![]() Short integers can be used to store numbers between 0 and 2 16 - 1, or 65,535. Arithmetic in such computers can be done in bytes, but it is more often done in larger units called "(short) integers" (16 bits), "long integers" (32 bits) or "double integers" (64 bits). Most modern computers store memory in units of 8 bits, called a "byte" (also called an "octet"). You can download it from the IRIS Home Page (). A good freeware program called Iris is available for download on the Internet. The first thing you need to start processing an image is a program to view it. 1 Surface plot of a portion of a CCD chip. The ADC factor is the constant of proportionality to convert ADUs into the amount of charge (expressed as a number of electrons) stored in each pixel.įig. This number is in arbitrary 'units', so-called 'analogue data units' (ADUs). Thus, the charge which has accumulated in each pixel is converted into a number. It is possible to estimate the amount of light that has fallen onto each pixel by examining the amount of charge it has stored up. The size of the charge increases cumulatively as more photons strike the surface: the brighter the illumination the greater the charge. The arrival of a photon on a pixel generates a small electrical charge which is stored for later read-out. The CCD is placed in the focal plane of a telescope so the light-sensitive surface is illuminated and an image of the field of sky being viewed forms on it. The light sensitive face is rectangular in shape and subdivided into a grid of discrete rectangular areas (picture elements or pixels) each about 10-30 micron across. IRAF tasks are denoted with the character font' Century Gothic'.Ī CCD (Charge Coupled Device) is best described as a semiconductor chip, one face of which is sensitive to light. In the following we assume that the user has loaded the IRAF and SAO image DS9 software tools. CCD images of a low-populated field at various exposure times 10 bias frames before and 10 after the observationsģ. The students will learn how to assess the quality of a CCD image, calculate the appropriate aperture to extract instrumental astronomical magnitudes and become familiar with the calibration techniques of astronomical images (BIAS & FLAT-FIELD).ġ. Prior to the derivation of astronomical magnitudes the CCD images have to be corrected for a number of effects. It is highly configurable and extensible to meet the evolving needs of the astronomical community.ĭS9 supports advanced features such as multiple frame buffers, mosaic images, tiling, blinking, geometric markers, colormap manipulation, scaling, arbitrary zoom, rotation, pan, and a variety of coordinate systems (including Image, Physical, Detector, and WCS). DS9 supports the direct display of FITS images and binary tables, multiple frame buffers, region cursor manipulation, many scale algorithms and colormaps, and easy communication with external analysis tasks. It also incorporates the new X Public Access ( XPA) mechanism to allow external processes to access and control its data, GUI functions, and algorithms. ![]() It is a Tk/Tcl application which utilizes the TkSAO widget set. Reference Manual SAOImageDS9 Reference ManualĭS9 is the next version of the popular SAOtng display program. ![]()
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