Deep Black Balancing

[Eugene Kosarovich]

How often do the rest of you do a "deep" black balance?

I do a normal black balance at the start of each day of shooting, but I'm not clear how often to do a "deep" black balance. The "deep" black balance being when you hold down the switch for 5 seconds or more and it does the long and more complicated black balance that includes stuck pixel remapping and repair.

This process isn't mentioned in the manual, but this is how a Sony engineer told me it works when I looked into how these cameras deal with stuck pixels before I bought the camera.

I had planned to only do this every month or so, but having seen an annoying stuck pixel on my last shoot that I couldn't see during the shoot, I'm now thinking I should do it at the start of each day of shooting.

[Greg Boston]

Actually, that's not quite correct. Black balancing is only looking to set the individual pixel output to zero current with a closed iris (true black condition). These small currents are produced by internal 'thermal noise'. The normal black balance (momentary toggle), does one channel. Repeating the same momentary toggle, you'll see that it goes to the next channel. And after the third toggle, all three channels are done. The extended hold on the switch will force all three channels to be done at once, creating fresh reference data and takes longer.

Pixel masking is a manual process performed in the service menus and there are two sets of data retained in memory, one for the normal shutter speeds, and another for slow shutter which can reveal hot pixels that aren't present at normal shutter speeds and thus shouldn't be removed from the image under normal shooting modes.

Black balancing can't shut down a truly stuck (lit) pixel. It's essentially a short circuit that produces maximum output current all the time, even in total darkness. By contrast, a dead pixel is an open circuit that produces no output regardless of how much light is hitting it.

-gb-

[Eugene Kosarovich]

So if a momentary toggle black balance only does one color channel, doesn't that imply that one should always do it three times? Wouldn't the R, G, and B channels all need to be adjusted to zero for a correct black balance?

I know the service menus do allow manual pixel masking, for pixel problems that the camera can't correct itself.

But now that I look up what I wrote down when I talked to the engineer, he said that most of the problems are Residual Point Noise which the camera can correct via the long black balance. I believe this is the zero current issue you mention. But then he went on to say that it would switch to masking where the RPN couldn't be fixed, it would remap interpolated data in place of the bad data for up to a 4 pixel wide area.

It's possible I misunderstood him, maybe all the pixel masking is manual and limited to a 4 pixel wide area? But automatic was the way I understood it from the conversation I had with the engineer at the NJ Sony Service Center before purchasing, cause I wanted to find out what the latest tech was to deal with pixel issues, considering there are 4 times more pixels in the F3xx than on my DSR-300A, and I'd had pixel issues with that in the past.

Well, as long as I only hit RPN that can be fixed like this time, I'm happy. :)

[Stewart Menelaws]

I use the black balance on occasion's, but certainly not every day we are going to be using our F350 which is mainly for general commercial work. I have noticed what appears to be the odd stuck pixel (if that's what it is) after flights, that were clearly visible on an HD 8.4" monitor - black balancing (approx 5 second hold) has always cleared the problem. Checking the camera at a later stage on a larger HD monitor confirmed that the repairs were successful. Certainly the F350 has been very reliable.

Regards, Stewart.
www.studioscotland.com

[Alister Chapman]

That's been my experience too. The odd stuck pixel that a 5 second WB removes.

[Steve Phillipps]

There was one on my F355 when it got it out of the box!
Steve

[Robert Schemitsch]

So, in the XDCAM, there is no memory-limitation on black balance and the dead pixel correction, like in the digibeta-cams?

[Eugene Kosarovich]

No, there is a memory limitation, but there is more memory in the XDCAM HD line of cameras than in previous cameras.

The engineer also told me that when the camera checks pixels, it checks all of them, including previously corrected pixels, so if the pixel "gets better" on its own, it can come back, and free that space in memory for other pixels that go bad. He said previous cameras couldn't do that, so they ran out of memory quicker. He said some pixels do get better on their own, so that is an advantage to be able to put them back in. I expect he only meant this for any automatic remapping, since I don't think it would override manual remapping.

I also had a bad pixel out of the box with my F335. Latest theories say cosmic rays are the main cause of them, which is why flying the cameras tends to cause more, with less protection from the atmosphere at those altitudes.