This is a crowd image. It was made by integrating 279 different astro photos of M16. All processing was done in PixInsight.

With this image I experimented with something new. The crowd image method yields excellent SNR due to the very high summed exposure time, but so far I've weighted all sub images equally 1:1. To increase the overall sharpness, this time I tried to weigh based on FWHM. First all images were aligned to a 7K master frame using distortion correction, and then I used SubFrameSelector to measure FWHM. Then I added a keyword to all the fits files based on the formula

WEIGHT = 1/FWHM^2

The result was a significantly sharper stack, with a slightly better SNR.

Normally I add an alpha channel to each file, and use the stacked alphas to make a sort of Flat frame, that describes the coverage of all the files. That method is described in the Elephant Trunk processing example in my gallery.

This time I took a different aproach. All the files were integrated with the weight keyword described above, low clipping and add/scale normalization. I've really experimentet with almost every possible combination in ImageIntegration, and this is the best way I've found so far. Because I work with very different nonlinear files, something that PixInsight is not intended for, many things have to be invented on the way.

The image is HaSHORGB with RGB colored stars, meaning that the nebulosity is a blend of SHO and RGB, and that Ha was used as luminance.

Image Credits (Thanks for sharing!

Adam Evans, Ahmet Kale, Alvinillo, Andolfato, André Lucas Melo, Andrea Pistocchini, Angel Requena, apricot, arcturus13, Astroluc63, B.J. Bumgarner, beta_kappa, betakappa, Bob Familiar, bradypo, Carlos Martín López, Charlemagne920, chripell, Chris Madson, Chris Ryan, Claustonberry, Cobbler, Creedence, Dan, Dan Watt, Daniele Malleo, Diego Cartes, docMario, Eddie Yip, Edi, Eduardo Mariño, felgari, Fernando Fogel, Flavastro, FranckIM06, Fred Locklear, galaad16, geco71, Igor Fulvi, Jan Curtis, Jason Ahrns, Javier R., Jim Keller, John Dalton, Jon Connell, Jonathan Powles, Jorge Gomez, Jose Carlos Castro, jpstanley, Jschulman555, Juan Lozano, Khayos., khyperia, l.hutton, Ljubinko Jovanovic, Loren Larson, Luc Jamet, Luca Argalia, Luca Billeri, Luis Argerich, Marc Van Norden, Marcelo Domingues, Mario Bertsch, Mark Mathosian, masa*wang, Matthew, Máximo Bustamante, Michael Karrer, Mike Durkin, Mike Markiw, Miodrag Sekulic, Miquel, Morten Balling, Neb_34, neptun, Nicholas Jones, Oliver Czernetz, Owen, Özgür Ünat, pascvale13, Paul Storey, PaulHutchinson, Pavel (sypai) Syrin, pfile, Phil Hosey, Ralph W, Richie Jarvis, RIKY, roxunreal, Ryan Shaw, s58y, Salvatore Iovene, Salvopa, Sergei Golyshev, Shane Poage, Shashikiran, Shashikiran Ganesh, Simon Bailey, Stephen Rahn, symulae, Tim, ttfnrob, vetenskapsman, Will Kalman.