How to use the command `pnmdepth` (with examples)

pnmdepth is an alias command for pamdepth which is part of the netpbm package. It is used to change the depth of Netpbm images, which include PBM (Portable BitMap), PGM (Portable GrayMap), and PPM (Portable Pixmap) formats. The depth represents the number of bits used to represent each pixel in the image.

Use case 1: View documentation for the original command

Code:

tldr pamdepth

Motivation: Viewing the documentation for the original command (pamdepth) can provide a comprehensive understanding of the available options and usage examples.

Explanation:

• tldr: This command is used to display simplified and concise command-line usage examples.
• pamdepth: This is the original command, which pnmdepth is an alias of.

Example output:

pamdepth

    Change the depth of a Netpbm image.

    - Change bit depth of image to 8 bit:
      pamdepth 16 img.pgm

    - Change bit depth to 1 bit, dither image:
      pamdepth -B -1 img.ppm

    - Change bit depth of image to 16 bit (for masks):
      pamdepth 1 < mask.pbm > mask.pgm

Conclusion: By using tldr with the original command pamdepth, users can quickly access simplified documentation for the pnmdepth command, gaining insights into its usage and available options.

Use case 2: Change the depth of a PBM image to 2 bits

Code:

pnmdepth 2 input.pbm > output.pbm

Motivation: In certain scenarios, it is desirable to reduce the depth of an image to reduce the file size or limit the number of colors used. By changing the depth to 2 bits, the resulting PBM image will only have 4 possible colors (2^2), making it suitable for simple graphics or black and white images.

Explanation:

• pnmdepth: The alias command for changing the depth of a Netpbm image.
• 2: The desired number of bits per pixel.
• input.pbm: The input PBM image file.
• >: Redirects the output to a file named output.pbm.

Example output: No output will be displayed, but the new image with a depth of 2 bits will be saved in the output.pbm file.

Conclusion: By using pnmdepth to change the depth of a PBM image to 2 bits, users can limit the number of colors in the resulting image, making it more suitable for certain applications such as technical diagrams or simple logos.

Use case 3: Change the depth of a PGM image to 16 bits, preserving grayscale values

Code:

pnmdepth 16 input.pgm > output.pgm

Motivation: In some cases, it is necessary to increase the depth of a grayscale image to improve its quality or allow for more precise editing. By changing the depth to 16 bits, the resulting PGM image will have a higher range of grayscale values, providing smoother transitions between shades of gray.

Explanation:

• pnmdepth: The command for changing the depth of a Netpbm image.
• 16: The desired number of bits per pixel.
• input.pgm: The input PGM image file.
• >: Redirects the output to a file named output.pgm.

Example output: No output will be displayed, but the new image with a depth of 16 bits will be saved in the output.pgm file.

Conclusion: Using pnmdepth to change the depth of a PGM image to 16 bits enables users to work with higher-quality grayscale images, suitable for applications such as professional photography or medical imaging.

Use case 4: Change the depth of a PPM image to 4 bits, applying dithering

Code:

pnmdepth -B -4 input.ppm > output.ppm

Motivation: When reducing the depth of a color image, applying dithering can help mitigate the loss of detail and prevent banding artifacts. Dithering introduces subtle noise or patterns to simulate additional colors beyond the limited palette. By reducing the depth to 4 bits and applying dithering, the resulting PPM image will maintain a visually appealing appearance even with a limited number of colors.

Explanation:

• pnmdepth: The command for changing the depth of a Netpbm image.
• -B: Enables the use of dithering.
• -4: The desired number of bits per pixel.
• input.ppm: The input PPM image file.
• >: Redirects the output to a file named output.ppm.

Example output: No output will be displayed, but the new image with a depth of 4 bits and applied dithering will be saved in the output.ppm file.

Conclusion: By utilizing pnmdepth to change the depth of a PPM image to 4 bits and applying dithering, users can preserve visual quality and reduce the file size of color images while maintaining a visually attractive appearance.