pnmtopng

Convert PNM to PNG

$ pnmtopng [input.pnm] > [output.png]

$ pnmtopng -compression [9] [input.pnm] > [output.png]

$ pnmtopng -alpha [alpha.pgm] [input.ppm] > [output.png]

$ pnmtopng -interlace [input.pnm] > [output.png]

pnmtopng [options] [file]

pnmtopng converts PNM (PBM, PGM, PPM) images to PNG format with lossless compression. It automatically selects the optimal PNG color type based on the input image.
The -alpha option attaches a separate PGM file as an alpha transparency channel. The -compression level (0-9) controls the deflate compression effort, and -interlace creates Adam7 interlaced PNGs for progressive display. The -transparent option designates a specific color as fully transparent. Part of the Netpbm toolkit; superseded by pamtopng.

-alpha file

Alpha channel file.

Compression level (0-9).

Create interlaced PNG.

Transparent color.

Gamma value.

pngtopnm(1), pamtopng(1)