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ppmmix reads two portable pixmaps as input and mixes them together using the specified fade factor. The fade factor may be in the range from 0.0 (only ppmfile1's image data) to 1.0 (only ppmfile2's image data). Anything in between gains a smooth blend between the two images.

The two pixmaps must have the same size.

SEE ALSO


ppm(5)

AUTHOR

16 November 1993

ppmnorm

ppmnorm—Normalize the contrast in a portable pixmap

SYNOPSIS


ppmnorm[-bpercent N | -bvalue N][-wpercent N | -wvalue N][ppmfile]

DESCRIPTION

ppmnorm reads a portable pixmap as input; normalizes the contrast by forcing the lightest pixels to white, the darkest pixels to black, and linearly rescaling the ones in between; and produces a portable pixmap as output.

It works by computing the relative gray level of each pixel as with ppmtopgm, and uses those values to scale the RGB levels. Note that this is different from using pgmnorm on the individual red, green, and blue graymaps (as produced by ppmtorgb3) and recombining them.

OPTIONS

By default, the darkest two percent of all pixels are mapped to black, and the lightest one percent are mapped to white. You can override these percentages by using the -bpercent and -wpercent flags, or you can specify the exact pixel values to be mapped by using the -bvalue and -wvalue flags. Appropriate numbers for the flags can be gotten from the ppmhist tool. If you just want to enhance the contrast, then choose values at elbows in the histogram; for example, if value 29 represents 3 percent of the image but value 30 represents 20 percent, choose 30 for bvalue. If you want to lighten the image, then set bvalue to 0 and just fiddle with wvalue; similarly, to darken the image, set wvalue to maxval and play with bvalue.

All flags can be abbreviated to their shortest unique prefix.

SEE ALSO


pgmnorm(1), ppmhist(1), ppm(5)

AUTHOR

Wilson H. Bent, Jr. (whb@usc.edu), heavily based on the pgmnorm filter by Jef Poskanzer.

7 October 1993

ppmntsc

ppmntsc—Make a portable pixmap look like it is taken from an American TV show

SYNOPSIS


ppmntsc dimfactor [ppmfile]

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DESCRIPTION

ppmntsc reads a portable pixmap as input and dims every other row of image data down by the specified dim factor. This factor may be in the range of 0.0 (the alternate lines are totally black) to 1.0 (original image).

This creates an effect similar to what I saw once in the video clip "You Could be Mine" by Guns'n' Roses. In the scene I'm talking about you can see John Connor on his motorbike, looking up from the water trench (?) he's standing in. While the camera pulls back, the image becomes "normal" by brightening up the alternate rows of it. I thought this would be an interesting effect to try in MPEG. I did not yet check this out, however. Try for yourself.

SEE ALSO


ppm(5), ppmdim(1)

AUTHOR

16 November 1993

ppmpat

ppmpat—Make a pretty pixmap

SYNOPSIS


ppmpat -gingham2|-g2|-gingham3| -g3|-madras|-tartan| -poles|-squig|-camo|

 -anticamo width height

DESCRIPTION

ppmpat produces a portable pixmap of the specified width and height, with a pattern in it.

This program is mainly to demonstrate use of the ppmdraw routines, a simple but powerful drawing library. See the ppmdraw.h include file for more information on using these routines. Still, some of the patterns can be rather pretty. If you have a color workstation, something like ppmpat -squig 300 300 | "ppmquant 128" should generate a nice background.

OPTIONS

The different flags specify various different pattern types:

-gingham2	A gingham check pattern. Can be tiled.
-gingham3	A slightly more complicated gingham. Can be tiled.
-madras	A madras plaid. Can be tiled.
-tartan	A tartan plaid. Can be tiled.
-poles	Color gradients centered on randomly placed poles. May need to be run through ppmquant.
-squig	Squiggly tubular pattern. Can be tiled. May need to be run through ppmquant.
-camo	Camouflage pattern. May need to be run through ppmquant.
-anticamo	Anticamouflage pattern; like -camo, but ultra-bright colors. May need to be run through ppmquant.

All flags can be abbreviated to their shortest unique prefix.

REFERENCES

Some of the patterns are from "Designer's Guide to Color 3" by Jeanne Allen.

SEE ALSO

pnmtile(1), ppmquant(1), ppm(5)

Page 411

AUTHOR

4 September 1989

ppmquant

ppmquant—Quantize the colors in a portable pixmap down to a specified number

SYNOPSIS


ppmquant [-floyd|-fs] ncolors [ppmfile]

ppmquant [-floyd|-fs] -map mapfile [ppmfile]

DESCRIPTION

ppmquant reads a portable pixmap as input. It chooses ncolors colors to best represent the image, maps the existing colors to the new ones, and writes a portable pixmap as output.

The quantization method is Heckbert's "median cut."

Alternately, you can skip the color-choosing step by specifying your own set of colors with the -map flag. The mapfile is just a ppm file; it can be any shape, all that matters is the colors in it. For instance, to quantize down to the 8-color IBM TTL color set, you might use the following:


P3

8 1

255

0 0 0

255 0 0

0 255 0

0 0 255

255 255 0

255 0 255

0 255 255

255 255 255

If you want to quantize one pixmap to use the colors in another one, just use the second one as the mapfile. You don't have to reduce it down to only one pixel of each color, just use it as is.

The -floyd/-fs flag enables a Floyd-Steinberg error diffusion step. Floyd-Steinberg gives vastly better results on images where the unmodified quantization has banding or other artifacts, especially when going to a small number of colors such as the preceding IBM set. However, it does take substantially more CPU time, so the default is off.

All flags can be abbreviated to their shortest unique prefix.

REFERENCES

"Color Image Quantization for Frame Buffer Display," by Paul Heckbert, SIGGRAPH '82 Proceedings, page 297.

SEE ALSO


ppmquantall(1), pnmdepth(1), ppmdither(1), ppm(5)

AUTHOR

12 January 1991

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ppmhist

ppmmake

ppmmix

ppmnorm

ppmntsc

ppmpat

ppmquant