White balance issue with the BMPCC4K

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Minduck

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White balance issue with the BMPCC4K

PostSat Jan 05, 2019 10:01 pm

I notised that my white balance was every time slightly off hit the BMPCC4K.
So I made a test and placed a greycard in my room to made a measurement.
I had a color themerate of 4100K in my room, I messured with a app and also made a test whit the GH5 and both set the WB correct. But the BMCC4K sets the WB on 2800K.
Can someone help me? Did anyone have the same issu?

Tanks
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rick.lang

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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 1:17 am

Interesting because I thought some others had reported their scenes were too yellow. In your situation, that setting would make things look too blue. I wonder if doing a factory reset would help if you are on the latest firmware.


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Australian Image

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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 1:22 am

I've been doing grey card and Munsell colour chart tests and the colour temperature comes out fine. That's with LED downlights as well as daylight.
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John Paines

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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 1:28 am

There are two odd behaviors with AWB. Where the scene temperature is 5000 or up, AWB can sometimes return an inaccurate value of 10000. When the light is around 4000 or less, 2600 is the incorrect setting. The 10,000 thing is intermittent, comes and goes for not apparent reason, but 2600 seems to be fairly reliably wrong with tungsten.
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Jamie LeJeune

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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 3:55 am

John Paines wrote:There are two odd behaviors with AWB. Where the scene temperature is 5000 or up, AWB can sometimes return an inaccurate value of 10000. When the light is around 4000 or less, 2600 is the incorrect setting. The 10,000 thing is intermittent, comes and goes for not apparent reason, but 2600 seems to be fairly reliably wrong with tungsten.


I haven't seen that so far the few times I've relied on AWB, but I haven't tested it extensively either with the pocket 4K. I'll make sure to test AWB more thoroughly and will report back.
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rick.lang

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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 4:03 am

Thanks, John and Jamie. I usually just set a custom white balance rather than use the AWB. Using CWB, tint may be harder to estimate than temperature, but as long as you’re in the ballpark, you’ll be fine adjusting in post. But I’m not shooting under the stringent requirements for white balance that may constrain many others.


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Minduck

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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 5:44 pm

I reseted the camera, but the issue remains.
I also tested it whit my Aputure 120D II (6000K) a few times, the nearest I get with the BMPCC4K was 5800K, most of the Time it sets the WB to 5200-5400K.
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Minduck

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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 5:45 pm

rick.lang wrote:Thanks, John and Jamie. I usually just set a custom white balance rather than use the AWB. Using CWB, tint may be harder to estimate than temperature, but as long as you’re in the ballpark, you’ll be fine adjusting in post. But I’m not shooting under the stringent requirements for white balance that may constrain many others.


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I testet it also whit my Aputure 120D (6000K).
The nearest I get was 5800K but most of the time it sets to 5100-5400K.
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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 7:51 pm

Minduck wrote:I also tested it whit my Aputure 120D II (6000K). The nearest I get was 5800K but most of the time it sets to 5100-5400K.


But which one is accurate? The Aputure 120D II is rated at 5500K, the previous model was 6000K, according to Aputure. So if the camera sets to 5100K-5400K, then it's pretty close given the inherent variations in LED lighting modules. The only way that you could confidently test the colour temperature is with a colour meter.
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Jamie LeJeune

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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 8:00 pm

Minduck wrote:I testet it also whit my Aputure 120D (6000K).
The nearest I get was 5800K but most of the time it sets to 5100-5400K.


You're assuming that a cheap LED light is going to be producing light at the exact kelvin at which it is rated. That's rarely ever the case. Plus, LED lights have spectral spikes that also affect the read. And, even tungsten and HMI bulbs aren't exact and will drift over time as they age. So, no light is going to be exactly a specific temp or tint. For example, before a professional film shoot with multiple HMI lights, one of the prep tasks is to use an accurate color meter and determine which gels will need to be added to each light to bring them all as close as possible, and even then it's ballpark, not dead on. This is the case even for the most expensive ARRI HMIs of all the same model as the bulbs are never the same exact temp and tint.

Also to note is that unless you're in a completely neutral grey environment, the color of any light bouncing off the environment will definitely affect the color of the light reflecting off the grey card.

All this stuff is somewhat relative rather than absolute. That said, I do find that BMD's auto white balance sets the temp and tint quite well if I point it at a grey card.
If you are using different light sources or needing to make sure a white background is really reading as white, I recommend checking out this article by Art Adams on using RGB parade for matching and balancing lighting temps + tints on set:
https://www.provideocoalition.com/art-manual-white-balance/
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joe12south

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Re: White balance issue with the BMPCC4K

PostTue Jan 08, 2019 9:51 pm

I happened to test just this with both the P4K and GH5. http://www.pocketluts.com/matching-the-pocket-4k-gh5/

Whether by AWB (grey card) or manually entering the WB, the P4K white balance and tint was more accurate to the sensor reading. (The GH5 has a slight green cast, the Pocket 4K has a very slight magenta cast.)

Unless you're trying to match the two shot for shot, the variance is pretty small, and even that is easy to correct out. I made myself a LUT to do just that.
Pocketluts: Purpose-built LUT system for the Black Magic Design Pocket Cinema Camera 4K
http://www.pocketluts.com/

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