New in PixInsight 1.8.5: PhotometricColorCalibration

Are we there yet? ;-)  :p

(In all seriousness I'm about to process an image and I'd like to reprocess one I'm not fully satisfied with, and I'm sure this new release would help. Hence I'm pondering whether or not I should wait for it ^^ )
This looks like an absolutely wonderful tool. Well done guys! Looking forward to playing with it. I will be updating a tutorial of mine to add this in once it's out. :)

Perhaps I can answer on Juan's behalf:

The latest version is still very much in early Beta revision, and has only been distributed to PTeam members. It cannot (and will not) be distributed outside of this small group as it does not yet have even something as fundamental as a fully-compatible installation procedure (which also likely to be all-new).

I know that users will very likely be super-keen to get their hands on the latest version and, trust me, "Good things will come to those that wait  :D "

The very last thing that Juan needs on his plate right now is an all-new version in circulation, being used by people who may then swamp the system with standard "great stuff, but how can I nake PixInsight Proces XYZfoo do bar" queries. Right now he needs to be given the time and freedom to eliminate the bugs that are already being identified by the PTeam users - so that when it does finally get released the queries are most likely being caused by genuine user-inexperience than by unidentified bugs.

Becoming part of the group of beta testers has always been 'by invitation only' - not that we are anything special, it is just that we have all worked hard to support PixInsight (many of us from the very beginning), which is why it is rapidly becoming the de facto astroimage processing software of choice - at all levels of the science.

However, I also know full-well that, if Juan feels that you would be a worthy contributor, he will be in touch (and, if he isn't, then don't worry or feel bad - it is probably because he is too busy trying to get the non-Beta version into your Update Repository as soon as possible  ;) ).
Early beta?
Niall are you sure about that ? 
Juan put the teasers on the release out six weeks ago.
(He was hoping for a June release originally) 

I would think it would be fairly well along by now.

Very excited about this feature as I see it just appeared on the latest Pixinsight.

Are there any notes on how to use it? I'm getting plate solving errors and don't really know what to do to fix it

Should PCC be run before or after background extraction? I would have thought after but am getting better results if I run it before.
Hi John,

It may well be that you choose to use PCC instead of DBE  ;)

Probably best to wait for a clear write-up to be released.
In my mind PCC should be used in the same flow as you would with BN/CC, that is after gradient corrections. Gradients can affect different colors different ways. DBE and ABE deal with that. If you color correct an image with a color gradient how could you end up with the correct color balance across the image.

As far as 'it looks better before' you still might need to play with the settings. A slight change to the Saturation threshold maybe but not likely. Change in the White reference can make a real difference. Also remove the Automatic limit magnitude and try a step up or down but generally no more then that. This is what I found while testing PCC.

Also remember if you are using the background Neutralization as in previous versions of PI with a preview, try without and the defaults. And the converse is worth a try also.

By using aperture photometry, PCC should, and does, give the same color correction factors before and after color gradient removal.

My preference, with DBE and ABE, is to correct the image with Normalize unchecked. This way a good background model will essentially produce a neutral background. Then the PCC background tweak will probably work better.

bob, is this simply because the gradients are so tiny relative to the signal in the stars? it makes sense that gradients would not matter if that's the case.

but for background neutralization gradients are still important, right?

Hi Rob,

Yes, the large relative difference in the signal is a factor. However, aperture photometry is essentially doing an ABE correction for each star. The process subtracts the local background, actually foreground, for each star before taking the measurements. This gives normalized readings across the entire image.

As for background neutralization gradients? Yes, of course, we must still apply DBE and ABE corrections to get a neutral flat background.

bob_franke said:
For future PCC users, I strongly recommend using the SDSS-DR9 data instead of the APASS whenever possible. The SDSS data are acquired with a 2.5m telescope and the APASS data with a 3.15cm.  Also, the SDSS folks are more experienced. Additionally, the APASS staff have freely admitted that some of their data are problematic.

I recently encountered a Southern Hemisphere field-of-view where the APASS data had obviously highly inaccurate (b-v) values. Also, the Sloan g' and r' filters produced poor RGB color correction. In the Northern Hemisphere, the APASS data have always agreed with the Sloan for color correction.

BTW Juan, will the PCC user interface return the RGB values used for the pixel math? I would like to compare with my results. I have no doubt that the PI routines are more sophisticated than eXcalibrator's white-star and linear regression.  Also, with direct access to plate solving, the PI process will be easier to use.

But will the results provide a significant difference in the final color? It can take a surprisingly large change in RGB factors to be noticeable in the final image.

Like I said earlier, I am a PixInsight user and find the program exceptional and powerful. I'm looking forward to taking PCC for a spin.


Sorry to be a bit slow.  How does one acquire the SDSS data and 'enable' it in PI?  In my installation the only Photometry catalogue available in the drop down menu is APASS.
Hi Bob,

For the moment, the only photometric catalog available in PCC is APASS. SDSS could be available in the future, but a few updates of this tool have higher priority.

Best regards,
For only 30% of the Northern Hemisphere, it may not be worth the extra download time to check for SDSS availability. :)