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Color shift on SONY DSR500


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#1 Jonathan Bryant

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Posted 02 November 2005 - 08:41 PM

Just recently I noticed a color shift when I switch between say auto white A and the preset even if they are both set to the same color temperature. Say I white balance on a at 3200k and then switch to preset which is at 3200k there is a obvious color shift when it should be the same since both is set for 3200k. On the DSR500 you can set the preset white balance to any color temp manualy which comes in handy with flourescents and such. I reset the camera to the factory presets yet still the preset white balance colors look bad. Should I be alarmed and send this to SONY to get maintaince?
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#2 Laurent Andrieux

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Posted 02 November 2005 - 09:06 PM

Is this color shift in the green/magenta cast ?

You see, when you make a balance the color temp value that appears in the VF is very unprecise, and, more than that, it won't tell you what correction is made on the green channel.

Color temp itself is based on the relative B/R values, but the balance is actually made on the 3 channels.

Having the information of a 3200 K temp when you make a balance doesn't mean your light matches the preset values, that are the ones of a standard 3200 K light with no green or magenta shift.

The first questions that come to my mind as to try todetermine if your camera has a problem would be :

- Are you sure you made this test and found this problem in a regular 3200 K Tungsten light (new bulbs, correct power, no cast due to reflections on the set, no neon bulbs not discharge lamp of any kind (they have green / magenta unregular casts)
- Does the preset value give you a good image in regular 3200 K tungsten light ?
- Does the white balance give you a good image anyway (even though it's a bit different from the preset) ?
- Is the image better in the preset position or when you do the manual white balance ?
- Do you have the same problem in every different filter position ?
- Is the cast mainly visible in highlights or does it affect especially the shadows ? If so, make a black level balance before the white balance, check that the iris fully closes to the 'cap' position when black level is operating, if not, give it an help closing properly when the automatic shutter tries to go to the capped position
- mind that the values manually computed are not necessarly reseted by the menu reset, esp. the white balance manual settings...
- Do you have a waveform/vectorscope ? if so, check on a white card what position is the best



Regards
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#3 Jonathan Bryant

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Posted 03 November 2005 - 11:51 PM

It is more in the highlights. Under tungsten lights and on preset at 3200k it is alittle more red than when i auto white balance to 3200k. Both are on filter one with a black balance. It was really noticeable when I was filming football at low tempertures the last 2 fridays. The stadium lighting white balances at 3700k but numerous times before I had have luck changing the preset to say around 3800-3900k to instead of using the auto white at 3700k. This gives me a picture that is a tad bit warmer and true to life in my oppinion without the warm cards. But now the any which way I adjusted the preset it was either too magenta or too green. The preset 3700k was way off from matching my auto white of 3700k why is that?

Thanks for your help. I love the cinematic movies you have done with dvcpro. Which model camera do you use?
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#4 Laurent Andrieux

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Posted 04 November 2005 - 05:14 AM

Magenta / red casts are pretty close, by eye, and it's not obvious to distinguish without a vectorscope, esp. when you have green casts due to the lighting...

So it's not easy to say if your different problems are actually related to one only or if it's more complicated than this. I would not take too much a valuable conclusion from what happens in such weird/special light as a stadium lighting. Who know if they changed the bulbs recently, or if the electrical power asn't changed for anyspecial reason etc.

Do your test under known conditions, anyhow.

Check your reset value and your monitor as well...

If you still notice the problem, I'm afraid you should give it a full check-up, as far as I know...

Off-topic : The work you refer to is only a student job that I coached (students don't drect, only do the technical jobs). We used AJD 610 Panasonic DVCPRO 25, and Philips LDK 140 DVCPRO 50, basically.
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