SYNOPSIS
pnmhistmap

[-black]

[-white]

[-max N]

[-verbose]

[pnmfile]

Minimum unique abbreviation of option is acceptable. You may use dou-
ble hyphens instead of single hyphen to denote options. You may use
white space in place of the equals sign to separate an option name
from its value.


DESCRIPTION
This program is part of Netpbm.

pnmhistmap reads a PNM image as input and produces an image showing a
histogram of the color (or gray) values in the input. A PGM input
results in a PBM output. A PPM input results in a PPM 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.

For example, from the following image produces the following his-
togram:

image histogram from image

If the input is PBM, pnmhistmap produces an error message and no out-
put image.


OPTIONS
-red

-green

-blue Include the indicated color component in the output. If you




-dots Plot the histogram as dots. By default, pnmhistmap plots bars.




-lval minpixval

-rval maxpixval




-height

-width These options specify the dimensions, in pixels of the his-









-black Ignore the count of black pixels when scaling the histogram.


-white Ignore the count of white pixels when scaling the histogram.



The -black and -white options, which can be used separately 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 color 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-


-verbose





LIMITATIONS
pnmhistmap assumes maxval is always 255. Images with a smaller maxval
will only use the lower-value side of the histogram. You can overcome
this either by piping the input through pamdepth or by cutting and
scaling the lower-value side of the histogram. Neither is a particu-
larly elegant solution to the problem.

The program does not allow you to specify the output size.


SEE ALSO
pgmhist, ppmhist, pgm, ppm


AUTHOR
Wilson H. Bent. Jr. (whb@usc.edu).



netpbm documentation 25 October 1993 Pnmhistmap User Manual(0)