"Enough light to generate a signal from the CCDs"

Eddie B

Eddie B

Active member
This is probably a stupid question, but I've been reading books on digital cinematography and lighting, as well as forum posts here and elsewhere, and there's one thing I don't quite understand. I have an idea, but I just want to confirm it.

In John Jackman's book Lighting for Digital Video & Television (Second Edition, page 3), Jackman says:

...you have to have proper exposure --- enough light to generate a signal from the CCDs and raise the signal to a proper level but not exceed the limits.
Click to expand...
I'd been struggling to understand this concept recently and reading this helped me figure out how to more accurately phrase my question to get the right answer. So here goes (sorry for it being long-winded, just want to be precise):

We all know that video noise is bad. I think most of us would also agree that sometimes, it's also important to have parts of the picture that are completely black (fans of David Lynch know what I'm talking about). When people ask how to get rid of video noise, they're always told to add more light. From this quoted section, I take the reason you're told to add more light is to generate a (better) signal from the CCDs. So my question is, does that necessarily mean you have to add light in every part of the picture?

In other words, if I have video noise but I want there to be some pitch dark shadows, can I just add light to the areas of the picture that I want to be lit (to generate the signal from the CCDs) and leave other areas in total darkness without worrying about noise in those areas?

I hope this question makes sense. I've really been trying to do my homework recently but I still struggle with some of these concepts. Thanks in advance to anyone who can help explain.
 
Ah; an awful typo in the topic heading. Sadly, I can't edit and correct. Gotta proofread these things better in the future...
 
The main issue with noise is gain, which is employed in low light situations. If the camera is set to expose properly on the lit areas it won't add gain to the dark areas, so there won't be an increase in noise in most cases. However, the dark background could make existing noise more noticeable if it's already a noisy situation. But in general, if the light parts of your scene are lit correctly the dark parts will be dark correctly.

One issue is that digital has a history of adding too much detail to blacks, but you can crush those with no problem later if it happens. Doesn't seem to be as much of a problem on newer cameras, where the manufacturers are making them with what we're already doing in mind.
 
This answers my question perfectly. I thought this was the case. Thank you for confirming it.
 
Lets simplify this.

Assume your camera understands light levels from 0 to 100. And let's say that anything below 10 has unacceptable noise.

The idea is to add enough light so that NOTHING is lit less than 10, and nothing is brighter than 100. Setting up the scenes for a minimum light level of 10 in this case is called establishing a base light level. When you get back to post, you can push those dark areas down and you won't have any noise.

Make sense?
 
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