Jump to content
Sign in to follow this  
wyager

Different algorithm for masks+stacks?

Recommended Posts

I recently tried stacking some photos of the same subject with different lighting (to eliminate glare in post) and ran into an annoying issue: stacks don't play well with masks. If you attempt to mask out an item inside a stack using a soft brush, you get an extremely sharp boundary instead of the gradual transition you want. I can see why it was implemented this way, but I would like to suggest a different algorithm that's slower but at least useful (and should get the result people want and probably intuitively expect).

 

Let's say you have 5 layers in the stack. You set the stack mode to "median". However, in one area of the image, layer 3 is causing an object to look too dark. You'd like to mask out layer 3 in that area, and that area should look like layer 3 isn't being included (and gradually transition as you'd expect using a soft brush on your mask layer). You'd like to mask out layer 4 elsewhere because it's making something look too light.

 

To get the intuitive/desired behavior, you would calculate the stack 4 times (2^<number of layers with masks>):

 

A: Stack color channels of layers 1,2,3,4,5

B: Stack color channels of layers 1,2,4,5

C: Stack color channels of layers 1,2,3,5

D: Stack color channels of layers 1,2,5

 

Let a_i be the alpha channel of image <i>

 

a_A = a_3*a_4

a_B = (1 - a_3) * a_4

a_C = a_3 * (1 - a_4)

a_D = (1 - a_3) * (1 - a_4)

 

To get the final color output of the stack, you calculate A*a_A + B*a_B + C*a_C + D*a_D

 

Or something along those lines. 

 

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...

Important Information

Please note the Annual Company Closure section in the Terms of Use. These are the Terms of Use you will be asked to agree to if you join the forum. | Privacy Policy | Guidelines | We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.