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Best Practices - merging images to correct exposure

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I'm looking for the "best" way to combine two images where an element in one image is dramatically overexposed and the other image has a correctly exposed version of that same element. Here its the moon against a background of stars and planets, where one image is long enough to get star/planet exposure and the other correctly exposes the moon itself.

Attached are five images:

  • One is a conjunction of Saturn, Jupiter, Mars, and the moon earlier this week. This was a 2-second exposure to capture the planets and a few stars, but the moon is badly overexposed (as I expected).
  • Second is a cropped moon that was correctly exposed.
  • My .afphoto file after I completed edits to the best of my ability using the steps described below.
  • The selection I made in step 7 to get rid of the moon.
  • The result of step 7.

I want to remove the over-exposed moon and replace it with the correctly-exposed moon. What is the best way to do this?

The solution I've landed on so far is:

  1. Open Overexposed.
  2. Place Correct.
  3. Move Correct to be the top layer.
  4. Resize Correct to match the size of Overexposed.
  5. Move Correct to the exact position of the moon in Overexposed, then hide its layer.
  6. Select the Overexposed (Affinity has this as the Background layer) layer.
  7. Use the Inpainting tool to get rid of the overexposed moon and smooth the sky as much as possible. I set Hardness to 25%, and leave Opacity and Flow at 100%. I set the brush diameter to roughly twice the moon's diameter and painted an ovoid shape. The result left some extra stars; I decreased the brush diameter to just larger than those stars (only 20 pixels) and made them go away too.
  8. Select the Correct layer, un-hide it, add a mask to it, invert it, then set its color to white.
  9. Zoom way in, find the moon, set the brush diameter to less than the moon's size and then expose the moon. I initially set hardness to about 37% and flow to 100%. I've discovered that opacity needs to be 100%.
  10. Repeatedly set color to black or white, reset brush settings and refine until only the moon is exposed but I don't end up with any black-sky artifacts just surrounding the moon.

The two issues I've seen, and for which I'm looking for help, are:

  1. In step 7, I can't seem to get back to a nice smooth sky once I get rid of the overexposed moon and halo. It's close, but there are obvious noise artifacts and I can't quite get the sky perfected. Is there some magic to this or is what I'm doing the best way, and I just have to be more patient and keep at it? It seems the more I work on smoothing, the worse the noise gets - how do I correct this? Since what I posted is a crop of a much larger image perhaps the lack of continuity between the removed moon area and the rest of the sky is less noticeable here, but in the full-size image it is very noticeable.
  2. In steps 9-10, it is really tedious. Is there a better (simpler, faster) way to do this? I think I finally got there but it took forever.

Or is there just an entirely different workflow that will get me where I want to be in a more efficient manner?

Thanks for any ideas.

Initial inpainting result - with extra stars.png

Inpainting around moon area.png

Cropped,_correctly_exposed_moon.TIF Overexposed_moon.tiff Saturn,_Jupiter,_Mars,_Moon_conjunction_composite.afphoto

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Didn't realize that PNGs would display inline. Ignore the one with several extra stars (the larger one). Note the slight "halo" effect in the smaller PNG with just one star visible at right - this is what I want to get rid of as my issue #1.

Thanks.

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Was the original photo of the correctly exposed moon taken at the same size as the others? If so, it may be worth trying an HDR Stack to see if that will do the trick.

John


Windows 10, Affinity Photo 1.8,3 Designer 1.8.3 and Publisher 1.8.3 (mainly Photo), now ex-Adobe CC

CPU: AMD A6-3670. RAM: 16 GB DDR3 @ 666MHz, Graphics: 2047MB NVIDIA GeForce GT 630

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16 minutes ago, John Rostron said:

Was the original photo of the correctly exposed moon taken at the same size as the others? If so, it may be worth trying an HDR Stack to see if that will do the trick.

John

Hi John, thanks for your help on previous questions.

It was taken at the same time, but with a longer lens. The panorama shot was taken with a 24mm lens and the moon was with a 200mm - I wanted to get better clarity with at least a hint of the craters etc. on the moon. I cropped everything except the moon itself from the 200mm image. As a result, the moon image pixel dimensions were smaller than the wider image but the moon took more pixels. I had to reduce size on the moon image when I Placed it, and I don't think it would work to use HDR merge in this situation - correct?

Here is the full panorama of my best effort on this so far. As you can see, the sky area around the moon is still not quite right - the halo I mentioned in my original post is visible, at least to my eye.

I do have another image shot of the moon at the same focal length but the moon in it is not as clear.

Saturn, Jupiter, Mars and Moon in conjunction panorama - small.jpg

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Quote

I do have another image shot of the moon at the same focal length but the moon in it is not as clear.

I would expect the image of the moon taken with a longer lens to show more detail. But does this image scaled down to match your other image of the moon that you mentioned show more clarity? If it is on a par, then using HDR may be worthwhile.

John


Windows 10, Affinity Photo 1.8,3 Designer 1.8.3 and Publisher 1.8.3 (mainly Photo), now ex-Adobe CC

CPU: AMD A6-3670. RAM: 16 GB DDR3 @ 666MHz, Graphics: 2047MB NVIDIA GeForce GT 630

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The correctly exposed moon layer doesn't need a mask; simply change its blend mode to Lighter Colour.

Try the Healing Brush Tool to hide the overexposed moon and halo. My screenshot shows the settings and the large source area I picked and dabbed onto a new layer. I erased a tiny spot from the healing brush layer to restore visibility of the quite bright star to the right of the moon.

Zipped .afphoto file (AP beta 1.8.3): Moon Composite.afphoto.zip

Healing_Brush.thumb.png.0f987e369f29f5b141fdf09de46f40e2.png

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Anon2, Thank you. Your suggestions were spot on.

It took me a bit to figure out how to make the healing brush trick work, so for those in future here it is:

  1. Create a new pixel layer.
  2. This is key: for Aligned Sources, set Current Layer & Below. I see you did this now, as I write this, but since your Apple version is slightly different than my Windows version I missed it before.
  3. Select the desired source area, and paint the fix.

That worked very well, leaving no halo area. Since you taught me to do it on a new layer it is also non-destructive and easy to try again the several times I borked the fix.

The blend mode trick was fantastic. So Much Easier! Brilliant!

John, I also learned about more about selective sharpening here. Applying sharpening to the entire image including the moon simply added too many artifacts, so I moved my Unsharp Mask layer below the moon layer and got the sharpening I wanted on the scene without the moon. Then I created a second Unsharp Mask layer as a child layer of the moon and was able to add back in some detail. The moon is so small in this image - only about 100 pixels or so - that there just wasn't much information to do anything with it.

I'm attaching a .jpg of my final image so you can see what your help created.

Thanks again, all.

Saturn, Jupiter, Mars, Moon conjunction panorama from Hood Canal Bridge medium size _DSC4367.jpg

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6 hours ago, John Rostron said:

 

 

I would expect the image of the moon taken with a longer lens to show more detail. But does this image scaled down to match your other image of the moon that you mentioned show more clarity? If it is on a par, then using HDR may be worthwhile.

John

Turns out the other image shot at the same focal length is too overexposed as well, so is not as clear. I tried various ways to get better clarity but by the time the moon gets down to actual size it is only about 100 pixels wide - not wide enough to provide much detail.

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