Hi -
From: [EMAIL PROTECTED]
Subject: [Mjpeg-users] Re: Mjpeg-users digest, Vol 1 #889 - 5 msgs
Hmmm, the digest form apparently obscures the initial Subject: -
was wonder what Vol 1 #899 - 5 msgs was all about.
It is a low volume group for the most part - would it be feasible
to use the individual article form I wonder?
Have you tried yuvcorrect -M STAT? It makes frame-by-frame histograms
No, I had forgotten about it.
INFO: [yuvcorrect] 020 00041 0 0
INFO: [yuvcorrect] 021 00432 0 0
INFO: [yuvcorrect] 022 02900 0 0
INFO: [yuvcorrect] 023 09386 0 0
INFO: [yuvcorrect] 024 16027 0 0
INFO: [yuvcorrect] 025 16109 0 0
INFO: [yuvcorrect] 026 12281 0 0
INFO: [yuvcorrect] 027 09313 0 0
INFO: [yuvcorrect] 028 06954 0 0
INFO: [yuvcorrect] 029 04929 0 0
INFO: [yuvcorrect] 030 03300 0 0
INFO: [yuvcorrect] 031 02051 0 0
INFO: [yuvcorrect] 032 01248 0 0
INFO: [yuvcorrect] 033 00681 0 0
INFO: [yuvcorrect] 034 00384 0 0
INFO: [yuvcorrect] 035 00204 0 0
INFO: [yuvcorrect] 036 00091 0 0
INFO: [yuvcorrect] 037 00041 0 0
So it looks like I have less of a spread than you, especially in CbCr.
Not much less though. The center in your case is similar - in
your case it's 25, in my test it was 28.
Sounds like you want to apply a nonlinear mapping that squeezes your
darker pixels closer together but leaves the rest alone. Perhaps a
Not really, at least I don't think so. What I _think_ I need
(and have the initial attempt running) is a _very_ selective
highpass filter (no pixels with Y' above 48 are even looked at)
that uses a 'midpoint' and a combination of clip and core. More below.
piecewise-linear extension to yuvcorrect? Have you tried adjusting
the gamma (a power nonlinearity curve) via yuvcorrect? That might
But that affects *everything*, not just the values that are similar
in value *and* close to black (where closeness is user specified).
Right?
have a similar effect. Or, you could just clip below some black
threshold, and then restretch what remains to the full range,
That's a bit too aggressive I suspect.
something like:
yuvcorrect -Y Y_1.0_28_235_16_235
Will that translate both 31/128/125 and 26/129/129 into 28/128/128?
or just clip:
yuvcorrect -Y Y_1.0_28_235_28_235
or clip and shift down (makes it darker though):
yuvcorrect -Y Y_1.0_28_235_16_223
I think what is wanted, and appears to be working is to specify
a 'center point' and a 'radius' for Y', Cb, and Cr (usually Cb and
Cr would be the same but they don't have to be).
Here's a small sample of real data from a 'black frame':
28 128 125
29 128 125
29 128 125
31 129 126
29 129 126
32 129 124
30 129 124
The distribution for the frame is:
Y 16 4669
Y 17 4434
Y 18 1645
Y 19 2228
Y 20 3909
Y 21 6750
Y 22 10897
Y 23 17327
Y 24 25437
Y 25 33738
Y 26 41316
Y 27 46068
Y 28 44184
Y 29 35925
Y 30 26505
Y 31 18060
Y 32 11277
Y 33 5925
Y 34 2862
Y 35 1329
Y 36 606
Y 37 274
Y 38 127
Y 39 73
Y 40 23
U 122 32
U 123 98
U 124 362
U 125 1222
U 126 3432
U 127 9572
U 128 20388
U 129 26756
U 130 16098
U 131 5866
U 132 1816
U 133 548
U 134 166
U 135 38
U 136 2
V 120 62
V 121 354
V 122 1624
V 123 6420
V 124 17160
V 125 24796
V 126 18654
V 127 10470
V 128 4858
V 129 1486
V 130 424
V 131 66
V 132 20
To reduce the random shades of grey problem what I want to do
is convert
23-31/124-132/124-132 into 28/128/128
but leave things like 49/125/128 and 16/200/64 alone.
What I have is a preliminary 'y4mblackfix' which takes allows me to
specify what pixels are to be considered identically black and to
subsitute the specified center point values. '-y 27 -Y 4
sets the centerpoint for Y' to 27 meaning that pixels with 23 thru 31
values will be examined to see if their Cb and Cr values qualify as
'black'. The defaults for the center point and radius for Cb and Cr
are 128 and 4 respectively (and usually are not changed). This means
that 23-31/124-132/124-132 pixels become 27/128/128 - the Y' values
23, 24, 25, 26 become 27 (clip) and 28,29,30,31 become 27 (core)
Similarily the Cr/Cb values 124,125,126,127 and 129,130,131,132
become 128. Undetectable to most human eyes (I really think) but
to the encoder it has a lot more redundancy in place of random
variation and that helps the picture quality in dim scenes.
Much less random/noise variation in the dark scenes and that should
keep grey blocks from dancing around the screen.
The tests so far show that after the fade in/out from black
