False Colour and Exposure confusion

[David Litchfield]

Can someone explain to me why I can get the RAW image to show clipping when using Exposure check, but when I then do False Colour in Redcolor nothing shows as clipping? If the sensor is clipping, Redcolor should definately show clipping. Its confusing and nobody I've worked with understands this either.

Cheers

Dave Litchfield

[Jaakko Rinne]

One possibility is that exposure check shows absolute clipping at the sensor level while false colour uses relative RGB values with the current gamma curve/ISO/etc. So if your RGB signal doesn't go to 100%, it won't show as clipping. Don't know if that's the cause, but at least to me it would sound like a plausible scenario.

[Stuart English]

One possibility is that exposure check shows absolute clipping at the sensor level while false colour uses relative RGB values with the current gamma curve/ISO/etc. So if your RGB signal doesn't go to 100%, it won't show as clipping. Don't know if that's the cause, but at least to me it would sound like a plausible scenario.

Yup that's essentially it. The role of the FLUT color science is to map the RAW sensor data into legal RGB space... you see the same thing on the camera.

[David Litchfield]

Thanks for the response guys. Lets see if I understand this correctly! If I've got a window thats blown out, the sensor is clipping but that is mapped to a legal RGB space so it shows it as 100% white. False Colour won't show it as clipping because its been brought within the legal levels?

If we're sticking with Redcolor for our workflow, surely this renders false colour useless as an exposure tool? The window is now within legal levels but its got f' all detail in it! That just doesn't make sense to me. It should still show that area as clipped. If i want to get a little bit of detail in that window and expose it just below clipping, false colour cannot help me in the same way that the exposure check in raw can.

[Stuart English]

The explanation of the above is the VIDEO (i.e. RGB) false color overlay is NOT an exposure tool. It's a video output level indicator, valuable when you have broadcast oriented work - such as live HD-SDI feeds and / or when you need to exposure primarily for skin tones, and the FLUT color science rolls off the highlights so that you don't create hard clipped whites. On the other hand the EXPOSURE (i.e. RAW) false color is overlay IS an exposure tool. Simply stated if you don't see red in the frame when you have this selected you are not clipped at the sensor level and therefore everything in that scene can be mapped into RGB space w/o clipping either.

Does that help ?

[Scott Crawley]

Sorry Stuart,

But I'm more confused about the VIDEO overlay now than I realized before reading this thread. It's not an exposure tool but it is useful "when you need to (check?) exposure primarily for skin tones..."? What are you saying here? It is not a general exposure tool but a task specific exposure tool for mid range values only?

The explanation of the above is the VIDEO (i.e. RGB) false color overlay is NOT an exposure tool. It's a video output level indicator, which valuable when you have broadcast oriented work - such as live HD-SDI feeds and / or when you need to exposure primarily for skin tones, and the FLUT color science rolls off the highlights so that you don't create hard clipped whites. On the other hand the EXPOSURE (i.e. RAW) false color is overlay IS an exposure tool. Simply stated if you don't see red in the frame when you have this selected you are not clipped at the sensor level and therefore everything in that scene can be mapped into RGB space w/o clipping either.

Does that help ?

[David Litchfield]

Thanks Stuart,

I understand all that, I just don't think its logical. You have 2 colour overlay modes each with a different logic. How can you say VIDEO false colour is NOT an exposure tool and then say its used for skin tone exposure, and presumably the other colours that are represented. Every Epic/One manual I've read would suggest it is an exposure tool. What would be the effect or harm of adding the red clipped colour to the VIDEO false colour overlay so that they match up with the raw?

Cheers

Dave

[David Litchfield]

I guess what I’m experiencing is counter to what I expect.

If I was shooting on Alexa I could look at the rec 709 view and think its really contrasty and the whites are horribly clipped, but I’d be safe in the knowledge (and could check) that on the LogC recording the highlights are looking fine. So I’d feel like my LogC is getting more of the sensor data and is a bit of safety net for those highlights.

That's how I feel about a RAW image. Its getting me more than the baked in rgb look does. But the overlay modes can suggest the opposite. If I was just going on the false colour alone, which a lot of dops are used to, its perfectly reasonable to think your exposure is fine because there are no Red warning colours, but the reality is you could be clipping without realising it. Therefore getting less of the sensor data than you think you are.

The solution then is you have to use 2 different overlays for one goal. Please just add red to false colour :)

[ericyoung]

It's been this way ever since FLUT was introduced, so if it changes, it needs to be announced prominently, otherwise lots of people will be confused all over again!

Rather than add it by default, I'd suggest an additional option tick box in False Colour menu. Red VIDEO (RGB) "clipping" would actually be indicating that FLUT was coming into play rather than clipping, as by definition FLUT makes hard video clipping impossible.

[Martin Stevens]

There already is RED in the VIDEO false color overlay.

Even the Epic Manual shows red as a color for Super white at 108-109 IRE