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diff --git a/sys/gio/stdgraph/stgpcell.x b/sys/gio/stdgraph/stgpcell.x
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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<gki.h>
+include	"stdgraph.h"
+
+define	ZSTEP		4	# bit to be tested (step function width)
+
+
+# STG_PUTCELLARRAY -- Draw a cell array, i.e., two dimensional array of pixels
+# (greylevels or colors).  The algorithm used here maps 8 bits in into 1 bit
+# out, using a step function lookup table.  The result is a band-contoured
+# image, where the spacing and width of the contour bands decreases as the
+# rate of change of intensity in the input cell array increases.
+
+procedure stg_putcellarray (m, nx, ny, ax1,ay1, ax2,ay2)
+
+short	m[nx,ny]		# cell array
+int	nx, ny			# number of pixels in X and Y
+int	ax1, ay1		# lower left corner of output window
+int	ax2, ay2		# upper right corner of output window
+
+real	dx, dy
+int	my, i1, i2, v, i, j, k
+include	"stdgraph.com"
+int	and()
+
+begin
+	# Set polyline width to 1 for max y-res.
+	call stg_ctrl1 ("LW", 1)
+	SG_PLWIDTH(g_sg) = 1
+
+	# Determine the width of a cell array pixel in GKI units.
+	dx = real (ax2 - ax1) / nx
+
+	# Determine the height of a device pixel in GKI units.
+	dy = max (1.0, real(GKI_MAXNDC) / real(g_yres))
+
+	# Process the cell array.  The outer loop runs over device pixels in Y;
+	# each iteration writes one line of the output raster.  The inner loop
+	# runs down a line of the cell array.
+
+	k = 0
+	for (my = ay1 + dy/2;  my < ay2;  my = k * dy + ay1) {
+	    j = max(1, min(ny, int (real(my-ay1) / real(ay2-ay1) * (ny-1)) + 1))
+	    my = min (my, int (ay2 - dy/2))
+
+	    for (i=1;  i <= nx;  ) {
+		do i = i, nx {
+		    v = m[i,j]
+		    if (and (v, ZSTEP) != 0)
+			break
+		}
+
+		if (i <= nx) {
+		    i1 = i
+		    i2 = nx
+		    do i = i1 + 1, nx {
+			v = m[i,j]
+			if (and (v, ZSTEP) == 0) {
+			    i2 = i
+			    break
+			}
+		    }
+
+		    # The following decreases the length of dark line segments
+		    # to make features more visible.
+
+		    if (i2 - i1 >= 2)
+			if (i1 > 1 && i2 < nx) {
+			    i1 = i1 + 1
+			    i2 = i2 - 1
+			}
+
+		    # Draw the line segment.
+		    call stg_move (int ((i1-1) * dx + ax1), my)
+		    call stg_draw (int (i2 * dx + ax1), my)
+
+		    if (i2 >= nx)
+			i = nx + 1
+		}
+	    }
+
+	    k = k + 1
+	}
+end