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Graphics from the command line Page 4 of 15

Listing 3. Sample output from pnginfo

sample.png... Image Width: 640 Image Length: 480 Bitdepth (Bits/Sample): 8 Channels (Samples/Pixel): 3 Pixel depth (Pixel Depth): 24 Colour Type (Photometric Interpretation): RGB Image filter: Single row per byte filter Interlacing: No interlacing Compression Scheme: Deflate method 8, 32k window Resolution: 0, 0 (unit unknown) FillOrder: msb-to-lsb Byte Order: Network (Big Endian) Number of text strings: 0 of 0

I am not aware of equivalent individual tools for other formats such as BMP, GIF, and JPEG.However, ImageMagick comes to the rescue once more, this time with a tool called identify.

# identify -verbose sample.png

Listing 4. Sample output from identify

Image: sample.png Format: PNG (Portable Network Graphics) Geometry: 640x480 Class: DirectClass Type: true color Depth: 8 bits-per-pixel component Colors: 142360 Filesize: 555.6k Interlace: None Background Color: grey100 Border Color: #DFDFDF Matte Color: grey74 Dispose: Undefined Iterations: 0 Compression: Zip signature: 361fe70ae623ef6f1fca44e0d29d157c2d701039fcf0f8625862925d881e13a4 Tainted: False User Time: 0.190u Elapsed Time: 0:01

You can see that identify displays a bunch of useful information about the image file, such as thesize of the image in pixels, the color depth of the image, and the image format.

pnginfo

I'd been a user of libtiff for quite some time when I started using PNG. At the time, there wasno tiffinfo equivalent for PNG files, which is why I wrote pnginfo. (You can downloadpnginfo from the link in Resources).

identify also has a -format command-line flag that allows you to specify only the information youwant to output. For example, if you were only interested in the image dimensions, you might use acommand like this:

# identify -format "%wx%h" sample.png