Making semi-transparent white pixels in an image all a single color

[nihilazo]

Hello, I have some images like these ones:



I would like to make the figures on the images (which are currently semi-transparent) be totally opaque, and go from the greyish color they are to being totally white (#ffffff). How would I go about this using convert? All of the images also have these different amounts of alpha on the figures, so I can't do a blind one-color-for-another replace.

[GeeMack]

I would like to make the figures on the images (which are currently semi-transparent) be totally opaque, and go from the greyish color they are to being totally white (#ffffff). How would I go about this using convert? All of the images also have these different amounts of alpha on the figures, so I can't do a blind one-color-for-another replace.

There are probably a few good ways to do this. My first thought was to threshold the alpha channel, and fill the positive with white. A command like this gets me pretty close to what you described...

Code: Select all

convert input.png -channel A -threshold 10% -channel RGB -fill white -colorize 100 output.png

You might be able to tweak the threshold percentage so it accommodates the range of alpha in your various images.

[fmw42]

Your alpha channel is the same as your base image. You can see that from comparing the results of

convert test.png -alpha off aoff.png



convert test.png -alpha extract alpha.png




My thought was to make the base image pure white and then threshold the alpha channel.

Code: Select all

convert test.png -channel rgb -evaluate set 100% +channel -channel a -threshold 50% +channel test1.png

Looking at GeeMack's solution, it appears to be similar but in the reverse order.

I thresholded the alpha channel more, so that the black lines in the image showed as transparency. If you do not want those outlines, then threshold at 0% (as user snibgo suggested below).

[snibgo]

As GeeMack says. To change "partially transparent" to "fully opaque", while leaving fully transparent unchanged, use "-threshold 0".

[nihilazo]

Thank you everyone! This works perfectly.