Canon SX40HS long expoisure noise problems - RAW Shooting and Processing - CHDK Forum
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Canon SX40HS long expoisure noise problems

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Offline samdgt

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Canon SX40HS long expoisure noise problems
« on: 29 / November / 2011, 15:05:56 »
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I really like to take night shots but I am having huge problems with WAY to much noise in the photos. I even try using lightroom to take some of it away but it is still not enough. What settings should I use for optimal noise reduction and clearity when shooting at night. I usually have around 30sec with iso around 150.
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Offline outslider

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Re: Canon SX40HS long expoisure noise problems
« Reply #1 on: 29 / November / 2011, 18:05:16 »
Well, I'm using ISO 80 and rather longer time. On P&S cameras even not very high ISO might cause a lot of noise. This is why P&S never have ISO such as 4000. I don't see too much noise on my photos using ISO 80, but ISO 200 is quite noised.

On the other hand - have you got dark frame enabled? I saw that disable the dark frame substraction increases the noise.

You could also post a sample photo, one can compare it with ones photos.

I have A LOT of noise on photos taken for 30 minutes or more than 1 h, but not in seconds.

You can copare with your photo:
http://chdk.setepontos.com/index.php?topic=6919.0

exposure: 2.5 hour (by raw sum of shorter exposures).
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Offline samdgt

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Re: Canon SX40HS long expoisure noise problems
« Reply #2 on: 30 / November / 2011, 15:32:53 »
Im pretty sure I had dark frame enabled. Should I have the raw buffer on or off? Also under the quality settings in chdk what should I set that to?

Another problem I am having is that I will set the iso to something and once I review the picture and check what the iso was set at for the picture it will be some oddball number other than what I had the ISO set at. For example last night I just took a picture in my room with the lights on and had the iso set to 15 and exposure set to 2 seconds. The picture came out really clear with very little noise but when reviewed the ISO shows it was set at 26!?!?
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Offline reyalp

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Re: Canon SX40HS long expoisure noise problems
« Reply #3 on: 30 / November / 2011, 22:17:29 »
Quote from: samdgt on 30 / November / 2011, 15:32:53
Should I have the raw buffer on or off? Also under the quality settings in chdk what should I set that to?
None of these will affect noise. Raw buffer cached will speed up DNG processing, otherwise makes no difference. The CHDK quality override only enables you to choose "super fine" quality on cameras that don't support it, and this generally just results in a larger image without visible improvement in quality.
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Another problem I am having is that I will set the iso to something and once I review the picture and check what the iso was set at for the picture it will be some oddball number other than what I had the ISO set at. For example last night I just took a picture in my room with the lights on and had the iso set to 15 and exposure set to 2 seconds. The picture came out really clear with very little noise but when reviewed the ISO shows it was set at 26!?!?
For unknown reasons, Canon uses two different kinds of ISO numbers, "real" and "market". The "market" values are used for display, but for technical reasons, CHDK uses the "real" values for ISO override.

That said, I'm not aware of any CHDK cameras that are actually able to override ISO lower than the normal Canon low value. The only way to verify this is by comparing image data of otherwise identical exposures (ideally raw, but jpeg is probably valid in most cases). The override value appearing in camera displays or exif should not be taken as evidence the override worked.

If your subject allows, stacking multiple exposures is a good way to increase SNR. Aside from that, there's really not a lot you can do given a particular exposure length and ISO, this is the price you pay for lots of megapixels on a tiny sensor and no software hack is going to fix it.
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Offline samdgt

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Re: Canon SX40HS long expoisure noise problems
« Reply #4 on: 01 / December / 2011, 00:20:21 »
So basically what your telling me is that while I am able to override to longer exposure time with CHDK the ISO override feature really does nothing? I am having all sorts of troubles getting this set up correctly.

Maybe I am asking to much out of this camera.

I will use CHDK and set the ISO to what "I" want it to be. It seems like it takes the value that I put in and multiplies it by around 1.5-2.0 depending on how high the ISO number I entered is.

I will have the camera set on a tripod and I will take 4 shots all same settings. The focal length will change from 6.7mm to some crazy number like 60926.4mm on shots 2 and 4 but on shots 1 and 2 it will remain 6.7mm

I am just having trouble figuring out what settings I have wrong or is it just a matter of the camera not being up to the task. I believe that using CHDK hypothetically you wouild be able to manually override settings on the camera which works for some settings but when reviewed there are incosistancies.

Your thoughts?
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Offline philmoz

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Re: Canon SX40HS long expoisure noise problems
« Reply #5 on: 01 / December / 2011, 00:28:27 »
Quote from: samdgt on 01 / December / 2011, 00:20:21
So basically what your telling me is that while I am able to override to longer exposure time with CHDK the ISO override feature really does nothing? I am having all sorts of troubles getting this set up correctly.

