Section: User Commands (1)
Updated: 25 October 1993Index
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pnmhistmap - draw a histogram for a PGM or PPM file
Reads a portable anymap as input,
although bitmap (PBM) input produces an error message and no image.
Produces an image showing a histogram of the color (or gray) values
in the input.
A graymap (PGM) input produces a bitmap output.
A pixmap (PPM) input produces pixmap output with three overlaid histograms:
a red one for the red input,
a green one for the green input,
and a blue one for the blue input.
The output is fixed in size: 256 pixels wide by 200 pixels high.
Ignores the count of black pixels when scaling the histogram.
Ignores the count of white pixels when scaling the histogram.
The -black and -white options, which can be used seperately or together,
are useful for images with a large percentage of pixels whose value is
zero or 255, which can cause the remaining histogram data to become
Note that, for pixmap inputs, these options apply to all colors;
if, for example, the input has a large number of bright-red areas,
you will probably want to use the -white option.
- -max N
Force the scaling of the histogram to use N as the largest-count value.
This is useful for inputs with a large percentage of single-color pixels
which are not black or white.
Report the progress of making the histogram, including the largest-count
value used to scale the output.
All flags can be abbreviated to their shortest unique prefix.
Assumes maxval is always 255.
Images with a smaller maxval will only use the lower-value side of the
This can be overcome either by piping the input through "pnmdepth 255"
or by cutting and scaling the lower-value side of the histogram.
Neither is a particularly elegant solution.
Should allow the output size to be specified.
Wilson H. Bent. Jr. (email@example.com
- SEE ALSO