DVX100 Contrast Ratio?

since there are different types of film and different types of video, it isn't fair to lump them that way and Joren Clark's numbers are wildly inaccurate for both.
 
but the thread is interesting. does the cine gamma actually widens the contrast ratio?

i mean, do i really get more details in the very bright and in the very dark with respect to the 'standard' mode where very dark is black and very bright is white?

(i know, i explained it pretty bad :) )
Andrea
 
he did mention "depending on what film".. btw, im only looking for a rough estimate.
lets say his figures are in the estimate, where would the DVX sit, roughly? could it be 300:1 - 500:1 - 1000:1???

im a clueless learning noob, so any figures that would ring close inough.. :undecided
 
human eye has a contrast range of 30,000:1 or expressed in terms of f/stops, roughly 15 stops.
the VariCam $66,000 HD camera is 4,000:1 or roughly 11 stops.

the DVX? no idea. nowhere near the human eye or a VariCam, but neither is it as low as 100.
your guess would be as good as mine.
 
Baluardo said:
but the thread is interesting. does the cine gamma actually widens the contrast ratio?

i mean, do i really get more details in the very bright and in the very dark with respect to the 'standard' mode where very dark is black and very bright is white?
Click to expand...
Yes, that is what it is supposed to do. The current generation is good. The next generation (i.e. - AG-HVX200) should be even better, at least I would hope so.
 
Another thing to note is that stops are logarithmic (ah, I can't spell), not linear. I've heard 5-6 stops thrown around as the dynamic range for the dvx and 8-9 for "normal" film (it can go higher, of course.)

Assuming 5 stops is 100:1 (it's not), then 8 stops would be 800:1 and 9 stops would be 1600:1. So the difference between 100:1 and 1000:1 isn't nearly as huge as it seems, plus it's not even a valid statistic at all since three stops of film lattitude get stuck so high up in the highlights they're barely visible with modern stocks.

Is there some truth to this, though? Certainly. Even modern 16mm stock knocks the socks off of the dvx in terms of dynamic range.
 
Well my DVX has 6 and 1/2 stops.

I don't care if I'm counting right or not, or how should I do it. For my own purposes it has 6 and 1/2 stops and finito.

What I did was shoot a gray card and open up the iris until it read 99% actually 98, one click on the iris before 99%, and I stopped down until it read 0% that was from 2.0 to 16 and 1/3, but I could not reach 0%, only 5% so I take it, between 1/3 and 1/2. (because the dvx adjusts exposure in thirds of half-stops, and reads exposure in half-stops.)

So six stops and a half.
 
Is there some truth to this, though? Certainly. Even modern 16mm stock knocks the socks off of the dvx in terms of dynamic range.
Click to expand...

I don't get it Policar, what do you mean with "even" modern 16mm stock? Aren't them the media with most latitude possible?
 
And lastly, a 1:100 ratio would be something like 6 and 1/2 stops, pretty accurate for me. And a 1:1000 ratio would be 8 stops (well 1: 1024, anyways), counting, for instance a TriX film, where the rule of thumb is 4 points up and 4 down, it is pretty accurate in my book. Am I tripping? That is why I too can't understand the 11stop range for the varicam, but I'm sure there are two different ways of measuring this...

From Blain Brown's Book on lighting, the eye perceives 7 stops of contrast (a ratio of 1:256), but of course, since we make the iris adjustments on the fly and automatically, the real world lighting ratios (of up to 10000:1) does not look as bad for us as it looks on video or film.
 
I just put the DVX through a quick test. I put a graduated gray card (from DV Rack) in front of the lens and lit it up. Then I used the "Spectra 60" to analyze the brightness level of one particular patch.

I adjusted the light so that at f/2.4 and 1/60th of a second, that chip was just barely, barely below clipping. Specra 60 was reading about 249/252/254, something like that.

Then I stopped down the lens as far as I could to get the chip as dark as I could, before crushing to black. It was still reading at f/16, so I then went to the shutter and had to raise that to 1/250 before I got that chip down dark enough that it was just above black (reading something like 12/13/14 on the Spectra 60). At 1/500 it was solid black, at 1/250 it was still showing some response.

So, if I translate those shutter adjustments into additional stops, it would mean a range of from f/2.4 to f/32. About 7.5 stops.

As far as why my numbers differ from taubkin; I can guess two things: first, using the Spectra 60 I was probably getting a lot more accurate feedback than taubkin with the "marker". Second, I do not trust any stop deeper than f/16 on the DVX. F/16 is okay, but things get really odd when you go past it. There are two 1/6-stops you can dip into, f/16+1/6 and f/16+1/3, but both have a tremendous impact on resolution and I don't trust them to be accurate f-stops.

In the testing I did, I was going for the absolute extremes, the very borders before clipping/crushing. May not be realistic. So, for a nice round number, I'd probably say we could split the difference and say it's 7 stops, top to bottom.

Assuming contrast ratios are measured using binary notation, 7 stops would mean a theoretical ratio of 128 to 1. 10 stops would be about 1000:1.
 