Maybe I am asking to much out of this camera.

I will use CHDK and set the ISO to what "I" want it to be. It seems like it takes the value that I put in and multiplies it by around 1.5-2.0 depending on how high the ISO number I entered is.

I will have the camera set on a tripod and I will take 4 shots all same settings. The focal length will change from 6.7mm to some crazy number like 60926.4mm on shots 2 and 4 but on shots 1 and 2 it will remain 6.7mm

I am just having trouble figuring out what settings I have wrong or is it just a matter of the camera not being up to the task. I believe that using CHDK hypothetically you wouild be able to manually override settings on the camera which works for some settings but when reviewed there are incosistancies.

Your thoughts?

The SX40HS is still a new port so there may be things that don't work correctly yet.

If you can provide more details on what you are trying I can try and replicate the problem.
Include details on the Canon settings as well as the CHDK settings you are trying please.
Also need to know which firmware version you have.

Phil.
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CHDK ports:
  sx30is (1.00c, 1.00h, 1.00l, 1.00n & 1.00p)
  g12 (1.00c, 1.00e, 1.00f & 1.00g)
  sx130is (1.01d & 1.01f)
  ixus310hs (1.00a & 1.01a)
  sx40hs (1.00d, 1.00g & 1.00i)
  g1x (1.00e, 1.00f & 1.00g)
  g5x (1.00c, 1.01a, 1.01b)
  g7x2 (1.01a, 1.01b, 1.10b)
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Offline reyalp

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Re: Canon SX40HS long expoisure noise problems
« Reply #6 on: 02 / December / 2011, 00:58:54 »
Quote from: samdgt on 01 / December / 2011, 00:20:21
So basically what your telling me is that while I am able to override to longer exposure time with CHDK the ISO override feature really does nothing?
No, I'm saying that CHDK ISO override has never (AFAIK) been shown to extend the the range significantly beyond what is available from the Canon firmware. This is unlike shutter overrides, which actually give you much longer and shorter exposures than Canon allows. The ISO override should work within the Canon range (taking into account the difference between "real" and "market" ISO), which is still useful if you want to set the ISO to something other than what the Canon firmware would have set, e.g. smart auto-ISO.

Some discussion of the real vs market ISO can be found in http://chdk.setepontos.com/index.php?topic=6396.msg67017#msg67017

Please keep in mind that CHDK operates by poking the guts of an undocumented system, without full understanding of how it works.
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Offline radioman193

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Re: Canon SX40HS long expoisure noise problems
« Reply #7 on: 13 / February / 2012, 11:41:06 »
If i could see one of your LONG exp. photos to see this "Noise" your speaking of .
but i do have a easy fix for the  HS long exp isue.

http://chdk.setepontos.com/index.php?topic=7583.0
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Offline Recyclojunk64

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Re: Canon SX40HS long expoisure noise problems
« Reply #8 on: 12 / May / 2013, 11:26:39 »
Sorry for resurrecting an old thread, but I want to be sure that I have the same issue with my SX40HS before I tear it apart to fix the grounding problem. I have been trying to take some long exposures, but in anything over several minutes produces a mosaic mess such as this example below taken with the lens cap on and dark frame subtraction enabled.

noise seems to almost increase exponentially with higher exposures.
Is this the same sort of problem that other people here have been talking about or is my camera just going psycho on me?
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Offline waterwingz

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Re: Canon SX40HS long expoisure noise problems
« Reply #9 on: 12 / May / 2013, 12:01:34 »
Quote from: Recyclojunk64 on 12 / May / 2013, 11:26:39
Sorry for resurrecting an old thread, but I want to be sure that I have the same issue with my SX40HS before I tear it apart to fix the grounding problem.
I'm not too sure I'd be taking my camera apart based on just radioman's advice. His images (now deleted) showed he was looking at "amp glow" - a purple color in one corner of the image.  And its not entirely clear that everyone agrees with his opinion on this subject - his "foil behind the sensor" might not be providing an electronic shield like he says - it might actually be a thermal barrier for example.  In any case,  your problem seems to be uniform across the whole image?  But its up to you if you want to try it - it would be interesting to see what results somebody else gets.

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I have been trying to take some long exposures, but in anything over several minutes produces a mosaic mess such as this example below taken with the lens cap on and dark frame subtraction enabled.
noise seems to almost increase exponentially with higher exposures.
Is this the same sort of problem that other people here have been talking about or is my camera just going psycho on me?
I see the ISO3200 on your photo.  AFAIK,  most people taking long exposures of things are using more "normal" ISO values ( in the range 80 to 400).   ISO3200 will really drive the sensor amps to the rails.  What happens if you repeat your experiment at ISO100?
« Last Edit: 12 / May / 2013, 12:07:50 by waterwingz »
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