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Retouching An Image In Photoshop
Recently, I imaged the Orion Nebula and my images were plagued by a familiar problem- the star Alnitak. Alnitak is one of the three stars that make up Orion's belt. All three are extremely bright. Alnitak, magnitude 1.85, sat quite out of frame, but is so bright it caused internal reflections in my telescope. These reflections showed up as bright streaks in the images.
You can see the reflections were the worst in lum, green, and blue. They were less present in red and almost invisible in Halpha. This posed quite a problem.
The reflections in masters of each filter. Notice how the reflections in each filter differ. That will be useful later.
This shows the framing of my images. The rectangle is my camera. I thought I was far enough from Alnitak to prevent reflections, but I was wrong.
Lum on the left, combined RGB on the right. Notice how the RGB reflections are in several different colors.
Retouching Luminance
Time to get to work in Photoshop. First, I tackled the Lum master. PS has several AI tools that can be useful, but none worked well with this large reflection. The lines were removed, but a new background was created with made-up details. It didn't look very good.
On to plan B.
Selection and prompt for PS AI.
What the AI came up with wasn't great.
Plan B ended up having several parts. First, I was able to get a reasonably satisfactory result using the Remove tool on a smaller section of the reflection.
That still left some streaks. I noticed the Red master wasn't affected by reflections in this area. Since this area of space is dominated by hydrogen (red), I copied the red master, put the copy above the Lum layer, and used a mask to hide all but the area with lines.
The retouching layers for Lum.
The first layer using the Remove tool.
After blending in the Red layer to cover the streaks. Some light streaks remained, but I used the Blur tool to break up the straight lines so they weren't noticeable. But this did leave a lighter area that didn't match, as shown.
The final step was to darken the area using Levels and a mask.
The levels mask.
Lum before retouching.
Lum after. This retains a pretty good approximation of the original data.
Retouching Color
The RGB data presented additional issues. The reflections came in several colors since each filter was affected differently. The most challenging reflections appeared as blue or green streaks across the image.
First, I used the Remove tool with small-diameter brush strokes to eliminate as many reflections as I could. I couldn't do them all, and a general blueish-greenish color was still left in the data.
(These adjustments are hard to see in these images. Trust me- they make a big difference.)
The streaks without the Lum corrections.
After the remove tool.
It took another three layers to remove the color left behind. First, I used a Hue/Saturation adjustment layer to target the blues and greens, adjusting their hue, saturation, and lightness to match the existing background. By targeting the specific colors, I avoided changing the hydrogen color.
A mask helped me limit the effect to that small image area. Without a mask, blue would have been removed throughout the entire image.
Next, I added a blank layer in Color blending mode, used the Eyedropper tool to select nearby nebula colors, and painted over the offending ones with a low opacity Paint brush (Layer 3). The effect may not be easy to see on your device, but it was a noticeable improvement.
Before painting.
After painting. The dark blue streak and the green areas are gone.
A few more minor adjustments were required. The painted area was darker than its surroundings, so I adjusted the brightness using a masked Levels layer and dodging and burning on another blank layer set in Soft Light blending mode.
Finally, I added a few more colors on a blank layer using the Paintbrush in color mode.
Final Result
Before retouching.
After retouching. I was able to retain a lot of the natural detail of the background and still remove most of the reflection.
Adding Ha data and stars completed the job. Click on the picture to see the entire image.
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