When I upsize the binned 2X2 color channels, do I check the "preserve flux" box when upsizing?
Thanks,
Joe Daglen

That may depend on what you plan to do with the image, but for the most part it doesn't matter.

"Preserving flux" means that the camera gain is retained. For example, if the gain = 2 electrons per ADU and you upsize by 2 then each resampled pixel contains only 1/4 of the photons that were captured by the original pixel. If you opt to not preserve the flux then the ADU in the resampled pixels will essentially be the same as the original pixels, which now means that the effective gain has been changed to 0.5 electrons per ADU. But if you opt to preserve flux then the gain remains at 2 e/ADU and the resampled pixels have 1/4 of the original ADU (because the ADU for each pixel has been spread over 4 pixels).

Preserving gain can be important if you are subsequently using that image in a stack with other images that were not resized (e.g. combining up-sized binned images with unbinned images) because gain is used by some data rejection procedures (e.g. Poisson sigma).

But often it is not necessary to preserve flux and doing so may result in an ADU range that is unsuitable for 16 bit files. For example, if you are resizing an image just prior to exporting to Photoshop (or whatever) via 16 bit TIFF or FITS then you should not preserve the flux.

Stan

Thanks for the quick response Stan. The original bin2X2 R,G,& B channels are upsized X2 to then form a single composite color RGB in CCDStack and then saved to 16 bit tiff to be combined in Photoshop with the bin1X1 Luminance channel. So I will NOT "preserve flux".
Thanks,
Joe