[xiph-cvs] r6724 - trunk/theora/doc/spec
giles at xiph.org
giles at xiph.org
Tue May 18 21:48:58 PDT 2004
Author: giles
Date: 2004-05-19 00:48:57 -0400 (Wed, 19 May 2004)
New Revision: 6724
Modified:
trunk/theora/doc/spec/spec.tex
Log:
Minor wording improvements and a few editorial comments.
<p>Modified: trunk/theora/doc/spec/spec.tex
===================================================================
--- trunk/theora/doc/spec/spec.tex 2004-05-18 22:32:26 UTC (rev 6723)
+++ trunk/theora/doc/spec/spec.tex 2004-05-19 04:48:57 UTC (rev 6724)
@@ -221,6 +221,7 @@
refuse to decode the stream if they are not.
These are used as place holders for future bitstream features with which the
current bitstream is forward-compatible.
+%RG: shouldn't this be 'MAY not increment...the version number'?
Such features will not increment the bitstream version number, and can only be
recognized by checking the value of these reserved bits.
@@ -273,7 +274,7 @@
Theora I currently supports progressive video data of arbitrary dimensions at a
constant frame rate in one of several $Y'C_bC_r$ color spaces.
-The precise definition the color spaces supported appears in
+The precise definition the supported color spaces appears in
Section~\ref{sec:colorspaces}.
Three different chroma subsampling formats are supported: 4:2:0, 4:2:2,
and 4:4:4.
@@ -313,7 +314,8 @@
%TODO: Talk more about implementation complexity.
Theora provides none of its own framing, synchronization, or protection against
- transmission errors; it is solely a method of accepting input video frames and
+ transmission errors.
+An encoder is solely a method of accepting input video frames and
compressing these frames into raw, unformatted `packets'.
The decoder then accepts these raw packets in sequence, decodes them, and
synthesizes a fascimile of the original video frames.
@@ -489,8 +491,8 @@
left, etc.
The second is \term{coded order}.
In coded order, blocks are accessed by super block.
-Each super block is traversed in raster order, similar to raster order for
- blocks.
+Within each frame, super blocks are traversed in raster order,
+ similar to raster order for blocks.
Within each super block, however, blocks are accessed in a Hilbert curve
pattern, illustrated in Figure~\ref{fig:hilbert-block}.
If a color plane does not contain a complete super block on the top or right
@@ -683,7 +685,7 @@
the pixels.
They have been written from top to bottom here to follow conventional notation,
despite the right-handed coordinate system Theora uses for pixel locations.
-
+%RG: I'd rather we were internally consistent and put dc at the lower left.
Many implementations of the DCT operate `in-place'.
That is, they return DCT coefficients in the same memory buffer that the
initial pixel values were stored in.
@@ -976,7 +978,7 @@
Unlike JPEG and MPEG, there is no requirement for each block to end with
a special marker.
If non-EOB tokens yield values for all 64 of the coefficients in a block, then
- no EOB marker is needed.
+ no EOB marker occurs.
Each token is associated with a specific \term{token index} in a block.
For single-coefficient tokens, this index is the zig-zag index of the token in
@@ -1407,7 +1409,7 @@
plane.
Similarly, they have half the number of horizontal super blocks, rounded up.
Macro blocks are defined across color planes, and so their number does not
- change, but each macro block has half as many chroma blocks contained in it.
+ change, but each macro block contains half as many chroma blocks.
The chroma samples are vertically aligned with the luma samples, but
horizontally centered between two luma samples.
@@ -1436,8 +1438,8 @@
Similarly, they have half the number of horizontal super blocks and half the
number of vertical super blocks, rounded up.
Macro blocks are defined across color planes, and so their number does not
- change, but each macro block has one quarter as many chroma blocks contained
- in it.
+ change, but each macro block contains within it one quarter as many
+ chroma blocks.
The chroma samples are vertically and horizontally centered between four luma
samples.
@@ -1502,6 +1504,11 @@
%TODO: Figures!
+%TODO: informational section for encoders:
+% When the chroma planes are subsampled, encoders SHOULD chose picture
+% offsets and dimensions that are even so that the subsampling
+% positions are reproduced cleanly.
+
\chapter{Bitpacking Convention}
\label{sec:bitpacking}
@@ -1815,7 +1822,7 @@
\item
Read 6 8-bit unsigned integers.
If these do not have the values \hex{74}, \hex{68}, \hex{65}, \hex{6F},
- \hex{72}, and \hex{61}, respectively then stop.
+ \hex{72}, and \hex{61}, respectively, then stop.
This stream is not decodable by this specification.
These values correspond to the ASCII values of the characters `t', `h', `e',
`o', `r', and `a'.
@@ -1955,7 +1962,7 @@
Frames are sampled at the constant rate of $\frac{\bitvar{FRN}}{\bitvar{FRD}}$
frames per second.
The presentation time of the first frame is at zero seconds.
-There is no mechanism provided to specify a non-zero offset for the initial
+No mechanism is provided to specify a non-zero offset for the initial
frame.
\item
Read a 24-bit unsigned integer as \bitvar{PARN}.
@@ -2439,15 +2446,16 @@
which \qi\ values.
A set of quant ranges is defined for each quantization type and color plane.
-To save space in the header, bit flags allow a set of quant range to be copied
+To save space in the header, bit flags allow a set of quant ranges to be copied
from a previously defined set instead of being specified explicitly.
Every set except the first one can be copied from the immediately preceding
set.
Similarly, if the quantization type is not $0$, the set can be copied from the
set defined for the same color plane for the preceding quantization type.
-This formulation allows, for example, the same set of quant ranges to be used
- for both chroma channels, as was done in the original VP3, or the same set of
- quant ranges to be used for INTRA and INTER modes.
+This formulation allows compact representation of, for example, the same
+ set of quant ranges to be used for both chroma channels, as was done in
+ the original VP3, or the same set of quant ranges to be used for INTRA
+ and INTER modes.
Each quant range is defined by a size and two base matrix indices, one for each
end of the range.
@@ -2456,6 +2464,8 @@
The base matrices for the \qi\ values between the two endpoints of the range
are generated by linear interpolation.
+%TODO: figure
+
The location of the endpoints of each range is encoded by their size.
The \qi\ value for the left end-point is the sum of the sizes of all preceding
ranges, and the \qi\ value for the right end-point adds the size of the
--- >8 ----
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