>I understand that the lowest "legal" Y' value is 16. I assume it comes
>right off my camera in the range 16-235? But the libdv and kino
Yep -- off the camera in 16-235 range.
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.
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.
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
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?
Dan
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