M42- processing is a skill (I ain't got!)

[Swoop1]

Three images from 15th January. The rig was my Sony a6300 with the Tamron 70-300mm zoom (set at 250mm) on my pre Omegon Mini Track clockwork mount. 1st image single unprocessed frame 10sec exposure f5.6 ISO3200.

Second image is a stack of 10 frames at same exposure plus darks and flats. This was processed in DSS which, when saved looked nothing like the finished article on DSS so I went to paint.net to fiddle. and came up with image 3.

Where did I go wrong post DSS? Was it my saving regime?

The yellow caste to the stacked images seems to show when I adjust stuff to make the detail stronger?

Edited to add- just found a post DSS stack save that looks more like the product I processed. I have had to convert from a 168mb TIFF to a jPeg to upload it-

 

Edited January 17, 2020 by Swoop1

[vlaiv]

Don't try to process things in DSS.

Just stack image and save result as 32bit tiff or 32bit fits file. Use latest Gimp to do basic stretch of the image and a bit of color balancing. Maybe try minimal approach first.

When stacking image in DSS there is option for background calibration - use RGB background calibration (that should preserve nice gray background).

If you want, you can upload result of stacking (still linear - don't adjust histogram in DSS) and I can show you first basic steps in Gimp.

[Swoop1]

Thanks vlaiv. How do I upload the raw stacked data?

[vlaiv]

Ok, yes, you have option to save your image stacked in certain format

Then you will be asked to choose a format - choose either 32bit fits or 32bit tiff (maybe this second as it is more compatible with image manipulation software - first format is for astronomical use)

Also don't apply any of adjustments, in fact - don't do any of adjustments at all.

Once you have your image (but it looks like you already found autosave.tiff - above, you can use that as well) - you can upload it to some file sharing service or google drive or whatever.

Maybe simplest one is we transfer. Just upload it there and you can share the link - it will last couple of days (after that your file will be removed from their servers and link will no longer be valid).

[Swoop1]

Thanks. I'll get on to that.

[Swoop1]

here is the We Transfer link to the stacked but unaltered data (lights, darks and flats).

https://we.tl/t-dXooLpJYnj

[vlaiv]

Ok, so here are steps to get basic stretch done in Gimp. I'm using Gimp 2.10.4-std windows install.

- Open up your tiff image in Gimp

- First step would be to use levels to do initial stretch so go to Color / Levels menu option and do following:

Take top slider and pull it left until brightest parts of nebula become bright enough - don't turn them white - that will clip detail. In your image - 4 stars of trapezium are not resolved and are burned out already, but you can watch nebulosity around them - as soon as it starts being too bright - stop with adjusting levels. It happens somewhere around 50 out of 100 (or slider half way to the left).

- next step is to move middle control in levels. Again go to same menu option - Color / Levels and this time adjust middle slider like this:

This is part you need to do by feel - as there is no particular guideline on how much to pull it - effects of it will be seen in next step, so if things are not good in next step - undo and repeat this step but less aggressively (less to the left).

- Third stretch with Color / Levels resets black point to it's regular value - again do the same Color / Levels but this time we move black point - or left most slider like this:

Here, rules are simple - you need to pull black level marker up to the foot of histogram. If your background looks too grainy and bad - you overdid previous step, undo it and repeat with less aggression. It is ok if there is a bit of grain in the background - we can fix that with denoising later.

- Next step would be slight curves stretch to bring out brightness of features. We do it via Color/Curves command, and we do following:

We need two points - one "anchor" point that we will not move - put it somewhere on the base of histogram - just make sure you don't move it - line should still be diagonal. Next you take a point somewhere on the middle and drag it up until you get nice brightness of the features - don't over do it as again you run a risk of burning out core (bright regions).

- Next step would be slight color correction - as image now has red cast due to LP. Simple way to do it is temperature correction:

Move intended temperature slightly lower and original temperature slightly higher - observe what happens to the image and stop where you feel it is good.

- next, let's do a little denoising. Select that layer and duplicate it:

select top layer and run menu command: Filters/ G'mic-Qt and select repair / Smooth (wavelets). Increase Threshold until you get rather smooth image:

after you need to add layer mask on this smoothed image - right click on that layer and add layer mask:

Set mask to inverted and gray scale copy of layer:

After that you can use that layer opacity to control how much noise reduction will be applied to final image (it will be more applied in dark areas due to layer mask - but with lowering of opacity you can have further control).

And voila - save your image and present it:

[vlaiv]

Actually there is much more to this data if processed properly. Due to original stack having only limited amount of data, but being rather large pixel count (6000 x 4000) and due to fact that stars are not quite good - we can safely bin that to regular size.

I've chosen bin x4 for picture size of 1500 x 1000 - which I feel is good representation of the image. Here is green channel extracted and treated as luminance layer (green in cameras is modeled as human vision sensitivity to brightness - so in principle it is ok to use it as luminance - add to that fact that sensor is twice as sensitive in green than in red or blue due to pixels in bayer matrix ...).

Here we can see full extent of M42 but also the Running Man above. Stars are also tighter in green because lens used is not well corrected for color and there is blue fringing otherwise.

[happy-kat]

I have followed this post and found it interesting with the great extra GIMP and processing information shared.

