Oblong Star Correction (entire image)

You may find that thanks to tracking error or a poor polar alignment your stars are oblong across the entire image. If the elongation isn't too large you can correct the problem using layers.

  1. Open your image
  2. Make a duplicate layer (we'll call it SC for star correction)
  3. Change the SC layer mode to Darken
  4. Use Filter > Other > Offset... and adjust the horizonal and vertical offsets to make the stars rounder.
  5. When you're done, merge the layers and save.

Don't forget that changing the SC layer opacity or using Edit > Fade can help weaken the effect of whatever you do.

Sometimes offsetting with whole pixels is a little coarse; perhaps a shift of 1 1/2 pixels would be better. The way to accomplish this is to enlarge your image, perform the offset, and then shrink the image to its original size. Size changes are performed using Image > Image Size... with the pixel dimensions expressed in pixels rather than percentages. Be sure to write down the image's original width before enlarging. Your enlargement should be by a factor of 3 to 5, and you only need change the width; Photoshop will maintain the image's aspect ratio if the little "chain link" icon is showing.

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