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Auto HDR by applying different ISO on same picture

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Auto HDR by applying different ISO on same picture
« on: 13 / September / 2008, 09:36:24 »
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Wouldn't it be possible to have different ISO-Levels applied on the same picture?
So the bright areas will get a lower ISO and dark areas a higher ISO. On every single pixel is the best ISO-Level applied.

-> This would result in a HDR like picture in just one shot.

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Offline PS

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« Reply #1 on: 13 / September / 2008, 12:53:40 »
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« Last Edit: 31 / January / 2011, 20:02:52 by PS »

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Offline fudgey

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Re: Auto HDR by applying different ISO on same picture
« Reply #2 on: 13 / September / 2008, 15:12:16 »
There may be a short settling time in changing ISO if it's an adjustable gain analog amplifier... would make it too slow to adjust for each pixel. If the hardware has separate (all simultaneously active) paths for several gain levels (and then fine tuning for a desired ISO value in software, much like Canon's software ISO 1600 modes sans the noise reduction), the highest non-saturated path could be selected and scaled in software.

Inaccuracy in gain would likely introduce visible distortion if an image is to use different gains for different pixels.

Anyway, certainly quite unlikely that these cameras could be used to test this. Even if they could, AFAIK we don't know how to directly read the sensor with success.

Re: Auto HDR by applying different ISO on same picture
« Reply #3 on: 14 / September / 2008, 00:58:37 »
Shooting RAW and apply some non linear curves would help?
Not sure this would help you: Custom processing for JPEG (Tone curve, CA ...)


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Offline fudgey

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Re: Auto HDR by applying different ISO on same picture
« Reply #4 on: 14 / September / 2008, 04:38:12 »
One thing I left out... what I wrote was mainly a noise reduction point of view, not HDR.

If you want to compress the dynamic range to a 8-bit JPEG on the fly by making bright spots less bright and dark ones less dark the curves feature indeed should work for this (of course without the noise reduction from ISO toggling).

But you really need to provide a curve to tell the camera how to compress. Even if you achieved this by toggling ISO, you would still supply a curve. If you don't, the optimal mathematical solution for each pixel would probably be 50% gray. And to create an image with 10 million gray pixels we don't really need to read the CCD at all...  :haha

What ISO toggling would give you is an increased dynamic range (higher than our current 10 bits), but the mapping that range to 8 bits would still be best done outside the camera.

 

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