Eclipse HDR

Moderator: jsachs

pbandurian
Posts: 12
Joined: May 11th, 2009, 7:39 pm

Eclipse HDR

Postby pbandurian » November 12th, 2017, 12:19 am

I photographed the recent 21 August eclipse and have a series of very nice looking images, which, if I can properly combine them should yield a very nice image of the solar corona, prominences, and the lunar disk as illuminated by earthshine. The problem is properly combining the images. Each HDR sequence consists of seven exposures with two stops between successive pairs. Combined with the approximately ten stop range of the camera sensor, a Canon 5diii, that's about twenty-four stops of tonal range or about 16 million to 1. Tone mapping this is a challenge for any piece of software.

Perhaps obviously, I'm thinking of trying PWP's HDR/stacking transformation. But, so far, without luck. Any suggestions? I've tried several without satisfaction: HDR Expose 3, Photomatix, PTAssembler, and Aurora HDR. Thanks.

Cheers, Peter

jsachs
Posts: 780
Joined: January 22nd, 2009, 11:03 pm

Re: Eclipse HDR

Postby jsachs » November 12th, 2017, 7:43 am

To use PWP for this purpose, you first have to take calibration photos of a test target and process them the same way you will process your photos. 24 stops is probably overkill and is beyond what the calibration can handle. The procedure is described in the white paper:

http://www.dl-c.com/Temp/downloads/Whitepapers/Stack_Images.pdf

Once you have assembled the images you will still need to apply a final shaping curve to determine how to map the available gray levels to something you can display and print with 256 gray levels. Usually this takes the form of a contrast-enhancing S-shaped curve.

PWP's approach is to try to create a composite image that preserves a wide dynamic range uniformly across the entire image by reducing the overall contrast. Photomatix takes a different approach by blending different parts from different images, depending on which has the best contrast at any given point. For some landscapes the results are pretty good. I tried Aurora HDR on some images recently and found the resultss garish and highly unrealistic, so I have no idea what they are doing.

Again, bear in mind that the final result will have to squeeze the 24 (or however many) stops into 256 gray levels somehow so nothing is going to make that happen without compromises.

You may have better luck using fewer images - maybe 3 - one exposed for the background sky, one exposed for the highlights and one in between.
Jonathan Sachs
Digital Light & Color

Bernard
Posts: 39
Joined: April 25th, 2009, 2:44 pm

Re: Eclipse HDR

Postby Bernard » November 12th, 2017, 7:45 am

pbandurian wrote: But, so far, without luck.
Cheers, Peter


Why ? What was the problem ?
Photomatix is probably one of the best, if you did not succeed .....
You could try SNS-HDR : https://www.sns-hdr.com/
Bernard


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