Detect Alpha Channel with ImageMagick

image png imagemagick jpeg alpha
brad picture brad · Apr 6, 2010 · Viewed 18.2k times · Source

Scenario

I would like to save images with alpha transparency as .png and images without alpha transparency as .jpg (even if their original format is .png or .gif). How can I detect whether or not an image has alpha transparency using ImageMagick?

Answer

msw picture msw · Apr 6, 2010

The ImageMagik command:

identify -format '%[channels]' foo.png

will print rgba or rgb if there is or is not an alpha channel, respectively.

There could be an alpha channel present with no data in it which wouldn't actually have any transparency, but that is a bit more complicated.

Related questions

Converting a PDF to PNG

I'm trying to convert a PDF to a PNG image (at least the cover of one). I'm successfully extracting the first page of the PDF with pdftk. I'm using imagemagick to do the conversion: convert cover.pdf cover.png This …

Read More
How to insert transparent PNG in PDF?

I am able to insert JPG image into a PDF document with DCTDecode filter. I think the all parameters should be the same for PNG image too, except the filter which should be FlateDecode. However, when I try to insert …

Read More
Creating a semi-transparent PNG with ImageMagick/convert

I have PNG files that I would like to convert the whole image to be semi-transparent. The image will be referenced in a KML file as an icon overlay for use in Google Earth/Maps. The following examples have been …

Read More