High Dynamic Range?

[Andre De Clercq]

Agreed Michal.

[Boyd Ostroff]

Originally Posted by Steven White

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

But are you sure the camera doesn't have internal undocumented ND filters like the PDX-10, TRV-950, HC-1000 and many other cameras? This design lets the camera stay in the sweet spot of the lens without ever using small apertures. Instead, one of several internal ND filters drops into the optical path.

The existence of these internal filters have been proven on the above mentioned cameras, but Sony has never published anything about them and the user has no manual control of their behavior.

[Steven White]

There's a difference between not documenting something and saying something definitively isn't there.

I can't agree that 8-bit (256 shades) is enough to reproduce dynamic range (or high contrast, whatever you call it)

I never said that it was. 8-bit is both a display limitation and a recording bandwidth limitation in the already highly compressed land of digital video. And before you quote 10000:1 contrast ratios on televisions, unless the television can take a standard input signall that supports 10000:1 - however that's tested - and put that on screen, such figures do little except tell you how black the blacks are compared to the whites on display - not in the signal supplied to the display.

The reason I'm even curious is becuase the game with camera dynamic range is to record as much useful information as possible - and is the same game we play with everything from gain to iris to shutter speed. Having a large dynamic range would be beneficial while shooting high contrast scenes, to enable more control over shadow detail and highlights for future colour correction. If it can't be adjusted manually though -it's all for nothing. I'd love to be able to carefully set white points, black points, and everything in between in camera.

And André! Cheers to a fellow in image processing. I did my M.Sc. in nuclear magnetic resonance imaging, and am currently playing with non-destructive testing methods.

-Steve

[Michal Laskowski]

I never said that it was.

Sorry, I thought you've said that, so it must be my english.

I did my M.Sc. in nuclear magnetic resonance imaging, and am currently playing with non-destructive testing methods.

Wow! That's really interesting!

[Steven White]

I thought you've said that

Hm... it's probably derived from this statement:

"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"

What I meant to indicate is that pretty much all the digital video and pictures you see on the web, TV, etc. are 8-bits per channel. People seem to be happy to differentiate - within all these 8-bit delivery formats - between scenes with high and low contrast, scenes with and without blown out highlights, etc. So the 8-bit isn't so much a limitation on the presentation... it's a limitation on the colour correction flexibility.

You've got all these people claiming some images scream "video" while others don't... yet they're all looking at 8-bit pictures. I argue 8-bit delivery isn't the problem - it's where these 8-bits come from. The more you can adjust gamma, and the values of black and white, the more you'll be able to specify the dynamic range for the image you want. Logarithmic, polynomial, inverted or sinusoidal for all I care... not to make the images "natural" but to make them what the "artist intends".

Getting what you want is in principle very easy from high dynamic range source... doing it from low dynamic range source isn't. In the HC1 you have a high dynamic range CMOS sensor and you've also got a 14-bit signal processor. I would expect there's a lot of flexibility in what the camera can pick out of those 14-bits before downsampling to an 8-bit export - but whether the folk who built the camera let you get at it, or whether they decide everything for you and pre-set it is the real question.

-Steve

[Andre De Clercq]

Steven, I always found image reconstruction from NMR data so challenging...much more sophisticated than what is being done in videoland. Is your NDT work still MR related? I always was interested to know how the MR related techniques like NQR used for NDT would affect our magnetic media when used in airports.

[Steven White]

found image reconstruction from NMR data so challenging

Totally off topic - but I really marvel at the genius of the NMR encoding schemes. I tip my hat to all the folk who came up with it originally - truly an elegant procedure.

Is your NDT work still MR related?

Not really... I'm working on detecting stresses in steel pipes using DC and AC magnetic techniques (known as flux leakage and Barkhausen noise respectively). It's still related to magnetism, and the work is for the nuclear industry... but spin polarizations and gyromagnetic ratios aren't so much a concern. Most ferromagnetic effects are due to electron dipole moment coupling.

how the MR related techniques like NQR used for NDT would affect our magnetic media when used in airports

I'd never heard of this until today (for shame!). After looking it up, I don't think it would have much effect. The QMR people don't seem to need a magnet and are operating with radio frequencies from MHz to GHz. I think they'd need pretty high power pulses to do much damage to magnetic media. Also, they're only trying to get a signal out of the samples - they're not trying to heat them up (think a microwave oven), so it's doubtful they'd do much damage. According to this article:
http://gazette.gmu.edu/articles/index.php?id=4925
it's all very safe. Notably amusing is the passage about the RF doing "damage" to "airport workers". Media terrorism at work. RF is non-ionizing radiation, and you're bathed in it all the time. Think cell phones, radio, and well, broadcast TV.

Ah! There we go... back on topic ;)

-Steve

[Andre De Clercq]

Thanks Steve

[Wayne Morellini]

Originally Posted by Michal Laskowski

I have to stand up for Radek.

I keep a reasonably open mind to Radek (and virtually anybody that has a reasonable attitude). I don't know everything, and can learn things off of him. I wouldn't even mind working with him on a job. We all start somewhere and learn more and more. To me it is about the exploring and learning of accurate information, of use somewhere. I've learned much over the last couple of years here (that I wish they taught at media school, would have been good help for picking equipment) and my head is aching just looking at some more of the stuff revealed in this thread ;) We can state things with a qualify like "maybe" and/or ask for verification or questions to better understand things, so those who do known can enlighten us, and reason things out. But it is upto the stater/questioner to determine, sort through, and receive the correct answers. I don't mind a bit of debate, as long as it is about determining the truth.

