From: ejmartin on
Slightly OT, I put together a little demo of what could be achieved by
eliminating amplifier/ADC noise from the signal processing chain. I
knew there was going to be an improvement, I was surprised by how
much, and the degree to which pattern noises are eliminated:

http://forums.dpreview.com/forums/read.asp?forum=1018&message=28749589
http://forums.dpreview.com/forums/read.asp?forum=1018&message=28750076

The proposed scheme seems so simple to implement, I wonder what the
hitch is...

emil

From: John Sheehy on
ejmartin <ejm_60657(a)yahoo.com> wrote in news:65d9585d-976f-4d52-ae38-
a61ce5d0278a(a)f36g2000hsa.googlegroups.com:

> Slightly OT, I put together a little demo of what could be achieved by
> eliminating amplifier/ADC noise from the signal processing chain. I
> knew there was going to be an improvement, I was surprised by how
> much, and the degree to which pattern noises are eliminated:
>
> http://forums.dpreview.com/forums/read.asp?forum=1018&message=28749589
> http://forums.dpreview.com/forums/read.asp?forum=1018&message=28750076
>
> The proposed scheme seems so simple to implement, I wonder what the
> hitch is...

Your result is probably a tad better than what you would get with two-
channel amplification, because you are getting different shot noise details
with the two shots, and they would be exactly the same with a dual-readout
of the same exposure, so your simulation has a "notch" in the shot noise of
1/2 stop where the ramped blend gives equal shot noise from both images.

--

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John P Sheehy <JPS(a)no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
From: Ray Fischer on
ejmartin <ejm_60657(a)yahoo.com> wrote:
>Slightly OT, I put together a little demo of what could be achieved by
>eliminating amplifier/ADC noise from the signal processing chain. I
>knew there was going to be an improvement, I was surprised by how
>much, and the degree to which pattern noises are eliminated:
>
>http://forums.dpreview.com/forums/read.asp?forum=1018&message=28749589
>http://forums.dpreview.com/forums/read.asp?forum=1018&message=28750076
>
>The proposed scheme seems so simple to implement, I wonder what the
>hitch is...

And we could improve the fuel efficiency of car by elimiting the
transmission and just having a combined 2nd and 5th gear.

I suspect that the key problem is that it's not possible to read out
the iso1600 image while continuing to expose the iso100 image.

--
Ray Fischer
rfischer(a)sonic.net

From: John Sheehy on
rfischer(a)sonic.net (Ray Fischer) wrote in news:488cb5bd$0$17200
$742ec2ed(a)news.sonic.net:

> I suspect that the key problem is that it's not possible to read out
> the iso1600 image while continuing to expose the iso100 image.

There is only one exposure in his scenario; it is simply read out in two
prallel channels with different gain. The high-gain one would clip away
the top 4 stops of the signal.

In his simulation, there are only two different exposures because he had no
choice in the matter.



--

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John P Sheehy <JPS(a)no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
From: Ray Fischer on
John Sheehy <JPS(a)no.komm> wrote:
>rfischer(a)sonic.net (Ray Fischer) wrote in news:488cb5bd$0$17200
>
>> I suspect that the key problem is that it's not possible to read out
>> the iso1600 image while continuing to expose the iso100 image.
>
>There is only one exposure in his scenario; it is simply read out in two
>prallel channels with different gain.

Then you have a noisy image at iso100. Not all the noise comes from
the amplifier. Much (maybe most) comes from the sensors themselves.
With few photos and then few electrons to read out there is more
sensitivity to randomness.

Of course you can increase the size of the sensors. Making them much
bigger improves their sensitivity and reduces noise at low light
levels. But the drawback there is you end up with a 2MP camera.

--
Ray Fischer
rfischer(a)sonic.net