pbmmake, pgmmake, ppmlabel, ppmmake, ppmmix, ppmntsc, ppmpat: add pages (#11435)

Co-authored-by: Sebastiaan Speck <12570668+sebastiaanspeck@users.noreply.github.com>

pages/common/ppmntsc.md

@@ -0,0 +1,20 @@
+# ppmntsc
+
+> Make the RGB colors in a PPM image compatible with NTSC or PAL color systems.
+> More information: <https://netpbm.sourceforge.net/doc/ppmntsc.html>.
+
+- Make the RGB colors in a PPM image compatible with NTSC color systems:
+
+`ppmntsc {{path/to/input_file.ppm}} > {{path/to/output_file.ppm}}`
+
+- Make the RGB colors in a PPM image compatible with PAL color systems:
+
+`ppmntsc --pal {{path/to/input_file.ppm}} > {{path/to/output_file.ppm}}`
+
+- Print the number of illegal pixels in the input image to `stderr`:
+
+`ppmntsc --verbose {{path/to/input_file.ppm}} > {{path/to/output_file.ppm}}`
+
+- Output only legal/illegal/corrected pixels, set other pixels to black:
+
+`ppmntsc --{{legalonly|illegalonly|correctedonly}} {{path/to/input_file.ppm}} > {{path/to/output_file.ppm}}`