A Surprising Look at Photoshop Subtractive Color Mixing

I expected the multiply blend mode to properly combine CMY separations into full color images. It does.

I was surprised to see how well the difference and exclusion blend modes accomplished the same task. You may assume it's because they are subtractive in nature, and so should be expected to perform subtractive color mixing, but in fact they mix pairs of colors in surprising and unnatural ways.

Category:

Education

Tags:

• subtractive color
• subtractive primaries
• CMY
• CMYK
• color mixing
• blend modes
• multiply
• difference
• exclusion

[bucktheusa]

The RGB seps just cancel out or combine to create the same, opposites of negatives. 6:53 is RB RG GB then inverted at 7:07 you have G B R, the exact colors that were filtered out in 6:53. The same combine to cSince we obviously know M+Y doesn't = C as it does in 5:58, it's actually just the inverted view of the GBR images overlapping as light (not ink). So when 1.RB & 2. RG combine they make C since their excluded counterparts are G and B.

[digitalArtform]

Here is the text of your accidentally deleted comment:

Number 3. is C since it is both GB being viewed as inverted C so that's why they are the same when 1+2. At 5:59 it's not actually a "negative" C and positive C its simply the inverted G (looks M) and (B looks Y). So when viewed under this artificial inverted color "filter"

It's just doing what RGB light does in real life only you are inverting the colors. But it is real.

[digitalArtform]

Look at 6:00 - consider the cyan negative and the cyan positive. Focus on the upper right corner of each, where the color is full cyan. Notice at 6:08 when cyan goes over cyan the result is black. In the real world so-called subtractive color mixing of a cyan filter with another cyan filter will not yield black. So-called subtractive mixing of cyan paint with cyan paint will not yield black. The difference mode is a mathematical curiosity that does not model subtractive color mixing in nature.

[digitalArtform]

R + G = Y, invert it and you get B?

No, you have to invert every element to repeat what I did there, or invert no elemnt. You can't just invert the result.

Here's the point: Difference and Exclusion are mathematical curiosities with no real world analogs. 'Subtractive' lighting is misnamed, as it is based on multiplication, so it is interesting to see the difference mode work at all with 3 layers, especially when it fails so oddly with 2 layers.

[bucktheusa]

C=R Y=B M=G

when inverted/differenced is

R=C G=M B=Y

So yes. If you had two projectors, a slide of R and of G and project them on a white screen it will make Y.

With my Sony camera on a tripod, I can set the effect to invert and VOILA!, there is your vibrant blue.

I haven't quite tried to invert light rays by reversing their wavelengths. It could end life as we know it.

[bucktheusa]

When you choose difference it just inverts MYC in your example positive to GRB negative.

When you crank up the background to black it just inverts the whole image colors and all.

When you combine G+B which is rendered as inverted under the current selection the R+G-B+ dragged over R+G+B- you get R+G-B- which is the exact same as the last Cyan image which is R-G+B+ but displayed as R+G-B- because it's inverted from it's natural state. The RGB dots show what I'm talking about.

[bucktheusa]

I still don't see what you were so surprised about in 6:08? Around 5:50 you crank up black but what actually happends is you invert the whole image and colors..before that they were negatives in GRB that started as CMY positives.

When inverted:

G='s -Magenta B='s -Yellow R='s -Cyan

[digitalArtform]

Crap. I meant to hit reply, and I hit remove on your other comment. Anyway. the bottom line is this: If you want additive color use Linear dodge or Screen on RGB seps. If you want subtractive color, use multiply on CMY seps. If you want to make $50 - my offer from the other comment still stands.

[digitalArtform]

I go over all of that in the video entitled 'Additive Color vs Subtractive Color' -- this video makes a different point, which I explain in a different comment here.

[bucktheusa]

Years ago in school they took three projectors each with a different colored lenses or slides and positioned all three (RGB) to overlap.

The creation of orange, violet, yellow at the intersections not to mention the unexpected creation of white in the middle will blow your mind.

The very idea that R G B light overlapped creates white light is still hard to believe unless you see it yourself!

You can might be able to do this with RGB cellophane and a few cheap flashlights.