[Kstars-devel] questions re: gathering images

[Luciano Montanaro]

Il Sunday 01 July 2007 21:37:45 Glenn Becker ha scritto:
> Luciano -
>
> I saved this set of instructions of yours from some time ago ...
>
> > which I obtained from the kstars m42 image with these steps:
> >
> > Convert image to RGB
> > Create a mask from a grayscale copy of the image (Layer->Mask->Add Layer
> > Mask)
> >
> >> From the layers dialog, select the mask (it should be already selected)
> >
> > Adjust color levels, with Tools->Color Tools->Levels
> > (I have used the "auto" function to find the minnimum, and set the mask
> > to opaque for values above 128, so luminous objects are visible, and the
> > rest of the images blends gradually to the background)
> > Apply the layer mask from the popup menu in the layers dialog
> > Save.
>
> I am trying to apply these steps to the NGC images I have, but there is
> one step I think I am not doing correctly: how do you "set the mask opaque
> for values above 128"? What I have tried is sliding the white arrow (in
> the "Adjust Color Levels" dialogue) in the slider under "Output levels"
> down to 128. This makes the image more diaphanous / transparent, but
> maybe too much so?
>

Ah, ok. I think I worked on the input levels. Actually, I've found you have to 
tweak both ends of the inbput so that your medium gray values for the galaxy 
is half-transparent... All we really want is for the images to blend well 
with the background, don't we?

> I am attaching a sample of what I have wound up with for NGC 5566. If I am
> not interpreting the instructions correctly, let me know (I'm not really
> a graphics guy, I admit - the help is much appreciated) & what I should do
> instead.
>
> Regards,
>
> Glenn
>
> +-----------------------------------------------------+
> Glenn Becker - burningc at sdf.lonestar.org
> SDF Public Access UNIX System - http://sdf.lonestar.org
> +-----------------------------------------------------+