Why is there only 14 bits in Canon/Nikon ?

[Mark Regan]

Hello,
I wonder why there is no 16 bits capture possible in Canons or Nikons?
It seems to be the main advantage in MF backs.
Why is there only 14 bits, which don't make a big difference to 12 bits?

[DarkPenguin]

The more bits you have the more data you have to move off the sensor and out to the buffer and memory card.  Since the value of 14 bits over 12 bits is somewhat questionable there doesn't seem to be much incentive to have to move ~15% more data.

[witz]

Hello,
I wonder why there is no 16 bits capture possible in Canons or Nikons?
It seems to be the main advantage in MF backs.
Why is there only 14 bits, which don't make a big difference to 12 bits?
[a href=\"index.php?act=findpost&pid=177743\"][{POST_SNAPBACK}][/a]

shoot raw and then export/save out of your raw app of your choice ( adobe raw, canon dpp, C1.. etc ) as a 16 bit tiff.

this is pretty much standard op even with MFDB's.

[Panopeeper]

I wonder why there is no 16 bits capture possible in Canons or Nikons?

Let's turn around the question: what information should be stored in 16 bits?

Increasing the bit depth does not contribute to the increase of useful image data on its own.

It seems to be the main advantage in MF backs

MFDBs have higher dynamic range, which requires more gradations. So, it is logical, that their raw images have greater bit depth.

On the other hand, 16 bits are exaggerated. The MFDB owners should think,. that tehy received something valuable for that money, even though they don't utilize it.

Why is there only 14 bits, which don't make a big difference to 12 bits?

This is funny: you are asking, why not 16 bits instead of 14, while claiming, that 14 bits don't make much difference compared to 12 bits.

For your math: 14 bits are *four* times more (in terms of stored data) than 12 bits - just like 16 bits can hold four times more data than 14 bits.

Btw, the Nikon D300 and D3 allow recording 14 OR 12 bit raw data, and as far as I can see, most users stick to 12 bits, even though that numerical range is nor fully utilized.

I am happy with the Canon 40D's 14 bits; that is somewhat more than necessary, but you know, why there is no row 13 on airplanes, no floow nr 13 in many houses, etc?

[Graeme Nattress]

The bit depth of of the AtoD needs to be high enough so that it has lower noise than the sensor. The newer sensors from Canon and Nikon are lower noise, hence they need a higher bit depth AtoD.

You can also, if you want, keep adding more bits on the AtoD, beyond what is necessary, and get no performance benefit. I don't know if anyone has done any real measurements on a MFDB, but I severely doubt them having a dynamic range that requires a 16 bit AtoD.

I do know of cameras in the digital cinema realm (no, not the one I work on) that record 16bits to file, but of those 2 are blank :-)

Graeme

[marcmccalmont]

It is interesting to note that the DSLR sensors are capable of more DR than MFDB sensors but either due to the A/D converters or circuitry the MFDB captures 2 stops more DR than the DSLR's?
Marc

http://www.clarkvision.com/imagedetail/dig...mary/index.html

[bjanes]

It is interesting to note that the DSLR sensors are capable of more DR than MFDB sensors but either due to the A/D converters or circuitry the MFDB captures 2 stops more DR than the DSLR's?
Marc

http://www.clarkvision.com/imagedetail/dig...mary/index.html
[a href=\"index.php?act=findpost&pid=177767\"][{POST_SNAPBACK}][/a]

The medium format users brag about the dynamic range of their cameras, but this claimed DR does not show up in the specs. For example, Roger tabulates data for the KAF 18000CE, a Kodak chip targeted to medium format digital backs. It is a 4904 x 3678 chip with 9 micron pixels. The full well capacity is 100,000 electrons and the read noise is 18 electrons, giving an engineering DR of 12.4 f/stops (the Kodak spec is 74 db or 12.3 stops).

