The contour values can be easily chosen using a combination of 4 keywords:
/NLEVELS, /LEVELS=[value_1,value_2,...], MIN_VALUE and MAX_VALUE.
(See Fig. 13 and
Fig. 15).
If the dominant colors of IMAGE_1 are light, it is often better to
draw the contour levels in black. This can be done by using the /BLACK
keyword (See Fig. 14). One can specify the
contour colors precisely by assigning to the C_COLOR keyword a scalar or
an array with values ranging from 0 to 255. The 256 values correspond
to the number of available colors displayed. If
C_COLOR=[10,20,100,150,255] (5 values) and the number of contours is
set to 8 (i.e. using NLEVELS=8) the colors used will be
[10,20,100,150,255,10,20,30]. If C_COLOR=-1 then each contour will
have a unique color and the colors will be equally spaced in the color
table.
The line style used to draw the contours can also be specified using
the C_STYLE keyword. C_STYLE can be a scalar or an array with values
ranging for 0 to 5 (0=solid, 1=dotted, 2=dashed, 3=dash-dot,
4=dash-dot-dot-dot, 5=long-dash). As was the case for C_COLOR,
C_STYLE considers the line style table periodic if more contours than
line styles are specified. If C_STYLE=-1, then positive contour levels are
marked with solid lines and negative ones with dotted lines.
A legend at the right of the display window can be included using the
/PUTINFO keyword. It contains the file names of the input images, the
color table of the color image, the values of all contours, and the
current date.
(See Fig. 15)