advpng - does not support grayscale pngs

[Nobody/Anonymous]

The latest version reports that it cannot process
this type of png.

PNG wriiten by "The Gimp", seems to read and
display correctly.

Any chance to add support in a upcomming release?

[Mikael Öhman]

For people who wants to use this in grayscale and possibly other unsupported bitdepths and color combinations I recommend using other png minimizers then use advdef afterwards.

[Kodo]

AdvPng can support palette but not support grayscale. So you must convert grayscale to palette first then use AdvPng. Here is the batch code(use ImageWorsener http://entropymine.com/imageworsener/):
cd /D "%~dp0"
for /R %1 %%a in (*.png) do imagew -noopt "grayscale" "%%~a" "%%~a"
pause
Just drag and drop the images' folder to this batch file.