Re: [APML] FM3A MLU and a manual stacking question

[Jerry Lodriguss <jerryapml@astropix.com>]

Hi Eric,

It is not obvious or intuitive, but if you want to stack multiple images in 
Photoshop as layers, you set the opacity of each individual layer differently.

A simple way to remember the percentage opacity you should use for each 
layer is to divide the layer number into 100.

For example:
Layer 1 (the background) stays at 100% (100/1)
Layer 2 should be at 50% (100/2)
Layer 3 should be at 33% (100/3)
Layer 4 should be at 25% (100/4)
etc.

You don't have to flatten each layer individually, you can flatten them all 
after you have changed the opacities of each.

Jerry




>The second question is about manual stacking of images in Photoshop (or the
>equivalent).  Let's say I have 3 nice images that I want to align and stack,
>and I plan to use the average blending mode by setting the opacity of each
>overlaid image to 50%.
>
>I start with the first image, which sits on the bottom with 100% opacity, then
>I overlay the second at 50%, and when I'm happy with the alignment, I flatten
>the image.  Then I repeat with the 3rd image.
>
>Here's the problem: Let's pick an arbitrary pixel in each image, and to narrow
>it down, let's say the RED value is 100 in the first, 100 in the second, 
>and 70
>in the third.  A real average would be 100+100+70=270/3=90.  But with the
>aboove method, after the first flattening, the red value sits at 100.  Then
>after averaging with the third, it is 100+70=170/2=85.  85 is not the real
>average.
>
>Does that make sense?  Any ideas on how to solve it?

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