How to Use the Command 'pamcut' (with examples)

Pamcut is a command-line utility from the Netpbm suite that enables users to extract a rectangular portion from a Netpbm image. This tool is particularly useful in image processing tasks where only a specific section of an image is needed for further analysis or manipulation. By allowing precise control over the exact portion of an image to cut, pamcut aids in efficiently managing image data without unnecessary processing.

Discard the specified number of columns/rows on each side of the image

Code:

pamcut -cropleft 10 -cropright 10 -croptop 20 -cropbottom 20 path/to/image.ppm > path/to/output.ppm

Motivation:

The ability to discard a specified number of columns or rows on each side of an image proves particularly advantageous when trying to remove undesirable borders or edges that may contain noise or irrelevant content. Often, images captured through cameras or scanners may have unwanted artifacts around the edges, which can diminish the quality of analysis or presentation if not removed.

Explanation:

• -cropleft 10: This option removes 10 columns from the left side of the image, clipping away unwanted left-edge data.
• -cropright 10: Similarly, this removes 10 columns from the right side of the image, ensuring a focus purely on the central portion.
• -croptop 20: This option eliminates 20 rows from the top, which might include headers or other non-essential parts.
• -cropbottom 20: This removes 20 rows from the bottom, potentially cropping out footer information that is not of interest.
• path/to/image.ppm: The input image file in Portable Pixmap (PPM) format.
• > path/to/output.ppm: Directs the command’s output to a new image file, presenting the cropped result.

Example Output:

After executing the command, a new PPM file, ‘output.ppm’, is generated. This file contains the original image minus a 10-column border on the left and right sides and a 20-row border on the top and bottom.

Keep only the columns between the specified columns (inclusively)

Code:

pamcut -left 50 -right 150 path/to/image.ppm > path/to/output.ppm

Motivation:

This use case is ideal when a user is interested in examining or processing only a vertical slice of an image, perhaps where pertinent data resides within a specific region. For example, in a wide-angle photograph of a cityscape, you may only want to focus on one building located between column numbers 50 and 150.

Explanation:

• -left 50: This parameter sets 50 as the starting column from which the image extraction should begin.
• -right 150: This designates column 150 as the endpoint for the desired image segment.
• path/to/image.ppm: The input image from which the desired columns are to be extracted.
• > path/to/output.ppm: Saves the specified vertical segment to a new file.

Example Output:

Running this command results in ‘output.ppm’ containing only the part of the image that spans from column 50 to 150, inclusive. This creates a vertical slice of the image, with all other columns discarded.

Fill missing areas with black pixels if the specified rectangle does not entirely lie within the input image

Code:

pamcut -top 0 -bottom 300 -pad path/to/image.ppm > path/to/output.ppm

Motivation:

When the defined rectangular area extends beyond the bounds of the original image, filling the extra space with black pixels allows for maintaining a consistent output size while ensuring that any out-of-bounds regions do not disrupt the continuity of subsequent data processing or presentation. This is particularly useful when preparing a series of images for uniform display or training deep learning models where input sizes must be consistent.

Explanation:

• -top 0: Initiates the cutting from the topmost row while considering the image’s height.
• -bottom 300: Specifies the lower boundary for cropping. If the image has fewer than 300 rows, padding is needed.
• -pad: This argument indicates that any areas beyond the image’s original dimensions should be filled with black pixels.
• path/to/image.ppm: The source image file for processing.
• > path/to/output.ppm: Outputs the padded image to a new PPM file.

Example Output:

Executing this command generates ‘output.ppm’, a file that includes data from the top row to the 300th row. Any rows beyond the input image’s size are padded with black pixels, ensuring a uniform output matrix.

Conclusion:

The pamcut tool provides a robust solution for fine-tuning the spatial dimensions of an image by allowing precise control over the cropping of specific regions. Whether you seek to remove noisy edges, focus on particular vertical slices, or uniformly scale output through padding, pamcut effectively facilitates these tasks, enhancing the image processing workflow. Its versatility in handling different cropping scenarios ensures it remains a vital component of the Netpbm utility suite.