"Centaurus A" Color Correction

From my geography (San Diego 32 degrees North), This object is very low on the horizon. Getting the "correct" color is a challenge in these circumstances. There is the challenge of correct balance in your RGB filters and the challenge of the variable effect of Atmospheric Extinction of different wavelengths affecting color balance. A "G2V" star color calibration was used to balance my RGB filters; Atmosperic Extinction factors were used to correct for the extinction. The final image and description are available on This Page. Here are the visual steps in getting there.

This first image is the Raw color used in a LRGB process. I think it is noticeably red. Mouse over the image to see the effect of the application of the G2V calibration. For my filters balance is at R:G:B 253:235:244 converted to an output of 255:255:255. So you can see that uncorrected all my images would be weakest on green and biased to red.

This image is the "G2V" calibrated image. Mouse over the image to see the effect of the application of the Atmospheric Extinction factors. The factors are from a table I created in Excel that gives typical values and factors. In this image I used a curves setting of R:G:B 128:128:128 converted to an output of 114:128:141.

All images and content remain the property of Jim Thommes - copyright 2003 - 2012

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