Hi everybody,
Further news on the next version of PixInsight. Today we have been working on an exciting new tool: PhotometricColorCalibration (PCC). We have a first working version with really outstanding results that I want to share with you all.
PCC performs automatic plate solving and photometry (both aperture and PSF photometry are selectable) to calculate RGB white balancing factors based on measured star fluxes, with respect to a user-selectable white reference. Photometric data are retrieved online from the
APASS survey through the
VizieR server and mirrors. The new PCC tool uses internally the latest versions of the ImageSolver and AperturePhotometry scripts, authored by Andrés del Pozo and Vicent Peris. Vicent is also the author of the internal PCC calculation algorithms. I am writing the C++ implementation, making the most of the new functionality of version 1.8.5 that allows us to execute JavaScript scripts from PCL-based C++ code to write hybrid PixInsight modules. This means that PCC is a regular PixInsight tool, not a script, with all its inherent benefits.
Here are a few examples that Vicent and I have been preparing to show you the kind of results you may expect from PCC.
First a wide-field DSLR image of the Milky Way, courtesy of Georg Viehoever:
On the left, the original RGB debayered image. On the right, the result after applying PhotometricColorCalibration. The good news is that PCC is really easy to use. If your image has approximate center coordinates and image scale metadata (as FITS header keywords), PCC is basically a one-button tool in most cases (or, speaking in pure PixInsight terms, a one-blue-triangle tool). The next example is a two-frame mosaic of the region around NGC 2080, in the Large Magellanic Cloud (data by Vicent Peris):
This is an image of the LBN 552 region acquired with the 1.2 m Zeiss telescope of Calar Alto Observatory:
The original combined RGB image, shown on the top-left, had already been white balanced using the average color of the stars in the frame as white reference. The newly calibrated image with PCC is on the bottom-right of the screenshot. The difference speaks by itself.
The last example is an image of M51, also acquired through the 1.2 m telescope of Calar Alto Observatory:
After applying PCC, the image shown on the right has been stretched nonlinearly with HistogramTransformation, processed with HDRMultiscaleTransform, and its color saturation has been increased with CurvesTransformation.
Besides its underlying high-accuracy astrometric and photometric analysis implementations, the most innovative and powerful feature of our new PCC tool is, in my opinion, the fact that it allows you to select one among numerous predefined, carefully generated white references. By default, PCC applies a white reference based on the average of the characteristic fluxes of Sb, Sc and Sd galaxies. This reference, which has been used in all of the examples shown above, is in our opinion truly representative of the deep space, and hence an unbiased, neutral white reference quite close to our documentary color philosophy. If you want to persist in making common conceptual mistakes, you will be able to use the G2V spectral type as a white reference—but PCC will allow you to select virtually any spectral type, along with several galaxy types, to calibrate the color of your images automatically and accurately in PixInsight.
A huge kudos to Andrés del Pozo and Vicent Peris, who are the authors of the excellent implementations and algorithms behind the new PhotometricColorCalibration tool. Thank you for your continued support and contributions, which make PixInsight an exciting platform in constant evolution.
