On 02/04/2016 02:30 AM, Oded Gabbay wrote:
On Tue, Feb 2, 2016 at 8:28 AM, <spit...@gmail.com> wrote:
From: Bill Spitzak <spit...@gmail.com>
The SIGMA term drops out on simplification.
Expanded the size slightly (from ~4.25 to 5) to make the cutoff less noticable.
The filter is truncated at a value of .001 instead of .006, this new
value is less than 1/2 of 1/255, rather than greater than it.
I'm just wondering how did you get to this result ?
Thats the value of the gaussian_kernel(2.5) verses
gaussian_kernel(2.125). I also checked some other literature and putting
the cutoff at 2.5 seems to be pretty common.
Oded
Signed-off-by: Bill Spitzak <spit...@gmail.com>
Acked-by: Oded Gabbay <oded.gab...@gmail.com>
---
pixman/pixman-filter.c | 7 ++-----
1 file changed, 2 insertions(+), 5 deletions(-)
diff --git a/pixman/pixman-filter.c b/pixman/pixman-filter.c
index b6f8eb4..10fa398 100644
--- a/pixman/pixman-filter.c
+++ b/pixman/pixman-filter.c
@@ -63,10 +63,7 @@ linear_kernel (double x)
static double
gaussian_kernel (double x)
{
-#define SQRT2 (1.4142135623730950488016887242096980785696718753769480)
-#define SIGMA (SQRT2 / 2.0)
-
- return exp (- x * x / (2 * SIGMA * SIGMA)) / (SIGMA * sqrt (2.0 * M_PI));
+ return exp (- x * x) / sqrt (M_PI);
}
static double
@@ -139,7 +136,7 @@ static const filter_info_t filters[] =
{ PIXMAN_KERNEL_BOX, box_kernel, 1.0 },
{ PIXMAN_KERNEL_LINEAR, linear_kernel, 2.0 },
{ PIXMAN_KERNEL_CUBIC, cubic_kernel, 4.0 },
- { PIXMAN_KERNEL_GAUSSIAN, gaussian_kernel, 6 * SIGMA },
+ { PIXMAN_KERNEL_GAUSSIAN, gaussian_kernel, 5.0 },
{ PIXMAN_KERNEL_LANCZOS2, lanczos2_kernel, 4.0 },
{ PIXMAN_KERNEL_LANCZOS3, lanczos3_kernel, 6.0 },
{ PIXMAN_KERNEL_LANCZOS3_STRETCHED, nice_kernel, 8.0 },
--
1.9.1
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