From: Roger N. Clark (change username to rnclark) on
John Sheehy wrote:

> Quantization is just the act of converting analog data to digitized
> integers. If there is no added noise in the process, then any analog
> range of values equivalent to one ADU will wind up with that single ADU
> value. For systems where absolute values matter, this means errors over
> any one ADU range, like -0.999 to 0, or -0.5 to +0.499, or 0 to +0.999;
> never +/- 1 as Roger suggests in other posts.

Gee, some simple research would prove you are wrong.
Try reading http://en.wikipedia.org/wiki/Analog-to-digital_converter
which is a pretty good writ-up.
For example, note the statement:
"Commercial converters usually have �0.5 to �1.5 LSB error in their output."
(section on commercial analog-to-digital converters.

Let's look at some noise in ADUs from a wide range cameras:

Camera Read Noise in ADU (or DN, or LSBs)
ISO: 50 100 200 400 800 1600
Canon 1DMII 1.2 1.3 1.4 1.7 2.5 4.8
Canon 5D 1.8 1.8 1.9 2.1 2.6 7.4
Canon 10D 1.4 2.0 3.9 6.4 13.
Nikon D50 1.8 4.0
Nikon D200 1.3 2.0 3.8 7.4 15.
Canon 20D 2.0 2.2 2.4 3.2 4.5
Canon S60 2.5
Canon S70 2.0 3.4 6.3 17.

The best noise is 1.2 ADU and the average of the lowest
7 values (iso 50 or 100) is 1.7 ADU.

Now let's look at a real device, e.g. a 14-bit converter from
Analog devices:
http://www.analog.com/en/prod/0,2877,760%255F788%255FAD7952,00.html
Note it says: �0.3 LSB typical, �1 LSB maximum.
Error depends on the speed of conversion. This device does
maximum 1 million samples per second. Canon's 1D Mark II
most do 100 million samples per second.

Here is Analog Devices summary of 14 and 16 bit A/Ds working at
~ 100 megasamples/sec:
http://www.analog.com/IST/SelectionTable/?selection_table_id=204
Notice that the SNR for 14-bit converters ranges 71.9 to
77.6 dB, and the lower SNR is for lower power devices (those that
would more likely be used in cameras). That's less than 12-perfect
bits equivalent. Also notice that no 16-bit converter reaches an
SNR above 80 dB (barely over 13 perfect bits equivalent).

12-bit converters do a little better,
http://www.analog.com/IST/SelectionTable/?selection_table_id=197
with SNR at 62 to 71 dB. 62 dB is less than 11 bits, consistent
with the noise observed in the cameras listed above.

Explore other converters:
http://www.analog.com/en/subCat/0,2879,760%255F788%255F0%255F%255F0%255F,00.html

Busted!

Roger

From: Paul Furman on
Roger N. Clark (change username to rnclark) wrote:

> John Sheehy wrote:
>
>> Quantization is just the act of converting analog data to digitized
>> integers. If there is no added noise in the process, then any analog
>> range of values equivalent to one ADU will wind up with that single
>> ADU value. For systems where absolute values matter, this means
>> errors over any one ADU range, like -0.999 to 0, or -0.5 to +0.499, or
>> 0 to +0.999; never +/- 1 as Roger suggests in other posts.
>
>
> Gee, some simple research would prove you are wrong.
> Try reading http://en.wikipedia.org/wiki/Analog-to-digital_converter
> which is a pretty good writ-up.
> For example, note the statement:
> "Commercial converters usually have �0.5 to �1.5 LSB error in their
> output."
> (section on commercial analog-to-digital converters.
>
> Let's look at some noise in ADUs from a wide range cameras:
>
> Camera Read Noise in ADU (or DN, or LSBs)
> ISO: 50 100 200 400 800 1600
> Canon 1DMII 1.2 1.3 1.4 1.7 2.5 4.8
> Canon 5D 1.8 1.8 1.9 2.1 2.6 7.4
> Canon 10D 1.4 2.0 3.9 6.4 13.
> Nikon D50 1.8 4.0
> Nikon D200 1.3 2.0 3.8 7.4 15.
> Canon 20D 2.0 2.2 2.4 3.2 4.5
> Canon S60 2.5
> Canon S70 2.0 3.4 6.3 17.

