Published : 9th February 2005
I didn't tune in on this discussion. Could someone review the black balance process for getting rid of bad pixels. Is it just doing black balance or is there more?
Also, a director asked me to explain what black balance does the other day and I couldn't give him a real clear explanation : anybody got the 25 words or less version?
The black balance "pixel fix" procedure, if your camera supports it is to press the black balance button and hold until the VF notifies you that the camera is doing more than black balancing. I forget the exact VF message text, but it will be obvious that you've moved on from black balancing. Do the procedure several times if you don't succeed the first time or second time or third or....
I believe you'll find several posts in the archives about this and the voodoo technology that sometimes fixing the "bad" pixel. Allow camera to warm up to reveal all the bad pixels before doing the procedure.
Black balancing is the same as white balancing only darker. That's the short answer that I can offer but Walter or others are way more qualified to explain. Basically your camera sets levels of the three colors so that black is neutral instead of blue black or red black, etc.
Randy "not an engineer" Miller, DP in LA
Blain Brown writes :
>I didn't tune in on this discussion. Could someone review the black >balance process for getting rid of bad pixels. Is it just doing black >balance or is there more?
Automatic Black Balance does three things in most all makes of cameras :
(Before any of the below, cap or fully close the lens.)
1) It sets the Black Set to the correct point so that when gain is varied, absolute blacks do not change.
2) It sets the Black Level of the RGB channels to just above the black clip point when the camera is shooting absolute black. (In actuality, the F900/950 ABB tends to set the black level a little too high in the absence of a reference file to the contrary, which is certainly preferable to the alternative of setting it too low and thus clipping the black detail.)
3) It performs automatic lit pixel concealment (or RPN - Residual Point Noise - in Sony-speak). This assumes that RPN on ABB is set to On in the Service Menu, which should always be the case. Having said that, it should be noted the automatic concealment will occasionally fail to conceal a lit pixel. When this happens, you have a few options :
A) Try multiple successive ABB passes, up to 8 of them in a row. I won't get in to how the algorithm works here, but that will often successfully conceal a reluctant pixel.
B) Try A above with a higher master gain setting, +6 or +12.
C) As a last resort, you can use the Manual RPN method provided in the Service Menu of the camera or the Installation Menu of the MSU 700/750 in the case of a Sony. This requires that you have a minimum of a D24 monitor connected via component output to the camera.
I do not recommend that anyone try this procedure unless they are very familiar with the process as one can make a lit pixel much worse by inadvertently selecting an adjacent pixel.
>The black balance "pixel fix" procedure, if your camera supports it is to >press the black balance button and hold until the VF notifies you that the >camera is doing more than black balancing.
I believe some cameras require you to black balance a dozen or more times before the pixel replacement software kicks in.
>Basically your camera sets levels of the three colors so that black is >neutral instead of blue black or red black, etc.
Exactly true. The color black can shift over time, the same as white can. A black balance resets black as being an equal balance of red, green and blue so that black is really black, and not a dark shade of another color.
Black balance can also affect other lighter colors in the image. I had an experience with an F900 where 3200k light hitting blonde hair looked green.
We discovered the black balance was skewed, and as soon as we corrected that the hair looked fine.
Often, excessive exposure to radiation can cause "dead pixels" or "hot pixels" :
Avoid air shipping unprocessed film and sensitive electronic gear during periods of intense "solar storm" activity, as cosmic radiation is more intense at high altitudes:
EI Customer Technical Services
Eastman Kodak Company
John Pytlak writes :
>Avoid air shipping unprocessed film and sensitive electronic gear >during periods of intense "solar storm" activity, as cosmic radiation is >more intense at high altitudes :
Will the shadow of the earth, by travelling or shipping on a night flight help block the direct rays of cosmic radiation? Or does this just get stirred up in the back eddies of the earth.
Director of Photography
John P. Pytlak wrote :
>Often, excessive exposure to radiation can cause "dead pixels" or "hot >pixels":
True for CCDs, but, apparently, less true for CMOS sensors.
Sorry, I'm not an expert on "space weather". I assume the answer is somewhere on the "Space Weather" website. I would assume the earth would somewhat shield electromagnetic radiation from a solar storm, so flying in the dark should help:
Here is an on-line radiation dose calculator for frequent air travellers :
EI Customer Technical Services
Eastman Kodak Company
Eric Adkins wrote :
>Will the shadow of the earth, by travelling or shipping on a night flight >help block the direct rays of cosmic radiation? Or does this just get >stirred up in the back eddies of the earth.
It will block direct rays, but some rays cascade in the atmosphere and follow the magnetic field lines of the earth towards the poles. So flights within a couple of hours of sunset/sunrise -- and depending on what latitude you are leaving and going to -- might not be considered 'dark' to cosmic ray flux.
Pacific Title Imaging