From c3d702538d60390309ee3728befd21e6185e72b8 Mon Sep 17 00:00:00 2001
From: homm <homm86@gmail.com>
Date: Thu, 16 Jun 2016 21:12:36 +0300
Subject: [PATCH] add BOX, HAMMING, MITCHELL filters to resample.c

---
 libImaging/Resample.c | 51 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 50 insertions(+), 1 deletion(-)

diff --git a/libImaging/Resample.c b/libImaging/Resample.c
index 01c9a2fcd..9010f3239 100644
--- a/libImaging/Resample.c
+++ b/libImaging/Resample.c
@@ -10,6 +10,13 @@ struct filter {
     double support;
 };
 
+static inline double box_filter(double x)
+{
+    if (x >= -0.5 && x < 0.5)
+        return 1.0;
+    return 0.0;
+}
+
 static inline double bilinear_filter(double x)
 {
     if (x < 0.0)
@@ -19,6 +26,16 @@ static inline double bilinear_filter(double x)
     return 0.0;
 }
 
+static inline double hamming_filter(double x)
+{
+    if (x < 0.0)
+        x = -x;
+    if (x == 0.0)
+        return 1.0;
+    x = x * M_PI;
+    return sin(x) / x * (0.54f + 0.46f * cos(x));
+}
+
 static inline double bicubic_filter(double x)
 {
     /* https://en.wikipedia.org/wiki/Bicubic_interpolation#Bicubic_convolution_algorithm */
@@ -33,6 +50,27 @@ static inline double bicubic_filter(double x)
 #undef a
 }
 
+static inline double mitchell_filter(double x)
+{
+    double fB = 1.f / 3.f;
+    double fC = 1.f / 3.f;
+    double fA1 = -fB - 6*fC;
+    double fB1 = 6*fB + 30*fC;
+    double fC1 = -12*fB - 48*fC;
+    double fD1 = 8*fB + 24*fC;
+    double fA2 = 12 - 9*fB - 6*fC;
+    double fB2 = -18 + 12*fB + 6*fC;
+    double fD2 = 6 - 2*fB;
+
+    if (x < 0.0)
+        x = -x;
+    if (x < 1.0)
+        return ((fA2 * x + fB2) * x*x + fD2) * (1.f/6.f);
+    if (x < 2.0)
+        return (((fA1 * x + fB1) * x + fC1) * x + fD1) * (1.f/6.f);
+    return 0.0;
+}
+
 static inline double sinc_filter(double x)
 {
     if (x == 0.0)
@@ -49,12 +87,14 @@ static inline double lanczos_filter(double x)
     return 0.0;
 }
 
+static struct filter BOX = { bilinear_filter, 0.5 };
 static struct filter BILINEAR = { bilinear_filter, 1.0 };
+static struct filter HAMMING = { hamming_filter, 1.0 };
 static struct filter BICUBIC = { bicubic_filter, 2.0 };
+static struct filter MITCHELL = { mitchell_filter, 2.0 };
 static struct filter LANCZOS = { lanczos_filter, 3.0 };
 
 
-
 /* 8 bits for result. Filter can have negative areas.
    In one cases the sum of the coefficients will be negative,
    in the other it will be more than 1.0. That is why we need
@@ -523,12 +563,21 @@ ImagingResample(Imaging imIn, int xsize, int ysize, int filter)
 
     /* check filter */
     switch (filter) {
+    case IMAGING_TRANSFORM_BOX:
+        filterp = &BOX;
+        break;
     case IMAGING_TRANSFORM_BILINEAR:
         filterp = &BILINEAR;
         break;
+    case IMAGING_TRANSFORM_HAMMING:
+        filterp = &HAMMING;
+        break;
     case IMAGING_TRANSFORM_BICUBIC:
         filterp = &BICUBIC;
         break;
+    case IMAGING_TRANSFORM_MITCHELL:
+        filterp = &MITCHELL;
+        break;
     case IMAGING_TRANSFORM_LANCZOS:
         filterp = &LANCZOS;
         break;