Is there a way to show the 'main' sensor noise in the same units
compared to this read noise? I think I understand that an AUD is the
smallest unit of info that can be read, right? And these AUDs are
essentially rounding errors, not random noise? If so I would expect them
to follow a more consistent increas like:

1.2 2.4 4.8 9.6 19.2 38.4

> The best noise is 1.2 ADU and the average of the lowest
> 7 values (iso 50 or 100) is 1.7 ADU.
>
> Now let's look at a real device, e.g. a 14-bit converter from
> Analog devices:
> http://www.analog.com/en/prod/0,2877,760%255F788%255FAD7952,00.html
> Note it says: �0.3 LSB typical, �1 LSB maximum.
> Error depends on the speed of conversion. This device does
> maximum 1 million samples per second. Canon's 1D Mark II
> most do 100 million samples per second.
>
> Here is Analog Devices summary of 14 and 16 bit A/Ds working at
> ~ 100 megasamples/sec:
> http://www.analog.com/IST/SelectionTable/?selection_table_id=204
> Notice that the SNR for 14-bit converters ranges 71.9 to
> 77.6 dB, and the lower SNR is for lower power devices (those that
> would more likely be used in cameras). That's less than 12-perfect
> bits equivalent. Also notice that no 16-bit converter reaches an
> SNR above 80 dB (barely over 13 perfect bits equivalent).
>
> 12-bit converters do a little better,
> http://www.analog.com/IST/SelectionTable/?selection_table_id=197
> with SNR at 62 to 71 dB. 62 dB is less than 11 bits, consistent
> with the noise observed in the cameras listed above.
>
> Explore other converters:
> http://www.analog.com/en/subCat/0,2879,760%255F788%255F0%255F%255F0%255F,00.html
>
>
> Busted!
>
> Roger
>
From: John Sheehy on
"Roger N. Clark (change username to rnclark)" <username(a)qwest.net> wrote
in news:45FF8497.8020101(a)qwest.net:

> John Sheehy wrote:
>
>> Quantization is just the act of converting analog data to digitized
>> integers. If there is no added noise in the process, then any analog
>> range of values equivalent to one ADU will wind up with that single
>> ADU value. For systems where absolute values matter, this means
>> errors over any one ADU range, like -0.999 to 0, or -0.5 to +0.499,
>> or 0 to +0.999; never +/- 1 as Roger suggests in other posts.
>
> Gee, some simple research would prove you are wrong.

Gee, maybe you should read what I actually write. I never said that the
low ISO read noise has nothing to do with the ADC. I said it wasn't the
*bit depth* that causes the noise, in reply to the idea that the noise
was a mathematical artifact of quantization. It is only reasonable that
in the design of ADCs, bit depth far beyond analog noise are not
worthwhile, in general, making the typical ADC only designed for a
worthwhile bit depth, putting them all in a close range.

If you google my posts in other forums, you will see that I have
concluded that the flat rate of read noise at all Canon DSLR ISOs
probably has something to do with the last stages, including the ADC. I
have not concluded, in along time, however, that it is because of the
bit depth of the capture. It is easy to quantize data further, and see
at what point on the quantization curve you are. The fact is, you have
to quantize ISO 100 by about two bits, and ISO 1600 by about 3 bits,
before you see more noise, due to the quantization.

> Try reading http://en.wikipedia.org/wiki/Analog-to-digital_converter
> which is a pretty good writ-up.
> For example, note the statement:
> "Commercial converters usually have �0.5 to �1.5 LSB error in their
> output." (section on commercial analog-to-digital converters.

If you had paid any attention to what I wrote, you would have seen that I
wrote "If there is no added noise ...". IOW, I was clearly and
deliberately taking the mathematical aspect of quantization into
isolation. I mentioned also in some other spot that it was not 100%
clear if you were talking about the mathematical act of quantization, or
the total effect of the ADC, incuding the noise it introduces. The fact
is, you used the exact term "+/- 1", which doesn't look like a real noise
figure, but a mathematical, theoretical one. For me to lean towards the
interpretation that you meant that the +/- 1 was a mathematical error was
only logical. Once again, your language leaves a lot of mystery.

