Using ppmhist (with examples)

ppmhist is a command-line tool that allows you to generate a histogram of the colors present in a PPM image. It can be useful for analyzing the color distribution in an image and extracting color information.

Generating a histogram for human reading

To generate a histogram that can be easily read by humans, you can use the -nomap option followed by the path to the PPM image file. This will print the histogram in a format that is more suitable for manual inspection.

ppmhist -nomap path/to/image_file.ppm

Motivation: When you need to quickly analyze the color distribution in an image and visually inspect the histogram, this option provides a concise and readable output.

Explanation:

• -nomap: This option tells ppmhist not to generate a colormap that maps colors to ASCII characters. It produces a histogram that simply lists the number of occurrences for each color in the image.
• path/to/image_file.ppm: This is the path to the PPM image file for which you want to generate the histogram.

Example Output:

  77: #FF0000  R:255 G:0   B:0    
  13: #00FF00  R:0   G:255 B:0    
  32: #0000FF  R:0   G:0   B:255  
   9: #FFFF00  R:255 G:255 B:0    
   2: #FFFFFF  R:255 G:255 B:255  

Generating a colormap with color histogram as comments

If you want to generate a PPM file that includes the colormap for the image and adds comments with the color histogram, you can use the -map option followed by the path to the PPM image file.

ppmhist -map path/to/image_file.ppm

Motivation: Generating a colormap with the color histogram as comments can be useful when you want to preserve the color information of an image while also providing a visual representation of the color distribution.

Explanation:

• -map: This option tells ppmhist to generate a colormap that maps colors to ASCII characters. It produces a PPM file where each color from the image is assigned a unique ASCII character.
• path/to/image_file.ppm: This is the path to the PPM image file for which you want to generate the colormap.

Example Output:

P6
# Generated by ppmhist
# Color histogram: 
#  77: #FF0000  R:255 G:0   B:0    
#  13: #00FF00  R:0   G:255 B:0    
#  32: #0000FF  R:0   G:0   B:255  
#   9: #FFFF00  R:255 G:255 B:0    
#   2: #FFFFFF  R:255 G:255 B:255  

Displaying the version

To display the version of the ppmhist command, you can use the -version option.

ppmhist -version

Motivation: Checking the version of ppmhist can be useful when troubleshooting issues or ensuring that you have the latest version installed.

Explanation:

• -version: This option tells ppmhist to display the version information.

Example Output:

ppmhist version 1.0.0