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diff --git a/upstream/debian-bookworm/man1/pamthreshold.1 b/upstream/debian-bookworm/man1/pamthreshold.1 new file mode 100644 index 00000000..b0b24805 --- /dev/null +++ b/upstream/debian-bookworm/man1/pamthreshold.1 @@ -0,0 +1,192 @@ +\ +.\" This man page was generated by the Netpbm tool 'makeman' from HTML source. +.\" Do not hand-hack it! If you have bug fixes or improvements, please find +.\" the corresponding HTML page on the Netpbm website, generate a patch +.\" against that, and send it to the Netpbm maintainer. +.TH "Pamthreshold User Manual" 1 "06 June 2007" "netpbm documentation" + +.SH NAME + +pamthreshold - threshold grayscale image to black and white + +.UN synopsis +.SH SYNOPSIS + +\fBpamthreshold\fP +[\fB-simple\fP] +[\fB-local=\fP\fIwidth\fP\fBx\fP\fIheight\fP] +[\fB-dual=\fP\fIwidth\fP\fBx\fP\fIheight\fP] +[\fB-threshold=\fP\fIthreshold\fP] +[\fB-contrast=\fP\fIthreshold\fP] +[\fIinputpamfile\fP] +.PP +Minimum unique abbreviations of options are acceptable. You may use +double hyphens instead of a single hyphen to denote options. You may use +white space in place of the equals sign to separate an option name +from its value. + +.UN description +.SH DESCRIPTION +.PP +This program is part of +.BR "Netpbm" (1)\c +\&. +.PP +\fBpamthreshold\fP thresholds a grayscale image. Thresholding means +dividing the image into background and foreground by comparing every pixel +to a thresholding value. +.PP +The input should be a PGM image or a PAM image of tuple type +GRAYSCALE or GRAYSCALE_ALPHA. However, pamthreshold doesn't check; it +just thresholds the first channel as if it were grayscale samples and +if there is a second channel, processes it as if it is a transparency +(alpha) channel. So if you feed it e.g. a PPM image, it will +work but produce probably useless results. +.PP +The output is a PAM with tuple type BLACKANDWHITE or +BLACKANDWHITE_ALPHA, depending on whether the input has a transparency +channel. You can turn this into a PBM (if you need to use it with an +older program that doesn't understand PAM, or you can't afford the 8X +amount of space that PAM uses for the image) with +\fBpamtopnm\fP. +.PP +The output is to Standard Output. +.PP +When the input has a transparency channel, \fBpamthreshold\fP includes +a transparency channel in the output. Since the output has maxval 1, the +transparency channel can indicate only fully transparent or fully opaque. +\fBpamthreshold\fP make it fully transparent where the input is more +than half transparent and fully opaque where it isn't. +.PP +The transparency function was new in Netpbm 10.43 (June 2008). Before +that, \fBpamthreshold\fP ignores any transparency channel in the input. +.PP +Another way to convert a grayscale image to black and white is to +dither. Dithering is using clustered black and white pixels such that +if you step back and look at the picture, you see varying levels of +gray. \fBpamditherbw\fP does dithering. + +.UN options +.SH OPTIONS +.PP +In addition to the options common to all programs based on libnetpbm +(most notably \fB-quiet\fP, see +.UR index.html#commonoptions + Common Options +.UE +\&), \fBpamthreshold\fP recognizes the following +command line options: +.PP +Without any options, \fBpamthreshold\fP uses a method based on the +iterative algorithm found in +the +.UR http://www.wikipedia.org/ +wikipedia +.UE +\& article +.UR http://en.wikipedia.org/wiki/Thresholding_%28image_processing%29 + \fIThresholding (image processing)\fP +.UE +\& to compute the thresholding +value. ( +.UR http://en.wikipedia.org/w/index.php?title=Thresholding_%28image_processing%29&oldid=132306976 +this version +.UE +\& of the Wikipedia article was current at the time of this +writing). It uses this threshold to globally threshold the image. +This should work well for most images. The program issues a message +telling you what threshold it used. (Netpbm messages go to Standard +Error, and you can turn them off with the Netpbm common option +\fB-quiet\fP). +.PP +Options \fB-simple\fP, \fB-local\fP, and \fB-dual\fP select other +methods. + + + +.TP +\fB-simple\fP +This selects simple or global thresholding, +i.e. \fBpamthreshold\fP compares every pixel to the threshold you +specify with \fB-threshold\fP. Those with a brightness greater than +or equal to the threshold become white; others become black. This +works well for black and white text pages scanned with a flatbed +scanner and is faster than the default method that iteratively +determines the thresholding value first. + +.TP +\fB-local=\fP\fIwidth\fP\fBx\fP\fIheight\fP +This selects local adaptive thresholding (also known as dynamic +thresholding) using the neighborhood which is the square \fIwidth\fP pixels +wide and \fIheight\fP pixels high centered on the pixel in question. +\fBpamthreshold\fP computes the threshold individually for each pixel of the +image. This can accommodate changing lighting conditions in the image. +Depending on the size of the neighborhood this can be quite slow. + +.TP +\fB-dual=\fP\fIwidth\fP\fBx\fP\fIheight\fP +This selects a dual thresholding algorithm using a global threshold +for low contrast neighborhoods and local thresholding otherwise. This +can preserve larger back- respectively foreground areas than local +adaptive thresholding. This algorithm was proposed in the paper +"An Approach To Licence Plate Recognition" by J.R. Parker and Pavol Federl. + +.TP +\fB-threshold=\fP\fIthreshold\fP +This sets the thresholding value for simple or local thresholding. The +value is a floating point number in the range [0, 1] directly proportional to +the Netpbm sample values, where 0 corresponds to black and 1 to the maxval of +the image. +.sp +If you don't specify this option, \fBpamthreshold\fP uses a threshold +of 0.5. +.sp +Without \fB-simple\fP, \fB-local\fP, or \fB-dual\fP, this option is +meaningless. +.sp +The meaning of the threshold depends upon the kind of thresholding +you do (as determined by other options). Roughly, pixels at least as +bright as the threshold become white in the output while others become +black. + +.TP +\fB-contrast=\fP\fIthreshold\fP +This sets the threshold to determine if a neighborhood has low contrast +or not for dual thresholding. The value is a floating point number in +the range [0, 1]. +.sp +If you don't specify this option, \fBpamthreshold\fP uses a contrast +threshold of 0.05. Without \fB-dual\fP this option is meaningless. + + + + +.UN seealso +.SH SEE ALSO +.BR "pamditherbw" (1)\c +\&, +.BR "ppmtopgm" (1)\c +\&, +.BR "pamtopnm" (1)\c +\&, +.BR "pam" (1)\c +\& + +.UN history +.SH HISTORY +.PP +\fBpamthreshold\fP was new in Netpbm 10.34 (June 2006). + +.UN author +.SH AUTHOR +.PP +\fBpamthreshold\fP is Copyright \(co 2006 by Erik Auerswald and released +under the +.BR "GPL" (1)\c +\&. +.SH DOCUMENT SOURCE +This manual page was generated by the Netpbm tool 'makeman' from HTML +source. The master documentation is at +.IP +.B http://netpbm.sourceforge.net/doc/pamthreshold.html +.PP
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