8 1/2 STOPS - latitude color grading chart

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boothba

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NOTE: 8 1/2 STOPS is the range of this test - not the range of RED's sensor. I would change the title of this thread if I knew how, as it has caused some confusion.
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This is a more thorough latitude test using some of the recently posted David Stump color charts.

Based on his notes I graded the base stop of f16 and then attempted to match that grade for f4, f5.6, f8 & f11 (for 4 stops of overexposure) and then f19nd.3, f19nd.6, f19nd.9 & fnd1.2 (for 4 1/2 stops of underexposure) - note that the f22 series were not posted at CML so I had to jump a 1/2 stop to the f19 series. All images were graded on discreet Inferno v5.54 using the original Color Corrector (not the Color Warper) - primary color grades only, not secondaries (or color grades through keys). All images processed at 1920x1080 from a scale/crop of original 4.5K.
 

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PART 2:

This is similar to a CML comparison test featuring the Viper, the F900, Fuji F400 & 5218 film stock. Here:
http://www.cinematography.net/Pages GB/Film-Digi-comparison.htm

Consider this a 'quick 'n dirty' layman's analysis until Mr. Stump's findings are posted. Nonetheless, based on these images I would conclude:

1.) Red's ability to handle underexposure is exceedingly good - to my eye notably better than the Viper, F900, F400 & 5218 tests above. 2 1/2 stops under grades nearly identical to base stop, with very little digital noise. Likewise 3 stops to 3 1/2 stops under should be passable for a 2K or HD finish. 4 1/2 stops under shows more pronounced noise and warmth, but with secondary color grading & degrain filter it could certainly pass for a SD finish - even 720p finish. Ultimately the extremely low noise of RED is as important as the native latitude when digging deep into shadows - much better than 90+++% of film scans that I've dealt with.

2.) Red's handling of overexposure is less impressive on these images - surprising given what we've seen on the Porsche and milk shots. Mild clipping occurs at 2 stops over - but nothing major. Above that the clipping increases and the green channel and less saturated colors tend to go rather quickly. Also curious is that the extreme highlights seem to get overstepped by the near-highlights during overexposure. The good news is that Mr. Stump has indicated his belief that there may be an additional stop of latitude in the highlights by tweaking the existing color matrix.

3.) Based on these latitude tests (and until things change (count on it)) I would probably choose to underexpose a half to full stop when faced with tricky shooting situations - like a back lit actor against the sky with sun in frame. I think the sky would blowout long before the actor's face would get irreparably crushed.

4.) I've heard a few complaints that the images (and specifically the blacks) are milky - but I would argue that this is vastly preferable to having an aggressive matrix that crushes the blacks in camera. There is an enormous amount of retrievable data in the toe of the film (er,... digital image...) that the colorist can sculpt to his pleasing. Crushing the blacks will likely be the easiest damn thing to do in RedCine so no-one should complain. In digital cinema - FLAT is GOOD! Don't believe me? Check out a dMin/dMax 10 bit log scan for feature film DI and fx work. Or shoot a nice piece of 50ASA film and do a sensitometry test - or toss it up on a telecine bay at default settings and see what you get. Even telecine one-light transfers tend to add significant contrast so most folks are not really used to looking at pure film.

5.) Last point: regarding the color tearing at the right of frame in the darker exposures - we all know that this was a synch issue caused by a pinched cable - riiigghhhtttt???? - so no need to make Jim or Greame take the time to explain it again - riiiighhhhttt?????....

Well that's my two cents. I'm really impressed by these latitude tests - and if David is correct about possibly improving the highlights, RED should be ready to shoot black bears in the arctic - or deep-cave spelunking, incandescent albinos - or whatever.... Finally, If anyone would like a much larger version of the attached comparison chart (or the individual HD stills) let me know - I had do down-res for hvxuser specs.
 
boothba... well said. We also believe we can improve the "over". And we also agree, along with other experts, that this camera can safely be set at ISO 320 to protect the top end without consequence. The lack of noise in the sensor helps in so many ways. We also agree completely that flat is good. It is easy to "snap up" the image from flat. Impossible to go the other way.

Jim
 
Remember there's no black offset calibration, hence the milkyness. Five seconds in a grade will fix that, and you won't see that anyway on camera raw or RGB images anyway.

