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# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
include <mach.h>
include <imhdr.h>
# MAXMIN -- Get the minimum and maximum pixel values of an image. If valid
# header values are available they are used, otherwise the image is sampled
# on an even grid and the min and max values of this sample are returned.
procedure maxmin (im, zmin, zmax, nsample_lines)
pointer im
real zmin, zmax # min and max intensity values
int nsample_lines # amount of image to sample
int step, ncols, nlines, sample_size, imlines, i
real minval, maxval
pointer imgl2r()
begin
# Only calculate minimum, maximum pixel values if the current
# values are unknown, or if the image was modified since the
# old values were computed.
ncols = IM_LEN(im,1)
nlines = IM_LEN(im,2)
if (IM_LIMTIME(im) >= IM_MTIME(im)) {
# Use min and max values in image header if they are up to date.
zmin = IM_MIN(im)
zmax = IM_MAX(im)
} else {
zmin = MAX_REAL
zmax = -MAX_REAL
# Try to include a constant number of pixels in the sample
# regardless of the image size. The entire image is used if we
# have a small image, and at least sample_lines lines are read
# if we have a large image.
sample_size = 512 * nsample_lines
imlines = min(nlines, max(nsample_lines, sample_size / ncols))
step = nlines / (imlines + 1)
do i = 1 + step, nlines, max (1, step) {
call alimr (Memr[imgl2r(im,i)], ncols, minval, maxval)
zmin = min (zmin, minval)
zmax = max (zmax, maxval)
}
}
end
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