Re: [APML] Adjusting mosaic frames

[Eric Royer <eroyer@club-internet.fr>]

Hello,
I have assembled 2 mosaics so far. Here is the method I used the second
time.
I assume that you have an image with 2 layers in Photoshop (one for each
frame). If you adjust levels before you assemble the mosaic be sure to
make the same adjustments in both frames (if your exposures are of the
same length and if you used the same scanner settings of course). It
will make the following much easier.
Do the stars match perfectly in the common part ? If that's not he case
the method below needs to be modified a little.

First, you must be sure that you have corrected vignetting in both
frames.
After that I find it is easier to select only one channel (start with
red) and adjust the lightness until the 2 frames match. Usually, they
won't match on the full length of the common part, so you have to adjust
them as you can. There can be a difference of + or - 3 or 4 in the
levels.
Do that for each channel and the junction should be difficult to see
when the image is displayed in full RGB colors.
Now to hide the remaining differences, you have to create a layer mask
(I think it's the right name in english but I'm not sure). If the mask
is white, you can see layer 2, if it is black you can see the
background. Select the common part and make a linear gradient from white
to black in this part of the mask. This should hide the remaining
defects.
If the stars in your frames are not exactly in the same position, you
can modify the mask so that the background has a gradient as a mask and
the stars have a white mask. But this trick is very time consuming. I
had to use it with my 8 frame mosaic of the milky way, and it took me a
lot of time !

By the way, can you tell us what object you photographed ? or maybe you
want to keep it secret until the mosaic is ready ...

Good luck and feel free to ask questions if the above is not very clear
(sometimes I have difficulties to explain things in english).

Eric

Peter Mumbower wrote:
> 
> Hi all,
> 
>         Just to clarify a little more. I have a 2 panel mosaic, with each panel
> having 3 negs to stack.  After I stack them in Registar and assemble the
> mosaic in Registar, I go to Photoshop, where I try to match the background
> for each panel, unsuccessfully. Should I be adjusting the levels in PS
> before I assemble the mosaic?


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