Creating Color Images

This guide shows you how to create one full-color image from your individual red, green and blue filter images.

Getting Started

Download all three images from your email in the FITS format (instructions found in the email).

Rename each of the three files clearly to identify which image was taken through which filter (such as “RingNebulaRed.FITS”). To find out which color filter was used, open the FITS header attached each file. Within the MicroObservatory Image processing software (mObsImage), select the Window menu, then FITS Header to view all the information on how this image was taken.

Start the microObservatory Image processing software (mObsImage). The link to obtain this free software is also found in your email. Note, it is best to close all other computer programs while processing your images.

Creating the Color Image

Open your three images. Using mObsImage, open the image taken through the red-passing filter. Do the same for the images taken through the green- and blue-passing filters. Select File from the menu, then Open image on local disk… or just drag the file onto the mObsImage program window. You should have three images open.

Adjust brightness and contrast. Under the Process menu, select Adjust Image. When the Adjust Image window opens, select the Auto button to get a good first look at the image. Further adjust the brightness and contrast by either sliding either of the small white triangles or typing in new Min: and Max: values as necessary to fine-tune the image. Do the same steps for the other two images as needed.

Align the images. Your three images will probably be slightly out of alignment. You’ll need to align, or “shift” the images to correctly combine all together. Under the Process menu, select Shift. Select one of your three images as the background image from the Background menu over which you’ll shift (i.e. align) the other two images. Then select another image to shift from the Foreground menu (if not already selected). You should see the background image through the slightly transparent foreground image. Using the mouse keys and/or the i,j,k,l keys, align the two images and then hit the Okay button. This aligning technique takes some practice at first. Aligning the same small, bright object found on each image is usually is the best method. Magnifying a small area of the image window helps the alignment. From the Magnification menu, zoom in by selecting a higher magnification and view the result in the smaller display window located at the upper right. Align the third image in the same way, making sure you use the same background image to align against!

Color each image red, green or blue. Start with the red-filtered image. Under the Process menu, select Color Tables / Red option. Your image will turn red. Then process the green-filtered image by selecting Color Table / Green to turn the image green. Finally, select Color Table / Blue for the blue-filtered image.

Stack the images. Assemble and check alignment. Under the Process menu, select Stack / Convert Images to Stack option. All three images are combined under one window, which you can individually view each and check alignment by pressing the bottom back and forth arrows.

Create the final color image. Now combine all three images into one color image. Under the Process menu, select Stack / Convert Stack to RGB. The program merges the three individual red, green, and blue images into a final full-color image. Congratulations!

Save the color image. Make sure you save your final color-processed image. Select the File menu and Save as… / GIF… option. Name the image file, for example “GREATColorImage.GIF”, as prompted.

Some Frequently Asked Questions About Color Images

Why are all my filter images grey?

The electronic detector on the MicroObservatory telescopes simply record intensity of light. True, with a red filter in place, the detector is only detecting red light, but all it cares about is intensity. The color information is assigned during processing.

How can I create a full color image if there are only three colors?

You can thank your eyes and brain for this. Every color you perceive can be created by a combination of red, green and blue light (these are called Primary colors). This is how a color TV works.

The images from telescopes such as Hubble have beautiful colors. How do they do it?

The beautiful images from Hubble and other major observatories do pretty much what you have just done - combine images taken through different filters, and a little artistic license to bring out the features of interest. Compare your processing to the way the folks at Hubble do it.

They’re pretty, but what can color images tell us?

Astronomers can discover an incredible amount of information about an object by the color of light it emits (by color we mean the wavelength, and the energy, of the light). The color can tell us the chemical composition of gas, the temperature (and therefore the type) of stars. It can give us an insight into the physical processes that are at work, and reveal the structure and even the history of a region of space.