St 4.Mac .File .Format

Santa Barbara Instrument Group 1482 East Valley Road · Suite 31 PO Box 50437 Santa Barbara, CA 93150 SBIG ASTRONOMICAL (805) 969-1851 INSTRUMENTS Applications Note ST-4 Image File Format for the Macintosh This applications note describes the format of image files created by the Macintosh version of the ST-4 host computer program (SBIG ST4). The image files contain the 8-bit pixel data for the 192 horizontal by 165 vertical pixel images as well as the telescope calibration factors, file note and cropping values, and the settings from the Contrast window. The pixel data is saved in the data fork of the file in left to right, top to bottom order: The first byte corresponds to the left-most pixel in the top line, the 2nd byte corresponds to the 2nd pixel in the top line, the 193rd byte corresponds to the left- most pixel on the 2nd line, etc. The data should be interpreted as unsigned bytes (values from 0 through 255). This is shown below in Figure 1. Data Fork Pixel x,y 1,1 2,1 3,1 ... 192,1 1,2 2,2 ... 1,165 ... 192,165 Byte: 1 2 3 ... 192 193 194 ... 31489 ... 31680 Figure 1 The resource fork of the image files contains several resources which are used to hold the telescope calibration factors, etc. Typically, these resources will only be of use to the SBIG ST4 program itself, but you might desire to interrogate them to find the exposure time, etc. Each of these resources is described individually below: Resource type 'ConT' ID 128 This resource contains the settings from the Contrast window. A C type definition for this resource is given below in Figure 2. The min and range entries are the settings from the Back and Range items, the zoom entry will be 0 or 1 for 1:1 and 2:1 respectively, and the three entries smooth, invert, and interpolate will be TRUE if those items were selected. typedef struct { int min, range; int zoom; Boolean smooth; Boolean invert; Boolean interpolate; } CONTRAST; Figure 2 May 1990 Resource type 'ImgI' ID 128 This resource contains the telescope factors accessed through the Info command in the Image menu. A C type definition for this …