Virtualdub capture histogram

In VirtualDub's capture mode, the histogram shows luma of the captured video; is it possible to adjust brightness and contrast levels to "stay inside the borders"...

what I'd like to know is: the red part of the histograms at left (luma black point) and right (luma white point) must never appear to obtain a good luma range (16-235), or they are just "red alert" - I mean, the histogram could reach those red parts but only for few moments - like the red part of analog audio meter?

Assuming you're capturing in YUY2 colourspace, and have checked the "extend luma range" option in virtualdub, you are able to capture luma values in the 0-15 or 236-255 ranges.

Of course, these values will get clipped on playback to 16 or 235 so it's best to avoid the luma extending too far into these ranges.

If I want to capture in YUY2 and didn't check the "extend luma range" options, and want to stay inside 16-235 range, the histogram MUST be only blue, or could occasionaly became red?

I mean, if the histogram on the left is red, the image falls between 0 and 15, and if it's red on the right, stay between 236 and 255? In that case, I should avoid the histogram to become red, right?