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avoid /0 in some cases in spcor 

see https://github.com/jcupitt/libvips/issues/252 and others
This commit is contained in:
John Cupitt 2015-04-08 09:40:31 +01:00
parent 5268f0280c
commit 2fb0f434a2
1 changed files with 15 additions and 6 deletions
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21
libvips/convolution/spcor.c
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@ -36,6 +36,8 @@
* - cleanups
* 7/11/13
* - redone as a class
* 8/4/15
* - avoid /0 for constant reference or zero image
*/
/*
@ -176,20 +178,20 @@ vips_spcor_pre_generate( VipsCorrelation *correlation )
sum3 = 0.0; \
for( j = 0; j < ref->Ysize; j++ ) { \
for( i = 0; i < sz; i += bands ) { \
/* Reference pel, and input pel. \
/* Reference pel and input pel. \
*/ \
IN ip = p1a[i]; \
IN rp = r1a[i]; \
\
/* Accumulate sum-of-squares-of- \
* differences for input image. \
/* Accumulate sum-of-squares-of-differences for \
* input image. \
*/ \
double t = ip - imean; \
sum2 += t * t; \
\
/* Accumulate product-of-difference from mean. \
*/ \
sum3 += (rp - spcor->rmean[b]) * (ip - imean); \
sum3 += (rp - spcor->rmean[b]) * t; \
} \
\
p1a += in_lsk; \
@ -265,8 +267,15 @@ vips_spcor_correlation( VipsCorrelation *correlation,
return;
}
c2 = sqrt( sum2 );
cc = sum3 / (spcor->c1[b] * c2);
c2 = spcor->c1[b] * sqrt( sum2 );
if( c2 == 0.0 )
/* Something like constant ref.
* We regard this as uncorrelated.
*/
cc = 0.0;
else
cc = sum3 / c2;
*q++ = cc;
}