Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - ChoJin

Pages: 1 ... 5 6 [7] 8
91
Gallery / Re: A glance at NGC7331 and adjacent areas
« on: 2016 September 08 06:23:04 »
nice one

why do you apply DBE after the stretch?

92
Could you explain further the layer robustness?

I always read that most of the noise is from layer1&2. Wouldn't it be less accurate to compute the noise value from layer4? Or maybe the idea is that it doesn't really matter as long as you can compare the values between the subframes?

93
Hello,

following
http://pixinsight.com/forum/index.php?topic=5764.msg39382#msg39382
and
http://pixinsight.com/forum/index.php?topic=8434
I'm trying to make sense of the noise evaluation functions (in both the standalone script and within the subframeselector)

obviously I have a few questions:
- why both scripts are not using BWMV() to scale the result and therefore improve the robustness to be able to compare properly the noises between frames/subframes?
- in subframeselector's noiseOfImage function I can see it is computing the value for layer4 first and going down to layer2 until it find a suitable value. Why?  I don't understand why we don't take the overall RMS or at least the layer1?

- and a side question: with the current noise evaluation in the subframeselector, if I'm using it, does it mean i'm giving up the improved scaled estimators from within the ImageIntegration Process? Should I therefore just use it to reject some frame and rely on the ImageIntegration Process for the weighting?

Sorry, I'm new to PixInsight, hence my questions might be very trivial for most of you

94
General / Re: dark subframes evaluation
« on: 2016 September 03 11:09:03 »
An extra question : considering the stats seem to be the same for the 18C-19C 2min dark frames vs the 12C-14C 5min dark frames, does it mean I could use them for either of those ranges and those exposure times?

95
General / dark subframes evaluation
« on: 2016 September 03 05:52:46 »
hello,

proudly using my brand new commercial licence ;-) I'm trying to analyze my darks to decide whether or not I could use them with my lights.

They were taken at mostly 19C vs mostly 15C for my lights (I have a canon 6D). I forgot to put pauses between the shots to simulate the dithering timeout.

I followed the post from http://www.blackwaterskies.co.uk/2015/02/pixinsight-dslr-workflow-part-2a-dark.html and used BatchStatistics to report the median and the MAD on all the darks I have (20s, 2m and 5m time exposure at iso1600)

I'm a little bit confused and I'd like some expertise if someone can provide some.

From what I can see (see the bottom of this post), the median is very stable, the MAD seems to increase very slightly with temperature, and decreases with the time exposure.

For instance, for 5m darks, the MAD seems to be the same between 15C and 19C (and even some 20C)

I have therefore mainly two questions:
- does it indeed mean i could use those darks with my 15C-17C lights or should I use a better estimator than the MAD?

- is there a way to analyze the lights before and after calibration to objectively see whether or not my darks are indeed removing noise (and not adding more than it subtracts)

any comments are welcomed!

here are the statistics:
Median MAD Temp Time
512   2   12   300
511   2   14   300
511   3   15   300
511   3   16   300
511   3   17   300
511   3   17   300
511   3   18   300
511   3   18   300
511   3   18   300
511   3   19   300
511   3   19   300
510   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   3   19   300
511   4   20   300
511   4   20   300
511   3   20   300
511   3   20   300
511   2   18   120
511   2   18   120
511   2   18   120
511   2   18   120
512   2   18   120
512   2   18   120
511   2   19   120
511   2   19   120
511   2   19   120
511   2   19   120
511   2   19   120
511   2   19   120
512   2   19   120
511   2   19   120
511   2   19   120
511   2   19   120
511   2   19   120
511   2   19   120
511   2   19   120
511   2   19   120
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   15   20
512   1   16   20
512   1   16   20
512   1   16   20
512   1   16   20
512   1   16   20
512   1   16   20
512   1   16   20

96
Image Processing Challenges / Re: IC 5070 should come out red
« on: 2016 September 03 05:30:34 »
Are you sure the pattern is RGGB? you could try exiftool on a raw file to check whether or not the header gives you the bayer pattern

97
General / Re: Having issues with master bias
« on: 2016 September 02 00:01:15 »
it's probably a stupid question, but just in case you were tired ;)
are you sure you put the camera's cap back on before taking the bias?

98
Off-topic / read noise vs dynamic range (and exposure)
« on: 2016 August 23 12:22:11 »
Hello

I have a kind-of math question about the tradeoff between the read noise and the dynamic range for the Canon 6D.

I have a hard time deciding between shooting at ISO800 vs ISO1600

according to http://clarkvision.com/reviews/evaluation-canon-6d/index.html

800  0.74      4.6      9900        11.1
1600  0.37      2.9      4900        10.7

(the value are slightly different at http://sensorgen.info/CanonEOS-6D.html but the idea is the same)

at ISO800, the 6D has a read noise of 4.6 with a maximum signal of 9900
whereas at ISO1600, the read noise drops further to 2.9 with a maximum signal of 4900.

After ISO1600, it becomes roughly linear.

