> Yep -- off the camera in 16-235 range.
(Ok, I fibbed...)
>Ok, I decided to test this out, and found some surprises. I have a
>Canon ZR40, a nothing-special DV camcorder that also records from
>video in or just digitizes and passes the video through via ieee1394.
I'll try out my Sony sometime this week, too...
>First I found the camera's range by shooting with the lens cap on and
>then by pointing it at a light. Pure black is about Y=20 and it never
>went below 16, but I easily got values of Y=250+ by overexposing the
>CCD - no internal limiting is done. (Looking at the RGB data, it
>seems the red sensor hits 255, while the others are less, possibly due
>to infrared which this camera does record somewhat). In normal usage
>though it seems Y never gets anywhere near 235.
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
a bit of extra visual detail that makes use of Y' headroom, and might
become useful if you are fading/blending. (Final Cut Pro allows for
staying in the Y'CbCr colorspace from DV-in to DV-out, and has a little
check-box to control superwhite clipping.)
>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.
(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.)
>in a way I'm happy my camera has a full range, but now I'm not sure
>how to process the output - do I rescale, clip, or create an "illegal"
>mpeg?
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.
And I still believe that the black-level and range are fine without any
additional offsets or scaling.
I've got access to some studio equipment at work; I don't know how well-
-calibrated it is, but I'll see if I can try your tests out myself later
this week.
-matt m.
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...
-------------------------------------------------------
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
