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better rounding in reducev orc path

This commit is contained in:
John Cupitt 2016-04-10 17:52:51 +01:00
parent f1635b873d
commit 511a0a7da5
2 changed files with 16 additions and 13 deletions
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10
TODO
View File

@ -1,8 +1,12 @@
- try
- have some zero elements in lanczos3 masks, can we improve mask sizing?
$ vips reducev ~/pics/babe.jpg x.png 2.666
eg.
get 254 for white, some rounding problem
$ vips reducev ~/pics/babe.jpg x.png 1.1
has an extra 0 at the end
- compare lanczos2 vs. 3, any differences?
- I like the new int mask creator in reducev, can we use it in im_vips2imask()
as well?

19
libvips/resample/reducev.cpp
View File

@ -240,13 +240,17 @@ vips_reducev_compile_section( VipsReducev *reducev, Pass *pass, gboolean first )
* image, otherwise write the 16-bit intermediate to our temp buffer.
*/
if( pass->last >= reducev->n_point - 1 ) {
char sixteen[256];
char thirtytwo[256];
char five[256];
char zero[256];
char twofivefive[256];
CONST( sixteen, 16, 2 );
ASM3( "addw", "sum", "sum", sixteen );
/* You'd think we might add 16 before dividing by 32, but we
* are really dividing by 64, since we right-shifted the pixel
* values on load above. So we add 32.
*/
CONST( thirtytwo, 32, 2 );
ASM3( "addw", "sum", "sum", thirtytwo );
CONST( five, 5, 2 );
ASM3( "shrsw", "sum", "sum", five );
@ -707,8 +711,8 @@ vips_reducev_intize( double *in, int *out, int n, int scale )
* high and low guesses are therefore n/2 either side of the obvious
* answer.
*/
high = scale + n / 2;
low = scale - n / 2;
high = scale + (n + 1) / 2;
low = scale - (n + 1) / 2;
do {
guess = (high + low) / 2.0;
@ -720,11 +724,6 @@ vips_reducev_intize( double *in, int *out, int n, int scale )
for( int i = 0; i < n; i++ )
sum += out[i];
/* If we've picked low and high correctly, see above.
*/
g_assert( sum >= low );
g_assert( sum <= high );
if( sum == target )
break;
if( sum < target )