It's great to know, that despite being a lazy bum with no standards whatsoever, I got the logics straight. God, I forgot about shutterspeeds! Sure, Barry, I totally believe your 7 to 7.5 stops. Besides, not all of the readings translate into usable latitude, especially the range from 20%-30% (extremely noisy).

Now I would nos expose to some reading and think that my camera will get 3 stops up and 3 down from that as I would with triX film (4 up and 4 down), because I think correct exposure with the video cam is much higher than 50%. I'd say 2 stops up and 4 down. Am I talking nonsense now?

Other than that, I'm still quite puzzled with the fact that the varicam reads 11 stops. Are they using the same rules as we are?

Thanks Barry for doing what I planned to do the right way!
 
Policar said:
Barry, they should update your status from "Moderator" to "God." That was amazing.
Click to expand...

All DVXuser faithful are hereafter encouraged to kneel and face Las Vegas at least five times a day, chanting: "There is no Barry Green but Barry Green. All praise be to Barry Green..."

Just kidding. We may not offer you much, but I guess we sure are good for your ego around here, Barry! :)
 
If I can help, I'm glad to. But all the praise and "god" stuff belongs directed towards the man upstairs, not towards me. I'm just a guy who tries to help people, and statements like that start to make me a little nervous (like the Almighty might stop throwing 2,000 lighting bolts at Terri Hartley and might cast an eye in my direction!) :)
 
My Crazy Experiment

My Crazy Experiment

While procrastinating, I did a little though experiment, then backed it up with a real experiment.

The idea came to me while doing some HDRI (High Dynamic Range Image) work in Maya. You can read a bit about HDRI here.

It would be really cool if someone else tried this as well, particularly those of you with two DVXs, a beamsplitter, a 35mm lens adapter, and a bit of old-fashioned gumption (a machine-shop would help too).

I put the DVX in my backyard, and shot a minute of video while slowly opening then closing the iris. The camera was locked down, and nothing was moving in the background. The scene was a combination of dark shade, and bright sunshine -- a typical nightmare scenario for video.

Then I captured two stills into Vegas, one underexposed, and one overexposed. They were one on top of the other. Then I created a mask (automatically, using "Secondary CC" luminance mask) to "punch a hole" in the overexposed areas, so that the under-exposed "bright sunshine" parts showed through.

The result is that the dark bits were perfectly exposed (from the over-exposed shot), and the bright highlights were perfectly exposed (from the under-exposed shot).

There were problems with solarization on the overlapping areas (but I already knew this would happen from the "thought experiment" stage), and it took a bit of fiddling to get a good (but not perfect) match. A bit more experimentation and I think we would be able to get a perfect image.

I propose that a rig be made consisting of two DVXs focusing on a beamsplitter (prism), with a single 35mm lens at the front-end. One DVX would be configured to overexpose, and the other to underexpose. This way you capture as extreme a latitude as possible, and can "set" or "fix" the exposure in the NLE while editing. This will add another step during post-production, and ideally a plugin or separate software will need to be written to automate this.

Seeing that there are quite a few of you who are into making "35mm adapters", there's not a big leap into making a "HDRI/V" (as snappy a name as I could come up with) adapter. Unfortunately I don't have the resources.

One potential problem is syncing the camera's, but we'll only know if this is a problem when a complete rig is made. I think that natural motion-blur may make this a non-issue.

If this does work, when the HDX comes out this rig will CRUSH film. Do you hear me, film? We're coming to get you. Your days are numbered! :laugh:
 
hehe,

Go on, someone do it....

I have done similar things in the past, but far simpler: I shot an interview with a blown-out window behind. After the interview, I kept the camera locked off and rolled for a minute or so unexposed so that the window was correctly exposed. In post I then replaced the blown-out window with the correctly exposed one. It is easier just to take a load of ND with you though!
 
What about the other link in the chain? Tape. It's interesting to test the camera for it's ability to capture light and dark but what happens when it's actually recorded and played back?

For all its ability to show instant results, its small size and its ability to be erased and used over and over, it still is some type of metal glued to a plastic strip. And it has limitations also.

I've always understood that the human eye can distinguish a contrast ratio of 1000:1, Film (movie or still) a contrast ration of 500:1 and video 5 to1.
A great test is to shoot 2 items one black and one white in direct sunlight and watch what happens. Detail is the thing to look for.

By the way, lighting to make videolook like film has become my personal holly grail.
I've seen many clips that you guys have created with beautiful examples that it can be done. The big question, for me, is what are the limits (in contrast) and yet still be able to have a dynamic difference in light and dark?
 
It can't be 5 to 1. 2 to 1 is one stop and 4 to 1 two stops. 5 to 1 is something like 2 stops and 1/3, too little dynamic range to be useful. It's just like this: Each f/stop is doubling the light quantity, so, in a contrast ratio I have to determine how many times a number was doubled and I'll know how many F/Stops it has:

2:1 - One Stop
4:1 - Two Stops
8:1 - Three Stops
16:1 - Four Stops
32:1 - Five Stops
64:1 - Six Stops
128:1 - Seven Stops
256:1 - Eight Stops
512:1 - Nine Stops
1024:1 - Ten Stops

And so on...
 
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