@sam_stickland try this - http://dl.dropbox.com/u/4235695/ColorChart1.mp4

But it'll be better once I've got some footage in a real environment with the chart in the shot for a few seconds.

OK, so just tested it using, same setup only with diffusion this time, manual WB by sampling, and it's still doing the exact same thing.

And tested it on unhacked GH2 as well, same parameters, same results. SO it's not a hacked matrix issue, it appears to be a GH2 issue.

I'm looking at the manual WB noise issue now.

@shian What does the MBR Color Corrector do with this footage?

http://www.mattroberts.org/MBR_Color_Corrector/

@nomad Which is why tungsten is a great light source for these kinds of tests. It's very stable, known and has just about the flattest spectrum emitted of any light.

jb

So you don't have a colour temperature meter to check against ? I think you should try to get your hands on one...

jb

@shian Couple of things to think about.

Do you have a colour temperature meter ? Because simply putting CTB on a tungsten light often won't get you 5600K. You have to meter it. It can also CHANGE during the day as heavy industry turn on and off the load on the electrical grid around you. You can get +/-30v on 240V near where I live. That can change the CT during the day as you're testing, even if you're metering it.

And for that matter, most of the time, uncorrected tungsten lights aren't ever 3200K in my experience. Variance in the age of globe, dust on the reflector and the operating voltage being not what it should be will all affect the CT of the light.

I just did some similar tests with the BMCC and the Tungsten lights I used were sitting at about 3000K. I ended up using 1/8 CTB on one lamp and 1/4ctb on the other to get it to 3200K at the target.

You should also try to diffuse the light. Although it might look like the light has an even field in terms of brightness, it rarely is across the field of the light it's projecting. Bouncing it and using multiple lights bounced then going through diffusion should even that out so that you know the exposure is even across the target.

So I use two lights and then bounce them into a 12x12 ultra bounce and then put that through a 12x12 1/4 grid. Also known as a WEDGE or BOOKLIGHT. Very flattering too for people FYI.

Bouncing light like this also warms them up, so again, this is where you need a CT meter to confirm you're getting what you think you're getting.

You also mentioned you used some "scrims" to "knock it down". So did you use scrims in one setup but not the other ? This will also affect the CT of the light shot to shot if you did this.

You should try this with multiple cameras to also eliminate variances in the camera setups themselves. Ideally you'd shoot two at the same time so you can then also match their operating temperatures (having turned them on at the same time)

You might want to consider looking at what OPTICAL CT correction filters do to the image instead of dialling in the electronic CT correction. Going the other way, many find they can get better results, especially with regard to noise by using an 80C or similar filter on a camera in daylight CT using 3200K lighting. Don't forget to allow for the exposure correction.

Many sensor CT native temps are 5000K, not 5500 or 5600k. Maybe look at shooting at that electronic setting as well. It might be the 5500 and 5600 settings are fudges.

It's interesting, although I wouldn't expect ANY camera to be perfectly matched doing this kind of exercise.

There are so many variables. I also find that the charts themselves are very hard to get consistent results from. They can be affected SO MUCH by the precise angle you hold them at relative to the camera and the light source. Try it with a grey card while you're metering or shooting and watch the values jump hugely.

Now I think the macbeth is an OK reference, but I've always found a grey card is more meaningful, because it has both grey and colour.

Also, take a look at what is probably the worlds worst website selling what I think are the world's best test charts. This guy makes charts mainly for machine vision cameras but also some photo applications. He has a nifty grey card that has colour opposite spots that when summed together make GREY, but they can more easily reveal a magenta - green shift. So many don't realise you can still hit a WB of 5600K but be massively GREEN or massively MAGENTA whilst still being spot on 5600K. WB only shows the white point, not the evenness of the spectrum. These cards reveal if there's a colour bias in your lighting. In other words, they more accurately reflect the evenness of the spectrum your test lighting is emitting because if a colour dot disappears or is more visible, then you know you have a spectral bias in the light you're using to illuminate the target.

http://fotowand.de/4958eng.htm

If you're in the US and don't want to try and order with the mainly german website then try the DOP shop.

http://thedopshop.com/index.php

jb

(and why is it that you yanks love 5500K and everyone else is 5600k ?)

I did not watch the video - but are you using Any Canis Majoris settings? These are known to use different formulas in the matrix than "normal" to achieve different results in different lighting.

@shian If the GH2's Daylight and Tungsten preset settings are giving you such different results then I'd try something like a Whibal card and perform a custom WB for each light source instead of dialing the WB. If the color discrepancies still exist then...???

I know you are reluctant about using custom WB with the GH2 because of noise but it may be worth doing a test in this case in order to see what's going on with the color shift.

FYI I use a Sekonic L-358 in incident mode and an 18% gray card for exposure. I'm well aware of the 12% versus 18% exposure difference. I ceased using gray cards for WB some years ago as I found different gray cards gave me different WB readings and that's why I bought a WhiBal card.

I'm also no expert in the field of video color correction. My background is photography (I'm new to this video caper!)

@shian I know you mentioned noise issues when setting manual white balance on the GH2 but have you ever used a WhiBal card or similar calibrated white balance reference card for manually setting the WB on the GH2? It appears many conventional gray cards are not totally color neutral.

I'd be interested to know if something like a WhiBal card for manual WB would still give the discrepancies you are seeing between the GH2's daylight and tungsten settings.

http://www.whibalhost.com/_Tutorials/WhiBal/01/