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Old 19-12-2012, 06:13 PM
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Shiraz (Ray)
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Shiraz is offline
Join Date: Apr 2010
Location: ardrossan south australia
Posts: 4,787
Hi John

missed this one somehow - sorry.

First off, have to agree with Asi - seeing is the key to any form of success and will often determine the best processing path. I generally drive 130k to my imaging site and have to be able to predict when the seeing will be good. I need a breeze off the sea combined with 200hPa winds of less than about 30kts to have any chance of really good seeing. If the wind is not off the sea (or there is no wind) I get tearing or rolling local distortion - if the jetstream is too strong the fine detail goes and the overall contrast often drops drastically. Local distortion can sometimes be stacked out - especially with AS!2 - but nothing can restore lost fine detail.

Equipment is a 300mm f5 Newt with 3x Barlow or 5x Powermate. Astronomik filters and possibly a dispersion corrector for use below about 40deg. Biggest payback from the corrector is for Saturn where it allows a broadband lum image to be obtained at high framerate. This can help a lot in some seeing. Also good for tidying up the blue channel with Jupiter. General observation would be that the corrector really only helps a lot when the seeing is good - which it almost never is at low altitude.

I use either Firecapture or ICCapture for the DMK21618 camera. Normally capture for 60 seconds per channel at 60hz for Jupiter and 100 sec 30/15Hz for Saturn, but occasionally will vary scale if seeing suggests that shorter exposures might help. Firecapture will not reliably run at 60Hz (drops about 10-20% of frames on my i7) so use ICCap when running at 60. Jupiter is better at 30Hz if seeing will allow - lower frame rate reduces read noise .

processing is:
1. castrator to centre up images
2. stack in AS!2 normally - maybe 40-50 points on Jupiter and perhaps 25 on Saturn. If the seeing works against AS!2, use R6 with an intermediate stack to generate a reference image from a single stack point and then use multiple stack points on the reference - this gets around the distortion that can occur with R6. also, R6 runs best if a prefilter is used to smooth noise - I use a scale of 4.
3. sharpen with AS!2 plus additional sharpening in R6 with linked wavelets used as sparingly as possible. The noise limiting capability of R6 is worth having. An alternative if enough frames have been stackable is to use multiple scales of VanCittert deconvolution in IRIS with median and Gaussian filters to control noise. Have found it important to use the same sharpening in all colour channels to keep final colours looking reasonable - different smoothing may be applied though.
4. colour combine RGB or LRGB in WINJUPOS using derotation of the stacked frames. this really helps tidy up the colours and has been a major advance in processing RGB. If there is still some residual mismatch between the colour channels, I will split the stacked image in IRIS and recombine with manual adjustment to remove the slight misalignment. If there is any residual noise on the planet edge, will use annular select in GIMP with feathered edge and reduce the saturation or blur around the edge. I have tried both combining multiple colour frames and video derotation in WINJUPOS , but with limited success to date.
5. tidy up the image in GIMP. Colour balance using the "grey point" add in to set a white point and then compare with a standard image (eg from Cassini, Pic du Midi or Trevor) to get the final balance and saturation as close as possible to "right". I try to use gamma of 1 throughout, unless the seeing has been so poor that contrast is almost gone - then will sometimes use modified curves to compensate. also sometimes use a very light adaptive smoothing which only removes noise in regions where there is little contrast - needs to be used very sparingly if at all.

would be very interested in any discussion. regards ray

Last edited by Shiraz; 20-12-2012 at 09:12 PM.
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