eXcalibrator and PI

[mmirot]

I was referring to Excalibrator. It uses stars in the images to compensate for extinction. The catalog stars are adjusted/calibrated to G2 standard I think.

Vicents, point is that we need a transmitted star light standard.
G2 color is based on reflected sun light. Deep sky objects only transmit light. 

Therefore we need a galaxy standard which is the sum of star colors transmitted. The galaxies choose would have to have low red shifts and no galactic dust extinction.

Perhaps Vicent and Juan would be better off by measuring their galactic standard and correlating the same reference stars in Excalibrator. It would take time to determine the factors of course but might save time in the end.

Max

[Niall Saunders]

Hi Sander,

This is why I always advise people to skip the RGB weighting effort that some folks seem determined to make. Just debayer and stack and let the image be green. Then calibrate and correct. No matter how smart the RGB weights are, you'll always have to correct anyway so you might as well skip the weights. That's why the debayer module doesn't have weights

That is bordering on Heresy!! You could get yourself banned by saying that on some other Forums

In fact, next thing you will be suggesting that we need to mess around taking R, G and B exposures for differing times or that RGB combinations can only ever work if you apply the correct, extinction-compensated, weighting factors at the time of combination.

And yet, when an image is massaged through the PI BackroundNeutralisation and ColourCalibration processes, why does it just then seem to 'look right', when us heretics have totally ignored the extinction-compensated, plate-solved, filter-adjusted, weighting factors that their proponents seem to insist are necessary?

Maybe our methods are frowned upon because we just don't have to work hard enough to achieve good results

[georg.viehoever]

Hi Sander,

This is why I always advise people to skip the RGB weighting effort that some folks seem determined to make. Just debayer and stack and let the image be green. Then calibrate and correct. No matter how smart the RGB weights are, you'll always have to correct anyway so you might as well skip the weights. That's why the debayer module doesn't have weights

That is bordering on Heresy!! You could get yourself banned by saying that on some other Forums

...

I also wonder what the value of this kind of calibration in "aestetic" image processing is. Even if you calibrate to G2V or catalogs: as soon as you give a non-linear stretch to your image, the star colors change anyway (e.g. bright stars become more white/loose color). If you goal is to produce scientifically valid colors and magnitudes, G2V or the eXcalibrator approach are probably valid approaches. If your goal is to visualize certain aspects of your target object (e.g. fine structures, or just its beauty), having "true" colors is less important. And for NarrowBand, true colors are even undefined.

BTW: after DBE and ColorCalibration, my images usually are quite close to what I consider natural colors...

Georg

[Redshift]

Can someone give me a link to eXcalibrator, I'd like to have a look?

Thank you

Dave

[georg.viehoever]

Can someone give me a link to eXcalibrator, I'd like to have a look?

Google helps: http://bf-astro.com/eXcalibrator/excalibrator.htm