Anybody who knows about RGB

#1

anyone,who knows about how to figure out the color RGB,i am confusing about the problem that how to caculate exactly what color multiply what color then turns out what color,if anyone know the method ,please let me know.

THX

#2

RGB color math has functions applied to vector pairs.

So;
RGB 1 = (R1,G1,B1)
RGB 2 = (R2,G2,B2)

RGB 1 * RGB 2 = RGB((R1R2),(G1G2),(B1*B2))

For example if you add Red (RGB 1,0,0) and Green (RGB 0,1,0)
You solve like so;
R= 1 + 0 = 1
G= 0 + 1 = 1
B= 0 + 0 = 0

RGB(1,1,0) = Yellow!

I hope i understood your question correctly.

#3

first of all ,thanks very much.but is there only one method to calucate,and you can recommond me the way to buy some books,or else the site to learn more about it?

#4

The first few chapters of The Art and Science of Digital Compositing by Brinkmann are quite nice for image processing math. The rest of the book is probably overkill if that’s all you need, though.

One tip that really opened my eyes on how RGB works is that the subtractive primaries: Cyan, Magenta and Yellow, are complementary to the additive primaries: Red, Green and Blue. In the example previously given, you see that illustrated for Yellow—removing the Blue channel entirely and leaving Red and Green at full luminance gives Yellow.

The same is true for Cyan (R=0, G=1, B=1) and Magenta (R=1, G=0, B=1). Thus, CMY are the secondaries in the RGB system.

All of the math is based on normalized values from 0-1. These values are obtained by dividing the color channel values by their bit depth. That is, Photoshop displays an 8-bit channel as having values from 0-255. If you divide the channel by 255, you will get a number in the range of 0-1. That is why multiplying gives a darker color. If you try to multiply 128 * 128, you will wind up with a clipped value, way above 255. .5 * .5 = .25, though. Photoshop will report the pixel’s value at 64, even though its own math doesn’t work that way.

If you’re interested in the actual blend mode formulas used by Photoshop, try out this site: Blend Modes.

#5

Here is a description:

http://www.digitalartform.com/multiply.htm

#6

PS doesn’t multiply 128*128, the internal math works with float values so everything gets converted to the [0,1] range before the function is applied, then converted back to lume depth, rounded to an integer;

( (128/255) * (128/255) ) * 255 = 64

I didn’t just give you one method, i showed you an example to demonstrate that RGB math is basically just 3D vector math. RGB is a 3D space like XYZ or UVW, and so mathematically works like any 3D Cartesian coordinate system. So any function you can apply to a 3D point, or vector, you can also apply to color. The key is that functions apply once per each vector pair. R with R, G with G, B with B. Once you know that, you can do pretty much whatever you want mathematically.

#7

Um… yeah, that’s what I said.

#8

Ah. Sorry if i misunderstood.

This bit;

If you try to multiply 128 * 128, you will wind up with a clipped value, way above 255. .5 * .5 = .25, though. Photoshop will report the pixel’s value at 64, even though its own math doesn’t work that way.

Seemed odd.

#9

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