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BitJazz
SheerVideo FAQ
Power: Introduction
How is compression power measured?
How powerful is SheerVideo?
 How powerful is SheerVideo?
For real-world photo-quality imagery, as measured on high-detail standard test data,
SheerVideo has an average compression power of 2.20 for RGB 8b;
2.84 for Y'CbCr 8bv 4:4:4;
2.43 for Y'CbCr 8bv 4:2:2;
and 2.32 for Y'CbCr 8bw 4:2:2.
As a non-destructive codec, SheerVideo's compression power is limited by the intrinsic information content (entropy) of the video.
For example, a blue sky will compress much better than a colorful meadow,
and pure white noise can't be compressed at all.
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How is compression power measured? The compression power, also known as the compression ratio, is defined as
compression power = uncompressed size / encoded size
Note that a compression power of 1.0 means no compression at all.
As a ratio of two sizes, compression power is a pure number, lacking any measurement unit,
so it is common to put an 'X' or a ':1' after the number, as in "2.0X" (two-times power)
or "2:1" (two-to-one power).
In video compression research, the compression power is normally measured on a set of standard reference set of real-world test data
consisting of 24 high-detail photo-quality uncompressed images,
each with a resolution of 768 x 512 RGB pixels at 8 bits per channel,
originally published in uncompressed TIFF format on Kodak PhotoCD PCD0992 (Copyright © Eastman Kodak).
Be very skeptical of any compression-power claims based on a nonstandard set of test images,
especially if the images are unavailable for third-party verification,
or if the test images are unspecified.
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