Focal Pointe Observatory
Astrophotography by Bob Franke

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These two images were created with RGB ratios of 1,1,1. Run your mouse over each image to see a view with eXcalibrator ratios.

For the first image, eXcalibrator calculated RGB ratios of 1.00 1.155 and 1.46.
For the second image eXcalibrator calculated RGB ratios of 1.00 1.305 and 1.533.

In all cases, pixel math was applied to the individual red, green and blue images to remove color bias. The eXcalibrator ratios were identical before and after removing the bias.

After creating the RGB images, the ones using the eXcalibrator ratios had a strong cyan bias. Pixel math was again used to remove this before stretching the images.

There is a significant difference in the eXcalibrator results. Unfortunately, the Sloan Digital Sky Survey star data were not available. The ratios were calculated with the NOMAD database. These data are sometimes inconsistent and unreliable. Removing statistical outliers left only nine stars for the color ratio calculations. And still, the standard deviation was relatively high. With the NOMAD data, more stars are needed to average errors.

The eXcalibrator color in the first image looks good. Without this color adjustment, the nebula is mostly red with almost no color variance. The eXcalibrator version shows some bluish-red areas. We often see this with emission nebula. Also, the bright star left of center correctly has a blue cast.

With the second image, the eXcalibrator ratios appear too extreme. Something about halfway between the non-corrected and eXcalibrator view is probably about right.