Legacy ImageMagick Discussions Archive

I need a png known to have transparent background. I built one starting from a pdf from powerpoint with
transparent background, magicked to png, checked this way following instructions elsewhere in this forum.

$ magick identify -verbose die12t.png | grep "Alpha"
Base type: TrueColorAlpha
Alpha: 8-bit
Alpha:
Alpha: graya(0,0) #00000000
png:IHDR.color_type: 4 (GrayAlpha)

I'd like confirmation that I'm OK. If not, what else should I do?

$ magick -version
Version: ImageMagick 7.0.5-1 Q16 x64 2017-03-04 http://www.imagemagick.org

ebolker wrote:I need a png known to have transparent background.

What does that mean?

The alpha statistics will tell you if the image has transparency. For example:

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    Alpha:
      min: 0 (0)
      max: 255 (1)
      mean: 94.4481 (0.370385)
      standard deviation: 123.141 (0.482908)
      kurtosis: -1.71183
      skewness: -0.536812
      entropy: 0.1282

The image has alpha varying from 0 (transparent) to 1 (opaque), with a mean of 0.37 (mostly transparent).

What my question means is that I did not know how to translate "Alpha = 0" to "background is transparent". Now I do. Thanks.

If you just want to know if the image is fully opaque or partially transparent, then you can use

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convert image -format "%[opaque]" info:

See https://www.imagemagick.org/script/escape.php

If you want to know if the image is totally transparent, then use

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convert image -alpha extract -format "%[fx:mean]" info:

if the result is exactly 0, then the image is fully transparent. If it is exactly 1, then it is fully opaque. If in-between, then some pixels have at least partial transparency.

Legacy ImageMagick Discussions Archive

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