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Having been advised months ago to do an initial data-stretch in DSS before going on to GIMP my images, I have finally given it a go (they don't call me lightning for nothing:)). Quite impressed with the improved result, but just want to check that I am aiming for the right thing (I don't find the help file in DSS to be particularly helpful - "The simplest way to understand how the different parameters are working is to change them and look at the result on the histogram") before I start reprocessing everything.

I tried to centralize the three colour pillars and then move the sliders so that the base of the curve over each colour filled as much of the width of the graph as possible. Then adjusted the luminence sliders so that the black line got as close as possible to running along the peaks of all the colour bits (excuse my technical jargon:D)

So, is what I was aiming for the same as what I should have been aiming for, or is there a procedure that will produce an even better result.

Many thanks.

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Just to let you know, the author of DSS says the image manipulation is intended for a quick look. He doesn't use it for processing !

Having said that, if it works for you......

Dave.

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Just to let you know, the author of DSS says the image manipulation is intended for a quick look. He doesn't use it for processing !
I think it was probably me that recommended this! The trouble is that GIMP is only 8-bit, so you really need to do some stretching in DSS otherwise it ends up very dark and very quantised in GIMP.

Having made the excuses, I actually think the manipulation you can do in DSS is actually pretty good, although very fine adjustments to the colour balance never seems possible.

Remember DSS does a log(sqrt) stretch by default by the way.

NigelM

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Yes, Nigel, it was ... just found the original post:

If you are using GIMP (which I do) you need to adjust the image in DSS first, so it looks reasonable to the eye, and remember to apply the changes when saving as a tiff. I wonder if you are doing this last bit? If you just save the 16-bit DSS image without applying any changes and open in GIMP you will get something like your picture.

NigelM

Can you confirm that what I am trying to do

I tried to centralize the three colour pillars and then move the sliders so that the base of the curve over each colour filled as much of the width of the graph as possible. Then adjusted the luminence sliders so that the black line got as close as possible to running along the peaks of all the colour bits (excuse my technical jargon:D)

is what I should be doing, or if I should be aiming at something else?

Thanks

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I usually have RGB Channels calibration switched on. This is supposed to make the three colour histograms overlap automatically and hence make the background 'grey'. Never seem to work terribly well for me, so I end up having to tweak this manually in RGB levels tab. I rarely, if ever, use anything other than the default log(sqrt) for the RGB tab by the way.

Once done, I up the saturation to 20% then adjust the luminance curve using the lower Midtone slider so it just starts to rise through the bottom end of the coloured histograms. For low contrast objects I then adjust the upper Midtone slider to make the curve steeper. A further adjustment of the lower slider may then be necessary. I have never found any use for the Darkness sliders! I sometime play with the Highlight ones to try to regain some colour in the stars.

Basically its just got to look nice on the screen at this stage!

NigelM

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Yes, if you are using an 8bit postprocessing package like GIMP then a pre-stretch in DSS makes perfect sense. It sounds like you are doing the right thing. Just make sure you don't cut into the lefthand side of the histogram peak too much...that will result in losing real data and could end up with black holes puched into your background...effectively increasing background noise.

Of course the best thing to do is take the unstretched 32bit Autosave.tif (or .FIT) file into a program that will allow you to do a histogram stretch on that. You will certainly notice a difference. But that requires getting one of those programs which costs money. :)

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