RGB Calculations – my last try

[Filip Vandueren]

Hi Peter,

I think dividing is a bad example…
What would you expect of white divided by 25% gray? 400% superwhite?
and divided by black…

Anyway, there’s no way to alter the output of a layer on the pixellevel using expressions.
There’s the calculations filter that does some basic combinations, but t
of course there are the layer modes:

Multiply, add, and classic difference.
Screen is not divide, although it has the inverse effect of multiply, it’s actually multiplying the negative of the layer’s.

Again, what output do you expect to see from dividing?
There might be a workaround,

[__peter__]

I am working for a long time now with the great book of Steve Wright.

And there is that greenscreen correction procedure that obviously needs dividing.
But I would be happy to know a workaround.

Thanks!

Peter

[Trent Armstrong]

Check this tutorial for AE 8 from Maltaannon.com

https://maltaannon.com/tutorials/AfterEffects/cePixelSampler/

Another way to gather the RGB values is to use the imageSample() expression. More information here:

https://www.motionscript.com/design-guide/sample-image.html

Trent

[Darby Edelen]

For those of us that are not familiar with the book you mention, what is the formula you are trying to enact in AE?

Filip echoes my concern about dividing values… Visible RGB values in AE all fall between 0 and 1. Dividing anything by a number in the range of 0 to 1 will give you a number that is either equal to or larger than itself:

x / {0...1} = {Infinity...x} *

Are you sure we’re not talking about multiplication?

*I have no idea if this is the right way to represent a set of real numbers between 0 and 1… but it looks good to me (;

Darby Edelen
Designer
Left Coast Digital
Santa Cruz, CA