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Originally committed as revision 15327 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Ramiro Polla
2008-09-14 22:15:11 +00:00
parent a9f8587e15
commit 4a0266a0ec
1 changed files with 12 additions and 12 deletions
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doc/swscale.txt
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@@ -24,18 +24,18 @@ Current (simplified) Architecture:
output output
Swscale has 2 scaler paths, each side must be capable to handle Swscale has 2 scaler paths. Each side must be capable of handling
slices, that is consecutive non overlapping rectangles of dimension slices, that is, consecutive non-overlapping rectangles of dimension
(0,slice_top) - (picture_width, slice_bottom) (0,slice_top) - (picture_width, slice_bottom)
special converter special converter
This generally are unscaled converters of common These generally are unscaled converters of common
formats, like YUV 4:2:0/4:2:2 -> RGB15/16/24/32. Though it could also formats, like YUV 4:2:0/4:2:2 -> RGB15/16/24/32. Though it could also
in principle contain scalers optimized for specific common cases. in principle contain scalers optimized for specific common cases.
Main path Main path
The main path is used when no special converter can be used, the code The main path is used when no special converter can be used. The code
is designed as a destination line pull architecture. That is for each is designed as a destination line pull architecture. That is, for each
output line the vertical scaler pulls lines from a ring buffer. When output line the vertical scaler pulls lines from a ring buffer. When
the ring buffer does not contain the wanted line then it is pulled from the ring buffer does not contain the wanted line then it is pulled from
the input slice through the input converter and horizontal scaler, and the input slice through the input converter and horizontal scaler, and
@@ -49,20 +49,20 @@ Main path
Input to YUV Converter Input to YUV Converter
When the input to the main path is not planar 8bit per component yuv or When the input to the main path is not planar 8bit per component yuv or
8bit gray then it is converted to planar 8bit YUV, 2 sets of converters 8bit gray then it is converted to planar 8bit YUV. 2 sets of converters
exist for this currently one performing horizontal downscaling by 2 exist for this currently, one performing horizontal downscaling by 2
before the conversion and the other leaving the full chroma resolution before the conversion and the other leaving the full chroma resolution
but being slightly slower. The scaler will try to preserve full chroma but being slightly slower. The scaler will try to preserve full chroma
here when the output uses it, its possible to force full chroma with here when the output uses it. It is possible to force full chroma with
SWS_FULL_CHR_H_INP though even for cases where the scaler thinks its SWS_FULL_CHR_H_INP though even for cases where the scaler thinks it is
useless. useless.
Horizontal scaler Horizontal scaler
There are several horizontal scalers, a special case worth mentioning is There are several horizontal scalers. A special case worth mentioning is
the fast bilinear scaler that is made of runtime generated MMX2 code the fast bilinear scaler that is made of runtime generated MMX2 code
using specially tuned pshufw instructions. using specially tuned pshufw instructions.
The remaining scalers are specially tuned for various filter lengths The remaining scalers are specially tuned for various filter lengths.
they scale 8bit unsigned planar data to 16bit signed planar data. They scale 8bit unsigned planar data to 16bit signed planar data.
Future >8bit per component inputs will need to add a new scaler here Future >8bit per component inputs will need to add a new scaler here
that preserves the input precision. that preserves the input precision.