While I have covered using FITS Liberator in another post, this post deals with using FITS Liberator with a FITS file that was taken using an OSC/RGB camera, and so all you have is one or more FITS files containing an RGB image (no individual FITS files – one for each filter). This post discusses the details of extracting the R, G, and B components (split the RGB from an OSC FITS) from the combined RGB FITS file, and then demonstrates how you can use the output of FITS Liberator along with Photopea.com to create an RGB image.
Sample Download
If you don’t have an RGB FITS file to use, or just want to follow along with this tutorial, download the sample observation of NGC6744 below.
The ZIP file contains a single FITS file that is an RGB image of NGC6744 – it has not been stretched so it is similar to what you would receive from Slooh.com’s Canary 3 telescope (I captured the image using Telescope.live and created the RGB image for this tutorial, but the results are similar to those that you would get using Slooh.com’s Canary 3).
Using FITS Liberator to Extract RGB Images from the RGB FITS
1. Start FITS Liberator and open your RGB/OSC FITS file
2. Under the Image data section, select the dropdown and ensure ‘Image 1, Plane 1’ is selected
The FITS file contains all three images, each in thier own plane. The planes are arranged in order, so plane 1 is the red image, plane 2 is the green image, and plane 3 is the blue image. The steps that follow extract each plane from the FITS file.
3. Click the Reset button on the right side
4. For the Stretch function, select Log(x) (you might select a different stretch function, depending on your data; however, for this tutorial, select Log(x))
5. Click the ‘Auto scaling’ button
6. Click ‘Save File’ and enter a filename that includes the name of the filter which in this case is Red.
7. Repeat from Step 2, this time selecting ‘Image 1, Pane 2’ and for step 6, use a filename that includes the name Green
8. Repeat from Step 2, this time selecting ‘Image 1, Pane 3’ and for step 6, use a filename that includes the name Blue
9. Close FITS Liberator
Use Photopea.com to Combine the Individual RGB Files into an RGB Image
1. Point your browser to Photopea.com
2. Open each of the files you created in steps 6, 7, and 8 above
3. From the menu, select File, New
4. Enter 2048 in the width and height boxes and click Create (I got the dimensions from one of the TIF files that was saved using FITS Liberator)
5. On the right side, where it says Layers, Channels, click the Channels tab
6. Select the Red file from step 2
7. From the menu select Select, All
8. From the menu select Edit, Copy
9. Click the word Red under the channels tab to activate it (ensure that Red is the only one with an eye icon next to it)
10. From the menu, select Edit, Paste
11. Repeat from steps 6-10, this time using the Blue file in step 6 and then select the Blue channel in step 9
12. Repeat from steps 6-10, this time using the Green file in step 6 and then select the Green channel in step 9
13. Click the eye icon next to RGB under the channels tab to reveal your RGB image
14. From the menu, select File and Save as PSD or export to the file format of your choice
This is the resulting image if you used the sample from this tutorial:
15. Use other options within Photopea.com to continue to edit your image
Conclusion
In this tutorial, you learned how to extract the R, G, and B images from a combined RGB FITS image using FITS Liberator.
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