trying to get a handle on false color and IRE

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NathanCole

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trying to get a handle on false color and IRE

PostSat Jun 16, 2018 4:47 pm

Hi, and thanks in advance to so many of you who have provided great information in these forums about the topic of exposure, IRE, false color, etc. As a relatively new video shooter (from a photography background) I'm trying to make sure I understand the lay of the land.

I know that there is a spectrum of opinion about how to set exposure on these cameras (I have the Ursa Mini Pro), so I want to know how wide that spectrum is!

I like using false color on my monitor, and from the Blackmagic manual, it looks like middle grey is placed at about 38 IRE , is that right? And skin tones one stop up from that, which on their scale appears to be about 50.

Since I shoot with green screen, I most often read advice to put skin tones at 70 IRE and the screen at perhaps 60. This is well above the false color scale given by Blackmagic, if I understand it right.

I'll admit that it seems a bit strange following the Blackmagic false color recommendations for a shot, then looking at the histogram and basically seeing nothing in the right half of the histogram (which would make sense if my skin tones at 50 IRE are the lightest thing in the shot).

So is it just two different techniques or opinions, putting the skin tones closer to 50 or 70? Just want to make sure I'm using my new equipment to its fullest!

Thanks,
Nathan
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John Brawley

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Re: trying to get a handle on false color and IRE

PostSun Jun 17, 2018 11:40 am

NathanCole wrote:Hi, and thanks in advance to so many of you who have provided great information in these forums about the topic of exposure, IRE, false color, etc. As a relatively new video shooter (from a photography background) I'm trying to make sure I understand the lay of the land.

I know that there is a spectrum of opinion about how to set exposure on these cameras (I have the Ursa Mini Pro), so I want to know how wide that spectrum is!

I like using false color on my monitor, and from the Blackmagic manual, it looks like middle grey is placed at about 38 IRE , is that right? And skin tones one stop up from that, which on their scale appears to be about 50.

Since I shoot with green screen, I most often read advice to put skin tones at 70 IRE and the screen at perhaps 60. This is well above the false color scale given by Blackmagic, if I understand it right.

I'll admit that it seems a bit strange following the Blackmagic false color recommendations for a shot, then looking at the histogram and basically seeing nothing in the right half of the histogram (which would make sense if my skin tones at 50 IRE are the lightest thing in the shot).

So is it just two different techniques or opinions, putting the skin tones closer to 50 or 70? Just want to make sure I'm using my new equipment to its fullest!

Thanks,
Nathan


I always say exposure isn't right or wrong. It's a choice.

What FC gives you is an INDICATION about exposure, but you still have to interpret that information.

For example, if you are looking at skin tone being about a stop higher than 50% (IRE38.2 from memory in LOG) then you have a good rule of thumb.

But.

What skin tone are you shooting ? An indigenous fellow from the deep outback of Australia or a Scandinavian hacker that never sees daylight.

Using your FC exposure tools, you 'd be dramatically altering the camera exposure to put those two disparate reflectivity's in the same FC zone.

What about if you have a dramatic scene where you want some lighting darkness and mystery. It makes no sense to be able to see someone's face at all then.

You have to use your common sense as well.

I find a histogram very not useful because it's a tool that works for stills photographers, but not so well for those of us in the always dynamic changing world of motion imaging. It's great if you like to follow the expose to the left theory, but that doesn't really work very well for motion work. It can create great difference sin shot to shot exposure and then when edited together you'll have a very difficult time trying to grade them to match. Something that still shooters don't really have to do.

That said, I tend to underexpose a little with Caucasians by about a stop as a starting point of where FC says you should expose. I carry this practice over from shooting Alexa.

JB
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Ben Johnston

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Re: trying to get a handle on false color and IRE

PostSun Jun 17, 2018 2:13 pm

Hi Nathan. JB gives the true picture above. But just to respond to your points about IRE values...

Traditionally, lighter skin tones around 70 IRE was a general target for broadcast video. However, assuming you're shooting in 'Film', the shots from your camera are designed to be adjusted in post production before they're finished. If you shoot ligher skin as you describe, then apply the stock 709 LUT to the shot, you'll probably see the skin jump up to somewhere around 70 IRE. In other words, you're not monitoring the finished image.

You could experiment with a few different exposure and post-production combinations for your green screen set-up, then stick with whatever works best. You could also try shooting in 'Video' and see if that suits you better.

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