How do I interpret Deringing Maps?

[Nocturnal]

Hi,

the deringing features in HDRWT and Atrous can output maps but I don't know how to interpret them. I searched the forum but 'deringing maps' gets no relevant hits. Can someone shed some light on this please? I'm writing part 3 of the PI series in Astro Photo Insight and I'd rather not write "forget about the maps, no one knows how to use them"

Thanks!

[Harry page]

Hi Sander

Good to see you back at the writing desk !!!!!!

can't help you on the Atrous maps , still can't get my head round it properly  

When I use the mask in HDR the maps seem to show darker areas for more  protection and when I increase the deringing amount the map becomes darker usually giving more protection to lower signal area's,  I am sure Juan will tell me I am all wrong  

I have mostly used the large scale maps , but very occasionally the small scale bit with a very small setting ( never more tan .05) as the result become very strange

Regards Harry

[Nocturnal]

Hi Harry,

yeah, during the summer I missed an 'episode' so it's time to get busy again. I suspect that the deringing maps are similar for both. For the article I'm only using HDRWT as I have most experience with that and it seems easier to get good results. Atrous is like a chainsaw. Great for cutting down trees but it'll take of your legs just as easily

[vicent_peris]

Hi Sander.

sorry, to date the deringing algorithms are not documented. I MUST write an article about them.

The purpose of outputting the deringing maps is to apply them manually. They are WAY MORE powerful if you apply them through PixelMath.

The deringing maps are applied by substracting them to the HDRW processed image. So you are correcting the Gibbs effect where the the deringing map is darker.

To output the deringing map:

- Put the right parameters of the HDRW algorithm.
- Activate the deringing checkbox.
- In case of making a small-scale deringing, put it at 1.0.
- In case of making large-scale deringing, put the small-scale deringing at 0 and put the large-scale one at 1.0. This is because the large-scale deringing is calculated after small-scale deringing is done. Anyway, you can put the right amount of small-scale deringing, and the put the large-scale amount at 1.0.
- Activate the Output deringing maps checkbox.

The resulting image will be always ugly because you are applying the deringing algorithms with an amount of 1. What we will do then is to modify the deringing maps, then apply the HDRW algorithm WITHOUT any deringing, and then apply the deringing maps through PixelMath:

HDWR_image - Deringing_map*K

where K is an amount you choose; generally this amount will not have the same value as the amount you put in the HDRW tool.

One note: sometimes the deringing map can have negative values, so visualization is very ugly. Just go the the IntensityTransformations category in the Process Explorer and use the Rescale module to rescale the values between [0,1].

Once you have a separate deringing map, you can modify it at your taste. It's very powerful to make curves or midtones adjustments to further isolate the ringed structures.

I will upload some examples in a couple hours.


Regards,
Vicent.

[Niall Saunders]

Hi Sander - I suppose I will finally have to 'ante up' for the AstroPhoto Insight subscription. I had avoided it for a long time, enjoying the download facility when it was free, and occsionally getting special dispensation from Al to obtain a 'one-off' for nothing (you can tell I'm Scottish, can't you  ).

But, seeing as Practical Astronomy appears to have gone bust (with most of my year's subscription  ), I should just move over to API (unless, of course, they can allow you to 'repost' your articles here, once a suitable time period has elapsed - this is the arrangement my Father and I have had with articles we have written for the Radio Society of Great Britain magazine, RadCom - we have permission to , eventually, republish the article on our own website, and often we just post the PDF version straight from their DTP software).

In any case, this current article might be worth the sub on its own merit !

Cheers,

[Nocturnal]

Hi Niall,

I'd hate for you to subscribe to the mag just for the HDRWT stuff. There's not that much there. It just shows how to experiment with values until you get an agreeable result. Most likely the values I use will work fine with your images though

API is a fine publication and well worth the measly few $ I think. But judge it for yourself