How to prevent background blacks from having noise

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davdav

Active member
Hi,

I have set up a makeshift studio to interview subjects. I light up the person/subject with three lights (main, fill-in, and head light). The back backdrop is not lit. My intention is for the subject to be well lit and the background to be pure black.

What I find is that the subject is indeed well lit, yet the HMC150 tries to find detail in the black background, and as a result introduces noise. It is distracting as the background appears to shimmer when viewed.

How do I prevent the HMC150 from creating this noise in the background? Remember that I want a pure black background behind the suject.

Any ideas?
 
Having shot the same setup, I would say that lighting could make a difference. Is there any light spilling onto the black background? I use black flags to deflect any of the key or fill lights from hitting the background so that there's maximum light contrast between subject and background. There was some home-grown video tutorial I used for setting up that lighting, but now I can't seem to find it.

But I did find this string on Creative Cow.
http://forums.creativecow.net/thread/35/857093

Hope it's helpful
 
Also, I've found the Creative Cow forum "Lighting Design Pros" to be extremely helpful. Some very experienced and helpful people on that forum.
 
ANY light falling on the background within the dynamic range of the camera means the background is not going to be black.

Prevent light falling on the to back drop, both by blocking the lights (using a flag) and by having the subject far enough away from the background, just like you would with green screen to prevent light spill to/from the subject. Also, try using black velvet as a backdrop material it works wonders :)

You can also try playing with the gamma curve and/or fix some of it in color grading.
 
I shoot this setup a lot and the guys are right on for the lighting aspects... My big thing I try to do is have my front sources be a bit higher so no shadows and spill on the Backdrop and also get some high key or bright sources to make sure your background drops off bigtime...


The other MAJOR thing is to push the master ped way negative.... I usually have it atleast around -30 or more depending. I've had it as high as -60 and it's very contrasty but I like that look anyway.... If you want some samples I have a ton on a website directory so just hit me up....
 
Thanks everyone for your help and advise. This problem is something I never anticipated as my experience is usually with film photography from years ago. Video issues like this never crossed my mind. I purposely used the low light capabilities of the HMC150 so that I would not have to light up the studio very bright - I have elderly subjects and did not want to fatigue them through a long session with hot lights. I now see that this approach brought the black backdrop within the dynamic range and the camera brought in noise into the background.

I will try with brighter lights, however I think the master ped solution is a good one to try first.

Thanks again everyone!
 
You can also play with distance from your lights to your subject - the closer your lights are to the subject the more fall off you will get on the background. For example, and this is pretty extreme, but illustrates the point. If your subject is 5 feet from the back ground an then your lights are 5feet in front of the subject, there will be 4 times more light on the subject. If you then move your lights forward to 2.5 feet from the subject, the turn them down to give the same exposure, there is now 8 times more light on the subject than background.
 
I also film older subjects quite often and you don't have to blast them with light. It makes them uncomfortable. Shooting film is no different in this regard. I shot film for over 20 years.

The trick to getting solid blacks is to get good contrast ratio. That's on Video, film, digital cinema, or a webcam. If you get that background 5 stops below key, you are GOING to get a black background. The problem is light spill. Most people simply do not control spill well enough to really get that light off the background.

Here's a simple check. Set up your lights without your subject in place, but with the background ready to go. Meter on that background whether using a handheld meter, a waveform monitor, or a built-in camera meter. Take your reading. Turn off your lights. The reading shouldn't change much if at all. If it changes any appreciable amount, you've got light spill hitting that background and it will raise your blacks into the noise range.

Practically all of this is easily handled in post, so I tend not to sweat it *too* much unless for some reason it's not going to get post treatment, it's going out live, or some other special circumstance.

FYI, the issue is the same trying to get a white background. Push that background about 5 stops above key and you'll have no problems getting a pure white background and a properly exposed subject.
 
PerroneFord said:
Practically all of this is easily handled in post, so I tend not to sweat it *too* much
Click to expand...

Thanks everyone again for your helpful advice.

PerroneFord - can you give me some pointers on how to fix this in post production? I am using Premiere Pro CS5. Any tips you, or any of the others, can give me would be greatly appreciated.

Thanks in anticipation.
 
In addition to all the other insights -- try the B.Press gamma curve. It's specifically designed for this situation. It crushes the blacks (reduces the appearance of noise) and boosts the mid tones.
 
AGMedia said:
try the B.Press gamma curve. It's specifically designed for this situation..
Click to expand...

Thanks AGMedia! Can you explain when to use the Master Pedestal and when to use the B.Press gamma curve? Do you have suggested settings to try of the B.Press gamma curve too?

Happy New Year everyone!!
 
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