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Old 05-12-2015, 01:32 PM
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pvelez (Pete)
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Pixinsight - play with my data - any interest?

Like many, I have switched to PI for all my data processing. It has been a very fruitful exercise. I'm quite content to have been inducted into the PI cult.

But...

I fear I am at the edge of my skill base. I can produce good images, but not images that I am happy displaying at full resolution in public. My main issues have been with sharpening and noise reduction - I suspect actually my issue is with developing suitable masks so I don't process against myself.

What I really need is some instruction - just some tips on where I am going wrong. I can't see myself getting to a workshop for some months.

So as a next best step, I'd like to see what can be done with my data. That way I can assess how far off beam I am.

My proposal. I have some good data of M74 taken over the last 6 weeks or so. Its taken with a Planewave CDK12.5 matched with a FLI 16803. All data was collected from the iTelescope facility at SSO so its nice and dark.

I have calibrated and combined the data using PI. It comprises:

10 hours Lum
4 hours each of R, G and B
2 hours Ha

All but Ha is in 5 minute subs - Ha is 30 minute subs. All unbinned.

Is there anyone interested in having a play?

If there is interest, I can upload the masters to a publicly accessible Dropbox.

Let me know here or via PM if you are keen.

Pete
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Old 05-12-2015, 08:17 PM
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OK

here is the link if you want to give this a go

https://www.dropbox.com/sh/cu16m1htm..._rME6mqMa?dl=0

Look forward to seeing the results

Pete
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  #3  
Old 06-12-2015, 11:36 AM
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pvelez (Pete)
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BTW - if you access this folder, please copy rather than move the files. I believe if files in a public folder can be altered by anyone who accesses it.

Pete
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Old 06-12-2015, 12:10 PM
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rmuhlack (Richard)
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I've still got training wheels on myself when it comes to LRGB processing, but here is my attempt. I did notice that there are a number of "dust motes" and artifacts in the luminance image that I would have expected to be dealt with by flats. I have cropped the image to remove the worst.
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  #5  
Old 06-12-2015, 01:23 PM
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Thanks Richard

yes, there are dust bunnies - the subs were taken over a 6 week period and the flats predate them - I suspect there has been some dust collecting.

Also, I had applied cosmetic correction to the Lum but not all the RGB - in case someone wanted practice in removing it.

Can't make it too easy can I

Pete
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Old 06-12-2015, 02:35 PM
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rustigsmed (Russell)
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yep some crazy gradients in there.

i don't have pixinsight but wanted to have a crack at doing LRGB

here is my version.

Russ
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  #7  
Old 06-12-2015, 03:07 PM
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Hi Pete,

Unfortunately, I was away for the weekend and have a busy week ahead. If I get a chance I'll have a quick stab at your data some time in the next few days.

Cheers,
Rick.
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Old 06-12-2015, 08:15 PM
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Quote:
Originally Posted by rustigsmed View Post
yep some crazy gradients in there.

i don't have pixinsight but wanted to have a crack at doing LRGB

here is my version.

Russ
Looks good Russ

the gradients are easily managed in PI - but they are a bit crazy - I wanted to provide the data warts and all to see how people manage it

Pete
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Old 06-12-2015, 08:17 PM
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Quote:
Originally Posted by RickS View Post
Hi Pete,

Unfortunately, I was away for the weekend and have a busy week ahead. If I get a chance I'll have a quick stab at your data some time in the next few days.

Cheers,
Rick.
Thanks Rick. If you have time, I'd love to see how you handle it.

I'll post my effort tomorrow - it an interesting exercise to see how different people process the same data. if nothing else it highlights that there is a fair amount of personal choice - taste I guess - when processing

Pete
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Old 06-12-2015, 09:16 PM
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Pete,

Needs bit more care and finesse but here's a quickie uploaded to my staging area on Astrobin (only visible via the link here). I like Richard's version too.

http://www.astrobin.com/full/230281/0/

I can post some notes on the processing steps if anybody is interested.

BTW, there was no Ha data?

Cheers,
Rick.
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Old 06-12-2015, 09:29 PM
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A subtle refinement to my earlier effort, also uploaded to my staging area on Astrobin. http://www.astrobin.com/full/230283/0/

This one isn't stretched so hard, and noise is a bit more under control.
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  #12  
Old 07-12-2015, 07:04 AM
cfranks (Charles)
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Quote:
Originally Posted by RickS View Post
Pete,

............
I can post some notes on the processing steps if anybody is interested.............

