Atmospheric extinction

[LD]

Hi All,
How do I adjust RGB channels for atmospheric extinction? In another program I've used I would multiply each channel master by the appropriate multiplier, but I can't figure how this is done in pixel math. Or is it done somehow along with my channel weights in RGB combination?
Thanks,
Larry

[Jordi Gallego]

Hi Larry,

I suggest  you to use "Channel math" that gives you posibility to apply linear correction factors to each RGB channel

Regards
Jordi

[Juan Conejero]

Hello Larry,

As Jordi has pointed out, you can give the ChannelMatch process a try. It works very well for this task.

A more general solution to this problem is PixelMath, though. To apply a linear color correction, just multiply each channel by the required constants. For example, say that your magic numbers are 0.95, 1.0 and 0.87 for the red, green and blue channels, respectively. Then the PixelMath expressions should be:

Code: [Select]

0.95*$target
$target
0.87*$target

To be able to write the above expressions, you have to uncheck the Use a single expression for all channels option on the PixelMath interface. Just drop the process to the target image, and you'll get the RGB channels balanced.

Of course, there's no need for the constants to lie within the [0,1] range. You can refer them to the green channel, which is more efficient because saves you a multiplication for each pixel. Just divide all multiplying factors by the green factor: R/G, G/G=1, B/G.

Hope this helps.

[LD]

Jordi and Juan,
Thanks for both the suggestions. Channel Math is new to me. I also did not realize that I could try a command in Pixel Math to cover all the channels versus one by one. More to play with!
Thanks again,
Larry