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Old 02-07-2009, 11:28 PM
jase (Jason)
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jase is offline
Join Date: Sep 2006
Location: Melbourne, Victoria
Posts: 3,916
Repairing colour flares and/or other colour anomalies

The technique defined below can be used to address colour related issues due to stars that are off the edge of frame. These stars, if bright enough, often cause colour flares that detract from the images appearance. The technique can also be used to address other colour related issues. In summary the concept is to copy a "good" piece of the sky that has contains the desired colour hue over the top of the offending colour flare. A follow up step brings the stars of the repaired area back to their original form.
  • Click on the lasso tool and set the feathering to approx 20 pixels
  • Using the lasso tool, select an area that is of same size and is relatively close to the colour flare area you wish to remove. The purpose of this exercise is to match the background hue of the surrounding area so the proximity to the area you're trying to fix is fairly important. At this point, don't worry if the selected area contains stars.
  • Copy and paste the lasso area so you now have a new layer that contains the small patch of the sky in which you've just copied.
  • Hold down the control key and move the mouse to shift the small patch over the colour flare area you wish to remove.
  • Now go to the Filters | Noise | Median
  • Increase the radius until you see no more stars in the small patch of sky that you've copied. If you don't like the median tool, dust and scratches, or the minimum filters can do a similar job. Median I've found works well in general.
  • With the patch layer selected, change its blend mode from normal to colour
  • You'll now notice that your colour flare has disappeared i.e. has been blending into the surrounding background hues. If it hasn't you may need to increase your selection size or reduce the feather.
...but don't stop there...look what you've done to the stars in the area that's been repaired...they've inherited the same background tone you copied. Easily fixed...
  • Select the original layer and use the colour range tool to highlight the stars. Alter the fuzziness slider until you get a good match.
  • Expand the selection by 2 or 3 pixels (or to your taste)
  • Feather by 2 pixels (or to your taste)
  • Then select the patch layer (important, make sure its selected!!)
  • Hit the delete key
  • POW! You've now brought the star colours back in the repaired you've deleted the selections from the patch layer so the colours come back through from the original layer.
  • If you find that the colour range tool selection wasn't ideal, you can always use the eraser tool to do a similar task, but I would recommend going back a few steps until you get the right selection i.e. manipulate fuzziness.
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