Black balancing

J

JitCam

Well-known member
Got a question concerning setting the black balance on the camera. Also just a thought before the question... could the noise that some people notice in shadows and dark areas be the result of not setting the black balance correctly??

Anyway my question is.. When setting the white balance, in the manual it tells you to place a white pattern in front of the camera so as to refrence off that in the light condition u are shooting... When setting the black balance do you have to have a black pattern to point the camera at? I couldnt find anywhere in the manual where it mentioned that.. It says specifically "Press the AWB button to adjust the white balance... Press and hold the AWB button to adjust black balance" .. So i assume you use the same white pattern for both white and black?

:beer:
 
JitCam said:
Got a question concerning setting the black balance on the camera. Also just a thought before the question... could the noise that some people notice in shadows and dark areas be the result of not setting the black balance correctly??

Anyway my question is.. When setting the white balance, in the manual it tells you to place a white pattern in front of the camera so as to refrence off that in the light condition u are shooting... When setting the black balance do you have to have a black pattern to point the camera at? I couldnt find anywhere in the manual where it mentioned that.. It says specifically "Press the AWB button to adjust the white balance... Press and hold the AWB button to adjust black balance" .. So i assume you use the same white pattern for both white and black?

:beer:
Click to expand...

Completely close the iris when you are black balancing the camera.
 
gregcotten said:
Completely close the iris when you are black balancing the camera.
Click to expand...

Never herd that before ?
Surly the camera needs to see something in order to evaluate the black balance.
I'm BBC trained and we were told to black balance straight after the white balance not changing any settings from the white balance.

Anybody ?

PS The noise many people are getting is from not doing a correct white balance, incorrect black balance will give you muddy blacks and could cause noise also.
 
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the black balance is an adjust to set the lower electrical level of the ccd.
So, you have to do it in total black, and the usual way, is closing totally the iris of the camera.
In fact, with a broadcast camera, with servo controlled lens, if you do a black balance, the lens automatically closes its iris... even at the BBC xD
 
Ah yes I wondered why the cameras went to black as the black balance engaged.
I suppose as I trained on broadcast cameras with servo lenses they didn't see the need to tell us about closing the iris as it's done automatically.
Cheers for the info.
 
so basically i close the iris and black balance right? Strange how they dont mention that in the manual.

thanx
 
You do not have to perform a black balance in the dark or with the lens cap attached -- in fact, you can't even do that, because the camera will do a white balance first, and that will fail if you are doing it in the dark.
 
The DVX and HVX will automatically close the iris, so you don't have to do anything different.

Closing the iris gives the camera a pure black signal, so it can then evaluate its CCDs and see if there is any signal being generated -- because there shouldn't. The camera can then adjust to make a pure black signal render as pure black, similar to how it renders a white card to look white. But it's not adjusting for ambient lighting conditions (as with a white balance).

If someone's having trouble with noise in the shadows or other gremlins, doing a black balance certainly wouldn't hurt. You should do it every once in a while anyway.
 
I think its worth mentioning that doing a good white balance will help reduce noise !
I've had quite a few shots look noisey on preset WB untill a manual WB was set.
 
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Thank you, JitCam for an interesting question for it raises interesting points. First off, I've always thought that calling black balance that was a bit misleading, as it's not the same as a white balance. With black, the Y channel is at whatever level you set the pedestal at (I think) and it's then (I believe) pure electronics: some threshold settings above dark noise that evens out the u and v channels.

With white balance, the circuitry evaluates the chroma content of the video signal to arrive at a neutral highlight grey, by balancing the chrominance channels. I think that's why if you leave the WB on a preset, the result can be quite noisy: the circuitry may have to work harder, shift colours further, to achieve the balance. Whereas setting it up manually, removes the need to make continual - and noise-generating - adjustments.

I guess it's a bit like geting the exposure right: you are rewarded with the biggest latitude. Like 4mat, i've noticed that careful manual WB produces cleaner shadows.
 
rgbuster, ive noticed cleaner images also with correct white balancing, and the thought occured to me about the black balance on the basis of correct black for the exposure, in other words the camera electronically setting values for the black.. I really think with the correct tweeking of certain settings u can get a crisp clean image.
 
Not that the Hvx doest already have a crisp clean image, i mean in conditions which might produce noise!
 
btw... I've never use a white to do a white balance... I prefer to use a regular Kodak Gray card instead of white paper...
 
polispol said:
btw... I've never use a white to do a white balance... I prefer to use a regular Kodak Gray card instead of white paper...
Click to expand...

Does it work well for you? I ask because the white balance is to tell the camera what is white is in the shot. I know using warm/cold cards is a useful tool, but never tried a gray. Its obviously working for you otherwise you wouldnt do it. So, now Im curious first thing tomorrow Im going to do a test with HVX and Canon A1.
 
It's not actually telling the camera what is white and what isn't.

It's telling the camera what a neutral color looks like, i.e. one without a color cast. Thus, white will work just as well as any gray with equal levels of primary colors.
 
I've always found that you get a truer overall colour balance is you take your WB
of a card or surface that is light grey, not white. and if you are working outdoors
tilt the card downwards slightly so it's not in direct sunlight (partial shade)
make sure you re white balance through the day, but i only ever black balance my XD every month or so. the HVX shut's the iris and black balances staright after wb

ian
 
I remember Jan stated that one should black balance every time that frame rate is changed, also when shooting format is changed.

Andreas
 
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