--- a/scripts/image/copper.m
+++ b/scripts/image/copper.m
@@ -46,7 +46,7 @@
   if (n == 1)
     map = [0, 0, 0];
   elseif (n > 1)
-    x = linspace (0, 1, n)';
+    x = [0:(n-1)]' / (n - 1);
     r = (x < 4/5) .* (5/4 * x) ...
       + (x >= 4/5);
     g = 0.7812 * x;

--- a/scripts/image/hot.m
+++ b/scripts/image/hot.m
@@ -45,23 +45,21 @@
 
   if (n == 1)
     map = [1, 1, 1];
-  elseif (n > 1)
+  elseif (n == 2)
+    map = [1, 1, 1/2
+           1, 1,  1 ];
+  elseif (n > 2)
     idx = floor (3/8 * n);
     nel = idx;
 
     r = ones (n, 1);
-    if (nel > 0) 
-      r(1:idx, 1) = [1:nel]' / nel;
-    endif
+    r(1:idx, 1) = [1:nel]' / nel;
 
     g = zeros (n, 1);
     g(idx+1:2*idx, 1) = r(1:idx);
     g(2*idx+1:end, 1) = 1;
 
-    idx = floor (3/4 * n);
-    if (any (mod (n, 8) == [0, 1, 3, 6]))
-      idx++;
-    endif
+    idx = 2*idx + 1;   # approximately 3/4 *n
     nel = n - idx + 1;
 
     b = zeros (n, 1);

--- a/scripts/image/rainbow.m
+++ b/scripts/image/rainbow.m
@@ -49,17 +49,18 @@
   if (n == 1)
     map = [1, 0, 0];
   elseif (n > 1)
-    x = linspace (0, 1, n)';
+    x = [0:(n-1)]' / (n - 1);
 
-    r = ((x < 2/5)
+    r = (  (x < 2/5)
          + (x >= 2/5 & x < 3/5) .* (-5 * x + 3)
          + (x >= 4/5) .* (10/3 * x - 8/3));
 
-    g = ((x < 2/5) .* (5/2 * x)
+    g = (  (x < 2/5) .* (5/2 * x)
          + (x >= 2/5 & x < 3/5)
          + (x >= 3/5 & x < 4/5) .* (-5 * x + 4));
 
-    b = (x >= 3/5 & x < 4/5) .* (5 * x - 3) + (x >= 4/5);
+    b = (  (x >= 3/5 & x < 4/5) .* (5 * x - 3)
+         + (x >= 4/5));
 
     map = [r, g, b];
   else