[xiph-commits] r12231 - trunk/theora/doc/spec

[tterribe at svn.xiph.org]

Author: tterribe
Date: 2006-12-21 09:14:24 -0800 (Thu, 21 Dec 2006)
New Revision: 12231

Modified:
   trunk/theora/doc/spec/spec.tex
Log:
Clarify that chroma upsampling is what any signal processing engineer would
 think it is, and nothing more.


Modified: trunk/theora/doc/spec/spec.tex
===================================================================
--- trunk/theora/doc/spec/spec.tex	2006-12-20 05:23:33 UTC (rev 12230)
+++ trunk/theora/doc/spec/spec.tex	2006-12-21 17:14:24 UTC (rev 12231)
@@ -1456,11 +1456,23 @@
 
 Theora supports several different pixel formats, each of which uses different
  subsampling for the chroma planes relative to the luma plane.
+A decoder may need to recover a full resolution chroma plane with samples
+ co-sited with the luma plane in order to convert to RGB for display or perform
+ other processing.
+Decoders can assume that the chroma signal satisfies the Nyquist-Shannon
+ sampling theorem.
+The ideal low-pass reconstruction filter this implies is not practical, but any
+ suitable approximation can be used, depending on the available computing
+ power.
+Decoders MAY simply use a box filter, assigning to each luma sample the chroma
+ sample closest to it.
+Encoders would not go wrong in assuming that this will be the most common
+ approach.
 
 \subsection{4:4:4 Subsampling}
 \label{sec:444}
 
-All three color planes are stored at full resolution - each pixel has a $Y'$,
+All three color planes are stored at full resolution---each pixel has a $Y'$,
  a $C_b$ and a $C_r$ value (see Figure~\ref{fig:pixel444}).
 The samples in the different planes are all at co-located sites.