Manual white balance and set noise bug

spacewig

On January 15 @shian made the following comment:

"Also, with all patches, I've discovered that the manual white balance sample and set function (the next to last option to the right) creates noise. You really need to either use one of the presets or dial in the balance by adjusting the temp (last option on the right), using the sample white function to set white balance creates something similar to the ISO bug, insane noise."

which generated nowhere near the amount of discussion I think this issue deserves.

I do all my white balance with a gray card, and I suspect many of you do also. From everything I've read, white balance is a necessary step to achieving a proper exposure and capturing a neutral image. Without a gray card it is very difficult for me - a non-pro and with limited experience - to know if my image is properly white balanced short of my opinion of what i see on the LCD screen on the back of the camera.

For now I have the following questions and invite anyone with knowledge/advice/solutions to comment:

*Can anyone else confirm this problem?

*Does the manual WB sample and set issue reported by Shian exist in all patches/firmware or just the Quantum V7 patch?

*Does the camera white balance by changing color temperature only or does it also modify the settings in the adjust screen in the WB menu (which looks like a target with the following codes at the NSEW positions: G+, B, M-, A)?

*If one does a manual white balance with a grey card, what is the most accurate way of achieving the same results using the Temperature and Adjust functions (thereby eliminating the noise issue reported by shian)?

Thanks in advance for your help.

Cheers!

csync

It's my understanding that the GH2 uses per-channel gain to create a white-balanced image. This means if you are shooting with something that needs to be corrected a fair amount, you'll see some additional noise in the gained color channels. I notice it a lot more when using CFLs that green spike, because the other channels are gained up to compensate, than I do with shooting in daylight, for what that's worth.

A useful question might be: is it better to do this in-camera with manual white balance or to do it in post?

I haven't tried dialing a temperature manually, so I'm not sure if this would be any different. My guess is that if I changed the color settings and color temperature to match the 'white balanced set' function, it would look very similar in terms of noise.

spacewig

"I haven't tried dialing a temperature manually, so I'm not sure if this would be any different. My guess is that if I changed the color settings and color temperature to match the 'white balanced set' function, it would look very similar in terms of noise."

In other words, there is no way to get around the noise issue when white balancing?

Also, @shian mentions that there is not as much noise when using one of the presets. Does that mean that the preset doesn't correct as much or that they are not subject to this noise issue?

csync

For what it's worth, I also tested using the "Daylight" preset, which seemed to have just as much noise as using the white balance set function. If I have the time tonight, I'll try to run through all of the white balance settings. I wouldn't be surprised though if the behavior is a little bit erratic. That is, it probably depends a lot on the specific lighting setup that you're using and the ISO you're shooting. I don't know the specifics on how color channel gain is applied with the GH2, but it's certainly possible that, just like setting ISO, it depends less on how much gain is applied and more on the initial settings to which it is applied.

(sorry if this is a little bit obtuse)

Etb

Mmm maybe i'm wrong, but i have read somewhere in other pv thread that there is a bug in the special color jog mode (stills) that can affect all others jog mode in color profiles..

I remember that the solution is to use the reset or restor default in the special color jog mode

I hope i have been enough understandable ^^.

spacewig

@csync

I will actually be making a test shortly myself and post results. Perhaps if we pool our results/observation we can get a better understanding of this issue. I certainly thank you for any contribution you can make towards this end.

@etb

I have not used the color jog mode as I infrequently use the GH2 as a camera. But thanks for sharing the information. Perhaps someone has additional insight on whether or not this has any bearing on WB'ing in film mode.

spacewig

Following are frame grabs of tests I did white balancing with preset, gray card (sample & set) and temperature adjust. Perhaps some can analyse these and offer insight within the context of discussion....

spacewig

In all the images posted above you can see yellow stripes running horizontally across the wall, moving down to up (see attached picture). I believe they were caused by the fluorescent lighting which I did not correct for as I only noticed flickering in the dark part of the image (doorway of pictures on top row).

Would changing shutter speeds correct this? I was shooting at 1/50, I am in North America.

nomad

Mains is 60 cycles in America…

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