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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 :)

Bit depth, resurrected

combatentropy said:
A week or so ago, someone asked whether a camera with 16 bits had any practical advantage over the Red, which uses 12 bits. I chimed in that 12 bits was plenty. The human eye is only about 8 or 9 bits, so, not only is 12 bits enough, but it gives room to play with.
Click to expand...

Yeah, that was me. I pretty much got the same answer, that the S/N ratio doesn't justify 16-bit A/D because the extra information will just be cleaner noise.

Combatentropy, I love your post! Can I make it into an article on 4khub, it's awesome.

Rich
 
There was a great breakdown on the maximal bit depth required for imaging at SMPTE:

An imager pixel of a given size (let's say 5 square microns, pretty normal for your standard 2/3" 1080 line sensor) can only catch so many photons per exposure at a given light intensity - its Qmax (although apparently this refers to electrons, not photons...). IIRC the number given in the example was around 15000 photons/electrons - meaning a 14 bit depth is all that's required, thanks to the magic of quantum physics.
 
combatentropy said:
10-bit log (correct me if I'm wrong, I may be misunderstanding this) records the values evenly, as you might have guessed in the first place. Even though 10 bits is only 1,024 shades, they are evenly distributed into chunks of 85 steps (1,024/12 = 85).
Code: 
F-stop    Digital value
--------+--------------
12        1,024
11          939
10          853
 9          768
 8          683
 7          598
 6          512
 5          427
 4          342
 3          256
 2          171
 1           85
Click to expand...

I'm not sure I understand this bit. A logarithmic curve to the "chart" that the ADC looks up it's values on would not be evenly distributed as far as pure light sensitivity is concerned. It assigns more numbers to the lower end of the brightness scale than the higher end. I suppose this would make it even in the context of your F-Stops. Is this what you meant?
 
combatentropy said:
I suggest a 16-bit ADC and immediately rolling that up into a 10-bit logarithmic space (still RAW though, the Bayer not interpolated into RGB yet) before recording.
Click to expand...

So the reason not just to stick with 16-bit log for the output is to again save on bandwidth and storage because we only need 85 "steps" per stop to satisfy our own human perception, and this is provided in 10-bit log?

So we would have 16-bit linear out of the ADC, but then an immediate in-camera resampling to a 10-bit log space for output?

That's pretty smart! Of course we know from the thread I posted that they originally had 16-bit out of the Mysterium, so who's to say that the RED 10-bit log output isn't already a result of the resampling from 16-bit that you are suggesting?

We'd need some RED team input on that one, of course you may have uncovered a in-house secret to thier stellar low light performance that they don't want to officially give away!

I'm with you, I think... but can I edit your post a bit for an article, maybe make it two? I'll run them by you first and still credit you as the author. I think you explained things in quite an easily understandable way.
 
I don't know where you get things from! We've never had 16bit a-to-ds on the Mysterium - they're 12bit and everyone knows that. Sure, we're saving 16bit tiffs from them, and we've captured files as 16bit raw (with 4 bits blank as the 12bit tiff format is totally incompatible with most everything) but it's always been a 12bit a to d - we're just learning how to make best use of that data!

Graeme
 
Graeme Nattress said:
I don't know where you get things from! We've never had 16bit a-to-ds on the Mysterium - they're 12bit and everyone knows that. Sure, we're saving 16bit tiffs from them, and we've captured files as 16bit raw (with 4 bits blank as the 12bit tiff format is totally incompatible with most everything) but it's always been a 12bit a to d - we're just learning how to make best use of that data!

Graeme
Click to expand...

Ok Graeme, it was a misunderstanding then. All that I remember being said was that you used to record 16-bits out, there was no way to know that this wasn't coming from the ADC until you just said so. I remember you saying 4-bits were blank, but even that wasn't really that clear, at least not to me. Judging even from this post, I wasn't the only one who misunderstood.
 
They were 12bit files padded to 16bit for compatibility with external tools.

Graeme
 
Get the Map

Get the Map

Anyone care to shed light on the term "mapping" in respect to A-D?



Mike Brennan
 
Mickjoebill said:
Anyone care to shed light on the term "mapping" in respect to A-D?

Mike Brennan
Click to expand...

The term "mapping" refers to the numeric value assigned to the quantizer's output. In some cases it can be as simple as COB or 2s complement conversion or could be more complex such as fitting the converters output word into a different number space (such as linear to log fit). This task can be accomplished in the quantizer or in the post processor (DSP).
 
At the end of all technical discussion, there is just one conclusion: if the picture feels good to me, it's ok. RED feels very good to me comparing what I get from every other digital camera. RED is defenitively the digital answer to 35mm in his best way. And after all, you can tell a bad story with the best camera, you can tell a marvelous story with a DV. It is somewhere between all of the technical possibility we have now. RED will definitively raise my understanding and quality to shoot pictures and stories. That's all, what counts I guess. I'm not very interested in people, which knows to much about technik and little about creating stunning pictures. The best technique is the one, which plays in the background, which don't need to show to much. What fascinated me from the very first moment at REDone was the concept of simpliticity. That you don't have to finish a picture in the camera, that RED is not overstuffed with technical nonsence and menus, nobody earnestly need (comparing to every existing Video Camera on the market). The RED is a digital 35mm camera and behind it, you need someone who is willing to tell stories, to set up beautifull pictures. Thats all, thats basic, that's my philosophy. Sorry for my english, guys.
 
Graeme Nattress said:
... but it's always been a 12bit a to d - we're just learning how to make best use of that data!
Click to expand...
I am a little confused:
Greame, does this mean that the AD-converter assigns more numbers to the lower end of the brightness scale than to the higher end?
Thanks for clarification in advance.
 
The a-to-d is a linear device, and the data from the sensor is linear to light, so the distribution of bits is linear. However, we perceive light in a non-linear manner, so the distribution of bits is not perceptually linear.

Graeme
 
Mapping

Mapping

khmuse said:
The term "mapping" refers to the numeric value assigned to the quantizer's output. In some cases it can be as simple as COB or 2s complement conversion or could be more complex such as fitting the converters output word into a different number space (such as linear to log fit). This task can be accomplished in the quantizer or in the post processor (DSP).
Click to expand...

It seems there is a lot? a little? that can be done in the mapping stage to introduce a more log like output, I guess this is a more important an idea for RED if recording RAW than with TV cameras where gamma curves can be applied before recording.

Is it preferable to do it in the quantizer than the DSP?

Over to Graeme for the corrections:)


Mike Brennan
 
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