Colour calibration - Anyone use eXcalibrator?

[swag72]

Wondering about G2V calibration in order to get the colours right in images, I stumbled upon eXcalibrator BF-Astro Freeware - eXcalibrator a freeware programme. There is also a user guide here.

Does anyone use this?

[swag72]

Does the silence mean that no one uses it? Or perhaps I am just getting my knickers in a twist about colour calibration in general!!!

[Sp@ce_d]

Hmm.. never tried G2V calibration but this looks interesting Sara..

I have no idea if it'll make a great difference or not but worth a try I suspect.. might give it a go if I can find some time off from building the obsy..

[Mark72]

I did use it; it's cumbersome but it's working. I'd rather use RBA WhileCal plug-in in PS.

[Sp@ce_d]

I did use it; it's cumbersome but it's working. I'd rather use RBA WhileCal plug-in in PS.

Do you have a link to info on this? The only thing Google throws up is this thread..

[RikM]

Photoshop Plug-in: WhiteCal | Deep Sky Colors - Astrophotography by Rogelio Bernal Andreo

[Sp@ce_d]

Ahh ok of course.. a typo...I'm slow tonight.. mind you google is normally quite good at "guessing" what you're after..

Thanks for that Rik..

[MikeD]

I have used G2V stars to determine the exposures I should be using to get balanced RGB data.

My calculations detirmind that I should be shooting at a ratio of R=1 g=1.3 and b=1.4 for my HX916 and astronomik RGB filters.

The big drawback was more darks required if I didn't want to scale darks.

As I am (when the skies clear) planning to try adding an LP filter into my imaging train again and decided G2V calibrated exposure lengths were again going to be a must, this is interesting as an alternative to look at.

Mike.

[swag72]

How do you ensure that when you do a G2V calibration that you are actually using the right star? For example, when I put the star into CdC and issue a slew command, I'm presuming that it will go to a fov that will contain at least a dozen stars. So how do I know which one it is?

This is the first stumbling block for me and I can't see a way over it.

[Sp@ce_d]

I have used GV2 stars to determine the exposures I should be using to get balanced RGB data.

My calculations detirmind that I should be shooting at a ratio of R=1 g=1.3 and b=1.4 for my HX916 and astronomik RGB filters.

The big drawback was more darks required if I didn't want to scale darks.

As I am (when the skies clear) planning to try adding an LP filter into my imaging train again and decided GV2 calibrated exposure lengths were again going to be a must, this is interesting as an alternative to look at.

Mike.

So, If I understand correctly, What you are saying here is:

Get the exposure & balance correctly calibrated at capture time rather than in processing?

[RikM]

I have just been having a play with the PS plug in and it's really quite good! I have been struggling to get star colours to come out right so was hoping something like this was available.

[MikeD]

How do you ensure that when you do a G2V calibration that you are actually using the right star? For example, when I put the star into CdC and issue a slew command, I'm presuming that it will go to a fov that will contain at least a dozen stars. So how do I know which one it is?

This is the first stumbling block for me and I can't see a way over it.

I use a G2V catalogue of stars in sky map pro, I slew to a G2V star and overlay a FOV window in sky map and compare the star field to insure I have the right star.

So, If I understand correctly, What you are saying here is:

Get the exposure & balance correctly calibrated at capture time rather than in processing?

That is the best way to do it IMHO.

A lot more work but, everything you can do at the scope will mean less to do in the processing.

That's why I put so much time into collecting as much good data as I can, 16 hours of data needs very little processing.

Mike.

mike. exposure.

[swag72]

Cheers for that Mike.

The PS plugin is interesting, but it's only telling you the RGB ratio of that image - Can't see how that would be useful for calibration overall.

[RikM]

If you find a G2 star, select it and run the plug in, you can then apply the correction values to the whole image.

[swag72]

Using this method Rik, the ratios for RGB would then be standard for all images, right?

[themos]

Resurrecting this thread because I just found out about eXcalibrator and used it last night on a OSC RGB image of the Heart nebula. It worked well for me. There's a problem with G2 stars explained here

http://cedic.at/arc/c09/sess/CEDIC09_Hubl.pdf

Briefly, we don't have spectral classification for many stars and you're unlikely to find a G2V star in a lot of astro-image fields. Also, a star maybe spectrally G2V but show much redder colour depending on intestellar stuff between the star and Earth.

Colour calibration based on B-V/V-R is more robust because we have BVR photometry data for many more stars.