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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 :)

Dynamic Range in Redlog files

J

James Cawte

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I'm completely new to Red - and have just processed a few test shots for a DOP using RedCine to output DPX files - Redspace/RedLog. I am importing into a Nucoda Filmaster at 1920 x 1080

The files are looking good, but I am seeing more clipped highlights than I was expecting.

I have looked at the histograms and the whole dynamic range appears inside the histogram boundaries. So I think I am getting the full camera range.

What is the dynamic range of this camera in stops?

Should I advise the DOP to back his exposure off by another half stop?

What is the best conversion to use when outputting HD frame size from 4k- Linear or one of the others?

The pictures seem a little jerky on pans - camera shutter is 180 - Does a wider shutter angle smooth things out any.?

DOP is shooting Monday so I would really appreciate any advice.
 
not that we don't believe you but it would probably be helpful if you could post a still or two and its corresponding histogram from a screen capture.
 
Check the Nucoda is reading in the full 10bit range in the log data. You should be able to compare the highlights in Redcine with that in Nucoda, and if they're more clippy in Nucoda, you know where the problem lies.

Graeme
 
Thanks for the responses

The dynamic I'm getting in the Nucoda is identical to what I'm seeing in Redcine - so what I'm asking really is 'what is the dynamic range of this camera' -10 stops + like neg or (say) 8 stops.

I'll see if I can get some screen grabs up.
 
JPEG illustration attached to this.

JPEG illustration attached to this.

OK - Here's an Image and its histo from Nucoda

DPX frame exported REDSPACE/REDLOG from Redcine - no grade or LUT applied.

I can't get to Redcine just now, but this is identical to the way it looks there.

I was expecting the camera to do better in the highlights than this - any comments.
 
Your highlights look to be hard clipped in camera.

Dynamic range of digital cameras is such that there is a hard clip point, and below that, the data is captured. The data will get noisier as it gets darker. All digital cameras work this way. The dynamic range is the difference between the clip point, and at what point you say "it's too noisy". That is different for each user. The engineering dynamic range is at what low light level can we no longer distinguish any detail - that point is 11.3 stops below clipping.

Exposure on a digital system is all about at what code value in the 0-4095 linear light range do you place mid grey. Place it high, and you get a low noise image, but little highlight headroom. Place it lower, and you will get more highlight range, but at the price of a noisier image.

So, in that respect, all digital cameras have the same highlight range, as in none at all (because they hard clip), but you can always trade shadow range (of which you have lots) for highlight range by reducing the exposure. To view a "normal" image, for each stop you reduce exposure, set the ISO a stop higher.

At what nominal ISO did you expose your image at? Did you not see in the histogram that your image was clipping in the sky?

Graeme
 
Thanks so much for this Graeme, I didn't shoot this stuff- I've never even got sight of the actual camera!- just a drive that arrived by courier.

My take was that this was hard clipped in camera - I just wanted a second opinion. Advice to the DOP check your histo and you can afford to back off on exposure a bit to hold the highlights.- He knows his stuff, but it's his first time with the Red.
 
If he's using Build 16, he can use the raw view mode to see actual sensor clipping. if the camera's in Redspace view mode then clipping will show up before actual sensor clipping because Redspace gamma is higher than rec 709 or some other options.
 
Yes, some modes will show clipping earlier, which means the raw is protected. This is not necessarily a bad thing as it means you can make a mistake in the field, but still be protected in the RAW in post.

Graeme
 
BE sure not to be blowing out some data in Redcine, you can use the COLOR button to check if there is some info hidden there. THe old redcine clipped the last stop in the highlights, the newer version that supported build16 removed this issue, but the latest version seems to clip highlights again as you raise exposure. I hope they fix it.
 
In my opinion the best way is to open the RAW files in Redalert and check with the ZEBRA function the clipping. If there is some, reduce the Exposure setting a little bit and see if there is information in the highlights coming up....
 
It's simple. RA! started life as my little R&D app that went all the way back to Frankie, well before REDCine was even thought of. RA! now has a life of it's own, especially with Deanan's additions and Rob's underlying codec code.

Graeme
 
James Cawte said:
OK - Here's an Image and its histo from Nucoda

DPX frame exported REDSPACE/REDLOG from Redcine - no grade or LUT applied.

I can't get to Redcine just now, but this is identical to the way it looks there.

I was expecting the camera to do better in the highlights than this - any comments.
Click to expand...

This illustrates a disadvantage of working with 'pre-baked' rgb footage transcoded from .r3d raw - it's not possible to know for certain what is in the raw file from looking at a DPX.

While it does look like clipping in camera, it's also possible that there is more to be had out of the highlights in the raw .r3d. This may not be getting rendered to the DPX because it has been overlooked in the process out of RedAlert or RedCine, and it's not possible to get back to without going into an application like Scratch, RedCine, or RedAlert and looking for more in the highlights.

It's very beneficial to make some shadow/highlight decisions prior to debayer - at the very least to examine the raw footage in the highlights and shadows you one knows for certain what one has to work with.

I have extensive experience grading r3d footage. If I can be of any assistance, please feel free to pm me.

regards,

jt
 
Graeme Nattress said:
It's simple. RA! started life as my little R&D app that went all the way back to Frankie, well before REDCine was even thought of. RA! now has a life of it's own, especially with Deanan's additions and Rob's underlying codec code.

Graeme
Click to expand...

How about a single app combining Redalert and Red Rushes? - shot adjustments and batch output under one roof?
 
I still agree that RED stick to one software only with the inheritance of RA and RC features, both available for Mac and Windows. I don't know about the rest.
 
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