The definition of compression power is
power = uncompressed size / encoded sizeFor example, a compression power of 2 means you can pack twice as much onto your disk. Attaining a power of 4, if that were possible, would mean you could squeeze in four times as much, which is twice as good as a power of 2. Note that a compression power of 1, represented by a black bar, means no compression at all.
As these statistics show, BitJazz's PhotoJazz, with a mean compression power of 2.47, is clearly the most powerful perfect-fidelity codec available for demanding real-world RGB 8b footage. Yet BitJazz's real-time SheerVideo codec, at a mean compression power of 2.20, averages within 11% of PhotoJazz's prowess. Not bad, considering SheerVideo is around 50X faster than PhotoJazz or any other perfect-fidelity image compressor worthy of the name.
For reference, StuffIt 6, the general-purpose compression utility from Aladdin Systems, compresses the Kodak RGB images by an average of 2.09 at 0.67 MiB/s, and Aladdin's DropZip compresses them by an average of 1.62 at 0.92 MiB/s.
For uncompressed native Y'CbCr video formats, SheerVideo is even more powerful, with a mean compression power of 2.84 for Y'CbCr 8bv 4:4:4 ('v408', 'VUYA', 'r408'), 2.43 for Y'CbCr 8bv 4:2:2 ('2vuy', 'yuvs'), and 2.32 for Y'CbCr 8bw 4:2:2 ('yuv2', 'yuvu'). Moreover, among perfect-fidelity codecs, only SheerVideo supports native video formats. All other codecs degrade the image on conversion from video format to RGB during compression, and degrade it further on conversion back to video format during decompression.
The RGB 8b compression figures here are for the original Kodak images, repackaged as a QuickTime movie; For Y'CbCr 8bv 4:4:4, the RGB movie was encoded with the standard equations in Recommendation ITU-R BT.601-4 and stored in the 'v408', 'VUYA', and 'r408' pixel formats (which differ from each other only in byte order and (for 'r408') in Y' offset). For Y'CbCr 8bw 4:2:2, the RGB movie was encoded with Apple's Component Video codec, which uses the 'yuvu' ('yuv2') pixel format; For Y'CbCr 8bv 4:2:2, the Y'CbCr 8bw 4:2:2 movie was then transcoded with the standard equations in Recommendation ITU-R BT.601-4, and stored in the '2vuy' and 'yuvs' pixel formats (which differ from each other only in byte order). The Y'CbCr images were tested at this nonstandard video resolution to simplify comparison. The sizes (in bytes) are taken from the sample-size ('stsz') table in the QuickTime movie.