Hello.
I try to perform DCT using oc_enc_fdct8x8_x86_64sse2(), and by Python-script
dct.py.
Results differ. Why?
Original pixel data block:
Morig = [
[28,28,28,28,28,28,28,28],
[28,28,28,28,28,28,28,28],
[28,28,28,29,29,29,28,28],
[28,29,28,29,29,29,28,28],
[28,29,28,28,28,28,28,28],
[29,28,29,28,28,28,28,28],
[29,28,29,29,29,29,28,28],
[29,29,29,29,29,29,29,29],
]
Result by libtheora:
* -3187 3 -3 2 0 -1 1 -1
* -5 -1 0 1 0 -1 -1 -1
* 4 0 3 0 1 2 2 2
* -4 4 5 -1 -1 1 1 2
* 2 0 2 0 -1 -2 -3 -2
* 2 1 -4 3 2 0 2 -1
* 2 1 2 0 1 1 1 1
* -1 0 0 1 0 0 0 -1
Result by dct.py:
-1479 55 50 47 39 30 21 10
52 -2 -1 -1 -1 -1 -1 0
52 -2 -1 -1 -1 0 0 0
44 -1 0 -1 -1 0 0 0
40 -1 -1 -1 -1 -1 -1 0
32 -1 -2 0 0 0 0 0
21 0 0 0 0 0 0 0
10 0 0 0 0 0 0 0
----
Source code of dct.py:
#!/usr/bin/python
# pixels
Morig = [
[28,28,28,28,28,28,28,28],
[28,28,28,28,28,28,28,28],
[28,28,28,29,29,29,28,28],
[28,29,28,29,29,29,28,28],
[28,29,28,28,28,28,28,28],
[29,28,29,28,28,28,28,28],
[29,28,29,29,29,29,28,28],
[29,29,29,29,29,29,29,29],
]
from math import sqrt,cos,pi
from sys import stdout
M = 8
N = 8
def dct(a):
print "---"
F = []
for u in xrange(N):
F = F + [[]]
for v in xrange(M):
s = 0.0
for i in xrange(N):
for j in xrange(M):
#print a[i][j]
li = 1
if (i == 0): li = 1/sqrt(2)
lj = 1
if (j == 0): lj = 1/sqrt(2)
d = li*lj*(a[i][j]-128)
#d = (a[i][j]-128)
d *= cos(((pi*u)*(2*i+1))/(2*N))
d *= cos(((pi*v)*(2*j+1))/(2*M))
s += d
s *= sqrt(2.0/N)
s *= sqrt(2.0/M)
F[u] = F[u] + [s,]
stdout.write(" %6d" % s)
stdout.write("\n")
return F
dct(Morig)
# END
Source code based on http://www.cs.cf.ac.uk/Dave/Multimedia/node231.html
formulas for 2D-DCT.
--
Alexander Lubyagin