Are Screen and Multiply the same modes on opposite sides?

[ivframes]

If you apply 10% Screen, flatten, then 10% Multiply, you will basically have the same looking image as if you didn't apply anything, with only a very slight change in the histogram.

Is this the sound logic? So for each Screen value, there's a Multiply value to counter that?

However, it's interesting that if you apply two layers of both Screen and Multiply without flattening inbetween, you will not have the same image and their positions related to the background will matter too.

[davescm · Accepted solution]

Blending uses standardised values i.e 0-255 becomes 0 to 1

Where A is the lower layer and B the upper

Multiply is simply A x B

Screen is 1-(1-A) x (1-B) 

Your numbers above do not mention the values of the upper and lower layer but to keep it simple lets assume you use a start value of 0.5 and multiply by 0.9 (corresponding to your 10%)  then screen using it's invert = 0.1 (again corresponding to your 10%)

The multiply is therefore 0.5 x 0.9 = 0.45

Screen uses 1-(1-A)x(1-B) so that becomes 1-(1-0.45) x (1-0.1) = 1- 0.55 x 0.9  = 0.505  so inverting the upper layer value and using screen does not return the value to the start.

Swapping the multiply and screen order gives a result of 0.495 so you will see a difference if you swap the multiply and screen layer order

Incidentally - I get the same results from applying each layer and flattening as I do from adding two separate layers

Dave