Starlight Xpress SXV-M8C - Manual (Page 18)

Handbook for the SXV-M8C Issue 1 Jan 2005
18
1) Make sure the ‘Auto Contrast Stretch’ is switched off and load your image into the
SXV_M8C program. Select ‘Merge’ and then ‘Subtract Dark Frame’. Pick the
appropriate dark frame and the software will then remove the dark signal from your
image, leaving it somewhat darker and slightly smoother than before.
2) The next step is to process the image into colour, but you may find that the
application of a gentle contrast stretch to the image before synthesis will improve the
colour result. Don’t overdo the stretch, as the colour range can then exceed the
dynamic range available, leading to uncorrectable colour errors. Make sure that you
keep a copy of the original file – just in case! Set the colour synthesiser to apply the
anti-alias filter and then run it.
3) The resulting image will probably still look faint and dull, with a pale orange or
green background due to light pollution. Try using the ‘Start point’ adjustment in the
Colour balance menu to get something close to a neutral background colour. Moving
up the red and green start points will reduce the light pollution tint in the background.
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, if 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. In many cases, a ‘Normal’
contrast stretch will give a good result, but may ‘burn out’ the bright regions and
leave the faint parts of the image rather lacking in brightness. To combat this, many