Section 2 - Introduction to CCD Cameras
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observer. In addition to the software provided with the camera, there are a number of
commercial programs available which will process and enhance electronic images. Images may
be made to look sharper, smoother, darker, lighter, etc. Brightness, contrast, size, and many
other aspects of the image may be adjusted in real time while viewing the results on the
computer screen. Two images may be inverted and electronically "blinked" to compare for
differences, such as a new supernova, or a collection of images can be made into a large mosaic.
Advanced techniques such as maximum entropy processing will bring out otherwise hidden
detail.
Of course, once the image is stored on a computer disk, it may be transferred to another
computer just like any other data file. You can copy it or send it via modem to a friend, upload
it to your favorite bulletin board or online service, or store it away for processing and analysis
at some later date.
We have found that an easy way to obtain a hard copy of your electronic image is to
photograph it directly from the computer screen. You may also send your image on a floppy
disk to a photo lab which has digital photo processing equipment for a professional print of
your file. Make sure the lab can handle the file format you will send them. Printing the image
on a printer connected to your computer is also possible depending on your software/printer
configuration. There are a number of software programs available, which will print from your
screen. However, we have found that without specialized and expensive equipment, printing
images on a dot matrix or laser printer yields less than satisfactory detail. However, if the
purpose is simply to make a record or catalog the image file for easy identification, a dot matrix
or laser printer should be fine. Inkjet printers are getting very good, though.
2.6.
Black and White vs. Color
The first and most obvious appearance of most scientific CCD image is that they are produced
in shades of gray, rather than color. The CCD chip used in SBIG cameras itself does not
discriminate color and the pixel values that the electronics read out to a digital file are only
numbers proportional to the number of electrons produced when photons of any wavelength
happen to strike its sensitive layers.
Of course, there are color video cameras, and a number of novel techniques have been
developed to make the CCD chip "see" color. The most common way implemented on
commercial cameras is to partition the pixels into groups of three, one pixel in each triplet
"seeing" only red, green or blue light. The results can be displayed in color. The overall image
will suffer a reduction in resolution on account of the process. A newer and more complicated
approach in video cameras has been to place three CCD chips in the camera and split the
incoming light into three beams. The images from each of the three chips, in red, green and
blue light is combined to form a color image. Resolution is maintained. For normal video
modes, where there is usually plenty of light and individual exposures are measured in small
fractions of a second, these techniques work quite well. However, for astronomical work,
exposures are usually measured in seconds or minutes. Light is usually scarce. Sensitivity and
resolution are at a premium. The most efficient way of imaging under these conditions is to
utilize all of the pixels, collecting as many photons of any wavelength, as much of the time as
possible.
In order to produce the best color images in astronomy, the most common technique is
to take three images of the same object using a special set of filters and then recombine the