This means that the user does C not have to specify an absolute brightness threshold for star C detection, and if the mean background brightness varies over the C frame, to the extent that the variations are smooth and large-scale, C to first order they will have no effect on the detection limit. The derived peak heights of the Gaussian functions are stored in a C scratch disk image file. Later they will be read back in, and local C maxima in the peak values will be sought. After undergoing a few C tests designed to select against bad pixels and bad columns, these C local maxima will be considered to be astronomical objects, better C image centroids will be computed, and the objects will be assigned C sequential ID numbers and will be written to a disk data file. This represents a 5 x 5 subarray taken out of the original picture.
C C Compute the size of the subarray needed.
As one final nuance, for this and subsequent calculations I propose C to subtract off the modal sky level. Otherwise, for faint stars on C bright backgrounds in large boxes, it is barely possible that C truncation error could affect the numerical results of the analysis. Now check to see whether the object is strongly elongated either C along the row or along the column. Compute the height of a Gaussian C function of x and a Gaussian function of y by least-squares fits to C the marginal distributions of the image data. That is, fit the C sum over y of the actual brightness values to the sum over y of the C values of the array G, as functions of x.