filter_kernels: add blur parameter to jinc

This affects all filters that use it, eg. ewa_lanczos. Setting it to
something like 0.95 can be done to make the filter a bit less blurry.

2 files changed, 10 insertions, 4 deletions

diff --git a/DOCS/man/vo.rst b/DOCS/man/vo.rst
index 7da0d2efff..4fdc0e26c7 100644
--- a/DOCS/man/vo.rst
+++ b/DOCS/man/vo.rst
@@ -340,6 +340,12 @@ Available video output drivers are:
             Scale parameter (``t``). Increasing this makes the result blurrier.
             Defaults to 1.
 
+        ``ewa_lanczos``, ``ewa_ginseng``, ``ewa_hanning``
+            Jinc function scaling factor (also known as a blur factor).
+            Decreasing this makes the result sharper, increasing it makes it
+            blurrier. Defaults to 1. Note that setting this too low (eg. 0.5)
+            leads to bad results. It's recommended to stay between 0.9 and 1.1.
+
     ``scale-radius=<r>``
         Set radius for filters listed below, must be a float number between 1.0
         and 16.0. Defaults to be 3.0 if not specified.
diff --git a/video/out/filter_kernels.c b/video/out/filter_kernels.c
index c49a8e113a..e6fa8aa24a 100644
--- a/video/out/filter_kernels.c
+++ b/video/out/filter_kernels.c
@@ -274,7 +274,7 @@ static double jinc(kernel *k, double x)
 {
     if (fabs(x) < 1e-8)
         return 1.0;
-    double pix = M_PI * x;
+    double pix = M_PI * x / k->params[0]; // blur factor
     return 2.0 * j1(pix) / pix;
 }
 
@@ -345,9 +345,9 @@ const struct filter_kernel mp_filter_kernels[] = {
     {"spline64",       4,   spline64},
     {"gaussian",       -1,  gaussian, .params = {1.0, NAN} },
     {"sinc",           -1,  sinc},
-    {"ewa_lanczos",    -1,  ewa_lanczos, .polar = true},
-    {"ewa_hanning",    -1,  ewa_hanning, .polar = true},
-    {"ewa_ginseng",    -1,  ewa_ginseng, .polar = true},
+    {"ewa_lanczos",    -1,  ewa_lanczos, .params = {1.0, NAN}, .polar = true},
+    {"ewa_hanning",    -1,  ewa_hanning, .params = {1.0, NAN}, .polar = true},
+    {"ewa_ginseng",    -1,  ewa_ginseng, .params = {1.0, NAN}, .polar = true},
     {"lanczos",        -1,  lanczos},
     {"blackman",       -1,  blackman},
     {0}