10D ISO 1600 is pushed one stop from 800

wrote:
Wolfgang Weisselberg wrote:

In the lottery I'd assume (nearly) equal chances.
With sensors I don't.

Of course there will be *ranges* of RAW data that are inlikely. Any
value less than 120 is unlikely with Canon DSLRs. However, every
*range* has both odd and even numbers, in equal distribution.

You assume that there is an equal distribution in the range,
concerning the physical sensor.

When the
same pixels are always odd and others always even, neither has the
chance of being the other, and there is one bit of precision missing.

To show to a sufficienrt degree that these self-same pixels are
_always_ odd or even, you'd need far more than one picture.

Even if in the "dark frame" range that observation is true ---
that does not make it necessarily true in brighter ranges at the
same ISO setting.

-Wolfgang

MarkH wrote:
Wolfgang Weisselberg wrote in news:9nsla2-

Oh yes, it is! Unless the 10D has a Foveon chip, which it hasn't,
3/4 of the data has to be interpolated. Think bayer patterns

When you do not understand how Bayer interpolation works, it would be
better if you did not post about it. Thank you.

You are right, I thinko'ed.

For those that are interested:
means that with a Bayer pattern sensor the final output will consist of 2/3
of the data being interpolated.

On the average, this is true, and for the green channel only 1/2
of the pixels need interpolation.

-Wolfgang

In message ,
Wolfgang Weisselberg wrote:

wrote:
Wolfgang Weisselberg wrote:

In the lottery I'd assume (nearly) equal chances.
With sensors I don't.

Of course there will be *ranges* of RAW data that are inlikely. Any
value less than 120 is unlikely with Canon DSLRs. However, every
*range* has both odd and even numbers, in equal distribution.

You assume that there is an equal distribution in the range,
concerning the physical sensor.

That is a very safe assumption to make; about as safe as assuming that
the floor is there when I get out of my bed in the morning.

When the
same pixels are always odd and others always even, neither has the
chance of being the other, and there is one bit of precision missing.

To show to a sufficienrt degree that these self-same pixels are
_always_ odd or even, you'd need far more than one picture.

I should have said in "the same pattern". I have looked at other
images, and the pattern is the same, except when the data is clipped at
4095.

Even if in the "dark frame" range that observation is true ---
that does not make it necessarily true in brighter ranges at the
same ISO setting.

I looked at image RAW data also; the same thing.

I really don't understand why you are so stubborn about accepting this
pattern. It's as plain as the grid on a graph paper, and only exists at
ISO 1600 and 3200. At 800 and below, any pixel can have an odd or even
value.
--


John P Sheehy

wrote:
Wolfgang Weisselberg wrote:
wrote:
Wolfgang Weisselberg wrote:

In the lottery I'd assume (nearly) equal chances.
With sensors I don't.

Of course there will be *ranges* of RAW data that are inlikely. Any
value less than 120 is unlikely with Canon DSLRs. However, every
*range* has both odd and even numbers, in equal distribution.

You assume that there is an equal distribution in the range,
concerning the physical sensor.

That is a very safe assumption to make; about as safe as assuming that
the floor is there when I get out of my bed in the morning.

Only assuming a sensor without non-random (coloured) noise and
a perfect digitizer.

When the
same pixels are always odd and others always even, neither has the
chance of being the other, and there is one bit of precision missing.

To show to a sufficienrt degree that these self-same pixels are
_always_ odd or even, you'd need far more than one picture.

I should have said in "the same pattern". I have looked at other
images, and the pattern is the same, except when the data is clipped at
4095.

Do I understand you correctly:
- you have looked at at least a dozen pictures with ISO
1600, of several opjects
- at least half a dozen of these pictures have been exposed
correctly for ISO1600
- all of these pictures are in RAW
- when converting the image file from camera RAW to readable
RAW again, the identical image comes out (why should any
'cheat at histograms' algorithm not be in the converter?)
- all these pictures show a pattern of stripes
- however, it's not always the same pixels that are even
and odd, this varies from picture to picture
- when you turn up the contrast way way high, you can
actually see the stripes
or am I missing something?


I really don't understand why you are so stubborn about accepting this
pattern.

I do accept that you have seen some pattern in an HEX editor (and
up to now I only remembered you writing of one single dark frame).

However, the DNG format is not very trivial --- see for
yourself[1]. For example, what is the orientation --- it is
set as a single byte and is not optional. Could your stripes be
horizontal (page 13)?

What is the BlackLevel, and the BlackLevel pattern (page 19)
and BlackLevelDeltaH and BlackLevelDeltaV (page 20) --- and could
that pattern, as substracted (see page 37), unstripe your observed
'stripes'?

It's as plain as the grid on a graph paper,

But whatever it is that you see --- is it what you think it is?

Without the raw data[2] (and not having a 10D, producing them is
kind of hard) I cannot see what you see, only what you show me,
interpreted through your eyes. Of course I am sceptic, I owe it
to myself.

and only exists at
ISO 1600 and 3200. At 800 and below, any pixel can have an odd or even
value.

But then you'd get only ..0 ..4 ..8 .12 .16 with 3200 (i.e. 2
unused bits), _unless_ 3200 has more analogue gain than 1600 ... do
you get that?

-Wolfgang

[1] http://www.adobe.com/products/dng/pdfs/dng_spec.pdf
[2] .cr2, not the already processed .dng

In message ,
Wolfgang Weisselberg wrote:

Do I understand you correctly:
- you have looked at at least a dozen pictures with ISO
1600, of several opjects
- at least half a dozen of these pictures have been exposed
correctly for ISO1600
- all of these pictures are in RAW
- when converting the image file from camera RAW to readable
RAW again, the identical image comes out (why should any
'cheat at histograms' algorithm not be in the converter?)
- all these pictures show a pattern of stripes
- however, it's not always the same pixels that are even
and odd, this varies from picture to picture

I lost track of this thread, but now I have a better demo. No, the
stripes are different in every image; however, they are being applied
very evenly (odd and even number constitute 49.8 to 50.2% of the
images). This is an ISO 1600 image from the 10D, but showing only the
LSB (0=black; 1=white)

http://www.pbase.com/jps_photo/image/38841732

As far as it affecting the image is concerned, it is certainly too much
of an offset to be useful dithering, if in fact some are +1 and some are
-1. I believe they are offset all the same way, though, as a blurred
blackframe tends to have similarly-striped sections that look lighter
and darker than each other, after the blur is histogram-equalized (i.e.,
significant low-frequency content).
--


John P Sheehy