How to use the command ppmchange (with examples)

PPMChange is a command that is used to modify PPM images by changing one color to another color. It offers various options to customize the color replacement process.

Use case 1: Exchange colors in an image

Code:

ppmchange oldcolor1 newcolor1 oldcolor2 newcolor2 ... path/to/input.ppm > path/to/output.ppm

Motivation: This use case is useful when you want to replace specific colors in an image with different colors. It allows you to perform multiple color replacements in a single command.

Explanation:

• oldcolor1: The color you want to replace in the PPM image.
• newcolor1: The color you want to replace oldcolor1 with.
• oldcolor2: Another color you want to replace in the PPM image.
• newcolor2: The color you want to replace oldcolor2 with.
• path/to/input.ppm: The path to the input PPM image file.
• path/to/output.ppm: The path to the output PPM image file where the modified image will be saved.

Example output: If we execute the following command: ppmchange #FF0000 #00FF00 #0000FF #000000 input.ppm > output.ppm, it will replace all pixels with the color #FF0000 to #00FF00 and all pixels with the color #0000FF to #000000 in the input.ppm image. The modified image will be saved as output.ppm.

Use case 2: Specify color similarity threshold

Code:

ppmchange -closeness percentage oldcolor1 newcolor1 oldcolor2 newcolor2 ... path/to/input.ppm > path/to/output.ppm

Motivation: In some cases, colors that seem different to us might be perceived as similar by the computer due to slight differences in RGB values. This use case allows you to specify a closeness threshold, ensuring that only colors within a certain range are considered for replacement.

Explanation:

• -closeness percentage: The percentage difference in RGB values that two colors can have to be considered similar. For example, if you set a closeness of 10%, two colors with a difference in their RGB values of less than 10% will be considered similar.
• oldcolor1: The color you want to replace in the PPM image.
• newcolor1: The color you want to replace oldcolor1 with.
• oldcolor2: Another color you want to replace in the PPM image.
• newcolor2: The color you want to replace oldcolor2 with.
• path/to/input.ppm: The path to the input PPM image file.
• path/to/output.ppm: The path to the output PPM image file where the modified image will be saved.

Example output: If we execute the following command: ppmchange -closeness 20% #FF0000 #00FF00 #0000FF #000000 input.ppm > output.ppm, it will replace all pixels within a 20% RGB value difference with the color #FF0000 to #00FF00 and all pixels with the color #0000FF to #000000 in the input.ppm image. The modified image will be saved as output.ppm.

Use case 3: Replace unspecified pixels with a color

Code:

ppmchange -remainder color oldcolor1 newcolor1 oldcolor2 newcolor2 ... path/to/input.ppm > path/to/output.ppm

Motivation: In some cases, you may want to replace only specific colors and leave the rest of the image unchanged. This use case allows you to specify a color that will replace all pixels in the image that are not specified in the other arguments.

Explanation:

• -remainder color: The color that will replace all pixels in the image that are not specified in the other arguments.
• oldcolor1: The color you want to replace in the PPM image.
• newcolor1: The color you want to replace oldcolor1 with.
• oldcolor2: Another color you want to replace in the PPM image.
• newcolor2: The color you want to replace oldcolor2 with.
• path/to/input.ppm: The path to the input PPM image file.
• path/to/output.ppm: The path to the output PPM image file where the modified image will be saved.

Example output: If we execute the following command: ppmchange -remainder #FFFFFF #FF0000 #00FF00 input.ppm > output.ppm, it will replace all pixels with the color #FF0000 to #00FF00 and leave all other pixels in the image unchanged. Any pixel colors not specified in the command arguments will be replaced with #FFFFFF. The modified image will be saved as output.ppm.

Conclusion:

The ppmchange command is a powerful tool for color replacement in PPM images. With its various options, it allows you to customize the color replacement process according to your specific needs. Whether you want to exchange colors, specify a color closeness threshold, or replace unspecified pixels, ppmchange provides the necessary functionality.