HALFTONE(1)

NAME
halftone - Translate a bw file to a halftoned bw file

SYNOPSIS
halftone [-hRSa] [-s squarefilesize] [-w file_width] [-n file_height] [-B contrast] [-I Number_Intensity_Levels] [-M Method] [-T Tone_Scale_Curve_Points] < file.bw

DESCRIPTION
Halftone reads a bw(5) format file from the named file, or from standard in if no file is specified, and reduces the number of intensity levels from 256 to a default of 2. Halftone trys to preserve as much information as possable by applying dither.

By default, the bw file is assumed to be 512x512 pixels. Specifying the -h flag changes the size to 1024x1024.

If the -R flag is specified random noise is added to the dither which can sometimes improve the results.

The -S flag causes a surpentine raster to be used rather than a left to right scan.

The -a flag is used when automatic file sizing is wanted. This does not work on pipes.

The -w file_width flag specifies the width of each scanline in the input file, in pixels.

The -n file_height flag specifies the height in scanlines of the input file.

-s squarefilesize sets both the height and width to the size given.

-B contrast will define a floating point value to be used as the Beta portion of a edge sharpening algorthm. The default is 0.0 which is no sharpening.

-I Levels defines the number of different intensity levels to use on output. The default is 2 (1 bit) and the max is 256 (8 bits).

The -M method allows a choice of dither methods. The default is 0 a Floyd-Steinburg diffused error dither, 1 is a 45 degree classical clustered halftone screen, 2 is a simple threshold dither, 3 is a 0 degree dispersed halftone screen.

The -T x1 y1 x2 y2 ... parameter is used to define a curve to be used as a tone scale. The resulting curve is used to map input pixels to output pixels. The default curve is -T 0 0 128 128 255 255 a curve suggested by Robert Ulichney in Digital Halftoning is -T 0 0 15 0 128 100 200 200 240 255 255 255.

FORMAT
A bw(5) file contains sequences of pixels. Each pixel is stored as one unsigned char. The first pixel in a bw file is the lower left corner of the image. The pixels proceed from left-to-right across each scanline, with scanlines being written from the bottom to the top of the image.

The output from halftone is scaled so that each intensity level is output as 255/Levels*value.

SEE ALSO
rt(1), pix-bw(1), bw(5), bw-fb(1)

AUTHOR
Christopher T. Johnson

SOURCE
SECAD/VLD Computing Consortium, Bldg 394
The U. S. Army Ballistic Research Laboratory
Aberdeen Proving Ground, Maryland 21005

BUG REPORTS
Reports of bugs or problems should be submitted via electronic mail to <devs@brlcad.org>.