#41 Encoding all white frames broken

open
nobody
5
2006-08-08
2006-08-08
No

Encoding completely white frames produces completely
green output. Thomas is aware of this but asked for it
to be posted anyway for tracking purposes. To quote him:

The issue is that the wavelet transform produces zeroes
everywhere except the DC band, which encodes the level.
The DC band is coded predictively, with zero as the
prediction for the top-left coefficient. So after
prediction the top-left coefficient is the only
non-zero coefficient, but its contribution, when
calculating the quantiser to use, is diluted by all the
zeroes. So a quantiser is chosen which kills all the
data. Hence all
zero from the wavelet transform, which (on I frames)
gives "digital green" as output.

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No, thanks