Dynapik offers a free online tool to change image types - no need to download anything. It's quick and easy to use. You can change your PGM images to GIF87 format. This tool works for both professionals and casual users. Convert your images to GIF87 in seconds.
Portable Gray Map
The standard uncompressed grayscale format.
PGM (Portable Gray Map) is the grayscale member of the Netpbm format family. It sits between PBM (1-bit black and white) and PPM (full color). It is designed to store grayscale images where each pixel has a value ranging from black to white, with typical depths of 8-bit (0-255) or 16-bit (0-65535).
Like other Netpbm formats, PGM has two sub-formats: P2 (ASCII) and P5 (Binary). The header defines the dimensions and the maximum gray value (Maxval). In P2, pixel values are written as plain text numbers separated by spaces. In P5, they are raw bytes. It is strictly a single-channel format.
Created by Jef Poskanzer in the late 80s to handle scanned photos that were better than 1-bit bitmaps but didn't need full color. It became a staple in computer vision research and Unix tools.
GIF 87a
The original 1987 specification of the Graphics Interchange Format.
GIF 87a is the original version of the GIF format, published by CompuServe in 1987. It introduced the core features that made GIF famous: LZW compression for small file sizes and support for 256 indexed colors. However, unlike the ubiquitous GIF 89a, this original version lacks support for transparency, animation delays, and metadata comments.
A GIF 87a file starts with the header signature `GIF87a`. It defines the Logical Screen Descriptor and the Global Color Table. While it supports multiple image blocks within a single file (which could conceptually form an animation), it lacks the 'Graphic Control Extension' block introduced in 89a. This means there is no standard way to define frame delays, disposal methods, or transparent indices.
Developed by CompuServe in 1987 to provide a hardware-independent, compressed color image format for their online service. It replaced the earlier RLE-based formats and was designed to be efficient over slow modems.
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