Does Deep Sky Stacker Produce HDR type output from wide ranging exposures ?

[Stickfarm8]

Greetings !

As I am learning (repeatedly !) to trust the histogram in the image capture software (BackyardEOS) a question comes to mind. Because my Photoshop skills at image processing still leave a lot to be desired I haven't been able to resolve this question based on actual imaging.

I have a lot of experience with HDR photography - particularly in aircraft museum settings, where you do a +2EV, 0 EV, -2EV image and merge the three together to get the wider dynamic range. My question is - if I do something similar with my exposures - say 300 sec, 180 sec and 120 sec, and stack thru Deep Sky Stacker - does it generate produce a similar effect as the HDR software I would use so that I can capture the spiral bands and the core in a wider range? 

In other words if the 300 sec exposure results in Andromeda's core being over exposed, but the detail in the band showing nicely, will the 120 second exposure compensate for the core overexposed in the 300 second exposure resulting in balanced image ? Or do I have to do this by merging the TIFFs produced of each exposure (3 tiffs - 300 sec, 180 sec, 120 sec) separately outside of DSS ?

Any help will be appreciated !!

[michael8554]

Not something I've tried but would guess that the DSS result will still show overexposure, you can't undo that. 

What will work is layers in image processing. 

Michael 

[wimvb]

Unless it has an hdr setting, dss will calculate the average of all three exposures. In true hdr, you want the best out of each exposure, not just their average. What you probably should do is create a master for each exposure, aligned against one single reference. Then you do hdr composition in photoshop or any other processing software. I know that Pixinsight has a process for this,  I'm not sure about other astro imaging software.

[ollypenrice]

DSS won't do this, I don't think. What it will do is weight all the subs in the same way, which you certainly don't want, since the improved S/N of the longer subs won't be given the weighting it deserves. Besides, the imager would always want to control the way the blending was carried out.

Personally I think that the need for multiple sub lengths is grossly over-rated and I rarely use them. The first thing to do is to look at the linear (unstretched) stack of long subs. Anything which is not saturated in that stack can be preserved in an unsaturated state in a fully stretched rendition by careful stretching. This might include the use of an HDR technique on a gentle stretch and a harder stretch of the same data. Or it might be done by a careful sequence of stretches using Curves.

My favourite HDR method for combining short and long subs, or soft and hard stretches of the same data, is this one, very well explained by the ever-helpful Jerry Lodigruss. http://www.astropix.com/html/j_digit/laymask.html

Olly

 

[8472]

Yes, there is a HDR stacking algorithm in DSS. You can group your different sub lengths in separately, too.

Will it will produce results you are satisfied with? Try it and see.