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 JXL format. This tool works for both professionals and casual users. Convert your images to JXL 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.
JPEG XL
The true next-generation successor designed to replace JPEG, PNG, and GIF entirely.
JPEG XL (JXL) is the most advanced image format currently in existence. Unlike WebP and AVIF, which are derived from video codecs, JPEG XL was designed from the ground up specifically for still images. This gives it unique superpowers, such as the ability to losslessly re-compress existing JPEG files to be 20% smaller without losing a single bit of data. It offers best-in-class lossless compression (beating PNG), best-in-class lossy compression (beating JPEG), and supports features needed for professional workflows like CMYK, layers, and ultra-high resolutions. However, its adoption has been slowed by political battles, most notably Google Chrome's decision to remove support in 2022, though Apple has since added full support in Safari 17.
JPEG XL uses a combination of two coding modes: VarDCT (Variable Block-size DCT) for lossy images and Modular Mode for lossless/artistic images. Its 'killer feature' is legacy JPEG transcoding: it can take the DCT coefficients from an old JPEG file and repackage them into the more efficient JXL container. This process is reversible, meaning you can convert your entire JPEG library to JXL to save 20% space, and convert them back to the exact original byte-for-byte JPEGs later if needed. It also supports 'progressive decoding' far better than any other format, allowing a high-quality preview to appear almost instantly.
The JPEG committee began the call for proposals for a next-gen standard in 2017. The final standard (ISO/IEC 18181) was published in 2021/2022, combining the best parts of Google's PIK and Cloudinary's FUIF proposals. Despite being technically superior, its rollout hit a wall when the Chrome team removed the experimental flag in late 2022, citing lack of ecosystem interest. However, Apple's adoption in 2023 (iOS 17/macOS 14) has breathed new life into the format.
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