[magick-users] average ignoring transparency

[Anthony Thyssen]

On Sat, 17 Jan 2009 13:19:32 +1100
magick-users-bounces at imagemagick.org wrote:

| Take three images as in the example:
| 
|     http://www.imagemagick.org/Usage/compose/#plus
| 
| What I'd like to be able to do is to only average parts of images that are not
| transparent.
| 
|               ____              ____               
|           .-'""    ""`-.    .-'""    ""`-.          
|        .-'              `..'              `-.       
|      ,'                ,'  `.                `.     
|    ,'                ,'      `.                `.   
|   /   don't         /          \         don't   \  
|  /  average        / average of \        average  \ 
| ;                 ;  two images  :                 :
| :                 :              :                 :
| |                 |     ____     |                 |
| :                 :.-'""    ""`-.:                 :
| :               .-'  average of  '-.               ; 
|  \            ,'   \   three    /   `.            / 
|   \         ,'      \  images  /      `.         /  
|    `.      / average `.      ,' average \      ,'   
|      \.   /  of two    \.  ,'  of two    \   ,'     
|        `-'    images    ,''.    images    ;-'       
|          :`-.,,____,,.-'    `-.,,____,,.-':         
|          |                                |
|          :                                :
|          :         don't average          ; 
|           \                              / 
|            \                            /  
|             `.                        ,'   
|               \.                    ,'     
|                 `-.              ,-'       
|                    `-.,,____,,.-'          
| 
| 
| Any ideas?
| 
| 
Do what everyone else does,  mask the resulting images with the
original using DstIn operators  (mask using the transparency shape given)

Average like most mathematicaly operators do not define what they should
do with regards to transparency!




  Anthony Thyssen ( System Programmer )    <A.Thyssen at griffith.edu.au>
 -----------------------------------------------------------------------------
     "When I became a man I put away childish things, including
      the fear of childishness and the desire to be very grown up."
                                                        -- C.S. Lewis
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     Anthony's Home is his Castle     http://www.cit.gu.edu.au/~anthony/