pbmnoise, pgmhist, pgmkernel, pgmnoise, pgmramp, pgmtexture: add pages; ppmhist: modify page (#12202)

pages/common/ppmhist.md

@@ -1,15 +1,16 @@
 # ppmhist
 
 > Print a histogram of the colors present in a PPM image.
+> See also: `pgmhist`.
 > More information: <https://netpbm.sourceforge.net/doc/ppmhist.html>.
 
 - Generate the histogram for human reading:
 
-`ppmhist -nomap {{path/to/image_file.ppm}}`
+`ppmhist -nomap {{path/to/image.ppm}}`
 
 - Generate a PPM file of the colormap for the image, with the color histogram as comments:
 
-`ppmhist -map {{path/to/image_file.ppm}}`
+`ppmhist -map {{path/to/image.ppm}}`
 
 - Display version: