View Full Version : m31 try
2008-Dec-23, 04:26 PM
after a couple months of clouds, had to try m31 despite it being 9 degrees. only got 2 hours before the cold sent my USB hub to electronics heaven. No darks, used the ED 80 with 0.8 reducer flattener with Rebel mod, guided with 11" SCT and PHD. 21 x 500 sec iso 1600. Acquired and processed with Nebulosity, resized and levels with Elements.
2008-Dec-23, 06:16 PM
That's a nice shot. Nicely framed, nice crisp stars too.
The center of the galaxy looks a bit clipped, have you tried brightening with curves instead of levels? That way you can bring up the faint areas without clipping the bright ones.
2008-Dec-23, 07:21 PM
don't have curves, but reprocessed a little less aggressive.
2008-Dec-23, 09:12 PM
It looks like you are trying to process both the core and the disk as one. Can't be done. Nor can it be done with just levels as that is a linear adjustment applied to non linear data. When the brightness difference is this great you have to process the core and disk separately then combine them. Curves is available for elements as a free plug in. See http://www.earthboundlight.com/phototips/photoshop-elements-curves.html for that info. If you use Elements 4 and above then see the link on that page for that in the box. Can't recall the name but it is something like Smart Curve for 4-6. Since Elements works in 8 bit mode it can't do what Photoshop can using 16 bit mode but it can do a lot to improve this image far beyond what I see here when all its features are used.
Copy the unstretched image to a duplicate layer. Now using curves process the core region in the top layer and the disk region in the bottom. Masks make this easier, not sure how available those are in which versions of elements. By masking out the core in the disk version and disk in the core version you can then combine the two retaining the best of each layer.
If masks aren't available then in the upper layer select the core using a feather of say 20 for the size image you posted. More if the original is larger. Make this selection before you duplicate the layers. Now using curves process the core in the upper layer and the disk in the lower layer (invert the selection in the lower layer to select the disk). After both are right invert the selection of each layer so now the top layer selects the disk and bottom later the core and fade those to parts to black. Now select the top layer again and combine using lighten mode. If they don't blend well just step back and do a bit of work on whichever layer needs it. Note that due to the feather as you dim the core or the disk the edges will fade away. This is what you want, not a sharp cut off. When combined the two will blend together. Not as much control this way as with masks but will work.
There are many other ways of doing this, this is just one of them. Note that curves itself works in an adjustment layer so you will end up with many layers before you flatten everything. This gives you lots of control and ability to go back you wouldn't have otherwise but can be confusing when you first start out. So be sure you are working with the right layer or you can wonder why something doesn't work or works differently than you expected.
An even simpler but less effective way is to just process the entire image for the core and forget the disk. Then select the core region using a feather as described above and copy that to the clipboard. Now bring up the original image with the burned in core and past the core to it. It will paste as a layer above the entire image. Set blend to 50% so you can see both layers and using the move tool roughly align the core copy then use the arrow keys to move it one pixel at a time until it is correctly aligned. Reset blend to 100% and combine. If you selected the edge of the copy correctly with the right feather then they should blend together, if not go back to the core image and try again based on what you learned. Serious imagers are now cringing but this will give a better result than what you have so far.
There's no need to be satisfied with a blob for the core if the original date wasn't burned in. With objects like M42 you have to take several exposures for the brightest, mid and dimmest regions and again process each for the detail it contains then merge them together. Usually though with M31 with the proper exposure time you can get the disk and core in one image but then will need to process the core separately.
2008-Dec-24, 09:49 PM
Very Nice image of m31, Great info from Rick, Merry Xmas and Clear Skies.
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