Legacy ImageMagick Discussions Archive

Bob-O-Rama wrote:I have a pile of files say 1.jpg, 2.jpg, 3.jpg,... N.jpg, all same size, depth, etc. I need to merge them together by averaging them. They would all have equal weight in the final image. Obviously I could loop through the images and perform the math on corresponding pixels. ( I may have to do this anyway to later allow for various blending methods to be implemented. ) But I'm assuming there is a way to do this is a more concise way. Any suggestions?

Ultimately I'm interested in some sort of HDR stacking method to sets of bracketed exposures.

Thanks!

-- Bob

fmw42 wrote:(Too bad there are not equivalent multi-image operators such as -multiply, -minimum and -maximum that work on more than 2 or 3 images at a time).

   convert *.jpg   -background white -compose multiply -flatten result.jpg

   convert *.jpg   -background white -compose darken -flatten result.jpg

   convert *.jpg   -background black -compose lighten -flatten result.jpg

   convert image1 image2 -compose difference -composite \
       -separate -background black -compose Plus -flatten \
difference.png

anthony wrote:

fmw42 wrote:(Too bad there are not equivalent multi-image operators such as -multiply, -minimum and -maximum that work on more than 2 or 3 images at a time).

There is, it is called -flatten but you need to set -background color appropriately first!

EG: here are your -multiply, -minimum and -maximum equivelents...

Code: Select all

   convert *.jpg   -background white -compose multiply -flatten result.jpg

Code: Select all

   convert *.jpg   -background white -compose darken -flatten result.jpg

Code: Select all

   convert *.jpg   -background black -compose lighten -flatten result.jpg

Note the color of the background used to so that it does play a part in the results.

I myself like to add up the channels of difference images

Code: Select all

   convert image1 image2 -compose difference -composite \
       -separate -background black -compose Plus -flatten \
difference.png

See IM Examples, Comparing Images, Difference images
http://www.imagemagick.org/Usage/compare/#difference
as well as Channels and Masks, Removing a Known Background
http://www.imagemagick.org/Usage/channels/#mask_bgnd


Of course without HDRI being enabled to handle data overflow, there is no equivalent for -average, which is why it has its own separate operation.