Question

I am converting some high-res iPhone images to low-res with batch processing using ImageMagick. I simply run the following:

convert [e-mail] -resize '50%' image.png

The problem is using pngcheck, it appears that the original @2x file is 32bit (where 8bits are an alpha channel) and in the down sized version, that is stripped away.

pngcheck output (before convert):

OK: [e-mail] (85×81, 32-bit RGB+alpha, non-interlaced, 94.6%).

pngcheck output (after convert):

OK: image.png (43×41, 8-bit palette+trns, non-interlaced, 4.8%).

Answer 1

You can use specifier to force output format.

convert [e-mail] -resize '50%' PNG32:image.png