Pamlevels User Manual(1) General Commands Manual Pamlevels User Manual(1) NAME pamlevels - effect a 'levels' transformation SYNOPSIS pamlevels -from1 from1 -to1 to1 -from2 from2 -to2 to2 [-from3 from3 -to3 to3] [-linear] [-fitbrightness] [pamfile] DESCRIPTION This program is part of Netpbm(1). pamlevels reads a Netpbm image from pamfile or standard input, applies a 'levels' transformation, and sends the result to standard output. It finds a unique transformation that maps color from1 to to1, color from2 to to2, and-if -from3 and -to3 are supplied-color from3 to to3. Trans- formations based on two mappings are linear in light intensity and those based on three mappings quadratic. The color-mapping options may be shortened to -f1...-f3 and -t1...-t3. Color values have the following format: color[:scale], where color is a Netpbm color specification ⟨libppm.html#colorname⟩ and scale an op- tional coefficient that is applied to the intensity (i.e. not gamma-ad- justed) of each RGB component of color. When the transformation is linear (i.e. uses two mappings) and pre- serves zero (i.e. maps black to black), it corresponds to multiplica- tion of light intensity by a constant and preserves color integrity(1). EXAMPLES In the examples below, \ denotes a line continuation: To brighten an image by setting a darker white point- pamlevels -f1 black -t1 black \ -f2 white:0.9 -t2 white in.ppm > out.ppm To adjust the white point- pamlevels -f1 black -t1 black \ -f2 rgbi:0.9/0.83/0.80 -t2 white in.ppm > out.ppm To set a lighter black point- pamlevels -f1 white:0.06 -t1 black \ -f2 white -t2 white in.ppm > out.ppm To increase brightness by compression- pamlevels \ -f1 black -t1 black -f2 white -t2 white \ -f3 white:0.5 -t3 white:0.6 in.ppm > out.ppm The latter tranformation is similar to gamma-correction. OPTIONS In addition to the options common to all programs based on libnetpbm (most notably -quiet, see Common Options ⟨index.html#commonoptions⟩ ), pamlevels recognizes the following command line options: -from1 -to1 -from2 -to2 -from3 -to3 These options define the mappings of input colors to output col- ors that anchor the transformation function. See DESCRIPTION ⟨#description⟩ . You must specify at least two of these pairs. -linear This option tells pamlevels to work with the intensity-linear variation on PPM where the samples are proportional to light in- tensity, rather than brightness (gamma-adjusted) as in true PPM. The input must be of this form and the pamlevels makes the out- put of this form. Note that the numbers in a color specification like rgbi:0.9/0.83/0.80 are brightness levels (gamma-adjusted) re- gardless of the input and output format. You cannot use this with -fitbrightness because that function is not implemented. -fitbrightness This option selects a transformation which is not very useful - it is linear or quadratic in brightness rather than light inten- sity of the pixels. There is no physical basis for doing it this way and the result is normally undesirable. Note that many tools other than Netpbm do the transformation this way. One use for this option is simply to demonstrate the poor result of this method. One advantage of this transformation is that it is faster, be- cause the input and output image formats use brightness values. The result is approximately correct. You cannot use this with -linear because that function is not implemented. SEE ALSO pnmnorm(1), pamrecolor(1), pnmgamma(1), pnm(1) AUTHOR This program was first submitted by Anton Shepelev (an- ton.txt@gmail.com). HISTORY pamlevels was new in Netpbm 10.83 (June 2018). DOCUMENT SOURCE This manual page was generated by the Netpbm tool 'makeman' from HTML source. The master documentation is at http://netpbm.sourceforge.net/doc/pamlevels.html netpbm documentation 13 June 2018 Pamlevels User Manual(1)
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