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Old May 1st, 2009, 07:30 PM   #1
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Strange WB results

Based on a suggestion from another member of this forum (Serena) I bought a set of Kodak 18% grey cards and I just tried a manual WB with my EX1. Something does not make sense.

The grey card read 4500K. Flipped the card over to the white side and press WB again and it reads 4000K. Closing the iris so the white card reads 50% and the CT reading is still around 4000K.

Unless I've missed something about the theory here the 18% cards are neutral grey and should give the exact same CT value as a white card. The spectral response graphs Kodak supply with the cards show close but not perfect tracking between the grey and white sides of the card, most markedly at the shorter wavelengths. Also Kodak suggest using the white side of the card for setting WB for video cameras.

Interested to hear any thoughts on this. When I have some time I'll try this under tungsten light. Not a big issue as the visual difference between 4000K and 4500K is pretty minor.
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Old May 1st, 2009, 09:42 PM   #2
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People on this forum expect way too much from those white balance #'s. They are just rough approximations . Likewise I'm not surprised that the color balance of a white surface and a grey one are different. Try comparing 2 ND filters.
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Old May 1st, 2009, 10:45 PM   #3
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Well, Bob has bought new Kodak cards which are made to a spec and that specifies very close spectral response from the grey and white surfaces. Bob's query has driven me out to check my cards, which are not new. In today's sunshine I got near identical WB on each side of the card (5100 & 5000), although my CT meter claims 4000 for the sunshine. We are in mid autumn with a diffusing clear sky (46S) and this isn't inconsistent with photo tables written for summer seasons, but maybe my elderly meter needs re-calibration (replacement doesn't seem worthwhile in the video age). There is a big difference using white printer paper for WB, this reading about 7000 on the camera and meter (the stuff fluoresces). My grey card is influenced a little by angle of reflection, so I was careful in setting normal to the lens axis. Also I set both to 50% brightness on the EX1 "meter".
Shooting a test card the colour balance looks right on vectorscope.
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Old May 2nd, 2009, 10:20 AM   #4
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Serena,
thanks for checking that for me. I'll conduct some more controlled tests, I was using the somewhat dodgy fluro lights in my office and I didn't consider that changing the angle of the card to the various light sources could make a differnece, duh!

Good point about the average piece of 'white' paper too. That's what I'd been using and after you jogged my memory about grey cards I thought I'd get a new set. My old ones faded away with my 35mm still camera, sigh.

Strange that more of us don't use grey cards. DSC labs had every chart under the sun for sale at NAB but didn't bring any grey cards. Seems I'm one of the few people to ask for one. Thankfully the Kodak ones are a heck of a lot cheaper than DSC's.
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Old May 2nd, 2009, 12:33 PM   #5
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I consider my purchase of the Vortex Media warm cards one of my smartest moves in obtaining a rich, warm look, particularly in interviews. They are not cheap, but then we are professionals are we not? We should have the best tools available, and I consider warm cards a must.
Vortex Media: VIDEO & PHOTO Tools and Training
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Old May 2nd, 2009, 02:19 PM   #6
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Sorry to be a curmudgeon about this subject, but all this discussion about the right card to use and buying a set of warm cards to bring on location so you can get exactly the right white balance seems to me both excessive and in the case of warm cards expensive. BTW - I do think getting a good (rich) white balance is important and worth taking whatever time is available.)

First, the best thing you can do to guarantee good color is a decent monitor. You can then adjust your color either by cheating your white balance or using in camera profile adjustments which are very fast and powerful on an EX-1.

Secondly, every professional cameraman I know carries around a 2" square gel swatchbook with 1/8- full CTO, CTB, and Minus Green gels available in seconds. You can use it on a piece of paper, a white napkin or whatever else is available and you can quickly dial in your white balance. (It does help to get used to seeing the difference between different white paper or sources.) Warm cards are simply copying this decades old practice.

