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"John Sheehy" <(E-Mail Removed)> wrote in message
news:Xns9D37E15B39E04jpsnokomm@216.168.3.70...
> "MikeWhy" <boat042-(E-Mail Removed)> wrote in
> news:hn9he2$b8u$(E-Mail Removed):
>
>> "John Sheehy" <(E-Mail Removed)> wrote in message
>> news:Xns9D37C7AD24BF0jpsnokomm@216.168.3.70...
>>> Paul Furman <paul-@-edgehill.net> wrote in
>>> news:hn4dn1$fb0$(E-Mail Removed)- september.org:
>>>
>>>> Alpine sunset at dusk with beautiful bright sky and clouds:
>>>> (and almost all scenes with a sky or important highlights)
>>>> -keep ISO low and use a tripod when needed.
>>>
>>> As computers/storage/firmware get faster, we could be shooting 16 ISO
>>> 1600 shots in rapid succession for an aligned ISO 100 composite, for
>>> a less read
>>> noise, and less camera shake blur, than "normal" ISO 100.
>
>> That's no bargain. That exposure is 4x as long as a single ISO 100
>> shot,
>
> No; total exposure time is exactly the same. ISO is linear.

ISO 1600 is 4 stops down from ISO 100, not 16 stops.

>> not counting 15 additional starts and stops.
>
> Well, this was a context where everything got faster ...
> I believe that there is a new P& or 4/3 camera that does something like
> this now. If it is truly a "tripod" type shot, then the extra time is not
> much of an issue. You'll just have hyphenation of anything moving against
> the background, though.

Please check the numbers; I'm pretty sure you have part of that wrong.
Stacking 8 exposures shot at (virtual) ISO 25600 might be what was intended.

Hyphenated, versus simply smeared in the single longer exposure. No biggee.

>
>> (The world is
>> divided into 10 kinds of people: those who get it, and those who
>> don't.)
>
> Just a bit ...

100 * 2^4 = 1600.
100 * 2^8 = 25600.
100 * 2^16 = 6553600.

John Sheehy wrote:
> Paul Furman <paul-@-edgehill.net> wrote in news:hn8fkj$u80$(E-Mail Removed)-
> september.org:
>
>> Closest Nikon has is to underexpose then lift the shadows.
>
> Well, Nikon has a number of cameras with very "liftable" low-ISO shadows.
> Canon is plagued with excessive shadow banding at low ISOs. The 7D has a
> lot of banding at low ISOs, but much of it is fixed pattern (and some
> apparently caused by poor firmware correction), and could have conceivable
> be calibrated out. I can get a decent small web-image from my 7D at ISO
> 100 under-exposed 8 stops, after subtracting a stack of blackframes.

Be interested to see an example of shadow banding at low ISO on the 7D -
a fragment at full resolution PNG lossless compressed would do.

Regards,
Martin Brown

John Sheehy wrote:
> Martin Brown <|||newspam|||@nezumi.demon.co.uk> wrote in
> news:8t2mn.90995$(E-Mail Removed):
>
>> Be interested to see an example of shadow banding at low ISO on the 7D
>> - a fragment at full resolution PNG lossless compressed would do.
>
> I'll soon be making examples for a thread on DPReview; I'll try to link to
> the images here.
>
> I've actually seen the banding in OOC JPEGs in deep shadow areas, without
> any pulling up of the shadows (ALO off).

If you can find one of these OOC JPEGs I would be interested to take a
look at it. My curiosity is peeked. The most obvious cause would be some
kind of rounding error in the transfer function from RGB to YCC.

Please send one to me privately at the odd looking reply to address.
(no alterations needed it is valid when unmodified)

Certain other well known leading packages have very similar faults
although the damage is usually most annoying in highlights where clear
chroma to luminance bands can appear in highlights.

A green to magenta diagonal gradient put through the JPEG encode/decode
cycle a few times is a very good test of rounding errors in the codec.
any rounding errors and it will break up into chunky bars of colour.
>
> There are basically two components to 7D low ISO banding; one is the
> typical recent-Canon non-fixed banding with lots of low-frequency content.
> The other is unique to the 7D, at least as a general problem. It is
> potential deep modulation of every 8th column of pixels, and different
> blackpoints for odd and even pixel rows. Some people are lucky, in that
> none of the 8 vertical lines in the 8-line period are deep, but most 7Ds
> have at least one period member that's pretty deep.

