the open source implementation of
PGF is an image file format for natural images, which offers both lossless and lossy compression. Because of its progressive resolution/quality enhancement, it is best suited for quick previews of large images. Just after a few percent of decoding a thumbnail image is available. Then the resolution/quality improves stepwisely up to the maximum. PGF convinces by its compression and decompression speed. The image quality remains very good thereby and is usually better than with JPEG. The lossless compression of PGF results in shorter time in smaller file sizes compared with PNG and lossless JPEG.