gpnm
This package implements an encoder and decoder for PNM image formats. It can be used with Go's image library. It covers all formats as defined by the 'P1' to 'P6' specifications.
File formats
Each format differs in what colors it is designed to represent:
- PBM is for bitmaps (black and white, no grays).
- PGM is for grayscale.
- PPM is for "pixmaps" which represent full RGB color.
Each file starts with a two-byte magic number (in ASCII) that identifies the type of file it is (PBM, PGM, and PPM) and its encoding (ASCII or binary). The magic number is a capital P followed by a single-digit number.
| Magic Number | Type | Encoding |
|---|---|---|
| P1 | bitmap | ASCII |
| P2 | graymap | ASCII |
| P3 | pixmap | ASCII |
| P4 | bitmap | Binary |
| P5 | graymap | Binary |
| P6 | pixmap | Binary |
The ASCII formats allow for human readability and easy transfer to other platforms (so long as those platforms understand ASCII), while the binary formats are more efficient both in file size and in ease of parsing, due to the absence of whitespace.
In the binary formats, PBM uses 1 bit per pixel, PGM uses 8 bits per pixel, and PPM uses 24 bits per pixel: 8 for red, 8 for green, 8 for blue.
Usage
go get github.com/hexaflex/gpnm
import "image"
import _ "github.com/hexaflex/gpnm"
...
img, format, err := image.Decode("myfile.pnm)
...
References
License
Unless otherwise stated, all of the work in this project is subject to a 3-clause BSD license. Its contents can be found in the enclosed LICENSE file.