[Wayne Morellini]

Radek,

I'll do a summary of what I think I know (qualifier statement), please disregard all my previous statements, I think this is more accurate (any comments, anybody?). Latitude proper, is the range of light the sensor can record, and the bit range determines the fineness this range of latitude canbe divided up into. Even though the bits don't cause actual reduction in latitude, they do cause usable stops below the minimum value to be lost. For instance (using low values) say the sensor pad well mechanism has a capacity of 1024 electron volts (ev) and after 8 bit conversion the minimum value is 4, to stops maybe lost). If it had a capacity of 256 ev, then the minimum value would be 1, but no usable stops are there to be lost. Note the latitude did not change, the one with bigger well capacity still had 4 times more latitude, even in the smallest value. So yes, you can get more stops, but only if they were lost in the first place. Sorry to use the specific technical terms, but there are a number of similar confusing terms surrounding this.

Another thing that clips the lowest usable stops is noise, normally called Signal to Noise ratio. Noise is produced by many circuits in the camera from sensor mechanism to A/D converter to D/A and analogue output connector. So you can only get more than 8-bits effectively usable if signal to noise ratio is high enough to let you (approx 60+bits for 10 bits) it can go so high (especially using gain) to wipe out the lower bits of 8 bit video.

These might be the internal technical measurements of a sensor chip, but they are not the ones used in tests, as lens systems, Quantum Efficiency of light conversion and Fill-factor on the sensor also effect the outcome.

Lens aperture canbe used to compress light range down to fit the well capacity of the camera (increasing latitude of the shot the camera can deal with) but at the expense of increasing the DOF. To stop this you use ND filters to reduce the light range, but I would imagine that maybe the pass through response curve is bias against the bottom end, producing some clipping there.

Quantum Efficiency, is the concession rate of photons to usable electron volts, 10% QE requires 4 times more light than 40% QE, so given the same well capacity 10% works in two stops brighter light (though probably requires two stops more light to overcome noise). Similarly, the fill factor (the amount of the sensor surface that actually collects light) also determines the amount of light (on downside the missed light increases noise).

[Wayne Morellini]

Originally Posted by Kin Kwan

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.

Kin

I suspect this is the case, sample shots look like it, but I don't know for sure. I have asked if somebody could read that section of the brochure in Japanese to verify, but didn't get an answer. The dual slope and gain changing techniques are really other tricks to get higher latitude. One resets the pixel and re-samples to get more range, and the other applies gain (from what I can tell) to achieve similar affect.

[Lorin Thwaits]

Being curious about how the exposure control works on my HC1, I recorded a section of tape cycling through all 24 different settings in sequence. Then when playing back I turned on the "Data Code" feature to see what aperture and gain were being chosen for each setting. From that I made up a chart. Interesting was that across a broad range of the 24 exposure "notches", the aperture and gain settings are the same! A total of 8 notches all have f4 and 0dB gain! How can this be since that part of the range definitely modifies exposure in a noticeable way? After pondering over it for a bit, I realized that just like you folks have been pondering here, there must be another third parameter getting tweaked, a choice of what range of bits to grab out of the 14 bits coming out of the CMOS sensor! Here is a write-up of what I think Sony did to implement their exposure control to obtain high dynamic range from the CMOS sensor. It's a little long, and includes a chart, so I decided to put it on its own page:

http://hdvforever.com/hdv/exposure

There is a fair degree of speculation regarding which specific bit ranges are used in which specific exposure settings, and some of the marketing literature on EIP hints at the process being a bit more complex than what I've described here, but based on everybody's musings I expect something like this was used in the HC1 to achieve its excellent dynamic range it offers in well-lit settings.

Hope you enjoy the read.

-Lorin

[Andre De Clercq]

A 5 bits window at the highest gain setting is really low...besides the patchy noise also banding must be horrrible, or is it masked by the noise? Gamma corrections arlready takes about two bits,maybe including WB. Are you shure there is no analog gain change before ADC in these low level situations?

[Steven White]

Interesting Lorin!

The only thing I'd hold contention with is your "bit-range" description.

You don't "pick" 3-14 of the 14 possible bits, you store each number on a 14-bit scale. That is to say, each channel has 16384 possible shades from black to white. You then process the colour, and down sample to 8-bit (256 shades) for final rendering.

In other words, you sample each pixel with 14-bit precision - what you vary between settings is the voltage you assign to 1 and the voltage you assign to 16384. So if you have a possible range of 0 V to 5 V, in one case you sample 0 to 1 V, the next case 1 V to 2 V, the next range 2 V to 3 V, etc.

-Steve

[Gerald Lunn]

Lorin,

Isn't the camera adjusting the shutter speed for that mid part of the range? If they don't go lower than 1/30th for the low light (unless you specifically tell it to) they have the whole range up to 1/10000th. There are 8 stops between notch 5 and notch 13 which is a range of 256:1 - just about exactly the difference between 1/30th and 1/10000th (333:1)

I cannot see how they would be playing with the 14 bits in the way you suggest - that would remove all the flexibility to do the shadow/highlight DSP that Sony claims!

Gerald