This is a fast process using StarTools as it helps me as I get to try with data I haven't been able to capture, hope you do not mind.

 too binned this down to 25% of original, cropped and then processed. Though I am going to have another play and pick up on Vlaiv comment on the green channel and I will separately remove the bloat (the aim) on the blue channel and see what it yields.

[geeklee]

@Swoop1 Hope you don't mind another processing of the data.  Here's a little bit of work from APP (DDP, light pollution removal, very quick star colour calibration )

[Swoop1]

Thanks for your input and tutorial vlaiv. Very useful as, for me, self learning software packages is difficult. I'm a VHS type of learner (front loader like a VHS machine) so respond better to demonstrations.

Thanks to everyone else for your input. I hope you can make better use of my data than I currently can!

[vlaiv]

Here is the best I was able to pull out of this data:

Hope you like it. I'll do another step by step tutorial later to explain how I managed to process the image like this.

It's going to be a bit more involved tutorial - it's a bit "advanced" stuff as it includes another piece of software (also free as gimp) and plugin that I wrote for it (background removal).

[jager945]

Quickie in 1.6 beta;

---

Type of Data: Linear, was not Bayered, or was Bayered + white balanced

Note that you can now,  as of DSS version 4.2.3, save your images without white balancing in DSS. This indeed allows for reweighing of the luminance portion due to more precise green channel. However, since this dataset was colour balanced and matrix corrected, this is currently not possible.
--- Auto Develop

To see what we got. We can see a severe light pollution bias, noise and oversampling.
--- Crop
Parameter [X1] set to [1669 pixels]
Parameter [Y1] set to [608 pixels]
Parameter [X2] set to [3166 pixels (-2858)]
Parameter [Y2] set to [2853 pixels (-1171)]
Image size is 1497 x 2245
--- Rotate
Parameter [Angle] set to [270.00]
--- Bin

To convert oversampling into noise reduction.
Parameter [Scale] set to [(scale/noise reduction 35.38%)/(798.89%)/(+3.00 bits)]
Image size is 794 x 529
--- Wipe

To get rid of light pollution bias.
Parameter [Dark Anomaly Filter] set to [4 pixels] to catch darker-than-real-background pixels (recommended in cases of severe noise).
--- Auto Develop

Final global stretch.
Parameter [Ignore Fine Detail <] set to [3.9 pixels] to make AutoDev "blind" to the noise grain and focus on bigger structures/details only.

--- Deconvolution

Usually worth a try. Let Decon make a "conservative" automatic mask. Some small improvement.

Parameter [Radius] set to [1.5 pixels]
Parameter [Iterations] set to [6]
Parameter [Regularization] set to [0.80 (noisier, extra detail)]

--- Color

Your stars exhibit chromatic aberration (the blue halos) and DSS' colour balancing will have introduced some further anomalous colouring in the highlights.

--- Color
Parameter [Bias Slider Mode] set to [Sliders Reduce Color Bias]
Parameter [Style] set to [Scientific (Color Constancy)]
Parameter [LRGB Method Emulation] set to [Straight CIELab Luminance Retention]
Parameter [Matrix] set to [Identity (OFF)]
Parameter [Dark Saturation] set to [6.00]
Parameter [Bright Saturation] set to [Full]
Parameter [Saturation Amount] set to [200 %]
Parameter [Blue Bias Reduce] set to [1.39]
Parameter [Green Bias Reduce] set to [1.14]
Parameter [Red Bias Reduce] set to [1.18]
Parameter [Mask Fuzz] set to [1.0 pixels]
Parameter [Cap Green] set to [100 %]
Parameter [Highlight Repair] set to [Off]

What you're looking for in terms of colour, is a good representation of all star (black body) temperatures (from red, orange and yellow, up to white and blue). Reflection nebulosity should appear blue and Ha emissions should appear red to purple (when mixed with blue reflection nebulosity). M42's core should be a teal green (O-III emissions all powered by the hot young blue O and B-class giants in the core, this colour is also perceptible with the naked eye in a big enough scope). As a useful guide for this object, there is a star just south of M43 that should be very deep red (but I was unable to achieve this at this scale with the signal at hand).

Final noise reduction (I used Denoise Classic for this one as the noise is too heavy for "aesthetic" purposes).

--- Filter
Parameter [Filter Mode] set to [Fringe Killer]

Put stars with their halos in a mask and click on the offending star halos and their colours. This should neutralise them.
 

--- Wavelet De-Noise
Parameter [Grain Dispersion] set to [6.9 pixels]
 

Hope you like this rendition & wishing you clear skies!

 

Edited January 18, 2020 by jager945

[happy-kat]

That's great IVO, I used 1686 beta pretty much similar but your stars are neater through I'd used the fringe killer as well. I'll look at your post to learn sharper tricks on choice as I like your version more.

[Swoop1]

@vlaiv. Quick question- when opening a file in Gimp, Open OR Open as layers?

Thanks

Matt

[vlaiv]

1 hour ago, Swoop1 said:

@vlaiv. Quick question- when opening a file in Gimp, Open OR Open as layers?

Thanks

Matt

I guess it would be simple Open.

I don't remember ever using Open as layers

 

[Swoop1]

Cool. Thanks