Section 2 - Introduction to CCD Cameras
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 a CCD image is that it is 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 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 images electronically to produce a color composite or RGB color image. SBIG offers as an option a motorized color filter wheel. The accessory is inserted between the telescope and the CCD head. An object is then exposed using a red filter. The wheel is commanded to insert the green filter in place, and another image taken. Finally a blue image is taken. When all three images have been saved, they may be merged into a single color image using SBIG or third party color software.
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