A question about ISO on a hacked Canon dRebel

I've loaded the hacked code into my dRebel and it works fine, so far.

When I set ISO to 3200, is this done by bit shifting or analog
amplification ?

In some usenet group someone said that 800 _might_ be the fastest
native speed of the sensor, and that 1600 was done by shifting bits,
not by amplification.

I'm sure I don't understand the pros and cons of either aproach.
Amplification may just increase noise, shifting is at th eexpense of
dynamic range, and still picks up noise. Right ?

Comments ?









--

a d y k e s @ p a n i x . c o m

Don't blame me. I voted for Gore.

"Al Dykes" wrote in message
...
I've loaded the hacked code into my dRebel and it works fine, so far.

When I set ISO to 3200, is this done by bit shifting or analog
amplification ?

In some usenet group someone said that 800 _might_ be the fastest
native speed of the sensor, and that 1600 was done by shifting bits,
not by amplification.

I'm sure I don't understand the pros and cons of either aproach.
Amplification may just increase noise, shifting is at th eexpense of
dynamic range, and still picks up noise. Right ?

I think it's a shift left which doubles the binary value and that would
equal one f-stop. I have a 300D (not hacked) and have not found ISO 1600 to
be all that useful. It's noisy and ISO 3200 would be worse. I also know
that some DRebel users like ISO 1600 and 3200 and get decent results with
noise reduction software ... just not to my liking.

Al Dykes wrote:

I've loaded the hacked code into my dRebel and it works fine, so far.

When I set ISO to 3200, is this done by bit shifting or analog
amplification ?

In some usenet group someone said that 800 _might_ be the fastest
native speed of the sensor, and that 1600 was done by shifting bits,
not by amplification.

I'm sure I don't understand the pros and cons of either aproach.
Amplification may just increase noise, shifting is at th eexpense of
dynamic range, and still picks up noise. Right ?

Pretty much. I don't know how many stops of pre-A/D gain there are. Bit
shifting (up) will 'noisify' shaddow detail and put high dynamic detail at risk
of obliteration. You will get more quantization noise (the pattern created by
unfiltered digital amplification) which may make smooth/dark areas look lumpy.

Beyond the mechanics above, the s/w in the camera is also optimizing its
conversions from the sensor reading when converting to JPG (and in the PC when
converting from RAW to TIFF/JPG, etc.) These are very privy to the OEM.
Minolta for example have something in the camera called: "CxProcess™ III Image
Optimization" and there's no telling specifically what goes on in there...
analogous signal processing takes place in pretty much all digital cameras.

From the Minolta site: "Konica Minolta’s exclusive CxProcess III technology
brings out the best from the Maxxum 7D’s 6.1-million effective pixel APS-C size
CCD. CxProcess III optimizes color saturation, edge sharpness, and
highlight/shadow contrast to ensure that colors are rendered true-to-life.
CxProcess III also suppresses noise during slow-shutter imaging, and assures
rich textural detail and spatial perspective for vivid yet natural reproduction
of skin tones, clouds, and other subjects with delicate surface textures."

Cheers,
Alan
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"Alan Browne" wrote in message
...
Al Dykes wrote:

From the Minolta site: "Konica Minolta’s exclusive CxProcess III
technology
brings out the best from the Maxxum 7D’s 6.1-million effective pixel APS-C
size
CCD. CxProcess III optimizes color saturation, edge sharpness, and
highlight/shadow contrast to ensure that colors are rendered true-to-life.
CxProcess III also suppresses noise during slow-shutter imaging, and
assures
rich textural detail and spatial perspective for vivid yet natural
reproduction
of skin tones, clouds, and other subjects with delicate surface textures."

Cheers,
Alan
--
If you ever find yourself in one of those rare instances when you get the
Minolta and a pair of Canon (20D and 1D,II) DSLRs together at the same time
to compare the quality of output, you might discover a major contridiction
in the quoted text.

"Al Dykes" wrote in message
...
snip
.....

In some usenet group someone said that 800 _might_ be the fastest
native speed of the sensor, and that 1600 was done by shifting bits,
not by amplification.


a d y k e s @ p a n i x . c o m
---------------
You might want to look at the D70 review in Dpreview where there are side
by side comparisons of the resulting noise output between the D70 and the
300D (with normal firmware) are displayed. The "character" of the noise at
1600 is described as "blotchy" vs. more fine grained for the D70.
This *might* confirm the comment made about the 800 native speed
limitations.
Regards,
Don F

In message ,
"Charles Schuler" wrote:

I have a 300D (not hacked) and have not found ISO 1600 to
be all that useful. It's noisy and ISO 3200 would be worse. I also know
that some DRebel users like ISO 1600 and 3200 and get decent results with
noise reduction software ... just not to my liking.

One reason why quality nose-dives at the higher ISOs is not just the
noise itself; higher ISOs are often used in environments with poor
*quality* lighting, not just low quantity lighting. There tends to be
more shadows and highlights in indoor lighting, especially when the
walls, floors and ceilings are dark, or spotlights are used.

If you shoot ISO 1600 outdoors with good lighting, you might not even
notice the noise until close inspection.
--


John P Sheehy

In message ,
(Al Dykes) wrote:

I've loaded the hacked code into my dRebel and it works fine, so far.

When I set ISO to 3200, is this done by bit shifting or analog
amplification ?

3200 uses shifting.

In some usenet group someone said that 800 _might_ be the fastest
native speed of the sensor, and that 1600 was done by shifting bits,
not by amplification.

That may have been me. I remember getting the same values from my 10D
in the RAW data that I got for ISO 3200. I have better means of
verifying this now, and will give more exacting details. I was going by
DCRAW's output, which is kind of funky. Now, you can take a test shot
in RAW mode, convert it to an uncompressed Adobe DNG, and look at the
RAW data in all its rawness.

I'm sure I don't understand the pros and cons of either aproach.
Amplification may just increase noise, shifting is at th eexpense of
dynamic range, and still picks up noise. Right ?

Comments ?

I suppose that at the highest amplifications, amplification artifacts
become so strong that one stop of amplification might be worse than one
stop of quantization, so above ISO 800 or 1600 they switch to the
shifting, to make the "experience" of using different ISOs a smooth
transition. I don't know why they didn't use intermediate values other
than powers of two; say an amplification of 24x and multiply the numbers
by 1.333. Maybe that causes banding in the shadows, or the computation
takes too much time, but if the numbers were left alone, it could be
compensated better in a RAW converter where there would be no
intermediate posterized data.

Personally, I would like a custom function that turned on pure
amplification mode, and let *me* do the under-exposing, including
intermediate ISOs above 800, where things tend to change fast.

UPDATE:

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