10D ISO 1600 is pushed one stop from 800

I just took blackframe and super-overexposed white wall images at ISOs
800, 1600, and 3200 on my 10D. I converted them all to uncompressed DNG
files, and looked at the RAW data in a hex editor (set to look at the
data as decimal numbers, assuming 16-bit unsigned data). The data
patterns are the same for the 1600 and 3200, and both are a little
strange. You get a long string of even numbers, then a long string of
perfectly alternating odd and even numbers, then a long string of odd
numbers, then a long string of alternating numbers again. I don't know
if it's the camera or the DNG converter that is doing this to the data
(adding or subtracting one to blocks and striped blocks), but it's quite
clear that there are only 11 bits used for both ISO 3200 *AND* ISO 1600.
Here is some sample data from the ISO 1600 blackframe:

http://www.pbase.com/jps_photo/image/38034746

Note how only the vertical stripes marked have odd numbers.
--


John P Sheehy

In article ,
wrote:

I just took blackframe and super-overexposed white wall images at ISOs
800, 1600, and 3200 on my 10D. I converted them all to uncompressed DNG
files, and looked at the RAW data in a hex editor (set to look at the
data as decimal numbers, assuming 16-bit unsigned data). The data
patterns are the same for the 1600 and 3200, and both are a little
strange. You get a long string of even numbers, then a long string of
perfectly alternating odd and even numbers, then a long string of odd
numbers, then a long string of alternating numbers again. I don't know
if it's the camera or the DNG converter that is doing this to the data
(adding or subtracting one to blocks and striped blocks), but it's quite
clear that there are only 11 bits used for both ISO 3200 *AND* ISO 1600.
Here is some sample data from the ISO 1600 blackframe:

http://www.pbase.com/jps_photo/image/38034746

Note how only the vertical stripes marked have odd numbers.

So what?

In message ,
Randall Ainsworth wrote:

Here is some sample data from the ISO 1600 blackframe:

http://www.pbase.com/jps_photo/image/38034746

Note how only the vertical stripes marked have odd numbers.

So what?

So, you aren't very bright if you replied to an on-topic thread that
doesn't interest you.
--


John P Sheehy

wrote in message
...
In message ,
Randall Ainsworth wrote:

Here is some sample data from the ISO 1600 blackframe:

http://www.pbase.com/jps_photo/image/38034746

Note how only the vertical stripes marked have odd numbers.

So what?

So, you aren't very bright if you replied to an on-topic thread that
doesn't interest you.

Well, I'm interested but as someone who is ignorant of what I'm looking at I
have no idea what the significance of the odd numbers is even after reading
your post 3 times.

Greg

In article ,
wrote:

So, you aren't very bright if you replied to an on-topic thread that
doesn't interest you.

Who gives a **** about the sequence of 1's and 0's? It's the end result
that's important...it's about photography.

"Randall Ainsworth" wrote in message
...
In article ,
wrote:

So, you aren't very bright if you replied to an on-topic thread that
doesn't interest you.

Who gives a **** about the sequence of 1's and 0's? It's the end result
that's important...it's about photography.

This group's about Photography not digits ? ;oO

dylan wrote:
"Randall Ainsworth" wrote in message
...
In article ,
wrote:

So, you aren't very bright if you replied to an on-topic thread that
doesn't interest you.

Who gives a **** about the sequence of 1's and 0's? It's the end
result that's important...it's about photography.

This group's about Photography not digits ? ;oO

Well, actually, it's about SLR systems. I would have thought that a
better understanding of the internals of something might have enabled you
to make the best use of it? I think John is trying to explain something,
without shouting it too loudly.

Happy New Year,
David

In message ,
"G.T." wrote:


wrote in message
.. .
In message ,
Randall Ainsworth wrote:

Here is some sample data from the ISO 1600 blackframe:

http://www.pbase.com/jps_photo/image/38034746

Note how only the vertical stripes marked have odd numbers.

So what?

So, you aren't very bright if you replied to an on-topic thread that
doesn't interest you.

Well, I'm interested but as someone who is ignorant of what I'm looking at I
have no idea what the significance of the odd numbers is even after reading
your post 3 times.

Note that I said, "that doesn't interest you"; not, "that isn't clear to
you".

The odd numbers are a peculiarity; I don't understand them myself. They
occur in the raw data (which reads like english text in the image) not
at all at the beginning of the image (where all levels are even
numbers), then further into the image every other pixel has an odd
level, and there are sections that are all odd as well. The DNG
converter is not supposed to alter data at all, with the exception of
filling in defective pixels with interpolated data (which would result
in individual pixels breaking out of the pattern).

One speculation that I have is that Canon is doing this to make the data
look OK in a histogram (an equal number of odd and even values should be
expected

The fact, however, that the RAW data is all even or odd within patterns
suggests that the data is not really 12-bit at its source, but rather,
11-bit. What does this mean for the user? It means that you get the
same quality data by setting the camera to ISO 800 instead of 1600, if
you are shooting RAW, with an EC of -1. It also means that you get an
extra stop of highlights this way, as the camera would clip any value
above 2023 if the camera were set to ISO 1600.

For those of us who shoot in low light, this is actually very beneficial
to know. I have suspected that the camera is cheating ISO 1600 for a
long time, and consequently, I have been setting the camera to ISO 800
instead of ISO 1600 when shooting wildlife at dusk. That way, if there
truly is enough light for ISO 800, I will get the better ISO 800 image,
but if there is not enough light, it will shoot a shot that will "push"
to ISO 1600 with the same quality and more dynamic headroom than if the
camera were actually set to ISO 1600! I even set the EC to +1 at ISO
800 sometimes, if there aren't a lot of bright highlights. That will
make the aperture stop down more, when there is sufficient light
(effectively a better ISO 400 than if the camera were actually set to
ISO 400, because more bits represent the subject's dynamic range), but
will also work at ISO 800, or "1600" (as good or better than the camera
does 1600 with 0 EC) when necessary.

Also, "ISO 3200" or "H" is actually ISO 1600, under-exposed and pushed
by a stop, the same way.
--


John P Sheehy

In message ,
Randall Ainsworth wrote:

In article ,
wrote:

So, you aren't very bright if you replied to an on-topic thread that
doesn't interest you.

Who gives a **** about the sequence of 1's and 0's? It's the end result
that's important...it's about photography.

Digital photography completely depends on ones and zeros for the "end
result".
--


John P Sheehy

wrote:
In message ,
Randall Ainsworth wrote:

In article ,
wrote:

So, you aren't very bright if you replied to an on-topic thread that
doesn't interest you.

Who gives a **** about the sequence of 1's and 0's? It's the end
result that's important...it's about photography.

Digital photography completely depends on ones and zeros for the "end
result".


I think what he was saying is along the lines of, "It's not important to
me how a refrgerator works, as long as it keeps the beer at 38.7º F".

--
Frank ess