too much noise - RAW Shooting and Processing - CHDK Forum
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too much noise

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Offline Gripitoy

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too much noise
« on: 21 / February / 2009, 23:58:36 »
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hi, i was experimenting with chdk, why is it that i get too much noise? what is the prefered settings for this to minimize color noise? thanks... im very new to this..
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Offline reyalp

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Re: too much noise
« Reply #1 on: 22 / February / 2009, 00:14:04 »
It's hard to give you any useful advice with some idea of what you are doing.

In general, lower ISO and shorter exposures will have less noise. You can also enable dark frame subtraction. Depending on what you are doing, you may also be able to use various post processing techniques.

Most of this isn't CHDK specific.
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Offline friday

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Re: too much noise
« Reply #2 on: 11 / March / 2009, 21:19:50 »
For still pictures, its quite easy to eliminate noise and still retail the original detail. There was a thread about the same thing that had a link to a program that eliminated noise. But, in that link, there was a link from there that took me to a photoshop tutorial.

Basically, it entailed taking bracketed photos, similar to what you would do if shooting HDR shots. But, you only need a normally taken shot and a shot taken at +2EV.

In Rawtherapee (or any other raw conversion program), render the normal exposure with the usual settings. For the +2EV shot, lower the exposure level in Rawtherapee to -2. This gives you a photo that is a little washed out, but about the same brightness as the normal exposure shot.

Do you use gimp?

Well, I do, so the photoshop tutorial had to be adjusted. So, here is what I do in GIMP. Take the normal shot, make this the background layer. Open a new layer using the overexposed adjusted shot. Now, with this second layer, add a layer mask using a greyscale and inverted image. You should now notice much of the noise is gone, but colors will be off a bit. So, add a third layer using the original, normal exposure image, but add a layer mask using a greyscale image.

Flatten the image, adjust the colors, and you're done. No noise and the colors should be better than the original.

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Offline Gripitoy

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Re: too much noise
« Reply #3 on: 13 / April / 2009, 05:29:26 »
Quote from: reyalp on 22 / February / 2009, 00:14:04
It's hard to give you any useful advice with some idea of what you are doing.

In general, lower ISO and shorter exposures will have less noise. You can also enable dark frame subtraction. Depending on what you are doing, you may also be able to use various post processing techniques.

Most of this isn't CHDK specific.

okay, my settings are Iso=80 1/80 and still the raw image looks like i shot it at iso 1600
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Offline hotvedt

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Re: too much noise
« Reply #4 on: 13 / April / 2009, 08:53:05 »
Is it possible that this is the same that happens here:
http://chdk.setepontos.com/index.php/topic,3442.msg31756.html
?
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Offline reyalp

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Re: too much noise
« Reply #5 on: 14 / April / 2009, 01:46:06 »
Quote from: Gripitoy on 13 / April / 2009, 05:29:26
okay, my settings are Iso=80 1/80 and still the raw image looks like i shot it at iso 1600
What are you using to covert/view the raw ?
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Offline electronicfreak

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Re: too much noise
« Reply #6 on: 09 / June / 2009, 16:02:46 »
Quote from: Gripitoy on 13 / April / 2009, 05:29:26
okay, my settings are Iso=80 1/80 and still the raw image looks like i shot it at iso 1600
Generally, if you take RAW images, they can appear more noisy since the camera's noise suppression is not applied to RAWs. But with ISO80 it shouldn't look like ISO1600, maybe this can happen with extreme sharpening settings in your software.

The most likely reason for your problem is that the RAW image is underexposed. Most RAW conversion programs (as RAW therapee) will gain up underexposed images by default. Then the image appears quite normal but noisy.

First you should find out if this is actually your problem. With CHDK the camera can save the image as RAW and as JPG at the same time. If the image is underexposed, the JPG appears very dark. Possible reasons are mistakenly settings (manual exposure mode / exposure compensation / CHDK exposure replacement values).

 
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