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long exposure- noise reduction = amp glow

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Offline barberofcivil

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Re: long exposure- noise reduction = amp glow
« Reply #10 on: 06 / December / 2007, 19:25:30 »
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Quote from: neilp1 on 06 / December / 2007, 16:56:15
Quote from: barberofcivil on 06 / December / 2007, 16:31:19

Good news (or is it bad?)  I was able to replicate it on my A570, it is also present on my S2 (though it isn't as bright with the same settings it seems), both in the same location, a bright one in the top left corner and one much less visible near the top center.  It seems that this may be related to the CCD itself and not the camera model.

One interesting thing I found, is that the internal dark frame subtraction virtually removes it, so it still seems that there is some slight exposure difference between your image and manual dark frame for some reason.

Yeah, i never noticed it with the standard pre-chdk 15 second exposures. Only with the NR turned off. But thats to be expected. Ill just dark frame subtract out of the camera with the software i have.

I have no idea what is causing it, but I would tend to think it is internal to the camera, either an internal light (not likely) or thermal sensitivity of some sort (or even UV light from something is possible to).

good/bad news?? hmm, depends... good that it can be replicated under the same conditions, but kinda bad for the astrophotos that id like to do with it.

Although that kind of imaging is 3rd down the list so its tolerable. I have tried some software solutions for removing it, and have got a pretty good PS action that i made that can be used to get rid of it. Doing a normal darkframe subtraction followed by a little more PS and its pretty much taken care of. Cant really argue with it, since its a $140 camera, performing well out of its documented specification range. 

Thanks for verifying it for me. You do see this in the LCD screen right after capture, correct? This was the main reason i got into the discussion with the other chap- he maintains that seeing it on the LCD is 'impossible'.

Cheers!



No problem!  Yes it was visible on the LCD after taking the photo.  The problem also seems to not just be limited to the A570, the S2 is (was) a higher end camera in it's day, so it's not just the cheaper cameras.

Can anybody else replicate on other models?

Perhaps a good addition to the CHDK would be to add an option for darkframe where it is saved as an image but not applied.  This way you could easily get a darkframe matching the original (without the need for a lens cap even) but apply it manually if you'd like.  Perhaps I'll add this to the request board.
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Offline Kalli

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Re: long exposure- noise reduction = amp glow
« Reply #11 on: 07 / December / 2007, 15:03:14 »
Hi
A620: purple field in top left corner,    height: ~800 pixel, width: ~155 pixel, shutter at 65".

I suppose a heat source might be located in the camera close to that erea (resistance, IC...)
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Offline GrAnd

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Re: long exposure- noise reduction = amp glow
« Reply #12 on: 07 / December / 2007, 15:13:35 »
Quote from: Kalli on 07 / December / 2007, 15:03:14
Hi
A620: purple field in top left corner,    height: ~800 pixel, width: ~155 pixel, shutter at 65".

I suppose a heat source might be located in the camera close to that erea (resistance, IC...)

Flash?

Or the picture on the sensor is 180 degrees rotated? Then it can be battery supply IC.
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Offline barberofcivil

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Re: long exposure- noise reduction = amp glow
« Reply #13 on: 07 / December / 2007, 15:16:51 »
Quote from: GrAnd on 07 / December / 2007, 15:13:35
Quote from: Kalli on 07 / December / 2007, 15:03:14
Hi
A620: purple field in top left corner,    height: ~800 pixel, width: ~155 pixel, shutter at 65".

I suppose a heat source might be located in the camera close to that erea (resistance, IC...)

Flash?

Or the picture on the sensor is 180 degrees rotated? Then it can be battery supply IC.

I think neither.  The location is pretty much the same for both my A570 and S2 which have completely different bodies, the S2 has a pop-up flash.  The battery compartment seems somewhat removed from the CCD location.  There is also the issue of some glow at the top middle.  I could only see this by bumping up the brightness of the images.
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Offline neilp1

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Re: long exposure- noise reduction = amp glow
« Reply #14 on: 07 / December / 2007, 18:29:37 »

cheers guys!

I too only see the came in the centre top of the pic if i enhance levels, but the one in the left is there even without processing. Id love to see an internal schematic of the camera 'wiring'... im pretty sure its a component issue, likely the amplifier. I had a hardwire modded 300d that had the exact same purple glow in the same location before the mod, which involved relocating the amp about an inch further away fromt he sensor. Post mod had no glow in that area.

Thanks all to have verified this, i was getting a little paranoid it was just me. Post processing gets rid of it pretty good, so im not too concerned since it seems my specific camera is performing similarly to others.
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SeriousWorm

Re: long exposure- noise reduction = amp glow
« Reply #15 on: 15 / December / 2007, 14:37:01 »
Just wanting to add, I've first tried the CHDK firmware yesterday, and have been experimenting A LOT with it on my (only digcam) A570IS, and yes there is the purple fringing in the upper left corner, with NR off, on long expositions.

Attached is an example, I think the shutterspeed was 65 sec, don't remember the other settings (not sure if the ISO was 80, as it says in EXIF, I don't remember if forcing an ISO actually writes it to exif). Focus was at infinity, althought it kind of doesn't matter, heh. The room was pitch black, and I additionally blocked any photons of light with my hand, and a pillow. The JPEG was opened and saved with no processing at Q90, to fit into the attachment.
« Last Edit: 15 / December / 2007, 14:43:36 by SeriousWorm »
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Offline ke7doy

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Re: long exposure- noise reduction = amp glow
« Reply #16 on: 15 / December / 2007, 15:03:09 »
On my 570 IS I get only a faint purple patch, about an inch and a half in from the top left corner, about 25 pixles in diameter.  I am hoping that this info will help someone figure out what is going on!
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Offline hindenburg

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Re: long exposure- noise reduction = amp glow
« Reply #17 on: 16 / December / 2007, 21:03:37 »
Same problem here. Model G7. Firmware 1.00J.

BTW: it might not be a heat issue. I made these pics last night, after i let the cam cool down outside for a few minutes (-7 degrees celsius). The results were the same as in any inhouse temperature shots i made before.

Just for the record:                                       

 
Picture a                                     picture b
exposure: 65 sec.                      all the same but iso 80       
f/2,8                                               
iso 400                                               
nr off                                                   
« Last Edit: 17 / December / 2007, 08:57:37 by hindenburg »
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Offline urbient

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Re: long exposure- noise reduction = amp glow
« Reply #18 on: 22 / December / 2007, 17:01:38 »
that looks exactly like my pictures with the a640 ... same corners .
so what is that and does it only happen when noise reduction is turned off ?
i had it nearly that strong with 15"

chris
« Last Edit: 22 / December / 2007, 17:04:12 by urbient »
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Offline a710is

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Re: long exposure- noise reduction = amp glow
« Reply #19 on: 22 / December / 2007, 17:36:01 »
I am getting pretty much no purple corner at ISO 80 but getting it a bit at ISO 400
I have noticed that although the noise and purple corner are the same, turning off the lcd so its backlight provides a somewhat darker picture.
therefore, for best results at long exposures and high ISO turn off the lcd.
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