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How can I convert a JPEG photo to black and white (not grayscale) image like output of a FAX scanner, by ImageMagick?
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How can I convert a JPEG photo to black and white (not grayscale) image like output of a FAX scanner, by ImageMagick?
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According to this forum post:
However, if you want two colors only (black and white), then you need to threshold. For example, to select the color where above will be white and below will be black.
convert <input> -threshold xx% <output>
where xx is in range 0-100 (for percent).
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Dithering is clearer and more fax-like than a threshold cutoff:
convert <input> -monochrome <output>
For a less contrasty but more information-preserving kind of dithering, use:
convert <input> -remap pattern:gray50 <output>
1Note that if the output looks low-quality, you may need to set the density higher using the flag -density 150
(the 150 is a dpi value) – David Fraser – 2015-12-22T15:22:31.473
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According to this answer here:
If you have imagemagick installed:
true grayscale only:
convert source.jpg -colorspace Gray destination.jpg
true black and white:
convert source.jpg -monochrome destination.jpg
separate into gray channels:
convert source.jpg -separate destination.jpg
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I believe that Netpbm's pamthreshold is a much faster and more flexible solution.
For TIFF files, I do
$ tifftopnm test.tiff | pamthreshold | pamtotiff > bitonal.tiff
For Jpeg files you can do
$ jpegtopnm test.jpeg | pamthreshold | pamtotiff > bitonal.tiff
Pamthreshold is rather powerful (take a look at its man page).
http://unix.stackexchange.com/questions/108613/how-do-you-binarize-a-colored-image – Ciro Santilli 新疆改造中心法轮功六四事件 – 2015-09-25T19:35:15.823
No ImageMagick requirement: http://superuser.com/questions/75373/convert-color-photos-of-documents-to-good-black-and-white-bitonal-images
– Ciro Santilli 新疆改造中心法轮功六四事件 – 2015-09-26T08:21:16.357