Solar Processing... Over-Sharpening

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Lowjiber
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Solar Processing... Over-Sharpening

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Post by Lowjiber »


Quoting NASA...

"Our Sun is surrounded by a jacket of gases called an atmosphere. The corona is the outermost part of the Sun's atmosphere. The corona is about 10 million times less dense than the Sun’s surface. This low density makes the corona much less bright than the surface of the Sun."


When we capture a solar image of the center of the surface, the "thickness" of the corona is much less than when we capture an area closer to the limb. That results in a gradient across the surface that is lightest in the center, but darkening a bit as our eye travels toward the limb... That's a good thing because we want the surface to appear as a "ball".:)

When we capture a prominence, we are still looking through the density of the corona. Proms are nothing more than a dense cloud of incandescent ionized gas within the corona... Resulting in their beautiful "feathery" appearance. To prove the point, here's a NASA image of several proms surrounding Sun...
NASA IMAGE.jpg
Do any of those proms look like pieces of uncooked spaghetti? No. Why? Because the ionized gases are "mixing" with the gases of the corona.

As solar imagers we have to deal with the excessive corona gasses surrounding our prom and mitigate to a certain extent the corona over the surface. There are several ways to do that... Curves, Gradient blending, Levels, Burning, etc. But the most dangerous "tool" in the box is without a doubt SHARPENING. Don't misunderstand, sharpening is a legitimate tool when used properly, but overdo it and your image may look like it belongs in a comic book.

The small comparison below has an image on the left that was processed properly (It won some kind of award back in 2018.) On the right is the same image over-sharpened... Note that the surface looks contrived and the proms are beginning to get the uncooked spaghetti look. I've seen images sharpened even more, but couldn't bring myself to go any further. LOL
OVERSHARPENED.jpg
So new solar-heads, the next time you pull the sharpening pencil out of the crayon box dull it a bit before ruining your current masterpiece. :)

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Re: Solar Processing... Over-Sharpening

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Post by Gordon »


Thanks for the lesson John!

Your insight is always appreciated!!
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Re: Solar Processing... Over-Sharpening

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Post by notFritzArgelander »


Thanks for a very nice discussion of the perils of over processing. However there is one statement that is astrophysical problematic.
Lowjiber wrote: Tue Jul 28, 2020 3:48 pm
When we capture a solar image of the center of the surface, the "thickness" of the corona is much less than when we capture an area closer to the limb. That results in a gradient across the surface that is lightest in the center, but darkening a bit as our eye travels toward the limb... That's a good thing because we want the surface to appear as a "ball".:)
Because the corona is so transparent it is impossible for the gradient of brightness across the solar disk to be caused by differing thickness of the corona. In fact if there were no corona at all the gradient would still exist. The phenomenon is known as "limb darkening" and depends only on the properties of the photosphere and chromosphere.

https://en.wikipedia.org/wiki/Limb_darkening

The corona is irrelevant to this effect.
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Re: Solar Processing... Over-Sharpening

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Post by Ben Cartwright SASS »


If you show both images to non-solarheads they tend to prefer the sharper "spaghetti" look.

I wonder if some of the softness that we find right is caused by our atmosphere? How do space telescopes see the proms?
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