Handbook for the TRIUS SX-825 Issue 1 January 2015
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3) The resulting image will probably look faint and dull, possibly with a pale yellowish background,
due to light pollution so it is now time to process the ‘luminance’ (brightness and contrast) of the image
to get the best visual appearance. First, use the ‘Normal’ contrast stretch to darken the background by
setting the ‘Black’ slider just below the main peak of the histogram. Alternatively, you can use the
‘Remove Background’ option to let the software decide on the best setting. This will greatly reduce the
background brightness and the image will begin to look rather more attractive, although dark. You can
now try brightening the highlights with another ‘Normal’ stretch, in which you bring down the ‘White’
slider to just above the main image peak. The best setting for this is rather more difficult to guess and
you may need several attempts before the result is ideal. Just use the ‘Undo last filter’ function, if
necessary, to correct a mistake. Normal (linear) stretches can give a nice result on many objects, but
you may find that bright areas ‘burn-out’ badly with this function. It is often much better to use a ‘Non-
linear’ stretch to compress the brighter regions, while expanding the faint data. Here is the result of a
non-linear stretch on the M42 image:
