Netpbm Format is a collection of graphic formats designed to be easily read an understood by any platform and even by humans. To accomplish this, the formats store their graphic data in plain text format and do not use compression. Naturally, these graphics are much larger in size than their machine-optimized counterparts like JPEG and PNG.
Netpbm supports three main image types, portable pixmap format (PPM) for color graphics, portable graymap format (PGM), for gray scale, and portable bitmap format (PBM) for black and white. Each is essentially the same format, just with a different header. PPM has multiple variations to support more than 8-bit color depth and alternate channels.
I was surprised to discover this graphic format so late in life, especially since it has been around since the 1980s, because I've spent a lot of time playing around with various graphic formats and thought I was familiar with most of them. It wasn't until around 2010 that I heard of this format after using the export features of XPDF, but when I read about the format, I realized why it was so obscure. It is, for the most part, a terrible way to house graphic data.
- By storing data in a text file, rather than a binary file, the format is not just operating system independent, it's CPU independent.
- A human can easily "draw" a bitmap by entering numbers and spaces.
- The file size is massively larger compared to optimized graphic formats like PNG and even far larger than uncompressed formats like BMP.
- en.wikipedia.org/wiki/Netpbm_format - Wikipedia.