pamrgbatopng

View documentation for the current command

$ tldr pamtopng

pamrgbatopng [options] [pam_file]
Options:
    -alpha
    -alphathresh=val
    -alphafile=file
    -interlaced
    -text="text_chunk"
    -comment="text_chunk"
    -verbose

-alpha
    Informs pamrgbatopng that the input is an RGBA PAM, and its fourth plane should be treated as the alpha channel, preserving transparency.

-alphathresh=val
    Creates an alpha channel from a non-alpha input. Pixels whose luminosity matches val (0-255) become fully transparent, suitable for color keying.

-alphafile=file
    Uses a separate PGM (Portable Graymap) or PBM (Portable Bitmap) file as the alpha channel for the output PNG. White means opaque, black means transparent.

-interlaced
    Outputs an interlaced PNG image using the Adam7 algorithm, which allows for progressive rendering in compatible viewers.

-text="text_chunk"
    Adds a textual data chunk (tEXt) to the PNG image metadata. This option can be used multiple times for different chunks, typically in 'keyword=text' format.

-comment="text_chunk"
    An alias for the -text option, also used to embed textual metadata into the PNG file.

-verbose
    Prints informative messages about the conversion process to standard error (stderr), which is useful for debugging or monitoring.

pam_file
    The path to the input PAM or PPM image file. If this argument is omitted, the command reads image data from standard input (stdin).

pamrgbatopng is a specialized command within the Netpbm image processing suite, designed for converting Portable Arbitrary Map (PAM) and Portable Pixel Map (PPM) images to the Portable Network Graphics (PNG) format. Its key strength lies in its explicit support for images with alpha channels, allowing for the precise handling of transparency. While Netpbm also provides pnmtopng(1), pamrgbatopng offers more granular control over alpha channel interpretation, especially when dealing with RGBA (Red, Green, Blue, Alpha) PAM files or when needing to add an alpha channel from a separate file or based on a color threshold.

The command reads an input PAM or PPM image, typically from standard input or a specified file, and outputs a PNG image to standard output. It's particularly useful in image processing pipelines where precise transparency management is critical, such as generating web graphics with complex alpha masks, converting legacy image data, or preparing assets for games and multimedia applications. It seamlessly integrates into shell scripts, leveraging the flexibility of the Netpbm toolkit.

This command is designed for PAM/PPM (color) inputs. While Netpbm can convert PGM (grayscale) or PBM (bitmap) to PAM, pamrgbatopng expects color data for its primary function.
It's part of the Netpbm suite; therefore, the Netpbm tools must be installed on your system.
For simple PPM to PNG conversions without specific alpha channel requirements, pnmtopng(1) might be a more direct alternative.

Although its name suggests RGB, pamrgbatopng also correctly processes RGBA PAM inputs, directly utilizing the alpha channel for transparency in the output PNG. For non-RGBA inputs, it provides options (-alphathresh, -alphafile) to generate an alpha channel during conversion.

The command strictly outputs to the PNG format. If other output formats are desired, the PNG output would typically need to be piped to another Netpbm converter (e.g., pngtopam | pamto).

The pamrgbatopng command is a component of the comprehensive Netpbm graphics library, a long-standing collection of open-source tools for manipulating image files. Netpbm itself evolved from earlier image toolsets like PBMplus, which dates back to the late 1980s. As image formats and requirements grew more complex, particularly with the rise of alpha channels for transparency, Netpbm introduced the more flexible PAM (Portable Arbitrary Map) format. pamrgbatopng was developed to specifically leverage PAM's capabilities, especially its native support for alpha channels, providing a dedicated and robust method for converting these advanced Netpbm formats into the widely used PNG standard. Its development reflects the continuous adaptation of Netpbm to modern image processing needs.

pnmtopng(1), pam(5), ppm(5), png(5), netpbm(1)