giftopnm

Convert a GIF image to a Netpbm image pixel-for-pixel

$ giftopnm [path/to/input.gif] > [path/to/output.pnm]

$ giftopnm [[-v|-version]]

giftopnm [options] [giffile]
If giffile is omitted, giftopnm reads from standard input. Output is always written to standard output.

-verbose
    Prints detailed information about the GIF file and the conversion process to standard error.

-alphaout={alpha-filename|-}
    Writes the image's alpha (transparency) channel to the specified file. Use - to send it to standard output after the PNM image.

-alphamax=maxval
    Sets the maximum pixel value for the alpha output file. Defaults to 255.

-background=color
    Specifies the color to fill transparent pixels with. Can be a color name (e.g., "red"), hexadecimal color (e.g., "#FF0000"), or "transparent" to retain transparency.

-colorfuzz=color
    Used with -transparent to make the specified color match "close" colors, allowing for slight variations.

-transparent=color
    Specifies a color to treat as transparent, overriding any transparency information embedded in the GIF file.

-gamma=gamma
    Applies gamma correction to the output image.

-interlace
    Processes the GIF as if it were interlaced, affecting the order in which scan lines are output.

-map=filename or -cmap=filename
    Specifies a colormap file (in PPM format) to which the output image's colors will be mapped.

-truecolor
    Forces the output to be a 24-bit truecolor PPM, even if the GIF could be represented by a palette.

-fixcolormaps
    Attempts to correct malformed colormaps found in some GIF files.

-comment=text
    Adds a comment string to the header of the output PNM file.

giftopnm is a fundamental utility within the Netpbm image processing suite. It serves the purpose of converting Graphics Interchange Format (GIF) image files into one of the Portable Anymap (PNM) formats: Portable Pixmap (PPM) for color images, Portable Graymap (PGM) for grayscale images, or Portable Bitmap (PBM) for monochrome images. This conversion is crucial for interoperability, allowing GIF images to be processed by other Netpbm tools or piped into other image manipulation programs that understand the PNM formats. giftopnm handles various GIF features, including interlacing and transparency, and can be used in a pipeline, reading from standard input and writing to standard output.

While giftopnm handles most standard GIF features like interlacing and transparency, it typically processes only the first frame of multi-frame (animated) GIF files. For full manipulation of animated GIFs, specialized tools like gifsicle are usually required. The quality of output for very old or malformed GIF files might vary, though the -fixcolormaps option attempts to mitigate some issues.

giftopnm excels when used as part of a larger image processing pipeline. Its ability to read from standard input and write to standard output allows it to be seamlessly chained with other Netpbm commands (e.g., giftopnm image.gif | ppmtojpeg > image.jpg) or external tools, facilitating complex image transformations without requiring temporary files.

The command provides robust options for managing GIF transparency. By default, transparent pixels are rendered black. However, users can specify a -background color to fill these areas or use -alphaout to extract the transparency information into a separate PGM file, which can then be used as a mask for further processing.

giftopnm is a component of the Netpbm package, a venerable open-source project that originated in the late 1980s as the PBMplus toolkit. PBMplus was developed by Jef Poskanzer, and the Netpbm suite, which incorporates and extends PBMplus, has been actively maintained and expanded by various contributors over decades. The command's longevity is a testament to the enduring utility of simple, robust image conversion tools in the Unix philosophy of chaining small tools together. Its design reflects the Netpbm philosophy of handling "portable anymap" formats as an intermediate step for diverse image manipulations.

pnmtoppm(1), ppmtopgm(1), pbm(5), pgm(5), ppm(5), pam(1), gifsicle(1), gifview(1)