transparency - Check if image has alpha channel

How can I check if an Image has an alpha channel?

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"What have you tried?"

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  AlphaChannel and ColorSeparate[..., "A"] return a result even if the image had no explicit alpha channel.

  
  


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  We could check the number of results from ColorSeparate or ImageChannels, but that also depends on ColorSpace, which may also be a ColorProfileData object (for which it isn't clear how to determine the number of expected channels).

  
  

Answer

I just discovered this command (in the Properties and Relations sections of the AlphaChannel command)

ImageMeasurements[img, "Transparency"]

It returns True if there is an alpha channel and False otherwise.