Equal brightness for an image series.

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Equal brightness for an image series.

Postby Erik Krause » Thu Apr 04, 2013 4:21 pm

Hello,

I shot a series of images in a snowy landscape with a large snow covered meadow in the foreground, a distant town and a cloudy sky above. If I batch process these images the results have different brightness. In one image the snow is more white, in another one it is more gray. Source images where shot in full manual mode with -2EV, 0EV, +2EV. I tried both the lite and the trial version with Natural and Default preset.

Is there a way to convince SNS to output all images at equal brightness?
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Re: Equal brightness for an image series.

Postby Erik Krause » Sat May 04, 2013 10:02 pm

From the lack of response I assume that there is no way. A pity, since this would make SNS really unique. It would of course be necessary to analyze all images prior to processing them in order to get the appropriate values. The same technique could be used to smooth out brightness changes. A real benefit for those processing timelaps...
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Re: Equal brightness for an image series.

Postby phil68 » Sun May 05, 2013 7:17 am

Sorry, never had this problem... could explain the lack of answers
Nothing to do with pity :?

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Re: Equal brightness for an image series.

Postby Pjotr-One » Wed May 29, 2013 3:02 pm

Cant get the problem!
Naturaly a white with +2 EV is brighter than a white with -2 EV. Reduce the brightness of your monitor and you will see the effect at white too.
Nothing to do with the application.
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Re: Equal brightness for an image series.

Postby Erik Krause » Mon Jun 03, 2013 10:08 pm

Well, the problem is there, sorry if I couldn't make it clear. I use SNS to merge bracketed images before I stitch them to panoramas. Any brightness difference is clearly visible. The unblended preview of the panorama looks like this:
Zwischenablage01.jpg
Zwischenablage01.jpg (21.13 KiB) Viewed 8825 times

All source images where taken in manual mode, all exposed -2EV 0EV +2EV. Manual white balance. No brightness difference in the source images of the same exposure step. All processed the same with SNS-hdr preset natural. If you have a close look you can see that not only the brightness changes but also white balance is slightly different.

I know this problem from other HDR programs, where it is more exaggerated most of the time. Since SNS was praised for it's ability to generate flicker-less timelaps videos (where the flicker is caused by variations in brightness, too) I assumed the effect is less pronounced or even not present here. It is better, but far from perfect...
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Re: Equal brightness for an image series.

Postby Sebastian Nibisz » Mon Jun 03, 2013 10:59 pm

The amount of dynamics compression depends on the dynamics of the source images. SNS tends to be stretched histogram. In the case of differentiated source images should be loaded into the SNS the complex panorama.
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Re: Equal brightness for an image series.

Postby phil68 » Tue Jun 04, 2013 5:37 am

Sorry Erik, but to make HDR panorama, that is not a good method :( , use PTGUI instead , stitch the sets of brackets and then load the hole HDR panorama in SNS for tonemaping.

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Re: Equal brightness for an image series.

Postby Erik Krause » Wed Jun 05, 2013 8:26 pm

Phil, I use PTGui (and I know it very well, see the PTGui mailing list or the panotools wiki). And merging and tonemapping (or exposure fusion) before stitching is a valid and often used technique for bracketed panoramas, which avoids a fair number of problems. Usually the results are very good and PTGui is capable of correcting slight brightness differences. The finished panorama can be seen here: http://www.360cities.net/image/snow-cov ... merzhausen

Sebastian, processing the complete panoramas is not an option since this is a spherical panorama and SNS (like most other HDR programs with local tone mappers) causes artifacts in zenith and nadir. I'd like to have an option (if at all possible) for a batch of images to process them with equal brightness. This would also benefit HDR timelaps (which seems to be pretty popular ATM).
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Re: Equal brightness for an image series.

Postby Sebastian Nibisz » Wed Jun 05, 2013 9:05 pm

I will work to eliminate this problem.
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Re: Equal brightness for an image series.

Postby Pjotr-One » Thu Jul 04, 2013 5:12 pm

@Erik:
to avoid different brightness between the images shoot them in manual mode of your camera. In other case your camera takes a new messure with every picture!

Hope this will help!
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