In the past 24 hours, I have had three people on DPReview quote your work
to me, to prove that the 14 bits in the mkIII will automatically increase
DR by 2 stops, because current cameras are limited by 12-bit capture.
had you made it clear that it isn't the bit-depth itself, but the noise
inherent in real-world ADCs, people might be drawing more accurate
conclusions. There is only going to be 2 more stops of DR if the
blackframe noise drops to 1.3 14-bit ADUs (0.325 12-bit ADUs). The
Imaging Resource mkIII had ISO read noises of 4.88 14-bit ADUs and
greater (I get 7.91 in one file; this may have some kind of electrical
interference; I have to look closer for patterns).

> Let's look at some noise in ADUs from a wide range cameras:
>
> Camera Read Noise in ADU (or DN, or LSBs)
> ISO: 50 100 200 400 800 1600
> Canon 1DMII 1.2 1.3 1.4 1.7 2.5 4.8
> Canon 5D 1.8 1.8 1.9 2.1 2.6 7.4
> Canon 10D 1.4 2.0 3.9 6.4 13.

Those 10D figures are way off. They are 1.9, 2.8, 4.9, 9.0, and 18.0.
Perhaps your figures were taken from a blackpointed RAW blackframe.

The 5D figure is very high for ISO 1600, also. The 5D ISO 1600
blackframes I have here are all 4.6.

> Nikon D50 1.8 4.0
> Nikon D200 1.3 2.0 3.8 7.4 15.

I don't recall seeing values this low at the low ISOs in the Nikon RAW
files I had. These are probably taken literally from the RAW blackframe,
so they are automatically reduced to about 60% of what they'd be if they
weren't black-clipped, like the Canons.

> Canon 20D 2.0 2.2 2.4 3.2 4.5

> Canon S60 2.5
> Canon S70 2.0 3.4 6.3 17.

> Busted!

You should pay more attention. I never said no noise came from the ADC
stage or unit; I said the *bit depth* was not the problem.

Let me state my viewpoint with a very clear example; if you quantize a
12-bit Canon DSLR ISO 100 to 11 bits, it will lose little DR, much closer
to 0 stops than 1 stop.

If the 1DmkIII actually had noise of 1.3 14-bit ADUs, and you quantized
that RAW data to 11 bits, it would still have more DR at the pixel level
than a 12-bit RAW from existing 12-bit Canons.



--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS(a)no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
From: acl on
On Mar 21, 1:08 am, John Sheehy <J...(a)no.komm> wrote:

> > Nikon D50 1.8 4.0
> > Nikon D200 1.3 2.0 3.8 7.4 15.
>
> I don't recall seeing values this low at the low ISOs in the Nikon RAW
> files I had. These are probably taken literally from the RAW blackframe,
> so they are automatically reduced to about 60% of what they'd be if they
> weren't black-clipped, like the Canons.

Exactly: For the D200 at least, if you measure from areas where the
average signal isn't zero, you see clearly that a measurement from a
blackframe gives too low a stdev, consistent with clipping. This
occurs with dcraw and other software which uses it to read the data,
but it doesn't look like dcraw itself subtracts an offset or anything
(but I may have missed it).

From: Roger N. Clark (change username to rnclark) on
John Sheehy wrote:

> IOW, you can turn the last four
> least significant bits of any ISO 1600 from a current Canon into zeros,
> and gain only a tad of noise, and still be quite a bit cleaner than ISO
> 100 under-exposed by 4 stops, even though they are both quantized exactly
> the same.

Correcting the half truths is getting tiring.

Here is a demo: See figure 9 at:
http://www.clarkvision.com/photoinfo/night.and.low.light.photography

Here is the original raw data converted linearly in IP, scaled by 128:
http://www.clarkvision.com/photoinfo/night.and.low.light.photography/nightscene_linear_JZ3F7340_times128-876px.jpg

Now here is the same data with the bottom 4 bits truncated:
http://www.clarkvision.com/photoinfo/night.and.low.light.photography/nightscene_linear_JZ3F7340-lose-4bits_times128-876px.jpg

You lose quite a bit in my opinion.
It would be a disaster in astrophotography.

Roger