set palette defined (0 0.0 0.0 0.5, \
                     1 0.0 0.0 1.0, \
                     2 0.0 0.5 1.0, \
                     3 0.0 1.0 1.0, \
                     4 0.5 1.0 0.5, \
                     5 1.0 1.0 0.0, \
                     6 1.0 0.5 0.0, \
                     7 1.0 0.0 0.0, \
                     8 0.5 0.0 0.0 )

plot 'example_matrix.txt' u 1:2:3 with image