For comparison, the Canon 1DMIII has a full well of 70,200 electrons and a read noise of 4.0 electrons, giving a DR of 14.1 stops. Since the Kodak chip is higher resolution, the noise spectrum would be higher frequency (fine grained), which could affect the photographic DR. Any explanations? In the Kodak CCD chip, the ADC is external to the chip itself, but the DR of the sensor would be the limiting factor and a 16 bit ADC would not be able to increase the DR.

Bill

[John Sheehy]

The bit depth of of the AtoD needs to be high enough so that it has lower noise than the sensor. The newer sensors from Canon and Nikon are lower noise, hence they need a higher bit depth AtoD.

They have not improved beyond what Canon has been doing for years, though, in terms of read noise at base ISO.  The bottom line has been 1.25 12-bit ADUs (or equivalent), for which 12 bits is still satisfactory.  You need to get down around 1.1 before you can see quantization effects.  The Pentax K10D, AFAIK, is the only camera that really needs a 13th bit, at ISO 100, with a 12-bit read noise of 0.9 ADU.

You can also, if you want, keep adding more bits on the AtoD, beyond what is necessary, and get no performance benefit. I don't know if anyone has done any real measurements on a MFDB, but I severely doubt them having a dynamic range that requires a 16 bit AtoD.

The best I've seen there (P30) is about 1.25 12-bit ADU, also.  No real need for more than 12 bits.

I do know of cameras in the digital cinema realm (no, not the one I work on) that record 16bits to file, but of those 2 are blank :-)
[a href=\"index.php?act=findpost&pid=177758\"][{POST_SNAPBACK}][/a]

If they compress those two bits away, then that shouldn't do any harm.  A little LSB padding always affords the possibility of better handling by the converter.

[John Sheehy]

It is interesting to note that the DSLR sensors are capable of more DR than MFDB sensors but either due to the A/D converters or circuitry the MFDB captures 2 stops more DR than the DSLR's?
http://www.clarkvision.com/imagedetail/dig...mary/index.html
[a href=\"index.php?act=findpost&pid=177767\"][{POST_SNAPBACK}][/a]

A quick look through the page, I can't find exactly what you're referring to, but he may be using sensor specs for cameras he doesn't have access to, or their RAWs, and mfr specs are not to be trusted, or considered relevant in a full camera system.

Generally speaking, MFDBs perform similarly to smaller-sensor cameras at the pixel level; they have more pixels which lowers the noise further, and increases the DR, at the image level.

[John Sheehy]

For comparison, the Canon 1DMIII has a full well of 70,200 electrons and a read noise of 4.0 electrons, giving a DR of 14.1 stops.[a href=\"index.php?act=findpost&pid=177940\"][{POST_SNAPBACK}][/a]

That never actually happens.  The read noise you quote is for ISO 3200, and the full-well is for ISO 50.

[bob mccarthy]

That never actually happens.  The read noise you quote is for ISO 3200, and the full-well is for ISO 50.
[a href=\"index.php?act=findpost&pid=177950\"][{POST_SNAPBACK}][/a]

just curious

why would full well vary by ISO?

And does read noise vary much by ISO?

bob

[bjanes]

That never actually happens.  The read noise you quote is for ISO 3200, and the full-well is for ISO 50.
[a href=\"index.php?act=findpost&pid=177950\"][{POST_SNAPBACK}][/a]

Looking more closely at Roger's data, what you point out seems to be true. It does not make sense to use the read noise at ISO 3200 to calculate the DR at full well. Roger should revise his tables.

Bill

[bjanes]

just curious

why would full well very by ISO?

And does read noise very much by ISO?

bob
[{POST_SNAPBACK}][/a]

The answer is that the camera gain (electrons per 12 bit data number) varies with ISO. Look at Table 1a on the [a href=\"http://www.clarkvision.com/imagedetail/evaluation-1d2/index.html]Clark[/url] web site. For the referenced camera at ISO 50 each camera data number represents 30.62 electrons and at ISO 3200 the gain is 3.93 electrons/12 bit data number.

Therefore, a least significant bit error at ISO 50 represents more electrons.