Moreover in 25 years of video shooting I find that I routinely choose a combination of light CTB and minus green for my white balance - not currently available in warm cards. (That same combo can be preset into the EX-1 white balance function BTW)

There's nothing wrong with them, and I guess you can say they are more reliable than using different gels and different white cards all the time, but white balance is affected by so many issues - mixed light, the age of your bulbs, diffusion material, the angle of the card etc, that trying to be exact about the card itself seems misdirected to me. Usually you quickly cycle through a number of choices till you find something close. That and a decent monitor is all you need.

(Of course, if you have an engineer, scopes and a remote camera control, they'll pull out an expensive chart but then dial it in to taste anyway.)

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Old May 2nd, 2009, 06:11 PM   #7
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I shoot everything neutral and do any color adjustments in post. It's a lot more controllable.

It's sometimes harder to undo a color shift in post.
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Old May 2nd, 2009, 11:48 PM   #8
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It's a matter of opinion of course, but Hollywood sound mixers do adjust audio equalization as they record, and thousands of DP's worldwide use warm cards to get the best appearance on location ... I use warm cards, Tiffen filters, and other tools as I shoot. That's just me . . .
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Old May 3rd, 2009, 12:54 AM   #9
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Quote:
Originally Posted by Brian Barkley View Post
It's a matter of opinion of course, but Hollywood sound mixers do adjust audio equalization as they record, and thousands of DP's worldwide use warm cards to get the best appearance on location ... I use warm cards, Tiffen filters, and other tools as I shoot. That's just me . . .
That's also a valid approach. DP's often want to achieve a "look" that a colorist probably wouldn't have in mind unless he were on set. That's a true artist at work. And a gradient filter can do things which are sometimes impossible in post.
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Old May 3rd, 2009, 02:13 AM   #10
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Whatever is working for you is of course the best method and I don't mean to be a jerk about it, just that there are many ways to get a similar effect.

Dean if you are doing your own post or trust your colorist then neutral is fine. I don't generally do either.
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Old May 3rd, 2009, 02:20 AM   #11
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Leonard...

I'm my own colorist because this company is so small there's no one else available to do it. :-)

The one advantage of doing it all is understanding the potential pitfalls of the entire process, and knowing where one can (and can't) take shortcuts during production.
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Old May 3rd, 2009, 12:20 PM   #12
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Count your blessings. The rest of us are at the mercy of people who don't have time or the eyes to care as much as we would.
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Old May 3rd, 2009, 12:30 PM   #13
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Lots of different views on this ... I am basically an editor. I love the editing process, and have been doing it longer than some people in here have been alive (35 years). I edited film most of my career, having gotten into video editing only about 12 years ago. Since I am a one-man band, I do it all because I finance my projects with 'grocery money' and cannot afford to hire writers, cameramen, etc. I just find that I try to accomplish as much on location as I possibly can, including lighting, WB, etc. I am currently producing an extensive documentary in which I have already interviewed over 70 people, all indepth interviews, and all interior lighting. The warm cards have paid for themselves many times over, just on this one project alone. I also highly recommend the Chimera window patterns. They have saved my butt in many empty hotel banquet room settings. CHIMERA Window Patterns

Good luck to all of you, and your views on filmmaking. And remember, there are no stupid questions.
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Old May 7th, 2009, 02:10 PM   #14
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I bought and I tested the gray card NOVOFLEX, measuring the difference of gray and white is 150-200k is very good quality.
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Old May 7th, 2009, 05:34 PM   #15
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While I've never trusted my Kodak grey card from the start, it did measure up to a calibrated WhiBal grey card. I searched the Kodak site for specs on the grey and white cards. While they do list their cards as neutral grey, I don't see any manufacturing numbers. Paper ages easily with light exposure, and I wouldn't be surprised if one side aged faster than the other. Just leave a newspaper out in the sunshine for a day and compare it to a copy that didn't receive the sun exposure. I'd put my trust in plastic (Whibal) over paper for white balance.
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