We're still working on tweaking out the sensor. Also, remember dynamic range is the inverse of signal to noise ratio. With a digital system, nothing stops you clipping off the top, but you can just keep going down until you hit the noise floor.

Graeme
 
This sensor though is more like a 5K sensor though is it not? What happens to the light sensitivity when you look at the production 4.5K chips? Surely being less tightly packed with light receptive electronic thingies the light sensitivity will increase?

If it does increase how might that effect the latitude?
 
My bad - thought the test bed model was the only one with the sensor of 4.9K.

Got my memory wires a bit crossed.
 
Brook Willard said:
Is the extra .4K visible in the EVF as overscan for the operator's sake?
Click to expand...

This is a correspondence between Jim & Florian Stadler on the CML list:

"I want to see what's going on outside the frame lines.
I want to be able to spot that cable that's not hidden well enough...."

Florian Stadler, D.P., L.A.

You have that ability with RED. If you are shooting 4k, you WILL see 4.5k outside the recording area.

Jim

Jim Jannard
www.red.com
 
Hey Boothba, thanks for the post.

It's cool that we can now skip technical numbers (like 10-11 stops of latitude) and get to the point of actual useable latitude. 8 and 1/2
stops of actual latitude is awesome, and something I can believe in. As it stands, it seems that the latitude is on par with film, and won't dissapoint anybody who is tired of video cameras clipping.

The thing that you can underexpose almost 3 stops without sacrifice (especially for SD or maybe even HDTV) is great! For music video production, that ends up on the small screen, has limited budgets, and a very high quality demand, I can't think of a better feature.

Good work with the tests, and thanks for sharing!
 
David Stump determined that the Mysterium sensor is ISO 200, but he and many other experts will likely recommend shooting at ISO 320-400. That gives a ton of room for the highlights to survive and plenty of elbow room for a beautiful clean image.

Jim
 
Jim, do you think we can make it to 11+ f-stops of latitude DR when the camera is done next year?
 
There is a big difference between dynamic range (11+ stops) and exposure latitude. Somebody else step in and explain it. I'm tired.

Jim
 
Please do.

I am a little confused. If exposure lattitude and Dynamic Range are different terms, but we still speak of them in 'stops' lets talk about other cameras in terms of exposure lattitude for comparisons.

So far I've only heard about other cameras and film lattitude being described in terms of DR. For example, the HVX i think has 7 stops from what I've read, film 11 stops or more, I heard someone say they pushed a varicam to 10-11 but I find it hard to believe it's anywhere close to film's lattitude.

I dont mind which term is used, but it would be nice to have a reference for comparison. If Red has 8 1/2 stops of Exposure lattitude, what does a HVX have, film, and the current crop of high end HD cams?
 
Darkline, I agree. I could be wrong here, but isn't DR is Signal to Noise Ratio, it means how much you can keep exposing light from noise floor 'till you get saturated/maximum signal. Exposure Latitude is how many stops of exposure from dark 'till you get highlight blows out. So what is the difference? Is that DR by its definition?
 
Jannard said:
There is a big difference between dynamic range (11+ stops) and exposure latitude. Somebody else step in and explain it. I'm tired.

Jim
Click to expand...

Hi Jim,

I will try!

Latitude is the amount you can over or underexpose and still get a good result.

A scene with a 7 stops of dynamic range, could in theory be over or underexposed by 2 stops and stay within the range of a sensor that had 11+ stops of dynamic range.

On a bright sunny day there may be in excess of 11 stops of dynamic range, so exposure accuracy can be very important.

Stephen
 
Boothba,
Your gradings of the original test chart frames were interesting and provided
an initial insight into the current pictures out of the Mysterium.
Id really like to see the same tests done with ramps as I find Grey
steps and Color blocks very hard to find things like Color Banding. Its
also a great way to see what happens to the values just beneath those clip points.

It would be great to see some:
Grey scale 0-100 ramps
FINITE white steps from (in 8 bit termilogy) from 220 - 255
Finite Black Steps from 0 - 25
Full 75%RED-75%GREEN Ramps
FULL 75%BLUE -75%YELLOW Ramps.

grAdo
 
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