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  #21  
Old 20-04-2010, 09:18 AM
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oops

Last edited by mswhin63; 20-04-2010 at 09:39 AM.
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  #22  
Old 20-04-2010, 09:23 AM
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Originally Posted by mswhin63 View Post
I am also figuring out a few things with darks. Did a few a few days back.

First - If I alter the lights level do the flats get adjusted as well? It seems logical.
Second - the EOS450D has what the manual noise reduction which is supposed to take a dark and subtract it automatically. Is this proceedure any good?

Haven't had enough time to test it yet.
Altering the light level only changes the display not the actual data.
Note. Dark subtraction only works with raw or fits files. JPEG files have been compressed at the individual pixel level and this prevents the darks from subtracting the actual pixels affected.
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Old 20-04-2010, 09:38 AM
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Altering the light level only changes the display not the actual data.
Note. Dark subtraction only works with raw or fits files. JPEG files have been compressed at the individual pixel level and this prevents the darks from subtracting the actual pixels affected.
I'v been using adjusting RAW files prior to using them in DSS, I then use 16 bit TIFF files which I learn't does not alter the pixel base while it also provides the ability to adjust colour in DSS. When using RAW my final images alway come out Monochrome no matter how much saturation I use.

It would seem that the by adjusting the Lights to get more star that are present in the picture also bring ups the camera noise as well, I would also assume that darks would have the same thing and would need to subtract at the same level otherwise there would be a dis-proportionate SNR in the image. I have the same issue with Audio SNR as with IMAGE SNR.
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  #24  
Old 20-04-2010, 10:10 AM
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Guys,
you have to be aware that the purpose of INCR is not to reduce the noise, it is here to deal with hot pixels only.
What INCR actually does, it subtracts one dark frame from light frame.. This removes hot pixels from the frame, but at the same time doubles the noise power (because, noise being a random signal, it cannot be removed by subtraction - subtraction is the same thing as addition from the noise point of view).
This means that to arrive to the same S/N ratio in the final image, you have to stack a greater number of subframes, to average out the noise.
Practicality is another issue, and sometimes INCR is beneficial (when exposures are short and numerous)
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  #25  
Old 20-04-2010, 10:34 AM
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[QUOTE=bojan;583473](because, noise being a random signal, it cannot be removed by subtraction - subtraction is the same thing as addition from the noise point of view). QUOTE]

The statement correct especially about the addition of noise but most noise on CMOS sensors is more a manufacturing issue where each pixel is more sensetive to charge than another the noise can be somewhat predictable. This is the same as white and pink noise which is a manufactured noise which can be calculated out. I noticed this when brightening up multiple images I get the bars appearing on each image in the same place. The dark dosen't show this as it is too low for the eyes to see, but once the dark is brightened is can be seen as well.

The only noise left in a camera would be chip noise which is totally random.
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  #26  
Old 21-04-2010, 05:06 PM
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Certainly an interesting thread.

I have noticed, from my meagre experience, that INCR appears to give better images. But that said it takes up imaging time. So does doing darks at the end or imaging.

I am in the middle of building a new library of "darks". I noticed that with the rear LCD screen on (aka the exposure counter timer screen, not live view) produces a glow much like amp glow in the dark images.

I couldn't find the sub-menu to shut off the LCD screen completely. I can shut off the "live view" but not the exposure counter timer screen.

Easiest fix was to plug in a lead to the video out. This shuts off the rear LCD completely.

Edit:

Ahhhh Pressing the display button in the home screen shuts off the LCD completely. I was pressing it off only when it was in the countdown menu and thus it would re-activate the LCD display when that exposure was complete.

Last edited by wasyoungonce; 21-04-2010 at 05:34 PM.
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  #27  
Old 21-04-2010, 05:42 PM
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If you press the display button before shooting the timer display de-activates on the LCD. Just tested it while sitting here typing.
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  #28  
Old 21-04-2010, 06:15 PM
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If you press the display button before shooting the timer display de-activates on the LCD. Just tested it while sitting here typing.
Many thanks. Sorted.
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  #29  
Old 21-04-2010, 06:47 PM
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No probs, BTW I am not married to the camera, just happened to be with me at the time.
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  #30  
Old 21-04-2010, 07:29 PM
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Astrophotographers should never use ICNR. If your workflow needs darks at the same time as the lights, save/download the darks separately from the lights. This way many darks (of the same temperature) can be combined into a master the next day and applied to every light sub. When creating the master dark, software can eliminate cosmic ray hits from the individual darks and the dark current noise is reduced by sqrt of the number of darks subs used in the combine. A master dark with just 3 darks combined is far superior to one ICNR frame.

Fred: the adaptive feature in Maxim is "Dark Frame Scaling" in the Set Calibration dialog, the Auto-optimize setting is the interesting one for DSLR users.

Cheers,
EB
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  #31  
Old 21-04-2010, 07:36 PM
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Hi Malcom...too many fond memories with you camera to put it down?

Funnily enough, I noticed that when I view a dark frame with CS3 the hot pixels show up for around a second or so & then disappear (when using Adobe canon raw converter).

I think CS3 is finding & removing hot pixels.
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  #32  
Old 22-04-2010, 05:30 PM
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Oh nooooes.

A whole series of differing ISO darks I did have been auto rotated by camera.

I cannot rotate them back & keep them as cr2 raw files. I can rotate them with DPP but when I open them with photoshop they are back the wrong way.

I can rotate them with photoshop but it removes hot pixels and I cannot save as cr2s.

Yep you see it here 1st..."look at the idiot"!...Hrs of images lost.
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  #33  
Old 22-04-2010, 05:58 PM
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Quote:
Originally Posted by wasyoungonce View Post
Oh nooooes.

A whole series of differing ISO darks I did have been auto rotated by camera.

I cannot rotate them back & keep them as cr2 raw files. I can rotate them with DPP but when I open them with photoshop they are back the wrong way.

I can rotate them with photoshop but it removes hot pixels and I cannot save as cr2s.

Yep you see it here 1st..."look at the idiot"!...Hrs of images lost.
I did the same thing as well, but i did manage to rotate correct CR2 and also saved them as well.

I used Digital Photo Professional to do this.

I know some features of DPP aren't saved but I know rotations are. Just checked this while typing this post as well.
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  #34  
Old 22-04-2010, 05:59 PM
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OOP's didn't realise opening with Photoshop reverted them back. Maybe the only alternative is to produce 16bit TIFF with DPP and use them for the session.
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  #35  
Old 22-04-2010, 06:10 PM
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Thanks Malcom.

I cannot use photoshop as it removes the hot pixels and I suspect some of the noise automatically.

I really didn't want to convert them to a TIFF as i want to keep them for DSS etc.

Me thinks I'm up the creek!
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  #36  
Old 22-04-2010, 06:24 PM
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I understand, I convert them to TIFF before using them on DSS because I am having an issue with no saturation for CR2 files, still working on though. It would be interesting to see if I can get it working. The Darks I took were rotated and managed to rotate them to match but never used them as CRS is DSS yet. I will give it a go soon but delayed as I am having Out of Memory problems ATM.

I dont have photshop so I really can't say too much about that the issue with photshop, maybe DPP inverts them visually but not actually.
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