DSS problem on NGC7000

[Tommy B]

Hi folks,

After a terribly long run of bad weather I finally got a chance to get out and have a go at the North American Nebula. I got about 1h 30m's of data and ended up with an image I was really pleased with....but one thing is bothering me about it. When I was examining the individual 6 minute subs they showed a lovely variety of star colours. However when I put everything into Deep Sky Stacker the final image is robbed of these colour variations and no amount of processing seems to bring them back.

Heres a visual example,

The first image is a single enhanced sub and the second is the final stack. Anyone experienced this before? I have experimented with the DSS settings for hours and nothing seems to change.

[AndyUK]

Hi Tommy - Would you mind dropping your frames (subs/darks/flats/bias...) into a dropbox folder for me to have a look at...? I just want to have a play myself, and if the process I use has any +ve effect, I'll pass it on to you

(I'll send you a PM)

[26Left]

I get exactly the same with DSS. Nebulosity might be worth a shot. I find it preserves colours very well. It's not free like DSS, but there is a trial version.

[AndyUK]

Hi Tommy - This is a fairly quick first pass...

I stacked all your lights/darks in DSS (I personally always use Median Kappa Sigma which could be wrong of course!) and then I used a couple of processing tweaks in DSS before saving it with changes applied. I then opened it up in Photoshop and applied a few iterations of levels and curves, the last of which I used on selective channels just to change the colour balance a tad - I could have made this a lot redder, but this is just my colouring preference...

(I'll upload the straight TIF DSS output into my dropbox (and this version TIF and JPG) so that you can download it / them and play with it /them yourself.)

If this is the sort of thing you (or 26Left) are trying to get to, I'll detail what settings I used at the end of DSS stacking - It's pretty much a default which I adopted for DSLR images after Deneb (Nadeem) introduced me to it ()

I suspect that there's quite possibly more that could be done to (with) this, but I'm still very much a beginner on this post-processing lark...

[Psychobilly]

The colour should be there just needs teasing out... you could try boosting the saturation in DSS to see whats there... you should be able to pull it out of the Autosave.tif ...

Peter...

[26Left]

I'd say that quite an improvement. The trouble I have with DSS is that stars tend to become burnt out after the stack, even through they weren't in the subs. For me, this makes the star colours difficult to recover.

[Tommy B]

I must say Andy that that looks great. Your help is very much appreciated. Would certainly be interested in the settings you used.

Your attempt is exactly what im looking for :D

[PhoenixRising]

Me too please

[AndyUK]

(Hi Peter - Yes, I found that the DSS Saturation was the key in opening up the colour... )

Okay, here's the settings I used - The top bit is pretty standard registering/stacking stuff, but the "secret" is the processing bit at the bottom...

1. Register settings - 5% Star detection threshold and reduce the noise by using a Median Filter

2. Stacking Settings

Standard mode

Light - Median Kappa Sigma clipping

Dark - Median Kappa Sigma clipping and Hot pixels detection and removal

Flat - Median Kappa Sigma clipping

Bias - Median Kappa Sigma clipping

Alignment - Automatic

Intermediate - TIFF

Cosmetic - [NONE]

Output - tif

3. RAW files

AHD Interpolation

Set Black point to 0

4. FIT files

[NONE]

5. POST-STACKING

RGB/K levels - Align the 3 channels so that the steepest gradient of the curve is in alignment with the peak of the aligned channels

Luminance - Set the lower darkness slider to 90.1, set the upper midtone slider to 9 and adjust the lower midtone slider to fine tune the steepest gradient of the curve is in alignment with the peak of the aligned channels. Anything slider position I haven't mentioned I generally don't touch...

Saturation - Set to c. 21

Then apply and save as a tif file with changes applied

(NOTE: These are only default DSS settings that I use - They may be wrong and may not be the same as anyone elses, and there may well be better defaults... but it's what has worked for me to date (unless something better comes along ))

Then open in Photoshop...

[Glider]

In 3, what do you select for camera white balance?

[AndyUK]

Hi Glider - By default, I leave them unchecked...

[Psychobilly]

Yep thats pretty much how I use it...

Some targets my benefit from changing the "stretch" function this is done using the "silver" buttons to the left of the histogram sliders...