The >235 Y' values aren't uncommon --- I've seen that referred to as
"Superwhite". These values don't map to anything in R'G'B', though,
and need to be clipped if working in R'G'B'. Otherwise, consider it
Actually, my current denoise color-correction uses RGB, so I guess I'd
better be careful (or correct in YUV).
>Capturing from NTSC video in is another story altogether. Y values
>from 0-15 appear regularly, even after I cropped off the "extra" 16
>black columns. Further, in some cases Y never got above 200 (which
>led me to think I might need to add 16 for this case after all), but
>at least with one VHS capture I got the full range from 0 to 255. So
Hmmm. How regularly is regularly? It could just be dipping into the
footroom due to bad video levels in your analog source, maybe. That
old VHS VCR isn't the best reference source.
I found an easy way to see extreme levels. To see ultrablack use
"yuvcorrect -Y Y_1.0_0_16_0_255", so ultrablack shows up as black
while everything else is white. To see ultrawhite use "yuvcorrect -Y
Y_1.0_235_255_0_255", so ultrawhite is white and the rest is black.
It turns out most of the ultra black and white on the VHS is found at
edges, so it represents a really bad ringing transient response
somewhere. These are _really_ bad VHS clips to start with, so no real
surprise. In the broadcast video there is much less ultrablack, and I
think it's just noise.
(Do you really get 0's and 255's in there? I thought that they were
actually illegal values in Y'CbCr, to be used to indicating sync stuff
or other out-of-band info. The actual legal range should be 1-254 for
all planes.)
Yep - in one frame I have 41 0's and 59 255's. I believe you are
correct that they are illegal, but then yuvcorrect is my new best
friend...
Aside from the 0's and 255's, I don't think that any of that makes the
stream "illegal", nor an MPEG made from it. If any clipping is called
for, it will be at the decoder that finally puts it on your computer
screen or your TV.
I assume that a properly calibrated TV won't show any difference
between Y=16 and Y=1, though? Not that I have any of those
(calibrated TV's, that is)...
PS: Thanks for discovering the +16 offset in smil2yuv; that would have
annoyed me to no end if I had found out after burning plastic...
You're welcome. I somewhat recently got this camera and a DVD burner
(I have a new baby and need to send videos to the grandparents) and I
wanted to be sure when I started converting everything that I did it
right. I still won't, I'm sure, but I'm learning a lot.
Dan
-------------------------------------------------------
This sf.net email is sponsored by:ThinkGeek
Welcome to geek heaven.
http://thinkgeek.com/sf
_______________________________________________
Mjpeg-users mailing list
[EMAIL PROTECTED]
https://lists.sourceforge.net/lists/listinfo/mjpeg-users
