The Panda Eye effect occurs in your astro images when you use over-aggressive sharpening on astronomical images. The Panda Eye effect produces dark circles around stars as a result of over-sharpening an image. This effect is also known as the Gibbs effect.

This tutorial walks you through removing the Gibbs effect from the stars in your image. I assume that you’ll use Photopea for this tutorial; however, the directions can easily be adapted to Photoshop.

Result

This is a closeup view of Messier 8, the Lagoon Nebula, where the image has been sharpened aggressively:

The arrows indicate some of the stars that have dark halos around them – there are others in the image, however, these are the most obvious halos.

The technique described in this article removes the Panda Eye effect, to produce the following result:

You can see that the Panda Eyes effect is significantly reduced in the highlighted stars. The two stars on left still have some of the Panda Eye effect around them, to fix this, simply expand the selection to about six pixels and then apply the fix again.

Overview Of The Process

There are two important parts to this technique: selecting the stars and removing the Panda Eye effect.

It is important to get all of the stars properly selected for this technique to work. Note that during the selection process I have you expand your selection by 3 pixels. If the Panda Eye halos are larger than 3 pixels, expand your selection further. Moreover, if the selection includes parts of your target, deselect those areas by using any of the selection tools, by pressing and holding the ALT key on your keyboard when making those selections to remove them.

The second part of the process is to remove the Panda Eye effect from the stars in your image. The steps in this tutorial provide you with the details.

Selecting Stars

This part of the tutorial walks you through selecting the stars in your image.

Start by opening an image in Photopea that is over-sharpened. You can use the image from this article as a starting point if you don’t have an image at hand.

1. Duplicate the Background layer of your image (right-click the Background layer at the bottom-right side of the window, and select Duplicate Layer)

2. Select Filter – Noise – Dust and Scratches

3.  Slide the Threshold to 0 px

4. Slide the Radius slider over to the right until all of the stars disappear from your image. This dramatically changes your image, and this is expected; however, ensure that all of the stars disappear from your image as shown:

5. Slide the Threshold slider over to the right until you see most of your image without blurriness. You’ll notice missing stars and other artifacts, however, most of  the  image should appear to be normal, as shown:

6. Click Ok to commit the change

7. Change the layer’s blending mode to Subtract. You can find the Blending Mode in the dropdown above the listing of layers – it normally says ‘Normal’ with a small arrow next to it. Select Subtract from the drop-down

You now have isolated the stars in your image; now it’s time to select the stars.

8. From the menu, choose Select – Color Range

9. Select Replace for the Mode

10. Click a dark spot on your image

11. Click Ok

12. Click the eye icon next to the ‘Layer 1’ layer to disable it

13. Click the Background layer to enable it.

14. From the menu, choose Select – Inverse

You now have just the stars selected.

15. From  the menu, choose Select – Modify – Expand

16. Enter about 3px in the expand box. If your Panda Eye effect is larger, expand the selection some more.

Now you have selected the stars and the area affected by the Panda Eye effect. You should see selection markers around each of the stars in your image.

If all you see is a large rectangular selection area, you have made a mistake in the selection process. Go back to the beginning of this section and try again – follow the directions carefully.

The next steps remove the Panda Eye effect.

Remove the Panda Eye Effect From The Stars

Now that you have just the stars selected, you can remove the Panda Eye effect from the stars as follows:

1. From the menu, select Filter – Noise – Median

2. Enter or select 20px for the Radius and click Ok

The stars disappear from your image, and this is normal.

3. From the menu, select Edit – Fade

Note that this menu option (Fade) is available only immediately after you execute the preceding step. If you do anything else before doing this, the option will not be available.

4. For the Blend Mode, select Lighten

5. Click Ok

6. From the menu choose Select – Deselect

7. From the listing of Layers, right-click the ‘Layer 1’ layer and select Delete as you no longer need the layer

You have now removed the Panda Eye effect from the stars in your image. If you still see some stars with the Panada Eye effect, select them manually and apply the preceding six steps to them to remove the effect.

Conclusion

In this tutorial, you learned how to remove the Panda Eye effect from the stars of an over-sharpened astro image. You learned how to select just the stars in your image and then apply the correction to remove the Panda Eye effect from your image.