Author Topic: M42 HDR Tool leaves mono core  (Read 3191 times)

Offline Rod771

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M42 HDR Tool leaves mono core
« on: 2014 February 15 23:08:24 »
Hi everyone!

I have some data on M42 and have tried to create an image using the HDR tool. I have tried it a few times and always seem to end up losing detail and colour in the core.

The data was acquired using a C11 Edge HD with a Hyperstar lens and a Canon 60Da. I have taken 3 sec subs for the core and 30, 60 and 90 second subs for the rest of the dynamic range.

I have intergrated and calibrated each exposure and have applied DBE. The files can be found in the link below, please have a try and see if the core can be tamed. In my result I think I may have clipped the bright data when stretching?

https://www.dropbox.com/sh/lezad998xdd2ll8/3tyrmSzIx-

I have attached and Jpeg of my result for reference.

Thanks

Rod



Offline astroedo

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Re: M42 HDR Tool leaves mono core
« Reply #1 on: 2014 April 23 01:51:32 »
Hi Rod, I've downloaded your images and gave a very fast try.

The only thing that I've seen is that your images are VERY red, you probably have had a strong blue-green dominant at the beginning,  or the flat field was very blue, this probably resulted in a red image.

I've seen that in the core of the saturated stars you have about 0.8 R and less than 0.3 G and B.

Maybe it's only a problem of color calibration.
I've tried with Gradient HDRComposition, but the result is very simila to yours.

If I have the time this evening I will do a better try.

Bye

Edoardo
« Last Edit: 2014 April 23 04:34:40 by astroedo »

Offline astroedo

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Re: M42 HDR Tool leaves mono core
« Reply #2 on: 2014 April 23 04:17:19 »
Here's my try.

Since my PC is quite old and slow I've resampled the image 3x3 using integer resample, but this does not affect the processing (I suppose  :laugh: )

During HDRComposition I lowered the binarizing threshold to 0.23 because I've seen that the saturated stars in B and G channels was at about 0.28.

In this way the HDR image seems a little bit better.
followed a VERY simple processing: Histogram transformation, HDRMultiscaleTransform and Curves, masked with a luminance mask, for saturation enhancement.

I don't know if my approach is correct  :-\ , but seems to work  :P

bye

Edoardo
« Last Edit: 2014 April 23 04:36:05 by astroedo »

Offline vicent_peris

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Re: M42 HDR Tool leaves mono core
« Reply #3 on: 2014 April 23 05:15:27 »
Hi,

This is a topic I use to cover in my workshops. I always recommend to generate a lightness mask before applying the dynamic range compression. After this processing step, you can apply a color saturation curve through this mask to enhance the color in the more illuminated areas.

This happens because the dynamic range is also compressed in the color information. Thus, it seems that you have a mono core, but it's only a matter of color saturation. Color is not lost. Moreover, HDRMT enhances local hues, you will notice it after the color saturation curve.

Best regards,
Vicent.

Offline astroedo

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Re: M42 HDR Tool leaves mono core
« Reply #4 on: 2014 April 23 05:53:17 »
Thank you Vicent for explanation,

so my idea of lowering the binarizing threshold is not correct (or at least is not the solution)?

thank you

Edoardo

Offline vicent_peris

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Re: M42 HDR Tool leaves mono core
« Reply #5 on: 2014 April 23 06:10:05 »
No, the binarizing threshold in the HDRComposition tool must be set so it is within the linear range of your camera. This threshold sets the limit where the shorter exposure is put on the longer one. So, if the limit is in the non-linear range of your camera (close to the saturation point, but it depends on each sensor), you can have problems for making to composition. The 0.8 is a good compromise IMO.

V.

Offline Rod771

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Re: M42 HDR Tool leaves mono core
« Reply #6 on: 2014 June 15 20:11:56 »
Thanks for the feed back guys  :)

I have re processed the image following your suggestion Vincent. It worked, I was able to retain colour in the core.

Thanks

Rod