Each HRC image acquired at Ball or Goddard has a total size of 4.4 Meg and is in FITS format. The HRC image is contained in the science extension [sci,1]. The dimensions of each HRC image are 1062 columns by 1044 rows. In a single amp read-out, two 19-pixel wide physical overscan regions are masked at each end of the chip at columns 1-19 and 1044-1062. Each read-out is also accompanied by a virtual overscan of 20 rows at rows 1025-1044. A 1-pixel wide perimeter borders the entire data region.
As viewed in IRAF or IDL, the columns (1062 pixels) run horizontally and the rows (1044 pixels) vertically. The virtual overscan is always found at the top of the image. The read-out amplifier is located in the left-hand corner of its associated region. The physical overscan nearest the read-out amp is called the "leading" physical overscan. A corresponding "trailing" physical overscan may be also be present depending on the choice of read-out amplifiers. In Table 1 below, the row and column limits of the data and overscan regions are listed for the standard single amplifier read-out. A diagram of these regions is shown in Figure 1.
TABLE 1 : Single Amplifier Read-out
In the standard flight-software orientation, Amp A is located in the bottom-left corner and amp D in the top-right corner, as shown schematically in Fig. 2 (Note : In the standard STScI orientation, Amp A is in the top-left corner and Amp D in the bottom-right corner).