When you take an image using Slooh.com you typically get two PNG images as shown here in an observation of the Orion Nebula, or Messier 42:

The image on the left is a monochrome image and is taken at the point in the reservation when the Luminance filter is being used to capture M42.

The image on the right is the combination of Luminence, Red, Green, and Blue filters and is a color image. This image is great for astrophotography but you can actually do better than this.

Note: In some cases, you might find that there are more than one monochrome and more than one color image because the system you’re using has two telescopes. Hover over the image and select the image from the same telescope (wide field, versus ultra-wide field).

The result in the color image is very good because Slooh.com performs some post-processing on the image. Specifically, in this case, Slooh.com performs specialized processing on images of M42 because the tonal range is quite broad: there are areas of faint dust on the edges as well as a bright region in the center of the nebula. But, we can actually improve on this result.

Here is the image you can produce with the steps shown in this tutorial:

There is much more detail in the surrounding nebulous areas and the center is not as saturated as in the original images.

Processing M42 To Bring Out More Details In the Nebula

As with all of the other tutorials in this series, we’ll use Photopea.com to do our processing; it is a great alternative to software like Photoshop and GIMP, it runs on all platforms, and there’s nothing for you to install on your computer.

Start by downloading the images of M42 from Slooh.com – if you don’t have an image of M42 handy, you can use mine here (right-click each image and select Save As):

This is the Luminance image:

This is the LRGB image:

The only processing that has been done on these images is to resize them to 400×400 so they fit within the column width of this website.

Point your browser to Photopea.com, select File – Open and open each of the images.

Curves Adjustment on Luminance Image

Switch to the Luminance image and select Image – Adjustments – Curves.

The graph that pops up is the histogram of the image. I discuss the histogram in detail in this post, so if you don’t know how to read a histogram please visit this post.

The Curves adjustment is a very powerful adjustment and you’ll become more familiar with it throughout this series of articles. For now, understand that the graph in grey is showing you the distribution of pixels in the image and the line is how the input values across the bottom are mapped to the output values on the left side of the graph.

A classic Curves adjustment is to make the line on the graph an S shape as shown:

What this curve does is boost the amount of output for the pixels in the darker regions while protecting the highlights from becoming over-saturated.

Use your mouse and click at the locations shown by the two dots:

Next, drag the dots to the locations shown on the screenshot where I show the S curve (the one before this one), and note the change in the image. You’ll see more nebulosity appear in the darker regions and the bright area in the center will become a little less saturated.

Combine the Luminance With the Color Image

From the menu, select Select – All, and then pick Edit – Copy.

Switch to the color image and from the menu, select Edit – Paste.

Your color image is now monochrome – in fact, you have just pasted a copy of the monochrome image over the color one. Note the Layers in the bottom right of your screen – it shows the newly pasted image in Layer 1 and the color image in the Background layer:

Now we need to change the blending mode. At the moment, blending is set to Normal (note the word Normal above the layers). The Normal blending mode is to completely replace the layer below with the current layer. There are many blending modes.

Click the arrow next to the word Normal and find Luminosity in the list (it is near the bottom):

Repeatedly click the eye icon next Layer 1 and note the change to the image – you’ll see the nebulosity you revealed when you did the curves adjustment, plus you’ll find that the center of the nebula has some more detail in it.

Bring Out More Detail in the Shadows

Let’s perform another adjustment to bring out some more nebulosity. From the menu, select Image – Adjustments – Shadows/Highlights.

A box pops-up with some default settings and note the dramatic change in your image. Click the Preview checkbox to compare the before and after images.

What these settings do is increase the amount of shadows by 50% in the bottom 25% of the pixels of your image. The Radius setting affects how much feathering Photopea applies to your image.

Adjust the Amount and Tone sliders and note the changes to the image to get an idea of how the controls affect the image.

When ready, click the Reset button to return the tool back to its defaults and click Ok.

This is your final image. Compared to the original, there is more overall detail in this image in both the faint and bright parts of the image.

Save Your Image

From the menu, select File – Save PSD. This will save your file with the layers intact so you can return later to edit the image again. The file will be located in your browser’s Downloads folder.

You can also save in another format like JPG or TIFF – simply select File – Export As and select a format.

Conclusion

In this article you learned about the images Slooh.com produces for you, you learned the basics of using Photopea.com, you learned about the Curves adjustment, you learned about layer blending modes, and you learned about the Shadows/Highlights adjustment. In the next article, we’ll tackle a more slightly more challenging image.

Other Articles In This Series

This article is part of a five part series of articles on processing Slooh.com PNG images for astrophotography. Visit the main article for links to the other articles in this series: Processing Slooh.com PNG Images Series.