Cheers,
Rick.
I'd appreciate a look, Rick. I can never get my stars with a solid colour like yours. They usually have only a colour halo.
Thanks
Charles
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Old 07-12-2015, 08:52 AM
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Quote:
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Pete,

I can post some notes on the processing steps if anybody is interested.
I'm interested ! Thanks Rick
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Old 07-12-2015, 04:16 PM
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OK, so here is my effort. Its so-so and I’m sure it can be improved.

I am more impressed with the natural colours of Rick’s version though the brownish areas in the spiral of Richard’s image are also very appealing.

I’m keen to hear how others have approached this.

Here was my workstream – apply at your peril!

DBE on R, G, B and Lum

RGB

Linear Fit applied to R and B using G as the base
Combine RGB (using LRGB Combination)
DBE on the combined RGB
Background neutralisation using a preview from a fairly neutral area – hard to find as there is blotchy green and red favoured areas
Colour calibration using the same preview for background and a preview over the galaxy for white – structure detection off
Copy RGB
Histogram Transformation on original RGB
Channel Extraction – Lum to produce a Lum mask.
Copy Lum Mask and apply HDR Multiscale Transform – 4 layers with 3 iterations to remove the galaxy to make a Star Mask Base
Star Mask on Star Mask Base - Noise 3.5, Scale 6, Structure growth 1, 0, 1 and truncation 0.67
Masked Stretch on copied RGB
Applied star mask to Stretched RGB and added mask stretched RGB to RGB with Pixel Math ie replaced stars of stretched RGB with stars from masked stretched RGB
Built a galaxy mask with PixelMath using Rick’s funky “iif(star_mask1>0.1,0,$T)” expression to apply the star mask to the Lum mask and then made it fuzzy with Convolution
Reduced green with SCNR – don’t think I used a mask
Applied galaxy mask to RGB and boosted saturation with Curves Transformation – hit it a few times to bring out the colour – I am a sucker for bright colours in a galaxy
Adjusted black point with Histogram Transformation

Lum

Built lum mask by stretching a copy of Lum with HT
Produced PSF with Dynamic PSF – about 80 stars
Star Mask of Lum – using same technique discussed above
Deconvolution – 25 iterations, deranging using star mask for local support set to 0.7, global dark at 0.01. All other settings at default
Tried to reduce noise in background with MLT – couldn’t produce a linear mask that masked enough of the galaxy so gave up on linear noise reduction
Stretched with HT
Adjusted black point with HT
Produced a Lum mask and then used PixelMath to generate a galaxy mask
Reduced star sizes with Morphological Transformation with star mask applied – Erosion, size 5, amount 0.35 with 3 iterations
Sharpened stars with Multiscale Median Transformation with star mask applied
Sharpened galaxy with MMT with galaxy mask applied – more aggressive than star sharpening
Noise reduction with MLT with galaxy mask applied
Adjusted black point with HT
Increased contrast in galaxy with Local Histogram Equalisation with galaxy mask applied – amount 0.68

LRGB

Added Lum to RGB – Lightness 0.48, saturation 0.42 and Chrominance Noise Reduction on
Boosted saturation with Curves – galaxy mask applied

There are so many things in this image that I wrestled with – unsuccessfully. Here are a few:

1. I wasn’t able to get the noise in the background down. The more I pushed it, the more detail I lost in the outer regions of the spiral arms. I have 139 subs in the Lum and still can’t quite get a sharp enough distinction in the fainter areas.

2. The stars are not nearly as crisp as I’d like – the outer halos tend to get smudgy. I do see however that this is apparent in the other images as well.

3. Colour balance is challenging and I tend to have too much blue and red and not the warm hues of the others. Would love to now how you guys managed that.

4. My star masks aren’t quite the right size – so when I boost the saturation, the stars are mostly but not completely masked. So there are some nasty green and blue outer sections in the larger stars.

5. I’d love to know how to isolate the smaller stars. Giving a saturation boost to the larger stars leads to many deep yellow/red stars in the background. Is there a funky way to mask all but the largest stars?

One thing that I was keen to see – whether I am being skimpy with my imaging. On a galaxy I am for about 6 hours of Lum and 4 hours each of RGB – all unbinned. Looking at what R & R could pull out of these data, I suspect I need to spend more time on the imaging – or look at larger targets.

