Noise, Dynamic Range and Bit Depth in Digital SLRs

[ChrisLilley]

Came across this recent article, Noise, Dynamic Range and Bit Depth in Digital SLRs by Emil Martinec © 2008

http://theory.uchicago.edu/~ejm/pix/20d/tests/noise/index.html

The idea of noise reduction on raw data before debayerisation was particularly interesting; also some comments on pixel efficiency and headroom. Its really worth a read.
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[LucisPictor]

Thanks.
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[Rob Leslie]

very good link. I have to read through it a few more times.
I would like to see similar information about the Pentax K10 22 bit ADC. It is a shame they never mentioned it.
Of course Pentax started out with a pretty bad sensor so maybe their 22 bit trick only levelled things out.

I’m thinking about having this piece framed!
‘Other forms of noise reduction which do involve filtering are also performed in some circumstances by some camera models within the camera and before the sensor data are written to the memory card. Examples include high ISO noise reduction on the Sony A700’
‘The problem with these alterations of raw data is that the user cannot turn them off! Image data is irretrievably adulterated by the noise reduction process.’
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[Nesster]

Interesting reading.

I can't help but to draw comparisons with high end audio. There also the engineers in digital capture do the signal to noise ratio thing, the dynamic range thing. All very valuable and useful, of course.

But here's what turns out to be true perceptually:
a hard cut off at the bottom of the bit range produces an unnatural cut off in subtle detail. The introduction of noise (dither) to the incoming signal allows the digital system to encode information below the theoretical noise floor. In other words, a slightly noisier system has better apparent resolution.
In the other direction, the hard stop headroom requires recording engineers to be careful not to clip the sound. (Ie, they don't want blown out highlights!) One way they deal with this is through the use of limiters. Properly used, these will improve the subjective sound, but all too often improper use ruins the sound for the afficionado (while making the overall sound more commercial, as the RMS sound level is louder).

Finally, it turns out that the type of filtering used to remove ultrasonic sound has a definite impact on sound. Indeed, there is evidence that ultrasonic frequencies modulate with audible ones in nature, affecting perceived timbre.

I'm just wondering if some of these findings from digital audio have any translation to digital photography. If so, perhaps we've yet to see what a digital capture system is really capable of, even with current pixel map sizes. (In audio, past a certain point the advantage of more bits is in the ability to manipulate them while maintaining the minimum required actual bit depth - manipulation is always destructive. The sampling frequency, which sets the recordable bandwith, on the other hand benefits from being much higher.)
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[bob955i]

[Orio]

[bob955i]

It's old to the younger generation Orio....

Used on virtually every track between '83 and early '90's.

No mean feat.

Actually, I've got a DX21, a Sequential Prophet 5 rev. 2, Sequential Sixtrak, Drumtraks, an ARP Axxe and Korgs Poly-800, EX-800 and Poly-800 MkII.

The Prophet was made in '79.

[Orio]

Ah I was a synthesizer maniac in my early 20s.
I still have some: the DX7II-FD, a Oberheim OB-8 with MIDI modification, a Prophet-VS, an ARP Odyssey, and a Roland D-500 and Oberheim Matrix-6R in rackmount version.

Thinking about it, it was for me the same way it is now with old MF lenses versus autofocus: when people was selling the old analogue synths to buy the digital ones and the samplers, I was buying them (I mean the analogues), for almost nothing. I think I got the ARP Odyssey for the equivalent of today's 25 Euros. I got the Oberheim OB-8 for not much more, like 200 or 250 Euros.
Some months ago I found an ARP Odyssey sold on Ebay for close to 1000 Euros...
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Read list of equipment HERE

[bob955i]

I remember that time too - everyone was going for the latest digital wondertoy and offloading their old gear.

Nothing's really changed has it?

Your collection is worth a tidy sum though - the Obie 8, the Prophet and the Oddy in particular.

My Prophet has also been MIDIed.

[Orio]

[bob955i]