CMOS sensor

[Gunleik Groven]

as to the OP, Graeme stated a number of times - early on - tat silicone has a native response around daylight, and unless you have a filtering of the light, that will be the case for digital cameras.

From the cameras I have had the pleasure to examine, that sounds roundabout spot on...

[Graeme Nattress]

Native spectral response of silicon (so this applies to all cameras that use a silicon based sensor) is blue deficient. In as much tungsten light is also blue deficient, you could say that the sensor will produce an even white balance without correction at a colour temperature on the daylight side of things.

Native wb can be altered in a number of ways:

a) optically with a filter (possibly external or part of the OLPF/IR stack)
b) analogue gain
c) digital gain

We currently use digital gain as the optimum balance for our needs, but always re-evaluate this with every sensor design as part of our optimization process. Each sensor is different and behaves differently so it would be stupid to stick to one method dogmatically rather than do the proper evaluation each time.

Graeme

[Sidney L. Plaut]

Graeme,

I seem to remember in the Epic manual, that you should be able to see an evenly exposed image in ISO12000 in "false color / video" mode after you have black shaded - depending on
which color temp/ white balance and Gamma, I have not been able to go above iso3200?

[Christopher Barrett]

Thank You G!

Man. 80D used to be my go to filter when shooting daylight transparency in florescent. I'm gonna have to dig that thing back out for a test on my Reds.

[Blair S. Paulsen]

FWIW I have had better results with CTB filtration vs 80 series on digital. I believe it is because the mired shift of the 80 filters is designed for shooting daylight film stocks under tungsten which mandates specific photometric conversion properties and commensurate light loss. With a CTB filter you can move the color temp up the scale enough to improve channel balance without losing as much stop.

My typical usage is a 1/4 CTB filter when in a location where practicals play (or shooting available) with a 2700 - 3000K white point. The 1/4 moves me up to +/- 3400K which is back in the wheelhouse of the CMOS sensor/debayering algorithm and I only lose about 1/3 of a stop. You could make a case for correcting all the way to 5000K for "ideal" results but in many situations a filter that eats 1 to 1.5 stops creates overall underexposure issues that may lead to more pain than gain. YMMV.

Cheers - #19

[Graeme Nattress]

RED Colorimetry is defined by colour temp. If you use a filter to change the native colour temp, just beware that that is not how the colorimetry at that new colour temp was calibrated.

Graeme

[Blair S. Paulsen]

RED Colorimetry is defined by colour temp. If you use a filter to change the native colour temp, just beware that that is not how the colorimetry at that new colour temp was calibrated.

Graeme

Are you suggesting that the decode of my artificially shifted scene referred values via the 1/4 CTB filtration will be less accurate than if I had just shot 2800K clean and let the algorithm do the work? If so, that implies that the processing step adjusts the interpretation of the bayer data to create a more "pleasing" image even if some mathematical accuracy is compromised... If I am off base, I would love to know why.

Great chatting with you at NAB BTW.

Cheers - #19

[Graeme Nattress]

Not necessarily - just a "beware".

How it works is that we calibrate the colorimetry of the cameras under a wide variety of light sources, but as I mention above, we don't have any filters in the chain. We pick the appropriate calibration based on the one bit of info we have - the kelvin of the wb, which gives us the indication of tungsten, daylight, somewhere in the middle or "beyond".

In the extreme case of shooting tungsten light, but filtered to a ~6500k wb, you'd be using daylight calibration with what is still essentially a tungsten source, and I could well imagine the colours wouldn't be right. In that case you could set the wb back to 2800k or 3200k and then use RGB gain to adjust the wb and then you'd be using the correct calibration. But that's the most extreme circumstance.

In practical circumstances, you're shooting a warm light and leaving the image looking warm. You may be helping the sensor a bit with some filtering, but keeping the warm look. In that case I don't see an issue either way. Say you put some filtering on a tungsten light and cool it a bit, and wb neutral. You may still be absolutely fine as long as you're not changing the effected correlated colour temp by 1000's of kelvin.

Graeme

[paulherrin]

so basically, it's going to be best practice to nail the WB in redcine (or when shooting) and adjust other controls to taste from there. rather, than say - warming up your image by adjusting whitebalance. correct?

[Peter Lyons Collister, ASC]

Thanks for chiming in Graeme....

Now back to ACES