Update cheatsheets

ppmtoxpm

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# ppmtoxpm
+
+> Convert a PPM image to an X11 version 3 pixmap.
+> More information: <https://netpbm.sourceforge.net/doc/ppmtoxpm.html>.
+
+- Convert a PPM image to a XPM image:
+
+`ppmtoxpm {{path/to/input_file.ppm}} > {{path/to/output_file.xpm}}`
+
+- Specify the prefix string in the output XPM image:
+
+`ppmtoxpm -name {{prefix_string}} {{path/to/input_file.ppm}} > {{path/to/output_file.xpm}}`
+
+- In the output XPM file, specify colors by their hexadecimal code instead of their name:
+
+`ppmtoxpm -hexonly {{path/to/input_file.ppm}} > {{path/to/output_file.xpm}}`
+
+- Use the specified PGM file as a transparency mask:
+
+`ppmtoxpm -alphamask {{path/to/alpha_file.pgm}} {{path/to/input_file.ppm}} > {{path/to/output_file.xpm}}`