[magick-users] Make transparent background white in multiple PNGs

[Fred Weinhaus]

You may be able to use mogrify to process each image in one folder 
and place it with the same name in a second folder. Something like

create second empty folder
cd to first folder where your images are located

mogrify -path /fullpathto/secondfolder -format png -background white 
-flatten *.png

I am not sure that mogrify will allow -flatten. If not, then you will 
need to write a script to loop over each image and use convert

convert infile.png -background white -flatten infile.png

I am not sure what you can do about the dithering as IM will 
reprocess your image to one extent or another. It may or may not work 
out. So you will need to test it on one image to see about the above.

I hope that this will just flatten your transparency to white, but I 
really don't know what will happen with any specific dither pattern.

Also there is no guarantee that IM will not change the filesize 
either. Some things that can be done depend upon if you have 8 or 16 
bit images and are running IM in 8 or 16 bit mode. If your image is 
8-bit and you are on 16-bit IM, then you need to add -depth 8 to the 
commands. PNG compression controls can be used as well as PNG output 
formats.

see http://www.imagemagick.org/Usage/formats/#png

If your pngs are optimized then IM will probably produce larger sizes 
and you may need to use one of the other tools mentioned in this page 
to post process and reoptimize your png.




>I have a folder full of PNGs with transparent background
>and need to process all of them so as to
>
>* make the background white/add a white background
>* not change the filenames
>* not break dithering
>* not change the size of the images
>
>What would be the invocation?
>
>TIA,
>
>/BP