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Old 16-10-2010, 02:50 PM
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Question "HDR" with a CCD

Can I do "HDR-like" processing techniques with my QHY9 CCD? Just reading Humayun's comments in Marin Pughs widefield thread here and the 2 lots of exposures he captured to make this great image made me ponder the need to explore the options for multiple exposure lengths in CCD images when time and sky allows. My reasoning:
  • Although QHY9 is 16bit for great dynamic range, has relatively small well depth
  • 8" Newt sucks in the light and saturates stars in my images pretty quick (particularly with smaller QHY9 well depth)
  • Pixinsight now has some very nice HDR tools
  • Logically this should be a good way of going deep for nebulosity on DSOs while maintaining star detail and colours
Presumeably there would be a lot more fiddling about proportional to how many HDR "layers" you collect.

Is this something people do too often?
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Old 16-10-2010, 02:57 PM
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Bert (Avondonk) processes all his wide field images with HDR. A bit of a search should turn up some info.
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Old 16-10-2010, 03:03 PM
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Rob,

Instead of letting the software determine what pixel should get what value from each image in the "HDR" process, why don't you learn layer masking in Photoshop? You have far more control over the final image, and, don't end up with haloing, saturation defects and gradients which wouldn't exist were you to blend manually.

H
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Old 16-10-2010, 03:30 PM
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Quote:
Originally Posted by Octane View Post
Rob,

Instead of letting the software determine what pixel should get what value from each image in the "HDR" process, why don't you learn layer masking in Photoshop? You have far more control over the final image, and, don't end up with haloing, saturation defects and gradients which wouldn't exist were you to blend manually.

H
Similar to the 3 or 4 layers people do to get the trap in M42 I guess H? On my "todo" list is to start doing a separate layer for star processing, so I guess these are all facets of the same things?
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Old 16-10-2010, 03:48 PM
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Precisely.

The point being that you, as the processor, have the ultimate control in the amount you wish to show through each layer.

Using "HDR" routines leaves everything up to the software with very minimal input on your part.

Furthermore, learning layer masking in Photoshop will open doors to you in all kinds of image processing, not just astrophotographic.

I'm a bit of a zealot in this regard. I hate to see people spend thousands of dollars on hardware, only to let software let them down. Software should not be a weak link in the image capture and processing train.

H
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Old 16-10-2010, 03:55 PM
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Yes, you're not wrong there - became obvious fairly early on I was going to spend many hours in front of a screen to get anywhere with this endeavour
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Old 16-10-2010, 04:00 PM
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Hmmm. I'm a bit slow H - just noticed the 2 HDR references in your sig. Do I detect a bit of anti-HDR bias coming out here

(no sarcasm intended - if your amazing pics come out of layer processing I'm convinced!)
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Old 16-10-2010, 04:19 PM
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If you want to see good HDR (and, how it should be used properly):

http://www.youtube.com/watch?v=IOuNA7mMgYY

The year was 1997. If I'm not mistaken, Dr. Paul Debevec received a standing ovation at SIGGRAPH where he presented this. I am yet to see more realistic lighting in an animation to date. I used to be a 3D modeling/animation nerd in my younger years. I sometimes wonder where I'd be now if I kept up with it!

In a nutshell, HDR image processing was used after photographing chrome balls from different angles inside St. Peters Basilica. The basic idea being that the chrome balls capture all the specular light sources inside the building. A model of the building is then created and the chrome balls wrap (as it were) around the model providing global illumination; the highlights then become the light sources. So, there's no "artificial" light sources in the animation.

This, and, in video games, is where HDR excells. At the end of the day, if it works for you/whoever, and your images turn out how you want them to, then, more power to you.

H
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Old 16-10-2010, 07:42 PM
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I use EasyHDR and it has full control over all the parameters while simultaneously drawing on the data from ALL the different exposure stacks.

Below are a couple of pictures showing the controls of Easyhdr.

I can assure you there is nothing like adjusting an image with potentially a twenty bit dynamic range.

Bert
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Old 16-10-2010, 07:49 PM
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Here are the six images that produced the HDR.

The exposures are 7s, 15s, 30s, 60s, 120s and 240s twenty of each.

Bert
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Click for full-size image (CV_RZ_RG1.JPG)
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Click for full-size image (CV_RZ_RG2.JPG)
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Click for full-size image (CV_RZ_RG3.JPG)
132.6 KB28 views
Click for full-size image (CV_RZ_RG4.JPG)
160.3 KB34 views
Click for full-size image (CV_RZ_RG5.JPG)
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Click for full-size image (CV_RZ_RG6.JPG)
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Last edited by avandonk; 16-10-2010 at 09:17 PM.
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Old 16-10-2010, 08:01 PM
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Here is the image with the previous settings straight out of Easyhdr without using any further adjusting.

12MB

http://d1355990.i49.quadrahosting.co...10/m42hdrc.jpg

Bert
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Old 16-10-2010, 08:40 PM
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Here is an animated gif of the longest exposure and the HDR. You will see than the dim stuff is about the same but the overexposed stars are far better.

An gif 600k

http://d1355990.i49.quadrahosting.co..._10/hdrm42.gif

Bert
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Old 16-10-2010, 09:35 PM
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Thanks Bert - I'm always in awe of your widefield work, and this helps show a bit of the magic going on to bring your data together. I'll just have to get my hands dirty give it a try sometime versus layers and Pixinsight. Like most things in this hobby, I expect it will be a case of not which tool is best, but figuring out what to use where and how to make it work effectively.

Wonderful widefield Orion too BTW

Bert, while I'm learning, how would you suggest I stop down a nifty 50 (F/1.8 II) lens when I use it on my 450D? I believe you have made up something from a coffee tin? I'd love to try and bit more widefield this year, and I expect stopping down like this would help a bit more with dew until I sort out a heater solution.
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Old 16-10-2010, 11:21 PM
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Good luck, Rob. :cryface:

H
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Old 17-10-2010, 09:39 AM
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Its ok H - I'm not going to the dark side....
Hang on, I have already haven't I if I'm doing astrophotography!?
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