High Dynamic Range?
 

In reading the benefits of the CMOS technology, one rapidly encounters the term "high dynamic range" as one of the benefits of CMOS over CCDs.

It seems to me that a lot of the camera reviews and tests out there put a lot of energy into estimating the low-light performance of cameras (a known challenge for CMOS), but I was wondering if there were any comments, images, or tests on the HC1 that validate the claim by Sony that the CMOS chip offers higher dynamic range.

-Steve

Lmiting factor is recorder's 8 bit dynamic range. FX/Z1 CCD dynamic range many many times higher. CMOS even higher dynamic range but for practical purposes is meaningless because you just use ND filters with the CCD camera.

Radek

No - 8-bit only limits the number of samples from light to dark to 256 per channel... it does not define the spacing between those intervals, and hence has nothing to do with the dynamic range (from light to dark) of an image - only the number of possible steps. What I'm talking about is often referred to as lattitude - and is related to contrast, saturation and gamma.

-Steve

To Steve: I think in Kaku's post, Wayne Morellini said something about how the HC1 exposes pixels individually to provide proper exposure of the image. You should check out his post for the details.

To Radek: As far as I know, ND filters *do not* increase a camera's dynamic range. ND filters reduces the amount of light that enters the lens, so it darkens the whole image; preserving the range of brightness to darkness.

Like Steven mentions, dynamic range hase nothing to do with a/d conversion. The other thing to remember is that dynamic range doesn't tell anything about sensor sensitivity. It only defines a gayscale range from the (noise limited) lowest light levels in a scene up to the highest (saturation limited)levels.

Radek, I have nothing against you but based on the number of times you have posted incorrect information here, I think it would be better if you did a lot more reading/studying about video and a lot less posting.

I have to stand up for Radek. This sentence is not quite true:
8-bit per colour channel is the most limiting factor of dynamic range. It means only 256 shades are possible, you can set diffrent spacing between steps but this won't allow to display high dynamic range scene, because details will be greatly losts. CCD probably has today internal 12-14 bits range, we now have to compress it to 8-bit. There are some basic algorithms:
- linear compression (mostly seen in todays camcorders) causes that shadows are mostly black
- logarithm mapping - causes loss of contrast in highlights but shadows remain details
- local operators - the best one, retains details in highlights and shadows, but can cause halos around edges. It's very complex, HDV image (1440x1080) needs 1 seconds for one frame on todays PC (2GHz). Probably CMOS can be used to implement it in hardware, so I supose that's why this topic arise.

English is not native language for Radek and the same for me, so please a bit more forbearance.

BTW Kaku Ito already posted Bamboo clip that deals with dynamic range and there is no diffrence comapring to FX1. There is also Ban clip that shows what HC1 can achive: you see what's inside car but also almost no detail loss for outside bright environment.

I'm close getting MA in film, from one of best film schools in Europe, have worked in film, TV, including 35 mm, HD productions, have FX1E.

There are three kinds people, ones with ideas, which can sometimes be wrong, ones with no ideas, they can't be wrong. Then are people that will promote DVX or HD1 over Sony Z1. One can pretty much figure why.

Let's look at lattitude this way. Footcandle level on sunny day can be up to about 10,000. Camera has 32x ND filter. With that camera will function fine in brightest sunlight, without closing lens down. 32x ND filter mean reduction lighting level from 10,000 to 300 FC.

The camera will also work in 3 lux level, or 0.3 FC. 0.3 lux would be lighting on brightest area. Lighting in darkest area would be small fraction of.

Contrast ratio of scene will be much much lower than range of CCD. Will be limited by tape, not sensor.

Scene can be lighted with contrast ratio in tens, while sensor will work well in many times higher contrast ratio.

Radek

That statement presumes some kind of universal superiority of one particular model or manufacturer over all others. To push this sort of personal agenda consitutes a platform war. I will not allow that sort of highly undesirable behavior on my message boards. It simply will not happen here.

Technical inaccuracy is one thing, and it's forgiveable. Hidden agendas, however, are not. Radek, you'll need to contact me by email. You and I will have a private conference before I'll allow you to post here again. Thanks in advance,

This kind of thing can rapidly approach semantics... but I think it's fair to argue, that 99% of the digital images we see are limited to 24-bit (8-bit per channel) colour, and that there's a sufficiently wide range of possible contrast ratios, gamma curves that we can safely state 8-bit isn't the limitation on dynamic range... it's how those 8-bits are used. Going to 10-bit or 14-bit will most certainly improve the "quality" of the image by adding detail... but if you define "white=x and black=y" to fundamentally the same analog signal, if you continually increase the bit depth, at some point you'll just be measuring noise more accurately.

The lack of an ND filter on the HC1, and the "lack of necessity" of one, seems to clearly point to a very high range on the sensor, and the dynamic range of the actual footage will depend largely on how Sony implemented the controls. Considering the limitations of manual control on the HC1, I imagine the full utility of the sensor can barely be realized.

Perhaps in the future someone will implement a consumer CMOS camcorder with fully adjustable dynamic range and gamma. Wouldn't that be something?

I'll have to find that clip/shot.

-Steve

Michael, dynamic range is a property belonging to the analog world. Scene contrast ( real world dynamic range) on a sunny day is much higher than cam sensors can get. CMOS is the better device in thet respect. The number of bits used for digitizing analog values is rtelated to the target application. For video it is generally accepted that 8-bit depth resolution per color doesn't show contouring if applied in a overall linear chain. Signals from cam sensors need to be preprocessed (gamma correction, WB) and therefore more initial depth is needed, like 12bit and more. The processed values are then remapped on an 8 bit structure (interpolation).

I can't agree that 8-bit (256 shades) is enough to reproduce dynamic range (or high contrast, whatever you call it). I know the contrast ratio on a sunny day is much higher than cam sensor. But it's NOT possible to simply put this in 8-bits, be happy and say that 8-bit is enough and doesn't have anything to do with dynamic range. If we have contrast ratio of 10 000 : 1 (some of newest displays allow it) but still 8-bits then we stuck to nothing - the true scene with 10 000 : 1 will look on such display increadibly unnatural.
Just look here:
http://www.cs.huji.ac.il/~danix/hdr/hdrc.pdf
http://www.mpi-inf.mpg.de/resources/...map/logmap.pdf
If it would be so simple as you describe then above algorithms won't be necessary. And these algorithms can't be implemented real-time. Feel free to ask if you don't understand something in those papers.

8bit is only good enough to ensure lack of banding after gamma correction. If the camera were to record linear video, it would need to be at 12bits to eliminate banding.

Graeme

Michael, thanks, and be shure I do understand yr stuff. Already duing the time I was involved at Stanford University(CA) in medical image processing about 30 years ago and later, till 2 years ago as VP R&D at Barco (900+engineers in research) I was supposed to know where I was talking about. So no need for extra leads, maybe I could send you some of my reports and patents on image processing, including one on histogram optimisation (about yr local operators) for medical ultrasound imaging.

Andre, I was mostly replying to Steve post. You've written about contouring etc. and that's ok. So maybe we are floating at the barrier of my communication (my English is not perfect ;) ). I agree that 8-bits is enough to represent accurately image, BUT we need a bit diffrent capture devices that doesn't cause contrast compression but work more like our eye. Today available professional digital camcorders with ultra high dynamic range meets the problem how to compress the contrast to only 8-bit. Maybe with CMOS we are closer to this (human eye) approach and soon maybe we would not need to do any compression of dynamic range and the image will be displayed perfectly on our limited monitors/TVs.