Unfortunate given that JPEG relies on 8x8 periodicity.
>
> Canon does a very ****-poor calibration of blackpoint-by-line in their
> cameras; Canon does not guard against the pitfalls of complex readout, and
> hence, their Rebels have better shadow IQ than their semi-pro siblings with
> similar sensors.

I only have Canon Ixus P&S but I can't say I have ever had problems with
their black point calibration. Its main attraction is always being with me.

Regards,
Martin Brown

In rec.photo.digital John Sheehy <(E-Mail Removed)> wrote:
> Paul Furman <paul-@-edgehill.net> wrote in news:hn8fkj$u80$(E-Mail Removed)-
> september.org:

>> Closest Nikon has is to underexpose then lift the shadows.

> Well, Nikon has a number of cameras with very "liftable" low-ISO shadows.
> Canon is plagued with excessive shadow banding at low ISOs. The 7D has a
> lot of banding at low ISOs, but much of it is fixed pattern (and some
> apparently caused by poor firmware correction), and could have conceivable
> be calibrated out. I can get a decent small web-image from my 7D at ISO
> 100 under-exposed 8 stops, after subtracting a stack of blackframes.

Doesn't Nikon black clamp its images? If so for a fair comparison the
Canon images should be manually black clamped to the same extent.

--
Chris Malcolm

In rec.photo.digital John Sheehy <(E-Mail Removed)> wrote:
> Chris Malcolm <(E-Mail Removed)> wrote in
> news:(E-Mail Removed):

>> Doesn't Nikon black clamp its images? If so for a fair comparison the
>> Canon images should be manually black clamped to the same extent.

> Black-clipping the RAW data does not remove noise; that is a popular myth.
> It removes more signal than it does noise, lowering SNR ever so slightly.
> Most converters seem to clip Canon RAW data as soon as it loads, anyway.

> In fact, offsetted RAW data loses more noise with downsampling. When I do
> manual conversions step by step, I always leave Canmon RAW data with
> negative values near black, after subtracting the offset, and don't black-
> clip until it's absolutely necessary (display image). The negative values
> balance out the positive noise in any kind of noise filtering or
> downsampling, bringing means near black closer to linearity. In black-
> clipped RAW data, you are left with blacks that have means above black,
> different for the three channels after WB; a mess, which many companies
> deal with by just trashing the deep shadows by removing color, and/or
> blackening near-blacks with a tone curve.

I said "clamping" rather than "clipping" but I may have used the wrong
term. What I meant was I thought Nikon had decided on a black
threshold below which they would simply make the pixels completely
black. So the deepest shadows are perfectly black with no noise at
all.

--
Chris Malcolm

In article <hna1r1$s2r$(E-Mail Removed)>, MikeWhy
<boat042-(E-Mail Removed)> writes
>"John Sheehy" <(E-Mail Removed)> wrote in message
>news:Xns9D37E15B39E04jpsnokomm@216.168.3.70...
>> "MikeWhy" <boat042-(E-Mail Removed)> wrote in
>> news:hn9he2$b8u$(E-Mail Removed):
>>
>>> "John Sheehy" <(E-Mail Removed)> wrote in message
>>> news:Xns9D37C7AD24BF0jpsnokomm@216.168.3.70...
>>>>
>>>> As computers/storage/firmware get faster, we could be shooting 16 ISO
>>>> 1600 shots in rapid succession for an aligned ISO 100 composite, for
>>>> a less read
>>>> noise, and less camera shake blur, than "normal" ISO 100.
>>
>>> That's no bargain. That exposure is 4x as long as a single ISO 100
>>> shot,
>>
>> No; total exposure time is exactly the same. ISO is linear.
>
>ISO 1600 is 4 stops down from ISO 100, not 16 stops.
>
And 4 stops is 1/16th of the exposure, so 16 shots at ISO1600 is the
same exposure time as 1 shot at ISO100.

You seem to be confusing stops with # of exposures.

>100 * 2^4 = 1600.

Correct and put another way this shows:
2^1 (ie. 2) shots at ISO1600 is the same exposure time as one ISO800
2^2 (ie. 4) shots at ISO1600 is the same exposure time as one ISO400
2^3 (ie. 8) shots at ISO1600 is the same exposure time as one ISO200
2^4 (ie. 16) shots at ISO1600 is the same exposure time as one ISO100

>100 * 2^8 = 25600.
So 256 exposures at ISO25600 will take the same time as one at ISO100.

>100 * 2^16 = 6553600.
So 65536 exposures at ISO6553600 will take the same time as one at
ISO100.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)