Pulling dim Nebulae from the background using PhotoShop
you are proficient with PhotoShop this might be old hat to you.
However, I'm still trying to pickup the various tricks and
features available in PhotoShop for processing Astro-images. I recently
saw an image where the dim nebulae were clearly visible and asked Duncan
McCloud How he did that. These are the steps he uses.
create a Curves adjustment layer.
<ctrl> and click on faint gas in the image.
<ctrl> and click on dark background.
You'll see the points you just selected on the Curves graph.
The two points can be very close together, that's OK. If Photoshop
shows them as the same point, choose slightly brighter gas as your
Duncan likes to set a control point just below the dark background
point; this keeps the background from getting darker when you start
moving the curve. To do this just click on the curve below the
background point and press the up and right arrows on your keyboard
until it is snuggled up to the background point. Make sure the X and Y
values are the same.
Now the fun
part; select the point on the curve for the gas (<ctrl>-tab cycles
Then press the
up arrow on your keyboard and watch the gasses get brighter while
keeping the background a constant level. Don't get carried away, a
little movement on the curve goes a long way.
Duncan usually set a control point in the mid-range so it doesn't
get too bright . He also anchor it with a second point right next to it
so the highlights don't get lowered. Without the second anchor point,
the curve would flip all over the place, creating an unwanted look
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