Replace transparency in PNG images with white background

This works for me:

convert -flatten img1.png img1-white.png

Documentation references:

• -flatten command-line option
• -layers command-line option (-flatten is equivalent to -layers flatten)

here's how to replace the same image in all folders in a directory with white instead of transparent:

mogrify -background white -flatten */*.png

Welp it looks like my decision to install "graphics magick" over "image magick" has some rough edges - when I reinstall genuine crufty old "image magick", then the above command works perfectly well.

edit, a long time later — One of these days I'll check to see if "graphics magick" has fixed this issue.

I needed either: both -alpha background and -flatten, or -fill.

I made a new PNG with a transparent background and a red dot in the middle.

convert image.png -background green -alpha off green.png failed: it produced an image with black background

convert image.png -background green -alpha background -flatten green.png produced an image with the correct green background.

Of course, with another file that I renamed image.png, it failed to do anything. For that file, I found that the color of the transparent pixels was "#d5d5d5" so I filled that color with green:

convert image.png -fill green -opaque "#d5d5d5" green.png replaced the transparent pixels with the correct green.

I saw this question and answers which really help me but then I was needed to do it for a lot of files, So in case you have multiple images (PNG images) in one folder and you want to do it for all:

find ./ -name "*.png" -exec convert {} -flatten {} \;

Tried all, none worked. This one did:

convert input.png -channel rgba -alpha set \
            -fill none -opaque white \
            -fill white -opaque black \
            -fill white -opaque none \
            -alpha off output.png

It's -alpha off, NOT -alpha remove! iOS app store upload fails when there is an alpha channel in any icon!!

Here's how to do it: mogrify -alpha off *.png

This does the job for me:

magick convert OLD.png -background white -alpha remove NEW.png

Here is a starter image with a transparent background in case it helps with testing:

Also, for one-offs on PC, you can always open the PNG file in Windows Paint and click Save. This will automatically turn the transparency to opaque white.