Dark Dolphin swimming on a dark reef

[topheart]

HI All,

I tweaked the image very slightly.....


https://savannahskies.smugmug.com/Nebula/i-pKt3FqT/A

Thanks very much!
Tim

[strongmanmike (Michael)]

A worthwhile tweak Tim

This'd make a nice print

Mike

[topheart]

Thanks Mike!
Cheers,
Tim

[topheart]

Originally Posted by marc4darkskies

I don't know how you would do it in PI, but in PS, it's easy. Disclaimer: nothing will fix elongation perfectly but it can be mitigated if the elongation is of the order of about a pixel or two (at the outside) like yours. Much more than that and you'll still end up with misshapen stars or other artefacts.

In Photoshop:

• Flatten
• Enlarge the image by 300% (to allow sub pixel manipulations)
• Duplicate the flat layer
• Change the blending mode of the duplicate to Darken
• Select the whole image
• Zoom in to an edge so you can see the pixels and an elongated star
• Using "Free Transform", grab & shift an edge (on one axis) to reduce the elongation on that axis
• If the elongation is diagonal (elongation along 2 axes) repeat for the second edge/axis
• Always overdo it a bit and then use the opacity slider to blend the darken layer to achieve the best result (blink between the before and after)
• If only a corner is elongated, you may need to use a mask on the darken layer to expose only the elongated area (with a very large fuzzy brush to get seamless transitions)
• Reduce the image back down to 100% scale

NOTES:
1) Transforming from an edge will result in stars closest the the edge being altered the most while leaving those on the opposite edge unaffected. The effect will transition smoothly between the near and far edges/corners. This is good when elongation is more pronounced on one edge or corner.

2) If the elongation is uniform across the image then move the darken layer in the direction of the elongation rather than free transforming

3) it's not necessary to operate only on the stars since the whole image is affected by the elongation

4) if you have a star rounding application, script or plugin, that can help but only after the transformation. I don't use a star rounding tool

5) if you have a sharpen tool with motion blur that can also be beneficial (if the result is blended as darken) but it will affect the whole image equally and you will have a use a mask to isolate the area of the image affected by elongation

6) purists (and those with perfectly accurate equipment and guiding and zero flexure) hate this kind of stuff but as long as you only try to fix small elongations (of the order of less that two pixels) it can render the elongations practically invisible without significant side effects

Sorry, lots of words to describe something quite easy!

Hi Marcus,
Thanks for this. It did indeed (I think) make a positive improvement to the image and the stars did reshape without ( I think) any obvious artifacts, even though the star field is so crowded, so that was a good lesson to see the technique works even with an image such as this.
Thanks again,
Tim

[marc4darkskies (Marcus)]

Originally Posted by topheart

Hi Marcus,
Thanks for this. It did indeed (I think) make a positive improvement to the image and the stars did reshape without ( I think) any obvious artifacts, even though the star field is so crowded, so that was a good lesson to see the technique works even with an image such as this.
Thanks again,
Tim

Ah yes! I see the improvement Nicely done Tim and I'm glad the process worked for you. IMO, in many cases, it's the small things (usually easily fixed) that make or break a great image.