Blending mode to change red into orange

[scotwllm]

Hi all --

I'm trying to show someone that red, green, and blue are the primary colors, and not red, yellow, and blue. I know the visible light spectrum consists of long, medium, and shore wavelengths of light, and the difference between additive and subtractive color modes, and that our brains assign names (colors) to the 16.7 trillion possible tristimulus proportions perceived by jiggling pigments in our cone cells. I got all that part.

I created a red layer (255,0,0), placed a green layer (0,255,0)on top of it with the linear dodge (add) blending mode, and the layer is yellow (255,255,0). When I add a blue layer (0,0,255) on top with the same blending mode I get white (255,255,255). So far, so good.

Every kindergartner gets taught that red plus yellow makes orange. When I start with a red layer (255,0,0), and add a yellow layer (255,255,0) with the linear dodge (add) blending mode, I get yellow (255,255,0). I know there is no such thing as 510,255,0, but where did the excess 255 units of red light go? If I subtract (255,255,0) from (255,0,0), I get (0,-255,0). Would -255 green be the opposite of green, aka magenta? If I add yellow at 50% brightness (128,128,0), the screen looks orange (255,128,0), but the numbers add to 383,128,0. Where did the 128 units of red go? If I add blue (0,0,255), I get magenta at 50% saturation (255,128,255). 

I thought this would be simple to explain in Photoshop, and it probably is, but there's something I don't know.

Any ideas? 

[D Fosse]

Screen blend mode. That adds the numbers.

[Trevor.Dennis]

Other than creating gradients from one colour to another, I didn't think you could mix colours with Photoshop.  I shall be following this thread with interest. I've already learned something, although we know that RGB is an additive process, so perhaps I should have worked that out.

[scotwllm]

You're probably doing it all the time and didn't realize it. The very first adjustment fill layer is Solid Color. One of my favorite things I used to do when compositing was to create a stamp layer, Filter/Blur/Average, and change the opacity of the result to 10% or something like that or one of the blend modes. By changing the color of everything on the page in the same way, everything coordinates. 

[scotwllm]

RGB(255,0,0) + (255,255,0) results in (255,255,0) with the screen blend mode.

[c.pfaffenbichler]

edited

[Chuck Uebele]

Mixing paint is far different than mixing colors in PS, As mentioned, RGB is additive, while CMY is subtractive. With mixing paint, you are diluting each color with the other color. To get orange with additive RGB, you need to use Red and Green, with green at 50% opacity and with screen mode. Using the subtractive method, you need Yellow and Magenta, with Magenta at 50% on multiply mode.

[Trevor.Dennis]

Good stuff Chuck.  I am still learning.   I guess the thing with Photoshop is if we want orange, we just select orange, so we never need to learn how to mix colours.  It's really quite interesting though.

[Conrad_C]

Well, it depends…if someone uses Photoshop for digital painting, the Mixer Brush tool in Wet mode does mix red and yellow into orange, probably because the Mixer Brush tool is supposed to emulate how subtractive paint works. So that can exist in an RGB document where other layers are composited using different color mixing models.

[Trevor.Dennis]

I've seen this demonstrated Conrad, but I have not used the mixer brush enough to the get to grips with it, and it has several settings.