Sometimes your image contains a faint aspect, like a nebula or galaxy, and you’d like to enhance just the faint part without affecting the rest of your image. This article walks you through the process of isolating just the faint part of your image and then adjusting it to bring out more details, leaving the rest of your image unchanged.

The process uses a mask to isolate the faint part of your image so you can perform adjustments on just that part. I use Photopea.com because it is very similar to Photoshop, it’s easy to use, and there’s nothing to install on your system.

Source Image

This is the source image I’ll be using in this tutorial – it is IC 2177, the Seagull Nebula, captured using iTelescope.net:

Save this image by right-clicking it and save the image somewhere convenient on your system.

Result Image

This is the image after performing the adjustments in this article:

The nebula is more apparent while the rest of the image remains unchanged.

Overview Of The Process

These are the broad steps this article walks you through:

  1. Create an image of just the faint parts of your image by removing the stars from your image
  2. Use the image from step 1 as a mask
  3. Adjust the faint parts of your image to bring out the details

The rest of the article walks you through the process.

Isolating the Faint Parts Of Your Image By Removing Stars

Use the following steps to isolate the faint parts of your image by removing the stars from your image:

  1. Point your browser to Photopea.com
  2. Open your image (select File – Open)
  3. At the bottom-right of the Photopea.com window, right-click the Background layer and select Duplicate Into


  4. Under Destination, select New Project and click Ok

    This action creates a new image called Background.psd and makes it the active image. Your original image is still at the top of the screen, in the tab on the left.

    We’re going to remove the stars from this image, isolating just the nebula in the next several steps.
  5. From the menu, select Filter – Noise – Dust and Scratches
  6. Move the Threshold slider all the way to the left, or enter 1px for the Threshold
  7. Slowly move the Radius slider to the right until the stars in the image disappear (the nebula will become blurry too, and this is expected behavior). On my image, I found a Radius of 10px worked.

    This is what my screen looks like:



  8. Slowly move the Threshold slider to the right until you see the nebula in sharp focus; you’ll notice that there are dark areas where the stars used to be. On my image, I found a Threshold of 40px worked.

    This is what my screen looks like:



  9. Click Ok to accept the change

You now have isolated just the nebula from the rest of the image. Now you’ll use this image as a mask to perform adjustments on your primary image.

Performing Adjustments on Only the Nebula

Do the following to adjust your image:

  1. On the Background.psd image, select from the menu Select – All
  2. From the menu, select Edit – Copy

    We have copied this starless image to your clipboard, and now we’ll paste this starless image as a mask in your primary image.

  3. Using the tabs at the top of the Photopea.com window, click the tab for your original image
  4. From the menu, select Layer – Duplicate Layer
  5. From the menu, select Layer – Raster Mask Add (Reveal All)

    This action creates a new and empty mask on Layer 1. We’re going to paste the starless version of the image into the mask and will adjust it to bring out the nebula in more detail

  6.  Press and hold the ALT key on your keyboard and click the white square shown in Layer 1

    This is what my screen looks like:



  7. From the menu, select Edit – Paste

    Now adjust the mask to make the background darker and the nebula lighter

  8. Adjust the black point and midpoint sliders so that the nebula is brighter and the background is darker. Your image doesn’t have to look great, you just want to bring out the nebula as much as possible.

    This is what my screen looks like:


  9. Click the image next to Layer 1 as shown in the screenshot below:



  10. Move the midpoint slider, the slider in the center, to the left until you see the nebula brighten.

    This is what my screen looks like:



    The nebula is more visible now, but the saturation could be adjusted upwards to bring out more color.

  11. From the menu, select Image – Adjustments – Hue/Saturation
  12. Slide the Saturation slider to the right until the nebula is more staurated.

    This is what my screen looks like:



    The nebula has a slight green cast to it – the next steps remove the green cast.
  13. Click Ok to comit the saturation change
  14. From the menu, select Image – Adjustments – Levels
  15. In the Channel option, select Green
  16. Slide the middle slider to the right until the green cast becomes less apparent

    This is what my screen looks like:


  17. Click Ok to comit the change
  18. From the menu, select Layer – Flatten Image
  19. Save your image or export it using the File menu

You have completed the process.

Conclusion

In this article, you learned how to isolate faint parts of your image by removing the stars from your image and then using that starless image to enhance your main image using Photopea.com, which is very similar to Photoshop.