yuvdenoise.1

Motion JPEG编解码器源代码

.TH "yuvdenoise" "1" "24th May 2002" "MJPEG Linux Square" "MJPEG tools manual"

.SH NAME
yuvdenoise \- Motion-Compensating-YUV4MPEG-frame-denoiser

.SH SYNOPSIS
.B yuvdenoise
.RI [ options ]
.RI "</dev/stdin >/dev/stdout"

.SH DESCRIPTION
\fByuvdenoise\fP can be used to remove noise from movie images
in an YUV4MPEG2 stream. This is useful to reduce the bitrate       
needed to encode your captured movies for VCD and SVCD creation.

.SH OPTIONS
\fByuvdenoise\fP accepts the following options:

.TP 4
.BI \-X " Disable SIMD optimisations"
Disable the use of MMX/SSE enhancements if they would ordinarily be used.  This
is useful for testing to compare the C code against the SIMD code for timing
and accuracy. 

.TP 4
.BI \-t " [0..255] Denoiser threshold"
Accept any image-error up to +/- threshold for a single
pixel to be accepted as valid for the image. If the
absolute error is greater than this, exchange the pixel
with the corresponding pixel of the reference image.
(default=5)

.TP 4
.BI \-l " [1..255] frames for a time-lowpassed pixel"
Average 'n' frames for a time-lowpassed pixel. Values
below 2 will lead to a good response to the reference
frame, while larger values will cut out more noise (and
as a drawback will lead to noticable artifacts on high
motion scenes.) Values above 8 are allowed but rather
useless. (default=3)

.TP 4
.BI \-r " [8..24] search radius"
Limit the search radius to that value. Usually it will
not make sense to go higher than 16, especially for VCD sizes.
(default=8)

.TP 4
.BI \-b " <x>,<y>,<w>,<h> Border Setting"
If you already know parts of the image are and remain black over
the complete sequence of images you may use something like this:

yuvdenoise -b 16,16,704,560

This will set all the pixels in the image outside that search window
to pure black. The area outside the search window will not go
into the motion compensation algorithm which may give a moderate
speed gain in processing the movie. 

Sometimes it may be useful to have relative coordinates like this:

yuvdenoise -b 16,16,-16,-16

Provided there is a PAL-frame with 720x576 pixels, both options will
turn the same area into black.

.TP 4
.BI \-L " [0..255] luminance contrast"
Set luminance (Y Contrast) in percent. (default=100)  The default value of
100 skips performing luminance contrast adjustment entirely.

.TP 4
.BI \-C " [0..255] chrominance contrast"
Set chrominance (Cr/Cb Contrast) in percent. AKA "Saturation" (default=100)
The default value of 100 skips performing chrominance contract adjustment
entirely.

.TP 4
.BI \-S " [0..255] sharpness in percent"
Set sharpness in percent. WARNING: do not set too high
as this will gain bit-noise. (default=0)  A sharpness value of 0 will skip
performing the sharpening pass (and speed up denoising about 20%).

.TP 4
.BI \-F " deinterlacing"
Force deinterlacing. Default is to perform interlaced denoising.

.TP 4
.BI \-f " fast mode"
Fast mode. Use only Pass II (bitnoise-reduction) for
low to very low noise material. (default off)

.TP 4
.BI \-p " [0..255] Pass II threshold"
Pass II threshold (same as -t). WARNING: If set to values greater than 8 
you *will* see artifacts...(default=4)

.TP 4
.BI \-s " num"
Number of beginning frames to skip.  The first num frames are written
to stdout unfiltered.  This is useful for resuming an interrupted
job without having to duplicate work.


.SH HOW IT WORKS
Yuvdenoise works by temporal lowpass filtering. To avoid
motion-blur it transforms the previous image with a
motion-compensation as close as possible to the present frame. This
motion-compensation is performed on 4x4 pixel blocks. The result is
weighted and a block of the transformed previous frame is (depending
on a matching coefficient) either taken in full, blended with the
present image-block or discarded if the match is to bad.

This procedure implies that the motion-compensation is very exact. If
a video-encoder misses a transformed block it's not that bad, it only
encodes a difference block there. If the denoiser fails to find a good
matching block the only solution is to exchange the found block with
the original frame block. Therefor a great amount of time is spent to
find good matches. This is the main reason why the denoiser does not
run at full framerate at CIF resolution as you might have wished.

.SH TYPICAL USAGE AND TIPS
As it is self-adapting to the noise-situation found in the stream you
normally just can go without any options set:

lav2yuv my-video.avi | yuvdenoise | mpeg2enc -t 1 -o my-video.m1v

However, to obtain the best possible result, you should take note of
the following: 

1. Grab at the maximum possible resolution (PAL 768x576
pixels).  Do this even if you just want to create a 352x288 pixel
movie as downscaling reduces noise (and at no cost to
image-quality and/or sharpness in that case).

2. First denoise, then scale! There are some rare situations where the
denoiser itself may introduce artifacts (blocks, etc...). The
perceptibilty of these artifacts is reduced by this processing order.

3. If your movie contains black borders use the -b option to turn them
into pure black. This helps the encoder use fewer bits to encode the data.

4. You can greatly improve the recorded quality if you use correct
cables.  Only use HF-in (the antenna-cable ...) if you really can't
connect your VCR/Camcorder by other means (Composite, S-Video or
SCART-RGB).

5. If your movie is B&W only, then try the -B switch.

Having said all that, I normally use a command-line like this one:

lav2yuv movie.avi | yuvdenoise -b 8,64,-8,-64 | yuvscaler -O
SIZE_352x288 | mpeg2enc -f 1 -o movie.m1v

Have a lot of fun! ;-)

.SH AUTHOR
This man page was written by Stefan Fendt <[e-mail]>.

.SH FURTHER INFOS
If you have questions, remarks, problems or you just want to contact
the developers, the main mailing list for the MJPEG\-tools is:

.BR \fImjpeg\[e-mail]\fP

For more info, see our website at

.BR \fIhttp://mjpeg.sourceforge.net/\fP

.SH SEE ALSO
.BR mjpegtools (1),
.BR mpeg2enc (1)
.BR lavrec (1)
.BR lav2yuv (1)