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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Exposure 101...

Thank you Christian. Can I call them School Zone lights? :)

Is 18% the specific intensity of the famous "gray card" I always hear mentioned? I would love to really understand where the 18% comes from and why it would be good/popular choice for a simplified false color with only five levels.
 
Daniel Browning said:
I don't know. You might be interested in Thom Hogan's article about it.
Click to expand...

Oh!

"On printed material, it's claimed that the half way point between black and white reflects 18% of the light. So a neutral gray (not whitish or blackish) is 18% gray."

So 18% gray would be your middle point, which could be a useful reference to have, especially if you only had clipped on both ends and something like 5% from them.

Thanks for sharing, it is an interesting article. I have been itching to buy a cheap meter to play around when I am shooting something myself.
 
And 18% grey isnt in Zone five with Red? Or why should I adjust a lower ISO than 320 when using a lightmeter? Is it in Zone 6?
 
Historically, 18% is treated as the mid grey point because, as the article Daniel referenced points out, it's the mid-point between black and white. But digital systems often see mid grey as a somewhat lower value - like 12~13%, there's some variation to that, but it's typical that they hold mid grey a bit lower since it's easier for digital systems to dig info out of the dark than it is to not clip the high end. Many light meters also don't see mid grey as an 18% equivalent. Or at least not right out of the box...

Regardless of that, 18% is still a good value to identify with. After all, it is the true middle grey value within the visible spectrum. With REDCODE RAW it's nice because it's a known quantity - lots of 18% grey cards out there.

The article Daniel referenced is also dated -- nearly 6 years old. It doesn't seem to take into account that several newer RAW acquisition systems effectively shift their mid-grey point by altering the ISO adjustment, as is the case with RED RAW. As for meters, this is precisely the reason (or one of the main reasons) why newer and better meters have software for building metering profiles. ...Sekonic 758 for example.
 
Red team, would it be possible to have one button assigned as a 'color preview mode', from which to use the scroll wheel to switch between different modes? This way it would be really fast and easy to switch between black and white and false color, different meters/histograms etc. I'd especially like to use it to quickly change between false color, raw and edge highlight.. There are quite some handy tools in the camera to help us operate properly, but I still only use a few of them simply because of the time it takes me to go through the menus.
 
Sidney said:
whoa - David could you explain what you mean by white not being 100%? -
Click to expand...

In broadcast video terms, "white" is often limited to 100 IRE, though some cameras record beyond that. But in a 10-bit LOG recording, like in PanaLog, often "white" is set at 70 IRE to allow more overexposure information to be recorded. Then when you create a LUT or convert the image to broadcast gamma for viewing, you set white back at 100 IRE but you can use knee compression to fit overexposed detail back down into that range so it's not clipped-looking.

So people looking at LOG images on a waveform often make the mistake of thinking they are underexposing because white, like on a grey scale, is not hitting 100 IRE. So they overexpose until it does, which is why suddenly they think a 400 ASA camera like the Genesis is a 200 ASA camera, when it isn't.

I don't know how a RAW signal converted to color is supposed to look on a waveform, but most peoples' impressions of a RAW file is that it "looks dark" because it puts middle grey and white lower down than a broadcast video signal would.
 
David,

Let's say i set my camera to record whites in full sun at 70 ire (at least what the meters are showing).
Is that what Graeme calls "nominal white" ?

If so, 30 ire are left for headroom (very bright metal objects etc...)
Sounds a lot...no ?

And it sounds a lot like REDSPACE gamma does (shows for monitoring) compared to REC709 gamma.

Would like to learn more about this. :)

thanks!

Antoine
 
David Mullen ASC said:
So people looking at LOG images on a waveform often make the mistake of thinking they are underexposing because white, like on a grey scale, is not hitting 100 IRE. So they overexpose until it does, which is why suddenly they think a 400 ASA camera like the Genesis is a 200 ASA camera, when it isn't.
Click to expand...

I've met a couple gaffers who like to say that about the Red right now, but I always suspected they're methods for determining that would not mesh with my own. I would definitely not agree if they were going off methods you describe above, or some other camera based 720p out/waveform/video centric method.

These days I'm realizing I like the look of the camera better at 500 or 640...I'm beginning to not prefer the grainless look.
 
Patrick Tresch said:
I've even heard of dop working with an astro when shooting with a RED ONE...

... no comment.

Pat
Click to expand...

Quite a few actually. Is it a Swiss thing ?

Actually, it can be usefull, but must be used with precaution.

Cheers,
Damien
 
Ok, great. So RAW traffic lights does away with the potential for issues and mistakes, easy enough.

Could someone now please explain to me what the application would be for the color space guidelines.

I think I get the idea: If you know you will work with certain limitations and don't want to tweak everything in post it would be useful to know what those would be... right?

And for those of us with time to tweak would always benefit from filling the full histogram so as to capture the most info possible with the given bits available and later squeezing all of it into your final output... right?

A better explanation (or correction) of this would really help me.
 
Stuart English said:
I'd recommend that you set up Zebra for shadows to match the False Color Exposure Meter overlay.

Which would be LO = 0 IRE and HI = 5 IRE which is Dark Blue and Medium Blue.

Or set to the next higher pair of colors which would be LO = 2 IRE and HI = 8 IRE
Click to expand...

For my own projects I shoot VIEW RAW only and prel. grade in RED ALERT (at least my offlines/FCP), RED SPACE / RED SPACE.

For shadows I set LO = 0 IRE and HI = 14. Because 14 and below is where noise starts to show. At 14 it is no where as ugly as at 5 or less but it still provides a fast overview of where one must start watching out for low light compression artifacts. And if possible make more light, artificial or natural. For small projects it really simplifies matters in post.

For highlights I put LO = 103 IRE and HI = 108 IRE. Like many others have written, it makes most sense to me to expose just before clipping where the reds start to show. It is still possible to bring the exposure down in RED ALERT.

For some outdoor high contrast scenes FALSE COLOR (VIEW RAW) can work like a ”canvas”, where (at the touch of a finger) one is able to expose in such a way that the red level (clipping but not dead) very vaguely shines through (sort of like red noise) the orange one. I say "very vaguely" because more than that kills the scene. It has saved my shadows from unwanted noise and if used correctly the DRX tab in RED ALERT will recover any lost detail in the highlights.

/Calle
 
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