Does PhotometricColorCalibration replace ColorCalibration?

[wkrispler]

Hi,

I am very excited about the new Pixinsight release 1.8.5. Especially the new process PhotometricColorCalibration is very interesting.

Does it replace ColorCalibration or are there case where e.g. ColorCalibration delivers a better result? What about BackgroundNeutralization. Do I have
to apply BackgroundNeutralization and afterwards PhotometricColorCalibration?
Thx,
Wolfgang

[RickS]

Hi Wolfgang,

CC will still be useful for false colour targets (I sometimes use it with narrowband data) and where the FOV isn't covered by the APASS catalog.  PCC has an option to do background neutralization so you don't need to do this separately.

Cheers,
Rick.

[vicent_peris]

Hi Wolfgang,

In a given image it doesn't make any sense to use both PCC and CC because they simply do the same task. But PCC is not a replacement of CC. They represent different approaches to color in astrophotography:

- In ColorCalibration, you apply a white balancing relative to the image itself. In some cases, this is a good approach because you optimize the color representation inside the local white reference.
 
- In PhotometricColorCalibration, you refer the color representation of your picture to a source that's not inside the picture. This is a good approach when you want to know how the color of your picture is compared to a fixed white source. For instance, you can select the generic spiral galaxy white reference and apply it to multiple galaxy photos; some of them will be redder, some bluer, but all of them share the same white point.

In my opinion, we have now the complete set of color calibration tools in PixInsight. Now you have the freedom to choose one or another according to your personal preference and your goal with your picture.


Best regards,
Vicent.

[jtalbot]

I tried it out on an image of Sh2-88 in Vulpecula today and it failed (no stars detected). I would think this may be because the APASS data may not be covering this region.  There are no galaxies visible in the image so I picked a couple of different types of stars that I knew where in the image.

Processing image /var/folders/ts/6xqx2_cs2nndgxhj01w_h4h80000gn/T/PCC_G_85OZPN1IQSSF.xisf

Reading image:
/var/folders/ts/6xqx2_cs2nndgxhj01w_h4h80000gn/T/PCC_G_85OZPN1IQSSF.xisf
Loading image: w=3300 h=2476 n=1 Gray UInt16
20 FITS keyword(s) extracted.
Reference image: PCC_G_85OZPN1IQSSF
Calculating image noise: sigma=12.198 count=2.21% layers=4
Multiscale median transform: done
Multiscale reconstruction: done
Normalizing sample values: done
Aperture Photometry:
  Aperture: 9.000000 px
  Image resolution: 1.648864 sec/px
Calculating photometry: Processed 0 stars in 0.000000 seconds
Generating detected stars image
Applying STF to 'PCC_G_85OZPN1IQSSF_DetectedStars':
Processing channel #0:
LUT-based histogram transformation: done
Processing channel #1:
LUT-based histogram transformation: done
Processing channel #2:
LUT-based histogram transformation: done
Conversion to 8-bit unsigned integer sample format...
Writing output file: /var/folders/ts/6xqx2_cs2nndgxhj01w_h4h80000gn/T/PCC_G_85OZPN1IQSSF.csv
*** Error: Failure to process image file '/var/folders/ts/6xqx2_cs2nndgxhj01w_h4h80000gn/T/PCC_G_85OZPN1IQSSF.xisf': TypeError: area is null

*******************************
Processing image /var/folders/ts/6xqx2_cs2nndgxhj01w_h4h80000gn/T/PCC_B_69ZK7DHNAJY6.xisf

Reading image:
/var/folders/ts/6xqx2_cs2nndgxhj01w_h4h80000gn/T/PCC_B_69ZK7DHNAJY6.xisf
Loading image: w=3300 h=2476 n=1 Gray UInt16
20 FITS keyword(s) extracted.
Reference image: PCC_B_69ZK7DHNAJY6
1 view(s)
0 star(s)
0 PSF fittings
*** Error: Failure to process image file '/var/folders/ts/6xqx2_cs2nndgxhj01w_h4h80000gn/T/PCC_B_69ZK7DHNAJY6.xisf': Could not locate any stars in the image

*******************************
Photometry process finished:
   0 of 3 images processed successfully.
   3 images with errors.
   3 errors and warnings.

*** Error: Failure to calculate photometry: Image78
Reading swap files...
2995.460 MiB/s
<* failed *>

Jon

[jtalbot]

Vicent,

I was just thinking of another question.  If using "Average Spiral Galaxy" as a white reference, does there need to be a galaxy in the image.  I kind of guessed from reading the explanations about PCC that maybe there doesn't need to be.

Thanks

Jon

[wkrispler]

Thank you all for your answers, especially Vicent. Very usefull

[Ryderscope]

  PCC has an option to do background neutralization so you don't need to do this separately.

Cheers,
Rick.

A quick question. Given that PCC has the inbuilt Backgroun Netralization, do we still need to do a small preview of the background? There does not seem to be any option in the PCC dialogue box to select a background preview image.

Thanks,
Rodney.

[vicent_peris]

  PCC has an option to do background neutralization so you don't need to do this separately.

Cheers,
Rick.

A quick question. Given that PCC has the inbuilt Backgroun Netralization, do we still need to do a small preview of the background? There does not seem to be any option in the PCC dialogue box to select a background preview image.

Thanks,
Rodney.

Yes. You have the "Region of interest" in the background neutralization section. Create a preview and select it by pressing the "From preview" button.

Best regards,
Vicent.

[Ryderscope]

  PCC has an option to do background neutralization so you don't need to do this separately.

Cheers,
Rick.

A quick question. Given that PCC has the inbuilt Backgroun Netralization, do we still need to do a small preview of the background? There does not seem to be any option in the PCC dialogue box to select a background preview image.

Thanks,
Rodney.

Yes. You have the "Region of interest" in the background neutralization section. Create a preview and select it by pressing the "From preview" button.

Best regards,
Vicent.

Thanks for the quick response Vicent. Will give that a try.
Rodney.

[Warhen]

Hi Jon, It's been a year since we've seen each other- did no one answer you?! No ASG need be present in the image, this is a 'candle' for reference only. An ASG of Vicent's specifications should have all spectral classes of stars to serve as an ideal white reference.

Start with a subframe and 'Acquire from Image' the coordinates. It's not a blind solver, it needs help. Make sure the pixel size and f.l. are correct. Second, play with the parameters to see if you can get stars detected- increase the magnitude limit to say, 16. Try lowering the Log slider. Good luck!

[jtalbot]

Hi Warren,

Thanks for the reply.  I actually have been very successful with photometric color cal since I posted the question.  I think I must have just done something wrong the first time I tried it.  Its worked just fine ever since and I used it on all my images since summer.

Best,

Jon