ImageMagick: Replace RGB channels with white, retain Alpha - image-processing

Question

I have an image created in a Affinity Designer, which has the following channels:
R, G and B:
Alpha:
When I use this image in other places (Unreal Engine), I get small black artifacts on the edge of the shape due to the black part of the RGB channels. The only important information I need is the alpha channel.
How can I use ImageMagick to replace the RGB channels with white, while retaining the alpha channel?

Answer 1

Here is a simple way to do the in ImageMagick:
First, since you did not provide the actual image, I will reconstruct it from the rgb.png and alpha.png
convert rgb.png alpha.png -alpha off -compose copy_opacity -composite image.png
Now, to make the rgb part white, simply do:
convert image.png -fill white -colorize 100 result.png
Now to see that the rgb parts are fully white, we do:
identify -verbose result.png
.
.
.
Channel statistics:
Pixels: 512
Gray:
min: 255 (1)
max: 255 (1)
mean: 255 (1)
standard deviation: 0 (0)
kurtosis: -4.9152e+52
skewness: 9.375e+35
entropy: 0
Alpha:
min: 0 (0)
max: 255 (1)
mean: 187.152 (0.733931)
standard deviation: 109.252 (0.42844)
kurtosis: -0.822401
skewness: -1.05578
entropy: 0.336307
So the rgb components are a constant 255 (white) and the image is now white with an alpha component.

Answer 2

Try the following...
magick \( input.png -fill white -draw 'color 0,0 reset' \) \
\( input.png -alpha extract \) \
-compose Copy_Alpha -composite \
output.png
I'm sure there's better ways to do the above. Reading the input.png twice, and extracting the alpha channel is bit redundant.
The first part replaces all RGB channels with white, but also clears the alpha channel.
input.png -fill white -draw 'color 0,0 reset'
The second part grabs the alpha channel.
input.png -alpha extract
Finally, we copy the extracted alpha values back over the white image's alpha channel.
-compose Copy_Alpha -composite
If your using ImageMagick-6, then replace magick with convert, and Copy_Alpha with Copy_Opacity.
Best of Luck!