Bill

[marcmccalmont]

I'm not sure what it means but if I do a RAW conversion of a  5D file and a P30 file the P30 fills the histogram (16 bits) the 5D does not (12 bits)
I used ACR as a common converter with the same settings then I adjusted the whites to match.
Marc
5D
[attachment=5320:attachment]
P30
[attachment=5321:attachment]

[Panopeeper]

I'm not sure what it means but if I do a RAW conversion of a  5D file and a P30 file the P30 fills the histogram (16 bits) the 5D does not (12 bits)

It means nothing on its own. If you post the raw images, we can talk about *those* histograms.

[duraace]

The bit depth of of the AtoD needs to be high enough so that it has lower noise than the sensor. The newer sensors from Canon and Nikon are lower noise, hence they need a higher bit depth AtoD.

You can also, if you want, keep adding more bits on the AtoD, beyond what is necessary, and get no performance benefit. I don't know if anyone has done any real measurements on a MFDB, but I severely doubt them having a dynamic range that requires a 16 bit AtoD.

I do know of cameras in the digital cinema realm (no, not the one I work on) that record 16bits to file, but of those 2 are blank :-)

Graeme
[a href=\"index.php?act=findpost&pid=177758\"][{POST_SNAPBACK}][/a]

Are you saying 12 bits can have more noise than 14 on higher ISO or lower light? If true that would be a  reason for choosing 14bits on my D300.

[Mark Regan]

Thanks for answering, even if some are way too complex for me, I think I get the idea.

[DiaAzul]

Hello,
I wonder why there is no 16 bits capture possible in Canons or Nikons?
It seems to be the main advantage in MF backs.
Why is there only 14 bits, which don't make a big difference to 12 bits?
[a href=\"index.php?act=findpost&pid=177743\"][{POST_SNAPBACK}][/a]

Ignoring the noise versus signal debate. One of the greatest problems with Analogue to Digital converters is settling time of the input signal and also the amount of time it takes for the converter to actually 'compute' the digital value of the signal - The more bits of precision required then the longer it takes to do a conversion; the greater the precision required the longer you have to wait before the output of the channel amplifiers settle at the actual value of the input (pixel output) signal (slew rate limitation of the amplifiers).

For MF backs with typically low frame rates they can allow longer for the signal to settle and for the A2D converter to compute the code i.e. slowing the process down allows a greater bit depth. Nikon and Canon are pushing both sensor size (megapixels) and frame rate so, in order to live within the constraints of technology, need to limit the bit depth of the measured signal. If they reduced frame rate or sensor size then bit depth could be increased.

The other alternative is to run more A2D converters in parallel, which Canon and Nikon do to a certain extent. The problem then becomes ensuring consistency across the conversion pipeline (calibration of each converter) and cost (available silicon for implementation of the A2D converters).

Irrespective of noise if Canon/Nikon could make a marketing claim for 16-bit conversion without it costing too much they would do it, even if it didn't improve image quality.

[marcmccalmont]

It means nothing on its own. If you post the raw images, we can talk about *those* histograms.
[{POST_SNAPBACK}][/a]

Give me an hour and I'll post the raws through usendit
Marc

P30: [a href=\"http://download.yousendit.com/C223886E0467675D]http://download.yousendit.com/C223886E0467675D[/url]

5D: http://download.yousendit.com/3D785E3F6389F29D

[BernardLanguillier]

My un-substantiated guess is that it has little to do with technology in fact.

The main reason is the existence of a carefully thought out release roadmap in which manufacturers have basically agreed to progress a a reasonnably slow pace in order to make sure that they will have appealing new features to deliver in their next generation bodies.

For high end users, bit rate is a characteristics that has marketing value, and manufacturers have IMHO understood that it was in their best shared interest to keep some bullets like this one availabe for the next round of fight.

What are the odds that Canon and Nikon, working on totally different technological/supplier communities, come up precisely at the same time with 14 bits sensors, nearly within days of each others?

This is the same reason why we are progressing mostly from 10MP to 12MP instead of going from 10MP to 14 or 16MP.

Cheers,
Bernard