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diff --git a/pkg/images/tv/display/findz.x b/pkg/images/tv/display/findz.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<imhdr.h>
+include	"iis.h"
+
+# FINDZ -- Estimate the range of greylevels Z1 to Z2 containing a specified
+# fraction of the greylevels in the image.  The technique is to sample the
+# image at some interval, computing the values of the greylevels a fixed
+# distance either side of the median.  Since it is not necessary to compute
+# the full histogram we do not need to know the image zmin, zmax in advance.
+# Works for images of any dimensionality, size, or datatype.
+
+procedure findz (im, z1, z2, zfrac, maxcols, nsample_lines)
+
+pointer	im
+real	z1, z2, zfrac
+int	maxcols, nsample_lines
+
+real	rmin, rmax
+real	frac
+int	imin, imax, ncols, nlines
+int	i, n, step, sample_size, imlines
+
+pointer	sp, buf
+pointer	imgl2r()
+include	"iis.com"
+
+begin
+	call smark (sp)
+	call salloc (buf, ncols, TY_REAL)
+
+	ncols  = IM_LEN(im,1)
+	nlines = IM_LEN(im,2)
+
+	# 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 = iis_ydim * nsample_lines
+	imlines = min(nlines, max(nsample_lines, sample_size / ncols))
+	step = nlines / (imlines + 1)
+
+	frac = (1.0 - zfrac) / 2.
+	imin = frac * (ncols - 1)
+	imax = (1.0 - frac) * (ncols - 1)
+	rmin = 0.0
+	rmax = 0.0
+	n = 0
+
+	do i = 1 + step, nlines, max (1, step) {
+	    call asrtr (Memr[imgl2r (im, i)], Memr[buf], ncols)
+	    rmin = rmin + Memr[buf + imin]
+	    rmax = rmax + Memr[buf + imax]
+	    n = n + 1
+	}
+
+	z1 = rmin / n
+	z2 = rmax / n
+
+	call sfree (sp)
+end