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G15, Strange Light in Pictures

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Offline granite4brains

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Re: G15, Strange Light in Pictures
« Reply #10 on: 12 / November / 2013, 14:17:36 »
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Quote from: reyalp on 12 / November / 2013, 13:38:08
Is the camera taking a dark frame or not? This should be very easy to tell, if it is, then it will be "busy" for exactly the same amount of time as the original exposure.

It would not be at all surprising if the CHDK dark frame control was broken on this port. It might also only be broken at certain settings.

It would be helpful if you can do a controlled test, you don't need to wait until there is a scene you actually want to shoot, just set the exposure settings and check if the dark frame is actually taken or not.

All else being equal, amp glow will be worse at high ISO.

Sorry, I should have specidied that.  Yes, this time the camera took a dark frame on every shot.

This is what seemed bizarre.  The time prior it was set to "auto" and sometimes it would take one, sometimes it wouldn't.  Every time it took a dark frame, the "amp glow" was gone.

This time out, I had it set to "on" and I got a busy signal every time, i.e. it took a dark frame every time.  So I was fully expecting the problem to be solved.  Instead I got the "amp glow" on every shot.  And the color of the glow changed to green.

I'll probably take it out again this weekend and try a few different things to try and narrow down what is going on.
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Offline reyalp

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Re: G15, Strange Light in Pictures
« Reply #11 on: 12 / November / 2013, 16:00:17 »
Quote from: granite4brains on 12 / November / 2013, 14:17:36
This time out, I had it set to "on" and I got a busy signal every time, i.e. it took a dark frame every time.  So I was fully expecting the problem to be solved.  Instead I got the "amp glow" on every shot.  And the color of the glow changed to green.
Are your taking raw or jpeg, and how are you processing and viewing the images?

Can you post an image with the green problem? A canon raw or CHDK dng would be preferable if you have them.

I wouldn't expect amp glow to change color much, the actual accumulation of charge doesn't care what filter is on a particular pixel. White balance etc could affect what color it comes out in a jpeg, but it seems pretty consistent when I've seen it. The same goes for dark frame subtraction, it's hard to imagine a failure that would subtract some channels more than others. So maybe your green glow is a different problem.
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Offline waterwingz

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Re: G15, Strange Light in Pictures
« Reply #12 on: 12 / November / 2013, 16:09:04 »
Quote from: granite4brains on 12 / November / 2013, 14:17:36
This is what seemed bizarre.  The time prior it was set to "auto" and sometimes it would take one, sometimes it wouldn't.  Every time it took a dark frame, the "amp glow" was gone.
At the risk of butting into this thread, I get confused about the various references to AUTO.  I assume you mean the CHDK setting, but what are the rest of your camera settings?  Typically, a Canon camera will only take a dark frame for longer exposures ( more than 5 seconds maybe - I don't believe anyone has taken a definitive survey - and it may also be ISO related).   Any chance some of your shots were shorted than others ?

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This time out, I had it set to "on" and I got a busy signal every time, i.e. it took a dark frame every time.  So I was fully expecting the problem to be solved.  Instead I got the "amp glow" on every shot.  And the color of the glow changed to green.
Did anything else change ?  In particular,  were you shooting at a higher ISO setting ?

Quote
I'll probably take it out again this weekend and try a few different things to try and narrow down what is going on.
Tracking the camera exposure settings (especially shutter speed and ISO) and whether the dark frame additional interval occurred would be most helpful here.
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Offline outslider

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Re: G15, Strange Light in Pictures
« Reply #13 on: 12 / November / 2013, 16:11:48 »
This is only a casual suggestion, but you mention two facts:


- amp glow was now seen on DFS turned to be on
- amp glow changed color to green (so the color is like to be inversed)

so maybe somehow your camera uses some saved dark frame, not using the one it creates after exposure - if the saved dark frame had more intense glow than the current one, it's now substracted from the image yielding green glow.

I have no idea, where is this saved frame stored. Or maybe camera overcalculates something...
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Offline reyalp

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Re: G15, Strange Light in Pictures
« Reply #14 on: 12 / November / 2013, 16:15:37 »
Quote from: outslider on 12 / November / 2013, 16:11:48
so maybe somehow your camera uses some saved dark frame, not using the one it creates after exposure - if the saved dark frame had more intense glow than the current one, it's now substracted from the image yielding green glow.
This is not possible. If the canon firmware uses a dark frame, it is created immediately after the light frame and subtracted in RAM. The on-board flash is not large enough to store a full raw frame.
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Offline reyalp

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Re: G15, Strange Light in Pictures
« Reply #15 on: 12 / November / 2013, 16:17:44 »
Quote from: waterwingz on 12 / November / 2013, 16:09:04
Typically, a Canon camera will only take a dark frame for longer exposures ( more than 5 seconds maybe - I don't believe anyone has taken a definitive survey - and it may also be ISO related).   Any chance some of your shots were shorted than others ?
Per the first post, they were all using 30 sec http://chdk.setepontos.com/index.php?topic=10882.msg106859#msg106859
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Offline granite4brains

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Re: G15, Strange Light in Pictures
« Reply #16 on: 12 / November / 2013, 19:03:40 »
Quote from: reyalp on 12 / November / 2013, 16:00:17
Are your taking raw or jpeg, and how are you processing and viewing the images?

Can you post an image with the green problem? A canon raw or CHDK dng would be preferable if you have them.

I wouldn't expect amp glow to change color much, the actual accumulation of charge doesn't care what filter is on a particular pixel. White balance etc could affect what color it comes out in a jpeg, but it seems pretty consistent when I've seen it. The same goes for dark frame subtraction, it's hard to imagine a failure that would subtract some channels more than others. So maybe your green glow is a different problem.

I've been shooting mostly JPG, but I do have on batch from this last weekend that was JPG+RAW.

I'll try and put together an album with a few pictures showing what was going on from both weekends I went out.  (Hopefully, smugmug can take the RAW.)

Probably take me a few days, or maybe not until the weekend.

Thanks again for taking a look at this.
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Offline granite4brains

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Re: G15, Strange Light in Pictures
« Reply #17 on: 12 / November / 2013, 19:05:56 »
Quote from: reyalp on 12 / November / 2013, 16:17:44
Quote from: waterwingz on 12 / November / 2013, 16:09:04
Typically, a Canon camera will only take a dark frame for longer exposures ( more than 5 seconds maybe - I don't believe anyone has taken a definitive survey - and it may also be ISO related).   Any chance some of your shots were shorted than others ?
Per the first post, they were all using 30 sec http://chdk.setepontos.com/index.php?topic=10882.msg106859#msg106859

I think I shot a couple 25 sec exposures this time, as well.  But, yeah, they were all long enough to make for a very obvious "busy" signal while it took the dark frames.

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Offline waterwingz

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Re: G15, Strange Light in Pictures
« Reply #18 on: 12 / November / 2013, 19:44:02 »
Quote from: granite4brains on 12 / November / 2013, 19:03:40
I'll try and put together an album with a few pictures showing what was going on from both weekends I went out.  (Hopefully, smugmug can take the RAW.)
It would probably be better if you just uploaded the files to a file sharing site exactly as they came off your camera.    www.box.com works well for that.
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