Archived posting to the Leica Users Group, 2009/12/04

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Subject: [Leica] color accuracy vs. high-ISO performance
From: tgray at 125px.com (Tim Gray)
Date: Fri, 4 Dec 2009 13:44:43 -0500
References: <16221905.1259950491422.JavaMail.root@wamui-cynical.atl.sa.earthlink.net>

On Fri  4, Dec'09 at  1:14 PM -0500, Doug Herr wrote:
> There's an interesting thread on fredmiranda.com that discusses the 
> tradeoffs between sensor color accuracy and low-noise high-ISO performance:

It is partially true as far as I know.  After all, you could could simply 
throw on an ND filter over your sensor, reducing signal to noise (if you 
don't increase exposure to compensate).  CFA's reduce sensitivity similarly. 
However, there are many other factors which contribute to poor high-ISO 
performance.

Personally, I'd take just about everything you read on fredmiranda about 
technical details and science with a grain of salt.  Lots of funny logic and 
hearsay.  Not that we don't all do that at times.  But they seem to latch 
onto a certain idea and then try to apply it to everything, all the time.

> If this is true it could help explain the DMR's relatively poor high-ISO 
> noise performance along with its excellent no-fuss colors.  Comments and 
> additional technical insight are welcome.

That could have something to do with it.  As far as CFA characteristics go, 
you can see some of them in the Color Response tab of a camera's listing on 
dxomark.com.  I'm sure that is a simplistic view of things, but it's 
probably better than nothing.

I don't know how different the CFA's are on the M8 and the DMR, but the M8 
has quite a bit of green sensitivity in the blue channel which probably can 
cause some problems with color rendering.

(Let me see if I get this right:) It causes problems because our color 
systems use, for the most part, three *pure* colors, single wavelength, like 
RGB.  However, our sensors/film don't.  They see three bands of color, with 
varying sensitivities for different wavelengths across a given 'channel', 
which can be centered at different wavelengths as well from system to 
system.  This can cause metamerism, which can make reconstructing accurate 
colors a guess.

So for the most accurate color, we'd have very narrow bandwidth CFAs that 
were centered on R, G, and B.  But you'd throw out a ton of sensitivity.


In reply to: Message from wildlightphoto at earthlink.net (Doug Herr) ([Leica] color accuracy vs. high-ISO performance)