If I understood properly explanations at http://dslr-astrophotography.com/iso-dslr-astrophotography/ (and some other sources), it is therefore best to shoot at either ISO800 or ISO1600 to improve the SNR.

Now I'm puzzled to decide which one.

I also started to wonder if there were a way to mathematically compute in advance a proper exposure for a given target.

Let's say I want to image M31. ISO800 or 1600?
At ISO1600 I would be more likely to saturate the core since the dynamic range is reduced, but how long could I expose (ignoring sky fog from the light pollution at first)? Is there a way to compute (even roughly) that exposure or even decide which ISO to use without having to just experiment a lot?

In summary, what I'm basically asking is whether or not maths could help here to make an educated choice instead of pure experiments.

Any insights?

99
sorry i forgot to attach the image

100
@Andres.Pozo n/m, I just realized it was limiting the matching to my active previews and hence failing. It works fine if I delete the previews.
By the way, since I used a 2x2 drizzle during my stacking, and that my canon 6D has a 6.55um pixel size, am I right to use a 3.275 pixel size with the imagesolver?

101
Thank you very much to all of you for your help

I have a few further questions

@biosif could you describe the workflow you used?

@Andres.Pozo could you tell me which parameters/settings you used exactly with the imagesolver? I couldn't make it work at all although I tried a lot of different settings. I'm not quite sure what I did wrong, but it could never match and eventually failed after #25 tries or so. That would help me to reproduce your result if you could give me the settings you used.

@vicent_peris
- I saw the use of the linearfit in a tutorial, but I can't remember where. Does it hurt to use LinearFit? When is it really necessary then?
- in fact i used ColorCalibration 3 times, well knowing it wasn't making much sense. I was seeing some blue shifting after some processing. I'm guessing my initial white reference wasn't that great. I didn't save it, but it is roughly "Preview2" in the attached image.
Should I have used the whole image as a white reference? Or something much smaller/a subpart of the core of the cluster?
why is it bad to apply colorcalibration after stretching?

102
Image Processing Challenges / Re: Help on Gamma Centauri
« on: 2016 August 07 11:01:47 »
I think I found the mysterious galaxy on my image using SIMBAD: it's ESO 269-85 I think (I couldn't make the PI's imagesolver work on the image though, it doesn't detect the biggest stars and only the smaller ones, and therefore get confused)

Otherwise, no one for any feedbacks/tips/protips about my workflow on this image? I would very much appreciate some guidance, to learn good practices right from the beginning.

103
General / Re: ImageIntegration can't integrate 2 images?
« on: 2016 August 07 10:57:27 »
did you assign any weight on your images with PI?

104
Image Processing Challenges / Help on Omega Centauri (NGC 5139)
« on: 2016 August 04 12:14:03 »
Hello,

I'm on the trial period with PixInsight and I'm currently processing Omega Centauri with it as a first attempt.
Due to time constraints my data are limited:
10x60s lights, 10x60s darks, 10 flats and 10 bias with a takahashi epsilon D=210mm F=628mm with an astrophysics 900 mount and a Canon 6D (unmodified). Hence total integration time = 10min

I did my best with the data I have, and I would very much appreciate if anyone could give a try to show me what I could really achieve with better expertise.

here is a link to the preprocessed data, and my final images : https://www.dropbox.com/sh/a89wfj44xk4pmdo/AACFhnI5fHGzJMc7wuLujKF4a

Please find attached a screenshot of my workflow. Any comments are welcomed (some steps were not optimal I guess, for instance I had to redo the ColorCalibration multiple times due to a blue tint drift, I'm guessing my preview window for the white wasn't good enough initially)

I did a manual preprocessing following mostly the tutorial from http://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html

The result was better than what I got from DSS, thus I'm guessing I didn't do such a bad job for this first step ^^

I did my best with the data I captured and the hardware I have (a 4 year old macbook pro, I'm very patient) to fine tune any parameters, and I would love to see what you can do and what kind of workflow you would apply

NB: Also, artistically I have a hard time deciding between a full version of it and a crop version. I like the fact that in the full version you can see NGC5064, but with the cropped version, you can see the cluster better... which one do you prefer?

Cropped version (downsized): https://www.dropbox.com/s/n1uynn0puoddoa6/
full version (downsized): https://www.dropbox.com/s/cpjtuxd77htwzfy/

NB2: I'm desperately trying to identify the galaxy between roughly HIP 65144 and HIP 64867, close to NGC5064. You can see it as a blue galaxy at  http://dso-browser.com/deep-sky/6165/ngc-5064/galaxy if you zoom out and pan, but I can't find its name.

Anyway, any helps/comments/advices/feedbacks are welcomed and appreciated!

so far I really like PixInsight (but I hate my old slow laptop)  ;)

105
Bug Reports / Re: help pop-ups and hot keys in OSX version
« on: 2016 August 04 10:01:00 »
I'm on the trial version, with mac os 10.10.5 and i'm having the #1 issue as well. I thought it was because of my limited resolution on my old macbook pro (not officially supported), I therefore didn't say anything, but if it happens on the retina 5k as well I guess that's not it

Pages: 1 ... 5 6 [7] 8