pamenlarge

Enlarge the specified image by the specified factor

$ pamenlarge [[-s|-scale]] [n] [path/to/image.pam] > [path/to/output.pam]

$ pamenlarge [[-x|-xscale]] [xn] [[-y|-yscale]] [yn] [path/to/image.pam] > [path/to/output.pam]

pamenlarge factor [pnmfile]

factor
    An integer representing the enlargement multiplier. Each pixel in the input image will be replicated into a block of factor x factor identical pixels in the output. Must be a positive integer.

pnmfile
    The path to the input Netpbm image file. If omitted, pamenlarge reads image data from standard input.

pamenlarge is a specialized command-line utility from the Netpbm image processing toolkit. Its primary function is to enlarge a Netpbm image (any format: PBM, PGM, PPM, or PAM) by a specified integer factor. The enlargement is performed using a simple pixel replication method: each pixel in the original image is replaced by a block of factor x factor identical pixels in the output image. For instance, if you enlarge an image by a factor of 3, every single pixel becomes a 3x3 block of that same pixel's color.

This method is very fast and computationally inexpensive, making it suitable for quick previews or for cases where the blocky appearance is acceptable or even desired (e.g., pixel art). The command reads the input image from a file specified as an argument, or from standard input if no file is given. The resulting enlarged image is written to standard output. While effective for integer scaling, users should be aware that this technique does not interpolate pixels, leading to a "pixelated" or "blocky" appearance rather than a smooth, interpolated enlargement. For smoother scaling or non-integer factors, other Netpbm tools like pamscale are more appropriate.

pamenlarge uses a basic pixel replication algorithm for enlargement. This means that each pixel in the original image is simply duplicated to create a larger block of the same color. Consequently, the output image will appear "blocky" or "pixelated," especially when enlarged by a significant factor, as no interpolation or smoothing is performed. This method is not suitable for achieving smooth, high-quality enlargements typically expected for photographs or intricate graphics. For such purposes, a more sophisticated scaling algorithm like those provided by pamscale (which can perform interpolation) or other image manipulation tools (e.g., ImageMagick) should be used.

pamenlarge embodies the Netpbm philosophy of providing simple, fast tools for fundamental image manipulations. Its pixel replication method is computationally very inexpensive, making it extremely fast even on large images or older hardware. This simplicity also means it has very few options, making it easy to learn and integrate into shell scripts and pipelines, often chaining it with other Netpbm utilities like pnmtojpeg or pamtopng for format conversion after enlargement.

pamenlarge is a core utility within the Netpbm image processing package. Netpbm itself originated from the pbmplus package, which was developed in the late 1980s and early 1990s. The design philosophy of Netpbm tools, including pamenlarge, emphasizes simplicity, efficiency, and adherence to the Unix philosophy of doing "one thing well." pamenlarge was designed as a straightforward tool for integer-factor image enlargement, providing a basic but fast method suitable for its specific niche, particularly for pixel art or scenarios where a "blocky" aesthetic is acceptable. Its continued presence highlights the enduring utility of simple, robust command-line tools for image manipulation.

pamscale(1), pnm(5), netpbm(1)