Digitally Enhancing Astrophotos
Digitally Enhancing Astrophotos
By Amelia A.
Part 1: Turning a Grayscale image into a fullcolor .tif image
1. Open Scion Image
Scion image is a program that lets you combine multiple grayscale images (in this case we're going to
use M42) to create one full-color image.
2.Special->Load Macros->Select "Color"
3. File->Import->R-G-B
In step 3, you want to import the pictures in the following order: Red-Green-Blue, this is how the
program knows which pictures go where.
4. Stack the images and register them (windows to stack->register)
Registration is a process in which you pick the three different points on an image and identify where they
should be for each picture.
5. RGB to 8-Bit Color gives you an 8-bit (lowgrade) color image
6. RGB to 24-bit Color gives you a clearer color image which should look something like this:
Part 2: Enhancing the image using Adobe Photoshop
1. Evaluate the image
What does a histogram mean?
A histogram measures the range of lights and darks used in an image.
The histogram of a perfect picture will look like an evenly proportioned curve ranging from black to white.
Levels between the darkest dark and the lightest light are pretty well established in this image,
so only a slight alteration of curves and levels needs to be done.
In some cases though white and black points need to be set to control the image as a whole.
Also as you can see the image did not stack exactly right, as the stars which should be white points
are multicolored disks. This can be easily corrected later on in the touch-ups, the first focus is
adjusting the image properly overall.
2. Adjust the light and dark levels.
The type of image you're working with will determine to what extent lights and darks need to be adjusted.
A long exposed deep sky object will typically need more work than a shorter exposed one.
In the image above, the slider bars are used to tighten the field of unused pixel levels,
making the overall background darker and the center of the image lighter.
3. Adjusting the color
This is where an astrophotographer must make a decision, between the reality of the image's color versus the detail
brought out by giving the image false color. Much of the light in astrophotography is altered anyway from factors
such as light pollution and the devices the light passes through. Using Photoshop is by no means 'cheating'. It's merely
altering the intensity of pixels that already exist.
The color in the image needs to be adjusted to the extent where the most detail in the image is brought out.
Color in an astronomical image is somewhat more artistic than it is scientific.
For this particular image, I heightened the red and green while toning down the blue, because the gas from
the nebula is predominantly red. A significant amount of detail is added to the image with the color adjustments.
4. Re-adjust the dark/light levels in the image
5. Freehand: use the dodge/burn tool to make some areas darker and some lighter
What is the dodge/burn tool?
The dodge tool will lighten certain areas of the image to a certain extent, depending on the
amount of light exposure ranging from 0 to 100 percent. The best way to determine how much
the image needs to be lightened in a certain area is simply to play with the tool until the image
looks light enough.
The burn tool is used in a similar way, except instead of increasing the pixel intensity, it decreases it.
Shadows-Midtones-Highlights
These are the three dodge/burn settings.
Shadows evenly adds either white or black, depending on the tool.
Midtones either increases or decreases the pixel's intensity in between the shadows and highlights.
Highlights picks out either the darkest or lightest areas and increases their intensity.
6. Minor touchups (dust, scratches, star shifts)
Finally, the last thing I like to do is an unsharp mask which makes the overall final product look much clearer.
An unsharp mask is essentially 'making a blurred copy of a picture and subtracting it from the original'
(Covington, 230). This increases the amount of detail in the image as well as its overall clarity. Covington
suggests that the unsharp mask works best for bringing out detail in nebula, like in this one.
How to get to the unsharp mask...
filters>sharpen>unsharp mask
The Final Product...
This is an example of what a digitally retouched photo will look like!
More Step-by-Step manipulations...
(Click on the images below)
Saturn
M102, a galaxy
Bibliography
Covington, Micheal A. "Astrophotography for the Amateur". Cambridge: Cambridge University Press, 1999.
Lodriguss, Jerry. "Photoshop for Astrophotographers". Astropix LLC, www.astropix.com
RGB Images of M42 provided by the HOU image archive
"HOU Archive" 5 May 2004
http://hou.lbl.gov/telescope/archive.html.
Independent Study Acknowledgements
Special thanks to those who helped my astronomy endeavor this year...
Ms. Maciolek most of all, Julie K., the RATs,
Katrina Koski for the endless vapor-tube hallway fun,
Alain G. and all the other data mules,
plus everyone on Julie's page that helped us with Kitt Peak.