Create a False Color Image

Overview:

If ultra-violet or infrared filtered images of the objects are available, students may use these to explore the realm of false-color imagery. False-color images are those that code images made in non-visible wavelengths with a visible color such that we can 'see' an object in invisible wavelengths.

Explore:

It is important for astronomers to study objects in non-visible wavelengths as well as visible wavelengths of light. Modern space telescopes such as Chandra and Spitzer are regularly making new, important discoveries by imaging deep sky objects in non-visible wavelengths. Besides the visible light color image you created of your object, you can also easily create a false color image if you requested infrared or ultraviolet images of your object. Use the techniques learned in the previous activities with your IR or UV image(s). If you have saved copies along the way as asked, you should only need to correct your IR or UV image and then simply ALIGN the Infrared image to the others before combining. You can choose which colors you want to assign to each wavelength and which images you want to include.

Create:

1. Use HOU-IDL to open the infrared or ultraviolet image you will be using.

2. Subtract the sky value from the image.

3. Determine correction factors for filter transmission and camera sensitivity.

4. Correct image for camera sensitivity and then filter transmission.

5. Open your aligned images from earlier. Align your infrared or ultraviolet image to these images.

6. Choose two visible light images to combine with the non-visible light image.

7. Use the HOU-IDL 'Image Comparison: True Color' tool to combine the two visible light images with the infrared or ultraviolet image. Experiment on which colors you will use to represent what wavelengths.

8. Save your final image as both a FITS image and as a JPEG. Post these on your class Collaboratory work area.

Discuss:

Students can discuss different color-coding schemes they used to create the images. They can also discuss what additional information they have learned about their object by including non-visible wavelengths in the study of the object.