Comments/criticisms most welcome

Pete
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Old 07-12-2015, 04:30 PM
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looks good to me pete.

and wow! I don't know if I have the time to learn pixinsight! (but never say never in this hobby) it looks full on. however that DBE function seems very powerful - those gradients were quite intense.

one thing I noticed in Rick's version is the core, it has a great colour and sharpness to it. yours and Richards looks pretty similar to my eye although your blue is more cyan.

re: on being skimp on the colour data, Shiraz's recent galaxy photos are spectacular and he did bin at 2x2. maybe something to consider for the RGB?
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Old 07-12-2015, 04:52 PM
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One other suggestion I have with the imaging would be to increase the exposure time. You mentioned that you were doing 30 Ha subs, I personally would suggest doing closer to that with the luminance and even the RGB. 300s exposures with a 16803 at what I am guessing is ~ F/7 seems really short to me. The luminance had a background ADU of 15, if it has only been bias, dark and flat calibrated, you may want to get that value closer to 600 to get above noise level.
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Old 07-12-2015, 07:19 PM
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Here are my (quick & dirty) processing steps...

Luminance:
  • Crop
  • DBE to remove background gradient
  • Slight deconvolution - PSF sampled with Dynamic PSF, large star mask as local deringing support, clipped luminance mask to restrict decon to high signal areas
  • MultiscaleLinearTransform noise reduction using linear mask
  • HistogramTransformation stretch
  • Apply star mask: MorphologicalTransformation with Selection for mild star reduction
  • Clipped lum mask with stars removed: light LHE
  • Clipped lum mask with stars removed: slight MLT sharpen

RGB:
  • LRGBCombine R/G/B
  • Crop
  • DBE
  • ColorCalibration with galaxy as white reference
  • MLT noise reduction with linear mask
  • HT stretch
  • ACDNR noise reduction, heavy on chrominance noise
  • RGBWorkingSpace 1:1:1 (only affects lum extraction for masks)
  • Clipped lum mask: Curves saturation boost
  • Star mask: use MLT to blur chrominance (remove first few layers, set target as Chrominance). This helps improve star colour.
  • Hue curve to move cyans -> blue

Final combine:
  • LRGBCombine: combine Lum and RGB
  • Clipped lum mask: Curves saturation boost
  • ColorMask blue mask: curves boost blue, slight red boost, sat boost (ColorMask is my script, available from the PI forum)
  • Clipped lum mask: slight MLT noise reduction
  • Adjust black point

A clipped lum mask is created by taking luminance (copy of Lum data or extracted from RGB) and using HT to clip the bottom of the histogram.

A clipped lum mask with stars removed is created from a clipped lum mask and a star mask. I typically use a PixelMath expression like: "iif(star_mask>0.1,0,$T)" applied to the clipped lum. After removing the stars I'll use a mild Convolution to blur things up a little so there aren't hard edges.

If any of my other shorthand isn't clear, just ask.

Cheers,
Rick.
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Old 07-12-2015, 08:05 PM
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Quote:
Originally Posted by cfranks View Post
I'd appreciate a look, Rick. I can never get my stars with a solid colour like yours. They usually have only a colour halo.
Thanks
Charles
Charles: blurring the chrominance as described in my quickie workflow can help a lot with this. Sometimes targeted use of ColorSaturation can reduce the halos too.

Quote:
Originally Posted by pvelez View Post
2. The stars are not nearly as crisp as I’d like – the outer halos tend to get smudgy. I do see however that this is apparent in the other images as well.

5. I’d love to know how to isolate the smaller stars. Giving a saturation boost to the larger stars leads to many deep yellow/red stars in the background. Is there a funky way to mask all but the largest stars?

One thing that I was keen to see – whether I am being skimpy with my imaging. On a galaxy I am for about 6 hours of Lum and 4 hours each of RGB – all unbinned. Looking at what R & R could pull out of these data, I suspect I need to spend more time on the imaging – or look at larger targets.
Sounds like you used a few of my tricks already, Pete

I've been deliberately making my stars less crunchy since they are supposed to be soft and Gaussian. If you like them harder then a star mask and some sharpening will do it.

Dropping the scale in StarMask should get rid of the big ones.

4 hours each of RGB should be adequate. I'd go heavier on the Lum for most galaxies. 300 secs is really too short for your subs with that combination of scope and sensor. My set up is quite similar and I usually do 15 minutes on Lum and 20 minutes on RGB. If in doubt use the Shiraz method to make sure your subs are sky limited: http://www.iceinspace.com.au/forum/s...d.php?t=117010

If you are sky limited then there's no extra value in binning, especially on a KAF-16803.

Another area where you might be able to get some good SNR gains is with integration. If you're not doing it already, careful selection of rejection algorithm and rejection parameters can make a big difference.

Cheers,
Rick.
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Old 08-12-2015, 06:52 AM
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Thanks Rick.
Charles
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Old 08-12-2015, 09:58 AM
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Thanks Rick

I will download the ColourMask script and have a play with that. Your sample workflow is also very helpful. I will have another go at these data and see what I can come up with.

Pete
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