Blowing out windows - suggested f-stop, zebra settings, gamma knee

stephenvv

stephenvv

Well-known member
I've got a shot tomorrow of women delivering a monalogue in front of a window that is getting afternoon sun at about a 45 degree angle. I want the window to blow out and her face somewhat silhouetted but want enough fill to see a few details, hot spots on her face.

The shots will be mostly max telephoto, fairly tight shots. I'm thinking of bouncing light for filll and using no lights other than sun.

I want to set zebras for highlights on face and window - also wondering best gamma and knee for blowing highlights.

Model would be "The Shining" although I realize DV just ain't film...:undecided
 
The great thing about video is, you can see exactly what you're getting on the monitor. Not necessarily on the LCD, but on a TV or monitor. So I'd (strongly) recommend taking one along with you. That'll give you a lot more feedback than just the guesses we can offer here.

Regarding gamma and knee: the knee softens the transition to overexposure. You probably want to employ the knee, as I would figure you don't want an immediate transition from detail to blown-out, right? If so, don't use Cine gamma, which has no knee at all. All the other gamma curves provide for knee control. The knee works basically like a limiter works for audio, by rolling off the "volume" (or brightness) the louder (or brighter) the image gets.

High gamma preserves highlights, Low gamma preserves shadows. Presumably you'd want to use Low gamma, biasing the curve towards preserving your main image while giving less emphasis to the highlights (which will let them blow out easier).

Just be aware that blown-out highlights "bleed" into the neighboring pixels on the CCD. If the window isn't clearly in the shot, or the portion that the person's head is in front of doesn't need to blow out, then you'll probably be okay. But if you want a smooth transition from them to blown-out window (i.e., one pixel is their head, and the very next pixel is blown-out window) it might get kind of ugly. In the example you showed, the transition between her and the blown-out window won't be as clean if you do it in-camera. Works well in film, but a CCD-based video camera struggles with that sort of thing. Might be better to capture it just short of blowout, and then push the contrast in post or use a glow filter or something like that.

But, again, if you have an NTSC monitor with you, you'll see exactly how it looks and you'll know whether it'll work "in-camera" or if you need to do it in post.

Also, pay attention to the Detail Level menu setting. Higher detail levels add edges around contrast changes. I'd expect you'd want to use a lower detail level. But, again, check it on a monitor to see the real-world effects.


Blowing out windows is really quite easy -- it's AVOIDING blowing out the windows that's usually the hard part!
 
Thanks Barry - excellent feedback. Fortunately, the shot is here in my house, so I have a calibrated JVC monitor here to use on set.

Thanks for the clear knee and gamma explanation in reference to highlights. I had some vague ideas of how it might work (that I recalled from your book :laugh: ) but a friend considering a DVX purchase has it right now.

I did have the thought of not quite blowing out the window until post - I have both Vegas 6 and After Effects Pro with Color Finesse at my disposal, so I will heed your advice and avoid ulginess by overpushing highlight bleeding.

I don't have DV Rack, but use Vegas as a substitute, so I will check scope.

So far, there is not a cloud in the sky today, first day like this in couple of weeks - let's hope it holds so my light levels aren't changing every two minutes :undecided
I appreciate your time.
 
It went pretty well despite having lots of clouds and windows light levels changing 6 stops from beginning to end.

I ended up shooting exposing for shadows - leaving a little detail in the shadows, even though I was going to crush them back down somewhat in post, but if I needed the detail it was there. I tried to keep the window from being too hot using ND filters and iris, but sometimes the contrast was just too much, but changing clouds and setting sun meant window treatments etc. not practical.

So my raw footage looks somewhat like the before, except for no deep blacks - just muddy, but as you see, easily corrected in post without artifacts.

I did shoot low gamma, lower detail but as you can see when the window was very hot, edges did get rough, but for this piece, I can live with it. When window was very hot, I have some color fringing but should be able to minimize it in post.

Here on some quick samples - all I've done is just a 10 second Photoshop levels adjust:

http://www.stephenv2.com/pics/

thanks again for help and guidance
 
You must log in or register to reply here.
Back
Top