Quote:
Originally Posted by irwjager
So what's the difference between stretching and binning?
If I stretch the brightness levels, I trade off precision for signal
If I bin the image, I trade resolution for signal. or
If I stretch the brightness levels, gaps will start to appear in the histogram. Stretch the levels enough and you'll start to see banding and noise will become more apparent.
If I bin the image, the histogram will stay intact and appear smooth. I can bin as much as I want without ever seeing any banding (though my image will get smaller and smaller and uselessly bright).
That's how (and why) I use software binning in a nutshell! |
Wait a sec, it sounds as if you are working in only 8bits? CCDs produce images with much more than 8bits of dynamic range (10-14 is typical). And stacked images have even more (16 images in a stack could in theory get 4 more bits). Also the camera quantization levels are generally set to be smaller than the read noise. That way the discreet digital levels are not a limiting factor. That's why MaxIm DL and Mira do their processing in 32bit floating point, none of this banding occurs and there is no trade off in signal range-precision. Although I have seen banding on the display image when I had a large smooth ultra low noise profile, like that produced by a giant elliptical galaxy for which I had tons of exposure time on.
You would only want to software bin to make the image a) smaller and/or b) smoother by giving up resolution.
Cheers,
EB