yuvdenoise can be used to remove noise from movie images
in an YUV4MPEG2 stream. This is usefull to reduce the bitrate
needed to encode your captured movies for VCD and SVCD creation.
OPTIONS
yuvdenoise accepts the following options:
-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 according pixel of the reference image.
(default=5)
-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)
-r [8..24] search radius
Limit the search radius to that value. Usually it will
not make sense to go higher than 16. Esp. for VCD sizes.
(default=8)
-b <x>,<y>,<w>,<h> Border Setting
If you allready know parts of the image are and remain black all 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 absolute pure black. The area outside the search window will not go
into the motion compensation algorithm and therefor you might have a
speed gain in processing the movie.
Sometimes it may be usefull 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.
-L [0..255] luminance contrast
Set luminance (Y Contrast) in percent. (default=100) The default value of
100 skips performing luminance contrast adjustment entirely.
-C [0..255] chrominance contrast
Set chrominance (Cr/Cb Contrast) in percent. AKA "Saturation" (default=100)
The default value of 100 skips performing chroninance contract adjustment
entirely.
-S [0..255] sharpness in percent
Set sharpness in percent. WARNING: do not set too high
as this will gain bit-noise. (default=125) A sharpness value of 0 will skip
performing the sharpening pass.
-F deinterlacing
Force deinterlacing. By default denoise interlaced.
-f fast mode
Fast mode. Use only Pass II (bitnoise-reduction) for
low to very low noise material. (default off)
-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)
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
wightened 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.
TYPICAL USAGE AND TIPS
As it is self-adapting to the noise-situation found in the stream you
normaly just can go without any options set:
However, to obtain the best possible result, you should take care of
the following:
1. Grab at the maximum possible resolution (PAL 768x576
pixels). Even do this if you just want to create a 352x288 pixel
movie as downscaling reduces noise, too (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 real black. This helps the encoder a lot.
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 best
SCART-RGB).
5. If your movie is B&W only, then try the -B switch.
Having that sayed, I normaly use a command-line like this one:
