Target: Messier 106 (NGC 4258) in constellation Canes Venatici. Distance 22-25 million light-years.
Data acquisition: Adam Block, Mt. Lemmon SkyCenter Remote Observing Program.
Location: Summit of Mt. Lemmon, 9,157 ft, just north of Tucson, Arizona
Telescope: 32-inch Schulman, Aperture 800mm, Focal Length 5600 mm, Focal Ratio f/7.
Camera: SBIG STX-16803 CCD
Post-Processing software: CCDStack2 and PixInsight 1.8 RC4.
Exposures: Red, Green, Blue each 14 at 10 min, 5 at 15 min, unbinned, 3.6 hrs per color, 10.8 hrs total.
PixInsight tools used:
StarAlignment to register 58 files that had been calibrated in CCDStack2
ImageIntegration of Red, Green, and Blue files. Average FWHM of stars 5.13. Resolution 1.7 arcsec/pixel.
ChannelCombination to create RGB image
DynamicCrop to trim edge artifacts from stacking
DynamicBackgroundExtraction to remove background gradients
BackgroundNeutralization to adjust the colors to produce a neutral background color
ColorCalibration to white balance colors
At this point I have a linear RGB base image as a starting point for further processing.
HistogramTransformation for permanent stretch of RGB image
ChannelExtraction to make a CIE L* pseudo luminance image
LRGBCombination to apply the luminance to RGB, adjust color saturation, apply chrominance noise reduction
Use the pseudo luminance image as a luminance mask to protect low SNR areas for the next step
HDRMultiscaleTransform to bring out details of the galaxy core
Invert same mask to protect high SNR areas for the next step
MultiscaleMedianTransform to reduce background noise
CurvesTransformation to nudge contrast.