Using a color table is often quite useful in enhancing certain features of an image for analysis. As an example, the image in figure 2 uses the false color scheme entitled Hardcandy. This color selection has sharpened the difference between the flash of the impact and the ejecta, making the shape of the ejecta easier to define. Unfortunately, such color schemes do not correspond in any way to the true colors of the object under observation, and require a color bar (such as the one in figure 1) in order to interpret them. Furthermore, images shown using color tables, while informative, often appear cartoonish and unrealistic, and can obscure some of the more spectacular features of an image. For this reason the method of "true color" composition was created.
In true color composition a few pictures are taken of the same scene using different color filters. A filter will block all frequencies of light except for a certain color (or colors), and give a complete image of the scene in that color. In the case of astronomy, astronomers usually take pictures with three primary filters, red, blue, and green, and, using a computer, paint each image in its respective color. The three images are then combined together and the colors mix together. As figure 3 shows, when two or more of the primary colors overlap in any part of the image colors other than the primary three are produced. These composite images are then released and described as "true color."
True color images offer a glimpse of how the object might appear if it could be viewed with the naked eye. They provide stunning pictures of planets, moons, and comets that give them realistic faces. Such images fuel the imagination. They are, quite literally, the stuff that dreams are made of. Yet, true color images are not all sugar and spice, either. The resulting picture can vary greatly depending on the filters used, and the colors used to paint each filter image. These choices are still somewhat arbitrary, and depend heavily on the available filters, as well as the personal preferences of the astronomer making the image. This can result in images that while pretty and awe inspiring, still do not necessarily reflect the true colors of the astral body.
Color images are often some of the most dramatic and informative images in astronomy. In truth, however, the color is false, and not completely scaled to our eyes' response. The colors can vary from image to image and astronomer to astronomer with few bounds. Ultimately, they are nothing more than falsi colori.
Delamere, Alan. "More Falsi Colori" E-mail to Alan Delamere. Aug. 23, 2005.
Wilson, T., Nice, K. and Gurevich, G. "How Digital Cameras Work," HowStuffWorks.com, Aug. 26, 2005
Figure 1: An example color bar for the Hardcandy IDL color table. This color bar shows that the lowest values are displayed in dark blue and green and the highest values are shown in orange and forest green with this color table. This image was created by Noah Goldman for Deep Impact.
Figure 2: Impact of comet Tempel 1 shown using the Hardcandy IDL color table. The nucleus of the comet is visible in blue and maroon and the impact flash is ringed in multiple colors, reflecting the decrease in flash intensity further from the site of impact. This image was created by Alan Delamere for Deep Impact.
Figure 3: The three primary filter colors, red, green, and blue, mix together to create other colors. Red and green make yellow, green and blue make cyan, blue and red make magenta, and blue, green, and red make white. This is how astronomers create colors in true color composition. This image was created by the Maryland Institute College of Art. Reused with permission from www.mica.edu
|Noah Goldman first started working with Deep Impact as a student intern from the College Park Scholars program, a freshman-sophomore living-learning community at the University of Maryland. Noah has continued to work with the project working mostly on analysis but also writing articles for the website.|