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Can someone please explain me the following output of imagemagicks identify?

image.gif GIF 345x49 345x49+0+0 8-bit PseudoClass 256c 1.79KB 0.000u 0:00.000 I know the follwing:

I know that GIF is the file extension, 345 is the width, 49 is height, 8-bit is the color depth. 1.79KB is the file size.

But what does PseudoClass, 256c and 0.000u 0:00.000 mean?

If I verbose the output, I get even more results I don't understand:

  • Type: Bilevel
  • Base type: Bilevel
  • Depth: 8/1-bit
  • signature:
  • Artifacts: verbose: true
  • Tainted: False
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up vote 3 down vote accepted

Mostly guessing and copying from ImageMagick "Basics":

  • PseudoClass 256c – image uses a color map (color palette) containing at most 256 colors; standard for GIF images. (If the image specifies color values directly, it would be DirectClass.)

  • Type: Bilevel apparently means the image is a two-color monochrome. (Palette means the entire palette is used; TrueColor for 24-bit RGB and such; ...Matte suffix means an additional transparency value is used)

  • Depth: 8/1-bit – not entirely sure; 8-bit means 8 bits per value, which is standard for GIFs. The one bit could be the GIF transparency.

    (For "Palette" images, each pixel has one value, the color index in palette; for "TrueColor", each pixel usually has 3-4 values: R/G/B and optional transparency)

  • The signature property is a hash of the image.

Some properties are not about the file contents but about the in-memory image objects used by ImageMagick:

  • The verbose artifact means ImageMagick will output verbose information about the image; you added it by using -verbose.

  • Tainted is true if the image has been modified since loading.

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Just to add one thing that's missing from this answer, and which I had to ask on the Imagemagic forum to find out (…;... 0.000u is "User Time" and 0:00.000 is the "Total Elapsed Time" that it takes for identify to check the image. – Brian Z Apr 5 '15 at 4:14

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