Swscale has 2 scaler paths. Each side must be capable of handling
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
These generally are unscaled converters of common
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
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 input slice through the input converter and horizontal scaler, and
- the result is also stored in the ring buffer to serve future vertical
+ the ring buffer does not contain the wanted line, then it is pulled from
+ the input slice through the input converter and horizontal scaler.
+ The result is also stored in the ring buffer to serve future vertical
scaler requests.
When no more output can be generated because lines from a future slice
would be needed, then all remaining lines in the current slice are
converted, horizontally scaled and put in the ring buffer.
- [this is done for luma and chroma, each with possibly different numbers
- of lines per picture]
+ [This is done for luma and chroma, each with possibly different numbers
+ of lines per picture.]
Input to YUV Converter
- 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
- exist for this currently, one performing horizontal downscaling by 2
- before the conversion and the other leaving the full chroma resolution
- but being slightly slower. The scaler will try to preserve full chroma
+ When the input to the main path is not planar 8 bits per component YUV or
+ 8-bit gray then it is converted to planar 8-bit YUV. 2 sets of converters
+ exist for this currently: One performs horizontal downscaling by 2
+ before the conversion, the other leaves the full chroma resolution
+ but is slightly slower. The scaler will try to preserve full chroma
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 it is
- useless.
+ SWS_FULL_CHR_H_INP even for cases where the scaler thinks it is useless.
Horizontal scaler
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.
- The remaining scalers are specially tuned for various filter lengths.
- They scale 8bit unsigned planar data to 16bit signed planar data.
- Future >8bit per component inputs will need to add a new scaler here
+ The remaining scalers are specially-tuned for various filter lengths.
+ They scale 8-bit unsigned planar data to 16-bit signed planar data.
+ Future >8 bits per component inputs will need to add a new scaler here
that preserves the input precision.
Vertical scaler and output converter
- There is a large number of combined vertical scalers+output converters
+ There is a large number of combined vertical scalers + output converters.
Some are:
* unscaled output converters
* unscaled output converters that average 2 chroma lines
* bilinear converters (C, MMX and accurate MMX)
* arbitrary filter length converters (C, MMX and accurate MMX)
And
- * Plain C 8bit 4:2:2 YUV -> RGB converters using LUTs
- * Plain C 17bit 4:4:4 YUV -> RGB converters using multiplies
- * MMX 11bit 4:2:2 YUV -> RGB converters
- * Plain C 16bit Y -> 16bit gray
+ * Plain C 8-bit 4:2:2 YUV -> RGB converters using LUTs
+ * Plain C 17-bit 4:4:4 YUV -> RGB converters using multiplies
+ * MMX 11-bit 4:2:2 YUV -> RGB converters
+ * Plain C 16-bit Y -> 16-bit gray
...
- RGB with less than 8bit per component uses dither to improve the
- subjective quality and low frequency accuracy.
+ RGB with less than 8 bits per component uses dither to improve the
+ subjective quality and low-frequency accuracy.
Filter coefficients:
--------------------
-There are several different scalers (bilinear, bicubic, lanczos, area, sinc, ...)
-Their coefficients are calculated in initFilter().
-Horizontal filter coeffs have a 1.0 point at 1<<14, vertical ones at 1<<12.
-The 1.0 points have been chosen to maximize precision while leaving a
-little headroom for convolutional filters like sharpening filters and
+There are several different scalers (bilinear, bicubic, lanczos, area,
+sinc, ...). Their coefficients are calculated in initFilter().
+Horizontal filter coefficients have a 1.0 point at 1 << 14, vertical ones at
+1 << 12. The 1.0 points have been chosen to maximize precision while leaving
+a little headroom for convolutional filters like sharpening filters and
minimizing SIMD instructions needed to apply them.
It would be trivial to use a different 1.0 point if some specific scaler
would benefit from it.
-Also as already hinted at, initFilter() accepts an optional convolutional
+Also, as already hinted at, initFilter() accepts an optional convolutional
filter as input that can be used for contrast, saturation, blur, sharpening
shift, chroma vs. luma shift, ...
projects / frescor / ffmpeg.git / commitdiff