combine two commands that swap white for black into one - imagemagick

Question

I have a large number of images that are white with transparent backgrounds, and I would like to make them black with transparent backgrounds. It's simple enough to do with GIMP or BIMP, but with thousands of images, command-line seems a better way to go.
In ImageMagick, I've found that the following two commands do what I want:
mogrify -alpha set -channel RGBA -background black -flatten +repage -negate *.png
mogrify -alpha set -channel RGBA -transparent white *.png
However, I'd rather not make two passes. I've tried to combine them a number of different ways:
mogrify -alpha set -channel RGBA -background black -flatten +repage -negate +repage -transparent white *.png
mogrify -alpha set -channel RGBA -background black -flatten +repage -negate -alpha set -channel RGBA -transparent white *.png
mogrify -alpha set -channel RGBA -background black -flatten +repage -negate +repage -alpha set -channel RGBA -transparent white *.png
as well as a couple other permutations of the same ideas. All of them result in a purely black image. What am I missing?
Is there an easier way to invert black and white or at least convert white to black, but leaving the alpha layer untouched?
mogrify -negate *.png
converts white to transparent and transparent to white, and
mogrify -fill black -opaque white *.png
leaves behind messy white edges.

Answer 1

In ImageMagick you can do:
mogrify -format png -fill "rgba(0,0,0,1)" -opaque "rgba(255,255,255,1)" *.png
If your white is not perfectly white, then add -fuzz XX%
mogrify -format png -fuzz 5% -fill "rgba(0,0,0,1)" -opaque "rgba(255,255,255,1)" *.png
The issue is that you need to specify alpha values in your colors, since your image has transparency. Thus use rgba(r,g,b,a) values (note the a) or use hex values with #RRGGBBAA
If using IM 7, then mogrify is replace with magick mogrify
Here is an example using convert. I created a white image with transparency elsewhere from the logo: image.
http://www.fmwconcepts.com/misc_tests/transparency_invert/logot.png
Then ran
convert logot.png -fill "rgba(0,0,0,1)" -opaque "rgba(255,255,255,1)" logot_invert.png
Which returns black where the input was white and keeps the transparency unchanged.
http://www.fmwconcepts.com/misc_tests/transparency_invert/logot_invert.png
Is this not what you want?

Answer 2

Perhaps what you want is the following in ImageMagick. Just a guess until I can see your actual input files.
mogrify -format png -alpha off -negate -alpha on *.png

Answer 3

In ImageMagick, try
mogrify -alpha off -negate -alpha on *.png
This turns off the alpha channel inverts the black and white and then turns on the original alpha channel.
As a test, I did
convert aircon.png -alpha off -negate -alpha on aircon_fred.png
The equivalent of your two mogrify command is
mogrify -background black -alpha background -alpha off -negate -transparent white *.png
I had to replace your -flatten with the equivalent since one needs to reset the compose method to over afterwards for the -transparent to work. But mogrify does not accept -compose over.
As a simple test, I did
convert aircon.png -background black -flatten -negate -transparent white aircon_fred2.png
Another method similar to the first is just to make the whole underlying image black and keep the alpha channel.
mogrify -alpha off -fill black -opaque white -alpha on *.png
Again as a test, I did
convert aircon.png -alpha off -fill black -opaque white -alpha on aircon_fred3.png
However, my first method should give better antialiasing, since it keeps your original alpha channel. Your method will recreate the alpha via -transparent white and will have more stair-stepped aliasing.