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RAW averaging?

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Offline ragustin

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RAW averaging?
« on: 27 / January / 2010, 23:08:05 »
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Is RAW Averaging equivalent to HDR?
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Offline reyalp

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Re: RAW averaging?
« Reply #1 on: 28 / January / 2010, 05:38:01 »
No, it's essentially noise reduction.
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Offline barberofcivil

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Re: RAW averaging?
« Reply #2 on: 28 / January / 2010, 08:24:34 »
Quote from: reyalp on 28 / January / 2010, 05:38:01
No, it's essentially noise reduction.

Hmm, however, averaging bracketed RAWs would be similar to a simple dynamic range compression, nothing really fancy or artsy though like tonemapping. 

Bottomed out shadows and blown out highlights would have an incorrect weighting.  I wonder if a simple algorithm can be made to overcome that.  Sounds liek something else I may have to look into when I get time.
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Offline PS

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Re: RAW averaging?
« Reply #3 on: 29 / January / 2010, 12:34:07 »
Depends what you mean by HDR. You get Higher Dynamic Range by using RAW average.
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Offline jasolo

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Re: RAW averaging?
« Reply #4 on: 29 / January / 2010, 16:12:52 »
If I'm not wrong, when you RAW average three bracketed images you get an overexposed raw affected by the blown out pixels. For a +-2 bracketing: "normal" x values are in 0EV image, 4x in +2EV and x/4 in -2EV. Average then and you get:

(x + 4x + x/4)/3 = 1.75x  that it's less than one step (+0.8EV).

About getting a HDR in camera, I'm working in a solution that fuses RAWs from three bracketed images without the problems of HDR tonemapping. More info in this post: http://chdk.setepontos.com/index.php/topic,4737.0.html
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Offline barberofcivil

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Re: RAW averaging?
« Reply #5 on: 29 / January / 2010, 21:55:17 »
Quote from: jasolo on 29 / January / 2010, 16:12:52
If I'm not wrong, when you RAW average three bracketed images you get an overexposed raw affected by the blown out pixels. For a +-2 bracketing: "normal" x values are in 0EV image, 4x in +2EV and x/4 in -2EV. Average then and you get:

(x + 4x + x/4)/3 = 1.75x  that it's less than one step (+0.8EV).

About getting a HDR in camera, I'm working in a solution that fuses RAWs from three bracketed images without the problems of HDR tonemapping. More info in this post: http://chdk.setepontos.com/index.php/topic,4737.0.html

Yes, you're correct.  I got thinking down the linear line incorrectly.
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Offline reyalp

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Re: RAW averaging?
« Reply #6 on: 30 / January / 2010, 16:27:50 »
Quote from: PS on 29 / January / 2010, 12:34:07
Depends what you mean by HDR. You get Higher Dynamic Range by using RAW average.
Not really. If you take N shots with identical exposure settings in identical lighting, and average them, the final average will have the same dynamic range as any of the originals. The maximum possible dynamic range will be limited by what your sensor can do in a single exposure: Anything that is below black level or at max value in the originals will also be that way in the average. The only difference is that truly random variations are reduced. This doesn't extend the range in the way that bracketing would, but it may make the low end a lot more useful, since it would otherwise be dominated by noise.
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Offline PS

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Re: RAW averaging?
« Reply #7 on: 05 / February / 2010, 11:04:43 »
Unless whole signal is above noise floor I can't see reason why you won't get higher DR when noise level drops. Lowering noise uncovers lower values thus increasing usable DR.
« Last Edit: 11 / February / 2010, 14:44:16 by PS »
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