a   b   c   d   e   f   g   <-- classified as
 124   0   0   0   1   0   0 |   a = brickface
   0 110   0   0   0   0   0 |   b = sky
   1   0 119   0   2   0   0 |   c = foliage
   1   0   0 107   2   0   0 |   d = cement
   1   0  12   7 105   0   1 |   e = window
   0   0   0   0   0  94   0 |   f = path
   0   0   1   0   0   2 120 |   g = grass

a   b   c   d   e   f   g   <-- classified as
 202   0   0   0   3   0   0 |   a = brickface
   0 220   0   0   0   0   0 |   b = sky
   0   0 198   0  10   0   0 |   c = foliage
   0   0   1 202  16   1   0 |   d = cement
   2   0  11   2 189   0   0 |   e = window
   0   0   0   2   0 234   0 |   f = path
   0   0   0   0   0   0 207 |   g = grass

a   b  <-- classified as
1000 20 | a = class1
10 10   | b = class2

a   b   c   d   e   f   g   <-- classified as
 124   0   0   0   1   0   0 |   a = brickface
...

Accuracy = (124+110+119+107+105+94+120)/(124+0+0+0+1+0+0+0+110+0+0+0+0+0+1+0+119+0+2+0+0+1+0+0+107+2+0+0+1+0+12+7+105+0+1+0+0+0+0+0+94+0+0+0+1+0+0+2+120)
Accuracy = 779/810 = 0.961728

Accuracy = (202+220+198+202+189+234+207)/(202+0+0+0+3+0+0+0+220+0+0+0+0+0+0+0+198+0+10+0+0+0+0+1+202+16+1+0+2+0+11+2+189+0+0+0+0+0+2+0+234+0+0+0+0+0+0+0+207)
Accuracy = 1452/1500 = 0.968