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mkbitmap(1) General Commands Manual mkbitmap(1) NAME mkbitmap - transform images into bitmaps with scaling and filtering SYNOPSIS mkbitmap [options] [filename...] DESCRIPTION mkbitmap reads an image, and applies one or more of the following opera- tions to it, in this order: inversion, highpass filtering, scaling, and thresholding. Each operation can be individually controlled and turned on or off. The principal use of mkbitmap is to convert color or greyscale images into a format suitable as input for other programs, particularly the tracing program potrace(1). It is particularly useful for converting scanned line art, such as cartoons, handwritten text, etc., to high-resolution bilevel images. Highpass filtering can be used to ensure that foreground features such as lines and text are preserved, while at the same time compensating for un- even background. Optional blurring can be applied to smooth out the image and remove visual noise. Scaling is important because a scanned greyscale image contains more visual detail than a bilevel image at the same resolu- tion. By scaling the image to a higher resolution (using interpolation) be- fore thresholding it, some of this detail is preserved. Thresholding means converting a greyscale image to a bilevel image using only black and white pixels. Pixels that are darker than a certain threshold value are converted to black. Optional inversion is useful if the input image shows bright features on dark background, such as a picture of chalk drawings on a blackboard. Supported input formats are PNM (PBM, PGM, PPM) and BMP. The output formats are PBM for bitmaps, and PGM for greymaps. OPTIONS General options: -h, --help print help message and exit. -v, --version print version info and exit. -l, --license print license info and exit. Input/output options: filename If filename arguments are given, then mkbitmap will by de- fault create one output file for each input filename given. The name of the output file is obtained from the input file- name by changing its suffix to ".pbm" or ".pgm". If the name of the input file and output file would be identical, then an additional suffix "-out" is appended to the output file- name. If no filename arguments are given, then mkbitmap acts as a filter, reading from standard input and writing to standard output. A filename of "-" may be given to specify reading from standard input; the output for this argument will then be written to standard output. Each input file may contain one or more images. -o filename, --output filename write output to this file. All output is concatenated and directed to the specified file. This overrides the default behavior of creating one output file for each input file. A filename of "-" may be given to specify writing to standard output. Image processing options: -x, --nodefaults Turn off default options. Normally, the following options are preselected by default: -f 4 -s 2 -3 -t 0.45. The -x op- tion disables these defaults; thus, mkbitmap -x does nothing but copy a greyscale image from the input to the output. Other processing options can then be added one by one; e.g., mkbitmap -xf10 does only highpass filtering, mkbitmap -xt0.5 does only thresholding, etc. -i, --invert Invert the input image. If this option is chosen, it is ap- plied to the image before any other operation. It is used to deal with white-on-black images, such as photographs of chalk drawings on a blackboard. Note that the behavior of this option is not in general the same as inverting the out- put bitmap, unless the thresholding value is also inverted. -f n, --filter n Apply a highpass filter to the image. This filter is approx- imately Gaussian and non-directional. The effect is to pre- serve small detail while compensating for background gradi- ents. The parameter n is a radius (in pixels) which corre- sponds approximately to the size of details which should be preserved. More precisely, the filter is implemented by sub- tracting a blurred version of the image from the original image. The parameter n is equal to the standard deviation of the blur. The output of the filtering step is a normalized image whose average brightness is exactly 0.5. The default filter radius is 4. -n, --nofilter Turn off highpass filtering. -b n, --blur n Blur the image. The effect is to smooth out fine details and to reduce visual noise in the image. The parameter n is the blurring radius, and should be chosen small (1 is a good value to start with). This is implemented as an approxi- mately Gaussian, non-directional blur with standard devia- tion proportional to n. Blurring is applied after the high- pass filter, but before scaling and thresholding. If this option is not given, the default is not to apply any blur- ring. -s n, --scale n Scale the image by an integer factor n>0. Scaling is done after highpass filtering, but before the thresholding step. A scaling factor of 1 indicates that no scaling is to be done. Otherwise, interpolation is used to fill in the in-be- tween pixels. If the output of mkbitmap is to be used as in- put to a tracing program such as potrace, a scaling factor of 2 is recommended. This preserved the right amount of de- tail for the tracing algorithm to work well. If a scaling factor of 1 is used, too much detail is lost. If a scaling factor of 3 or higher is used, the interpolation tends to "invent" detail which was not present in the original image, thus preventing potrace from doing a good job. -1, --linear Use linear interpolation when scaling to a higher resolu- tion. This is slightly faster, but less nice, than the de- fault cubic interpolation. -3, --cubic Use cubic interpolation when scaling to a higher resolution. This is the default. It is slower than linear interpolation, but leads to better results. -t n, --threshold n Set the threshold grey value for bilevel conversion. The pa- rameter n is a brightness value between 0 for black and 1 for white. Any pixels below this brightness will be con- verted to black (thus, smaller values of n will lead to whiter output). -g, --grey Disable bilevel conversion. If this option is given, pro- cessing stops after the scaling step and a greymap is out- put. EXIT STATUS The exit status is 0 on successful completion, 1 if the command line was invalid, and 2 on any other error. VERSION 1.16 AUTHOR Peter Selinger <selinger at users.sourceforge.net> WEB SITE AND SUPPORT mkbitmap is distributed as part of the potrace package, and the latest ver- sion is available from http://potrace.sourceforge.net/. This site also contains documentation and information on how to obtain support. SEE ALSO potrace(1) COPYRIGHT Copyright (C) 2001-2019 Peter Selinger This program is free software; you can redistribute it and/or modify it un- der the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version. This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FIT- NESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. See also http://www.gnu.org/. Version 1.16 September 2019 mkbitmap(1)
NAME | SYNOPSIS | DESCRIPTION | OPTIONS | EXIT STATUS | VERSION | AUTHOR | WEB SITE AND SUPPORT | SEE ALSO | COPYRIGHT
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