Posting an image... - page 2 - Hello, I'm a NEWBIE - HELP!! (Newbies assistance, User Guides and thank you notes) - CHDK Forum

Posting an image...

  • 13 Replies
Re: Posting an image...
« Reply #10 on: 12 / October / 2012, 19:40:29 »
Thank you for re-doing that Blackhole.

Re: Posting an image...
« Reply #11 on: 12 / November / 2012, 21:21:45 »
For very long exposures, you may want to think about using a "darkframe" as well.  You should be able to google plenty of info on the subject.  But basically what you want to do is take a picture with the same settings (ISO, exposure, etc.) as your picture but with the lens cap on.  Optimally, it should also be taken at the same air temperature and camera temperature as your original. 

You can then subtract the noise from your darkframe from the original.  In Gimp load both pictures as a separate layer.  Put the darkframe above the original in the layer list.  Then set the layer mode to "Subtract".

On both my SX20 and a530 I get a patch of reddish noise bleeding down from the top left corner on long exposures.  It looks like you may have the same problem. Subtracting a darkframe gets rid of that nicely.

If you plan on doing a lot of astrophotography, you may want to look into Registax and DeepSkyStacker.  They're both free.

Ok xeju thank you, i have a question....

I have gotten rid of GIMP for now; can i subtract the dark layer in Photoshop Elements?


Offline blackhole

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Re: Posting an image...
« Reply #12 on: 13 / November / 2012, 02:02:45 »
I can not say for sure because I only use Photoshop, but you can try it and it does not cost anything. The problem may be the availability of work with layers.
Download the free trial version and try the procedure used in Photoshop.

1. Open your dark frame and the light frame
2. Click on the dark frame image,Select>All,Edit>Copy
3. Click on the light frame image,Edit>Paste
4. Select the dark frame layer and change the blending mode to Difference
5. Change the opacity of the dark frame to the desired value

Re: Posting an image...
« Reply #13 on: 13 / November / 2012, 07:22:07 »
Thanks again...


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