Hi,
In the implementation of VNC tight code , there is the following function.The
function try to determine whether vnc filters the image being coded,why can it do
this?Who can explain it for me?
Thanks anyway
Yours Sincerely,
Cao
int \
vncEncodeTight::DetectStillImage##bpp (int w, int h) \
{ \
bool endianMismatch; \
CARD##bpp pix; \
int maxColor[3], shiftBits[3]; \
int x, y, d, dx, c; \
int diffStat[256]; \
int pixelCount = 0; \
int sample, sum, left[3]; \
unsigned long avgError; \
\
endianMismatch = (!m_localformat.bigEndian != !m_remoteformat.bigEndian); \
\
maxColor[0] = m_remoteformat.redMax; \
maxColor[1] = m_remoteformat.greenMax; \
maxColor[2] = m_remoteformat.blueMax; \
shiftBits[0] = m_remoteformat.redShift; \
shiftBits[1] = m_remoteformat.greenShift; \
shiftBits[2] = m_remoteformat.blueShift; \
\
memset(diffStat, 0, 256*sizeof(int)); \
\
y = 0, x = 0; \
while (y < h && x < w) { \
for (d = 0; d < h - y && d < w - x - DETECT_SUBROW_WIDTH; d++) { \
pix = ((CARD##bpp *)m_buffer)[(y+d)*w+x+d]; \
if (endianMismatch) { \
pix = Swap##bpp(pix); \
} \
for (c = 0; c < 3; c++) { \
left[c] = (int)(pix >> shiftBits[c] & maxColor[c]); \
} \
for (dx = 1; dx <= DETECT_SUBROW_WIDTH; dx++) { \
pix = ((CARD##bpp *)m_buffer)[(y+d)*w+x+d+dx]; \
if (endianMismatch) { \
pix = Swap##bpp(pix); \
} \
sum = 0; \
for (c = 0; c < 3; c++) { \
sample = (int)(pix >> shiftBits[c] & maxColor[c]); \
sum += abs(sample - left[c]); \
left[c] = sample; \
} \
if (sum > 255) \
sum = 255; \
diffStat[sum]++; \
pixelCount++; \
} \
} \
if (w > h) { \
x += h; \
y = 0; \
} else { \
x = 0; \
y += w; \
} \
} \
\
if ((diffStat[0] + diffStat[1]) * 100 / pixelCount >= 90) \
return 0; \
\
avgError = 0; \
for (c = 1; c < 8; c++) { \
avgError += (unsigned long)diffStat[c] * (unsigned long)(c * c); \
if (diffStat[c] == 0 || diffStat[c] > diffStat[c-1] * 2) \
return 0; \
} \
for (; c < 256; c++) { \
avgError += (unsigned long)diffStat[c] * (unsigned long)(c * c); \
} \
avgError /= (pixelCount - diffStat[0]); \
\
return (avgError < 200); \
}
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