Update Nov 2019: This article was originally published in August 2019. Since then Slooh.com has made a FITS viewer called JS9 available to its members. While JS-4L is similar to JS9, some functionality is different. If you are a Slooh.com member and are looking for information about JS9, click to follow this link: Using Slooh.com’s JS9 FITS Editor To Create RGB Images (note that JS9 is also available as a standalone application outside of Slooh.com – I discuss JS9 in the preceding link)

In Part 1 of this series, I walked you through creating an image of the Trifid nebula using theMicroObservatory’s JS9-4L image processor; you can also download the sample files from that tutorial so you can follow along.

In this tutorial, we’ll use another image editor called Photopea to enhance the image further.

Starting Photopea and Opening an Image

Start by visiting the Photopea site at https://www.photopea.com/

PhotoPea is a Photoshop clone that runs completely in your browser!

You can use either Firefox or Chrome. The creator of Photopea says Firefox does better with larger images since it can take advantage of all of your computer’s memory whereas Chrome is more limited. The functionality of Photopea is identical between the two browsers.

Let’s start by opening the image we created in part 1 – select File – Open and open the PNG that we created

Curves Adjustment and Layers

We want to make the background darker while retaining the nebula. A curves adjustment is good for this purpose.

The Curves adjustment is a very powerful tool because you can change how the intensities of pixels are mapped to the final image. It’s great for preserving details while boosting contrast.

We’ll use an approach called non-destructive editing where I have you create layers for the adjustments. Doing this leaves the original image intact yet allows you to see what your changes will look like.

Start by selecting Layer – New Adjustment Layer – Curves. Your screen will look similar to this:

The diagonal line basically says that Photopea should map all pixels from black to white, one to one, so you don’t yet see any changes in the image.

Drag the dot on the bottom left of the window a little to the right: the background becomes darker as you do this. You are essentially adjusting black pixels here, making them more prominent.

Next, make the pixels that make up the nebula more prominent while slightly affecting the background adjustment you made. Put your mouse in the very center of the diagonal line, click and drag to the point shown in the following screenshot:

As you do this, the nebula becomes more prominent and the background becomes a little lighter. You can move that first dot at the bottom left a little more to the right to make the background darker again. Note the effect it has on the nebula – you want to achieve a good balance between making the nebula more prominent and the darker background.

Click the eye next to the curves layer as shown, to turn off this layer:

By switching the layer off, you can see that the original image is still intact and your adjustment resides on a separate layer. Click the eye again to turn the layer back on.

Let’s boost the colors in the image a little using a Vibrance adjustment.

Adjusting Vibrance

Layer – New Adjustment Layer – Vibrance to add the new layer

In the properties window, change the Saturation value to 20 – you can either drag the pointer over to the right or you can just enter the value. Toggle the layer off and on to see the effect – it’s pretty subtle but it makes a difference.

Next, let’s reduce the noise in the image.

Click View – Zoom In to zoom into the image a little. You can also zoom in and out using your mouse wheel – hold down CTRL and ALT and scroll your mouse wheel to zoom in and out.

Applying a Gaussian Blur to Reduce Noise

You’ll notice a lot of green, blue, and red pixels in the image – this is noise from the camera that’s attached to the telescope. Unlike Slooh’s cameras, which are cooled to about -30 Celsius, the MicroObservatory’s cameras are not cooled and their temperature varies with the ambient temperature outside, which contributes to noise in your final images.

We can reduce the noise a little by making another adjustment. Make sure the image layer is active – click the bottom layer in the stack of layers (it’s labeled Background).

Select Filter – Blur – Gaussian Blur to bring up a new window. The change you make using this command will change the image.

Select a pixel size of 0.6 px and toggle the Preview checkbox to see the dramatic difference it makes. Note as well that the blur also affects the detail in the nebula, so this value is a good balance between reducing noise and retaining detail.

Click Ok to commit the change.

Using the Spot Healing Tool to Enhance Your Image

Zoom in more and use the Hand Tool (highlighted in the screenshot below) to move the image around so it looks something like what you see in the screenshot:

You’ll notice that the green, blue, and red pixels are still present in the nebula and surrounding areas. The Gaussian blur did not completely get rid of those extra pixels. We’ll use the Spot Healing tool to remove the extra pixels from the nebula to make it look nicer.

The Spot Healing tool is a smart tool in that it is a content-aware paintbrush. What it does is it looks at the surrounding pixels and brushes over the area you select using those nearby pixels, which effectively removes defects without it looking like you painted over them.

Hover your mouse over the area on the left side of your screen, as shown on the screenshot and select Spot Healing Brush Tool.

Next, click the area at the top left of the screen, as shown in the screenshot below and enter 5px in the Size box.

What we’re doing here is adjusting the size of the brush. You can also increase and decrease the brush size by pressing the square bracket key on your keyboard (the bracket on the left makes the brush smaller and the bracket on the right makes it bigger).

Find one of the extra pixels, hover your mouse over it and click. The brush evaluates the pixels around it and uses the same pattern to draw over the pixels you selected. Some areas might be a little more stubborn and won’t disappear with just a click. In that case, slightly drag your mouse to paint over the pixels. When you drag your mouse, the tool evaluates more pixels to use to paint over the area you selected. If you find you want to undo something, press CTRL-Z to undo your last action.

You could go on editing for quite a while, but just stick to the nebula itself for this exercise.

Zoom out again and check your progress – your nebula should look much better now.

Save your work now. Click File – Save As PSD to save in Photoshop compatible format.

Cropping Your Image

With the image zoomed out, you can see there are areas at the bottom that don’t look good at all, so we’ll crop the image to exclude those areas. We can make this change on the image itself since we have already saved your work, so in case you don’t like the result, you can just load the image you saved.

Hover your mouse on the left side of the screen, as shown below, and select Crop Tool:

At the top of the screen, find where it says Free and change it to Fixed Ratio, and enter 1 in the W and H fields. What we’re going to do is select an area of the image that’s a square.

You’ll see a square show up around the edges of your image – zoom out if you don’t see it. Click the handle on the left (the small square) and drag it toward the center of the image. You’ll see the square getting smaller as you do this.

Move the square and resize it so that it looks something like this:

Once you have it, press Enter on your keyboard to commit the change.

Now save this image as a PNG or JPG – this is your final image.

Removing A Color Gradient

If your image has a color gradient on it (a color cast), try my tutorial here where I show you how to remove the gradient: Removing Color Gradient From Your Images. If you find that process removes too much color, there’s a less harsh version here: Remove A Soft Color Gradient From Your Images.

Conclusion

In this tutorial, you learned how to use Photopea to enhance an image. You learned about a Curves adjustment, Vibrance adjustment, you learned about Gaussian blur, and you learned how to use the Spot Healing tool.

In the next tutorial, I’ll show you how to use FITS Liberator along with Photopea to create an RGB image for even more control over the process.