draw a histogram for a PGM or PPM file
see also :
pgmhist - ppmhist
[-black] [-white] [-max N]
add an example, a script, a trick and tips
no example yet ...
... Feel free to add your own example above to help other Linux-lovers !
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
Ignores the count of black
pixels when scaling the histogram.
Ignores the count of white pixels when scaling the
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 unreadbaly small. 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.
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.
is always 255. Images with a smaller maxval will only use
the lower-value side of the histogram. 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.
the output size to be specified.
ppmhist , pgm, ppm
Wilson H. Bent.