Old 17-09-2017, 09:24 AM
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vlazg (George)
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An interesting comparison

I have always wondered how what we image would appear if we could see them.
Both these images are of the same data and processed similarly. The only difference is that in the 1st image i used Pixinsight"s Photometric Colour Calibration with no adjustment to saturation and the second was using both background neutralisation and then Color Calibration.

The tutorial from the developers of Pixinsight in its introduction states

" In version 1.8.5 of PixInsight we present PhotometricColorCalibration (PCC), a new tool to apply a white balance to deep-sky images based on photometry measurements of stars. In this article we describe the PCC tool, how it works, and some of its distinctive features. We also give some practical usage recommendations.

PCC is a very special tool for several reasons. Besides the quality of our implementation, what really makes PCC unique is the fact that it materializes our philosophy of color in deep-sky astrophotography, and primarily, our philosophy of image processing: astrophotography is documentary photography, where there is no room for arbitrary manipulations without the basic documentary criterion of preserving the nature of the objects represented. In deep-sky astrophotography, we understand color as a means to control the representation of information in the image. Following documentary criteria, such representation must be justified by properties of the objects photographed. This excludes, in our opinion, the classical concept of "natural color" based on the characteristics of the human vision, as applied to daylight scenes.

In the PCC tool, the default white reference is based on the average spectra of Sb, Sc and Sd galaxies. The average of these galaxies provides a source of the entire range of stellar spectral types and populations, so it can be considered as the best unbiased white reference, truly representative of the observed deep sky. Along with this default reference, PCC provides a rich set of precalculated white references, including spiral galaxies, elliptical galaxies, and most stellar spectral types. This allows you to select the most appropriate white reference in special cases, where you decide to maximize the information represented for some particular objects in the image. The possibility to choose one among a rich set of white references is also useful to understand the nature of the data, by analyzing color variations as a function of the properties of the represented objects. In this sense, PCC also materializes our vision of image processing as a creative and enjoyable activity: the how and the why are actually more important than the final product."

Where is the line between art and science
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Old 19-09-2017, 09:16 AM
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sil (Steve)
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PCC is just awesome. Takes a lot of guesswork and looking for reference photos to try to colour calibrate against. Using BN first you'r applying a curve to the data so its no longer linear for PCC. PCC just takes away a ton of work and lets newbies like me get well coloured (accuracy wise) images quickly without fuss. interesting to note the new Astro Pixel Processor program (APP) produces an integration frame colour calibrated very close by default to PI's PCC. So good to see improvements and options for users of all skill levels.

For both Art and Science!
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Old 19-09-2017, 09:30 AM
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RickS (Rick)
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Nice example, George.

Originally Posted by sil View Post
Using BN first you'r applying a curve to the data so its no longer linear for PCC.
BN only performs linear operations, so no harm done. I agree that PCC is a great tool!

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