Updated the near-lossless level mapping and make it correlated to lossy
quality i.e 100 => minimum loss (in-fact no-loss) and the visual-quality loss
increases with decrease in near-lossless level (quality) till value 0.
The new mapping implies following (PSNR) loss-metric:
-near_lossless 100: No-loss (bit-stream same as -lossless).
-near_lossless 80: Very very high PSNR (around 54dB).
-near_lossless 60: Very high PSNR (around 48dB).
-near_lossless 40: High PSNR (around 42dB).
-near_lossless 20: Moderate PSNR (around 36dB).
-near_lossless 0: Low PSNR (around 30dB).
Change-Id: I930de4b18950faf2868c97d42e9e49ba0b642960
Enable the WebP near-lossless feature by pre-processing the image to smoothen
the pixels.
On a 1000 PNG image corpus, for which WebP lossless (default settings) gets
25% compression gains, following is the performance of near-lossless feature
at various '-near_lossless' levels:
-near_lossless 90: 30% (very very high PSNR 54-60dB)
-near_lossless 75: 38% (very high PSNR 48-54dB)
-near_lossless 50: 45% (high PSNR 42-48dB)
-near_lossless 25: 48% (moderate PSNR 36-42dB)
-near_lossless 10: 50% (PSNR 30-36dB)
WebP near-lossless is specifically useful for discrete-tone images like
line-art, icons etc.
Change-Id: I7d12a2c9362ccd076d09710ea05c85fa64664c38
This compresses the uimage using lossless compression and controlable
decimating pre-process.
Code is under WEBP_EXPERIMENTAL_FEATURE while it's being experimented with.
Change-Id: I8b7f4cfcc3c6afc52a556102842bdbb045ed5ee8
new options:
dwebp -alpha_dither
vwebp -noalphadither
When the source was marked as quantized, we use a threshold-averaging
filter to smooth the decoded alpha plane.
Note: this option forces the decoding of alpha data in one pass, and
might slow the decoding a bit.
The new field in WebPDecoderOptions struct is 'alpha_dithering_strength'
(0 by default, means: off). Max strength value is '100'.
Change-Id: I218e21af96360d4781587fede95f8ea4e2b7287a
* allow reading from stdin for dwebp / vwebp
* allow writing to stdout for gif2webp
by introducing a new function ExUtilReadFromStdin()
Example use: cat in.webp | dwebp -o - -- - > out.png
Note that the '-- -' option must appear *last*
(as per general fashion for '--' option parsing)
Change-Id: I8df0f3a246cc325925d6b6f668ba060f7dd81d68
These are presets for lossless coding, similar to zlib.
The shortcut for lossless coding is now, e.g.:
cwebp -z 5 in.png -o out_lossless.webp
There are 10 possible values for -z parameter:
0 (fastest, lowest compression)
to 9 (slowest, best compression)
A reasonable tradeoff is -z 6, e.g.
-z 9 can be quite slow, so use with care.
This -z option is just a shortcut for some pre-defined
'-lossless -m xx -q yy' combinations.
Change-Id: I6ae716456456aea065469c916c2d5ca4d6c6cf04
New API options: WebPDecoderOptions.flip and 'dwebp -flip ...'
it uses negative stride trick.
Also changed the decoder code to support user-supplied
buffers with negative stride, independently of the
WebPDecoderOptions.flip value.
Change-Id: I4dc0d06f0c87e51a3f3428be4fee2d6b5ad76053
from man-pages (7):
provides a comma-separated list of related man pages, ordered by section
number and then alphabetically by name, possibly followed by other
related pages or documents. Do not terminate this with a period.
Change-Id: I6763b3b3a89f3c2e9ed5c1a4e9d05fb9ce85dd40
this enables webpmux to accept input files starting with '-' when using
-get/-set/-strip; -info & -frame expect an input file as one of their
parameters so no changes are necessary there.
Change-Id: I154eb6dc388258a7fb743ec76ba869bf9589be1b
This is to discourage generation of animated WebP images with ICC
profile, as
the real-world use-case for such images is rare at best.
Output of ICC/XMP metadata is now controlled by the '-metadata' option.
Change-Id: I8e3e29878c32bf46cbc661f50661bac602603c43
Even at high quality setting, the U/V quantizer step is limited
to 4 which can lead to banding on gradient.
This option allows to selectively apply some randomness to
potentially flattened-out U/V blocks and attenuate the banding.
This option is off by default in 'dwebp', but set to -dither 50
by default in 'vwebp'.
Note: depending on the number of blocks selectively dithered,
we can have up to a 10% slow-down in decoding speed it seems.
Change-Id: Icc2446007f33ddacb60b3a80a9e63f2d5ad162de
When '-mixed' option is given, each frame would be heuristically chosen
to be
encoded using lossy or lossless compression.
The heuristic is based on the number of colors in the image:
- If num_colors <= 31, pick lossless compression
- If num_colors >= 194, pick lossy compression
- Otherwise, try both and pick the one that compresses better.
Change-Id: I908c73493ddc38e8db35b7b1959300569e6d3a97
-> helps debanding (sky, gradients, etc.)
This dithering can only be triggered when using -preset photo
or -pre 2 (as a preprocessing). Everything is unchanged otherwise.
Note that this change is likely to make the perceived PSNR/SSIM drop
since we're altering the input internally.
Change-Id: Id8d4326245d9b828141de162c94ba381b1fa5813
We use the 'do not blend' option for creating independent frames.
We also mark the already independent frames as 'do not blend'.
This bounds the maximum number of frames that need to be decoded to
decode a given frame, thus leading to a much better decoding performance.
Change-Id: I7cef98af2b53751ec36993fd2bd54f7f4c4aad2b
Doesn't work with WIC
+ redirect some info messages from stdout to stderr
+ fix the error reporting upon output-writing error
Change-Id: I92b8bd7a15e656a3f3cdfbf56299f024e39453f8
new option: -blend_alpha 0xrrggbb
also: don't force picture.use_argb value for lossless. Instead,
delay the YUVA<->ARGB conversion till WebPEncode() is called.
This make the blending more accurate when source is ARGB
and lossy compression is used (YUVA).
This has an effect on cropping/rescaling. E.g. for PNG, these
are now done in ARGB colorspace instead of YUV when lossy compression
is used.
Change-Id: I18571f1b1179881737a8dbd23ad0aa8cddae3c6b
