Handbook for the TRIUS PRO-694C Issue 1 September 2020
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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:
The image now looks quite impressive and I hope that you like this result from this
simple processing.
Further small refinements are usually possible and you will become expert at judging
the best way to achieve these as your experience increases. As a rough guide, the
‘Filters’ menu can be used to sharpen, soften or noise reduce the image. Strong ‘High
Pass’ filters are usually not a good idea with deep sky images, as the noise will be
strongly increased and dark rings will appear around the stars, but a ‘Median’ filter
can remove odd speckles and a mild ‘Unsharp Mask’ (Radius 3, Power 1) will sharpen
without too much increase in noise.
