Compose Module Quest ion on Binning

[whixson]

When entering the total exposure time in the Compose module, how do you account for different Bins? I shot Lum at 1x1 and RGB at 2x2, 120 seconds each. Do I weigh the 2x2 bins with twice the exposure time?

Thanks, Wayne

[admin]

Exposure times only come into play if you want to add R, G and/or B to luminance (or create a synthetic luminance frame out of R, G and/or B). e.g. when the 'Luminance, Color' parameter is set to 'L, RGB' the exposure times are ignored. I should probably grey the controls out to avoid confusion.

Generally speaking, of course, it doesn't make too much sense to add the much "blurrier" R, G and B datasets to the luminance dataset to create a synthetic luminance dataset (e.g. 'Luminance, Color' parameter set to 'L + Synthetic L From RGB, RGB'). The whole reason people image R, G and B at bin 2x2 is to save time, as they don't care for the precision in the color channels and just want some coarse color data. This exploits the fact that humans are very bad at discerning changes in color, but are very good at discerning changes in luminance.

However, you could (software) bin your luminance data to 2x2 as well. Now you should be able to add your 2x2 RGB to luminance to the luminance signal to create a synthetic luminance frame. Quadruple your luminance exposure time if you do that (you are now using 2x2 = 4x as much signal per luminance pixel, yielding a SQRT(4) = 2x more precise luminance signal). Note that depending on your instrument and acquisition settings, your mileage may vary however, as hardware 2x2 binning may or may not be quite the same as 2x2 software binning (read noise will likely be lower, but dynamic range may have suffered).

Does that make sense?