Photoshop选择性滤色镜背后的数学/算法是什么？

Question

I'm working on an image-processing software on iPhone and get stuck in the selective color function as photoshop.

How to caculate new RGB values after selective color adjustment on a pixel via code?

I mean how to create a tool which has the same function as Photoshop's selective color(In Image->Adjustment->Selective Color).

Special thx!

Answer 1

Finally I sampled data of images which have be processed by photoshop, and got a quadratic curve with hue. But it is not exactly the same as photoshop's.

Answer 2

I have come across a code which uses image buffer to manipulate alpha of an image but the same can be used to manipulate rgb as well see this link

See this sample it will give a general idea of image manipulation in objective c

Answer 3

I too am trying to understand the math. Here are some observations from experiments with pure colors in "Absolute" mode, which as an end user is all I care about

1) As expected, adding the opposite of any color turns the starting color black. So 100% red + 100% cyan = black

2) Adding neighboring color does nothing. So 100% red + any amount of yellow or magenta = 100% red

3) Adding triadic colors converts the primary color into a neighboring. So 100% red + 100% green = 100% yellow

In RGB space this translates to something like

|r'|   |1, 0, 1, 1, 1, 0|   |r|
|y'|   |0, 1, 0, 1, 1, 1|   |y|
|g'|   |1, 0, 1, 0, 1, 1|   |g|
|c'| = |1, 1, 0, 1, 0, 1| * |c|
|b'|   |1, 1, 1, 0, 1, 0|   |b|
|m'|   |0, 1, 1, 1, 0, 1|   |m|

There is of course the adjustments for clipping, and black to white. Here is a more mathy discussion

http://blog.pkh.me/p/22-understanding-selective-coloring-in-adobe-photoshop.html