ts on how to create such an input file, 
see <a href="Read.html#ReadImageGrayscale">Read Image Grayscale</a>.  If the example given there has the
following code instead, 
<p>
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<TD>
<PRE>
<font color="#82140F">
open "awk 'BEGIN {               \
     for(i=0;i&lt;256;i++) {        \
       print((i - 50)/50, 1, 1)  \
     }                           \
   }' |"
read image colorscale hsb
</font></PRE>
</TD>
</TR>
</TABLE>
<p>

then a linea