Santa Barbara Instrument Group STL-1001E Operating Manual

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Santa Barbara Instrument Group STL-1001E Operating Manual Manual pdf 35 page image

Section 2 - Introduction to CCD CamerasPage 33observer. In addition to the software provided with the camera, there are a number ofcommercial programs available which will process and enhance electronic images. Images maybe made to look sharper, smoother, darker, lighter, etc. Brightness, contrast, size, and manyother aspects of the image may be adjusted in real time while viewing the results on thecomputer screen. Two images may be inverted and electronically "blinked" to compare fordifferences, 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 hiddendetail.Of course, once the image is stored on a computer disk, it may be transferred to anothercomputer just like any other data file. You can copy it or send it via modem to a friend, uploadit to your favorite bulletin board or online service, or store it away for processing and analysisat some later date.We have found that an easy way to obtain a hard copy of your electronic image is tophotograph it directly from the computer screen. You may also send your image on a floppydisk to a photo lab which has digital photo processing equipment for a professional print ofyour file. Make sure the lab can handle the file format you will send them. Printing the imageon a printer connected to your computer is also possible depending on your software/printerconfiguration. There are a number of software programs available, which will print from yourscreen. However, we have found that without specialized and expensive equipment, printingimages on a dot matrix or laser printer yields less than satisfactory detail. However, if thepurpose is simply to make a record or catalog the image file for easy identification, a dot matrixor laser printer should be fine. Inkjet printers are getting very good, though.2.6. Black and White vs. ColorThe first and most obvious appearance of most scientific CCD image is that they are producedin shades of gray, rather than color. The CCD chip used in SBIG cameras itself does notdiscriminate color and the pixel values that the electronics read out to a digital file are onlynumbers proportional to the number of electrons produced when photons of any wavelengthhappen to strike its sensitive layers.Of course, there are color video cameras, and a number of novel techniques have beendeveloped to make the CCD chip "see" color. The most common way implemented oncommercial 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 imagewill suffer a reduction in resolution on account of the process. A newer and more complicatedapproach in video cameras has been to place three CCD chips in the camera and split theincoming light into three beams. The images from each of the three chips, in red, green andblue light is combined to form a color image. Resolution is maintained. For normal videomodes, where there is usually plenty of light and individual exposures are measured in smallfractions 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 andresolution are at a premium. The most efficient way of imaging under these conditions is toutilize all of the pixels, collecting as many photons of any wavelength, as much of the time aspossible.In order to produce the best color images in astronomy, the most common technique isto take three images of the same object using a special set of filters and then recombine the