PS:  Since linear RGB pixels values are typically gamma-encoded representations 
of some absolutely recorded brightness, I suppose technically for a 
double-exposure you would have to un-encode the gamma (e.g. apply a Levels 
adjustment of 0.45 or so), merge the two source layers using Addition blending, 
then re-encode (e.g. 2.2 Levels adjustment).  I did some experiments using two 
layers with black-to-white gradients rotated 90 degres from each other, and the 
result of those adjustments was indeed pretty close to the "Screen" blending 
mode.  That's pretty interesting.

-- Stratadrake
strata_ran...@hotmail.com
--------------------
Numbers may not lie, but neither do they tell the whole truth.


Date: Sun, 4 Nov 2012 16:18:39 +0100
From: tobias.lu...@hfg-gmuend.de
To: ellimae...@gmail.com
CC: gimp-user-list@gnome.org
Subject: Re: [Gimp-user] double exposure


  
    
  
  
    Hello,

    

    afaik, the "Screen" blend mode is a more accurate reproduction of a
    double exposure. However, it will brighten up your image, so if the
    two photos weren't underexposed to begin with (which they are when
    you actually make a double-exposure on film), you'll have to adjust
    the values. Don't worry, the Screen mode doesn't result in clipping,
    so usually you don't loose all that much information.

    

    bw,

    Tobl

    

    

    

    Am 04.11.2012 16:10, schrieb Richard
      Gitschlag:

    
    
      
      
        If it's the term I'm thinking of there are maybe twenty
        different ways to do this in GIMP.  But all of them have one
        thing in common - you need to import both source images as
        separate layers in the same image window.

        

        From that point you can:

        1 - Set the top layer's mode to either Brightest or Addition
        (neither one precisely reproduces an actual double exposure, but
        they're close)

        2 - Keep the top layer's mode Normal and use the Eraser (or a
        layer mask) to fade the edges/transition between them.

        

        -- Stratadrake

        strata_ran...@hotmail.com

        --------------------

        Numbers may not lie, but neither do they tell the whole truth.

        

        

        
          Date: Sun, 4 Nov 2012 09:56:58 -0500

          From: ellimae...@gmail.com

          To: gimp-user-list@gnome.org

          Subject: [Gimp-user] double exposure

          

          Is there a way to use this program to create a double exposure
          effect?  I can do it with my 35mm camera manually while taking
          pics.  But was not sure if you can create the same digitally??
          

          
          Thank you!

            Jenn
          

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