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 HDR format. This tool works for both professionals and casual users. Convert your images to HDR 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.
Radiance HDR
The pioneering high dynamic range format for lighting simulation.
The Radiance HDR format (often called RGBE) is a raster image format designed for storing high dynamic range (HDR) data. Rather than standard 8-bit integers, it uses a specialized encoding where pixel colors are stored as Red, Green, and Blue mantissas sharing a single common Exponent (RGBE). This allows it to represent a vast range of luminance values, from direct sunlight to deep shadows, in a relatively compact 32-bit-per-pixel format.
The .hdr format consists of a human-readable header containing variables like exposure and gamma, followed by binary pixel data. The pixel data typically uses the 'Radiance RGBE' encoding. Each pixel is 4 bytes: one byte each for Red, Green, and Blue, and one shared Exponent byte. This 'shared exponent' scheme is efficient but introduces some limitations—if one channel is very bright and another is very dark in the same pixel, color precision can be lost (color banding).
Developed by Greg Ward in the late 1980s for the Radiance lighting simulation system. It was one of the first formats to enable practical HDR storage and became a de facto standard in the CGI industry for Image-Based Lighting (IBL).
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