out colours - just ask the supplier.