night shooting tip?

12 years 3 months ago #191145 by LeahJean84
I was lookin around on the internet i came across something that said if you take a night shot and it comes out kinda noisy you can take the same shot with the lens cap on, paste that image over the night shot in photoshop, then change the layer to difference and it will help clean up the image


has anyone ever heard of this? I have yet to really try but thought it was kinda odd


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12 years 3 months ago #191147 by Shupp98
That makes no sense. It would be the same as taking an image and then adding a layer that was just a black background. When you go to difference, all you're going to see is the outline of what the original image was. To reduce noise use noise ninja or neat image or equivalent.


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12 years 3 months ago #191148 by LeahJean84
yeah, I didnt think it made much sense to me either. Never used noise ninja i'll look into it.


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12 years 3 months ago #191150 by Tgauge9
Actually that's how you do it. It does make sense ... at least for the non-random noise due to the detector not being complete even (as in every pixel the exact same sensitivity.

This is called "dark subtraction." Every astronomer does it. The dark ( image with the lens cap on) has to be taken for the same amount of time as the original image. This is also how in-camera noise reduction is done (and why it takes 2x as long as the original exposure).


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12 years 3 months ago #191152 by LeahJean84
Thanks. Cant wait to try this.


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12 years 3 months ago #191233 by effron

Why so serious?
Photo Comments
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12 years 3 months ago #191241 by Caprici
Well I guess what they are thinking of is the HDR method of adjusting images by using images of multiple exposures. I have read some HDR techniques that use difference as part of their image adjustment technique some don't. I guess the logic is that the grainy areas which show up as lighter spots to the rest of the image can be cancelled out using a blacked out image( an image of a lower exposure) and the difference technique just like with the HDR method. My thinking is there is no actual image with a lens cap on so it is a bit odd when reading it the first time. I say it could not hurt to try though.

There are however easier ways or much safer ways to the image to get rid of graininess in an image. However it does not hurt to have many techniques in one's hat of tricks. Try it and let us know what happens.

Caprici
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