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add Advanced Decoding Interface

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You can now use WebPDecBuffer, WebPBitstreamFeatures and WebPDecoderOptions
to have better control over the decoding process (and the speed/quality tradeoff).

WebPDecoderOptions allow to:
 - turn fancy upsampler on/off
 - turn in-loop filter on/off
 - perform on-the-fly cropping
 - perform on the-fly rescale
(and more to come. Not all features are implemented yet).

On-the-fly cropping and scaling allow to save quite some memory
(as the decoding operation will now scale with the output's size, not
the input's one). It saves some CPU too (since for instance,
in-loop filtering is partially turned off where it doesn't matter,
and some YUV->RGB conversion operations are ommitted too).

The scaler uses summed area, so is mainly meant to be used for
downscaling (like: for generating thumbnails or previews).

Incremental decoding works with these new options.
More doc to come soon.

dwebp is now using the new decoding interface, with the new flags:
  -nofancy
  -nofilter
  -crop top left width height
  -scale width height

Change-Id: I08baf2fa291941686f4ef70a9cc2e4137874e85e
This commit is contained in:
Pascal Massimino
2011-06-20 00:45:15 -07:00
parent bd2f65f67c
commit d260310511
19 changed files with 2052 additions and 788 deletions
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25
man/dwebp.1
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@ -1,5 +1,5 @@
.\" Hey, EMACS: -*- nroff -*-
.TH DWEBP 1 "March 28, 2011"
.TH DWEBP 1 "June 20, 2011"
.SH NAME
dwebp \- decompress a WebP file to an image file
.SH SYNOPSIS
@ -32,6 +32,29 @@ Change the output format to PGM. The output consist of luma/chroma
samples instead of RGB, using the ICM4 layout. This option is mainly
for verification and debugging purpose.
.TP
.B \-nofancy
Don't use the fancy upscaler for YUV420. This may lead to jaggy
edges (especially the red ones), but should be faster.
.TP
.B \-nofilter
Don't use the in-loop filtering process even if it is required by
the bitstream. This may produce visible blocks on the non-compliant output,
but will make the decoding faster.
.TP
.B \-crop x_position y_position width height
Crop the decoded picture to a rectangle with top-left corner at coordinates
(\fBx_position\fP, \fBy_position\fP) and size \fBwidth\fP x \fBheight\fP.
This cropping area must be fully contained within the source rectangle.
The top-left corner will be snapped to even coordinates if needed.
This option is meant to reduce the memory needed for cropping large images.
Note: the cropping is applied \fIbefore\fP any scaling.
.TP
.B \-scale width height
Rescale the decoded picture to dimension \fBwidth\fP x \fBheight\fP. This option is
mostly intended to reducing the memory needed to decode large images,
when only a small version is needed (thumbnail, preview, etc.).
Note: scaling is applied \fIafter\fP cropping.
.TP
.B \-v
Print extra information (decoding time in particular).
.TP