Multiply Mix LAB vs RGB

Y
Posted By
yinako
Mar 11, 2007
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434
Replies
3
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Closed
Hi, anyone has more info on the multiply mode in photoshop in LAB mode? here some things I found out:

< http://yinako.wordpress.com/2007/03/11/multiply-mix-lab-vs-r gb/>

but I’m kind of in the dark as to how it works
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mix multiply rgb vs

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GA
George_Austin
Mar 14, 2007
Yinako,

You ask a very good question.

The multiply blend mode in RGB multiplies the normalized red values of the two colors being multiplied, the normalized green values, and the normalized blue values, producing the new normalized red, green and blue values of the product. "Normalized" means dividing by 255 to work in the range 0-1 rather than 0-255. There is no cross-channel interaction. That is the multiplications are confined within each R,G,B channel.

In LAB, the normalized Lightnesses of the two colors are multiplied to give the resultant normalized Lightness. Normalization here means dividing by 100 since Lightness ranges 0-100. In the a and b channels,
separately, multiply is applied to the INVERSE normalized values to produce the inverse normalized channel value. The algorithm here is:

(1-a) = (1-a1)(1-a2) in the a channel and

(1-b) = (1-b1)(1-b2) in the b channel

where a and b range -128 through 0 to +127 and their normalized values range from -1 through 0 to +1. Again, as in RGB, there is no cross-channel action involved in LAB multiplication. a1 and a2 are the two a-channel values of the colors being multiplied and a is the resulting a-channel value. Likewise b1 and b2 are the two b-channel values and b is the result of the multiplication.

Yinako, are you Japanese? It is my pleasure to work with you in any case but especially if you are from Japan for which I have fond memories, having visited there in the late seventies and been treated ever so graciously.

George
Y
yinako
Mar 14, 2007
Thanks George, this is valuable information. 🙂 Do you work for adobe? how do you come to know about it?
GA
George_Austin
Mar 14, 2007
Yinako,

"…Do you work for adobe?…" No.

"…How do you come to know about it?…" By asking questions such as yours and answering them myself by trial and error.

George

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