PNG forced to grayscale?

[Naerymdan]

I have a PNG image in RGBA format (The whole TrueColorMatte thing) and try to trim it (and repage it) and save it back as indexed (palette) with:

convert splash.png -trim +repage -type PaletteMatte newSplash.png
convert splash.png -trim +repage -type Palette newSplash.png
convert splash.png -trim +repage -define png:color-type=3 newSplash.png

But it consistently saves it as Grayscale no matter what I use. While it could seem that grayscale is like indexed but with white to black, IT'S NOT! It uses luminance and really plays badly with my rendering engine.

[fmw42]

what IM version and platform? perhaps you need to upgrade.

there have been many changes going on with PNG. see http://www.imagemagick.org/script/changelog.php




When I tried to do something similar on IM 6.6.7.4 Q16 Mac OSX Tiger, I still get a color image, but the transparency is lost.

convert logo: -resize 50% -transparent white -alpha on -channel rgba -trim +repage -type palettematte PNG8:logo_test.png

or even

convert logo: -resize 50% -transparent white -alpha on -channel rgba -type palettematte PNG8:logo_test.png

or even

convert logo: -transparent white -type palettematte PNG8:logo_test.png


In all 3 cases, the result is still color and palette, but transparency has turned black or is not created leaving white background.


Interestingly, this works:

convert logo: -transparent white gif:- | convert - -type palettematte PNG8:logo_test.png

But this does not:

convert logo: -transparent white miff:- | convert - -type palettematte PNG8:logo_test.png

[Naerymdan]

I'm using the latest and greatest 6.6.7-4, but I had the same problem with my 'old' 6.5.4-7

[glennrp]

Please send the original spash.png to glennrp at imagemagick.org or post a URL to it and I'll see if I can figure out what went wrong.

Verified that fred's last test case fails to preserve the transparency that exists in the MIFF.

[fmw42]

Verified that fred's last test case fails to preserve the transparency that exists in the MIFF.

Glenn,

This does not work either.


convert logo: logo.png
convert logo.png -transparent white -type palettematte PNG8:logo_test.png

Background remains white -- no transparency

Fred

[glennrp]

This was continued in
viewtopic.php?f=3&t=18074
The transparency also gets lost when you write to a MIFF instead of a PNG,
so the bug seems to lie in the palettematte conversion before the encoder is called.