From 72697f650c0d7890ee9fca2d61225749188aaf3c Mon Sep 17 00:00:00 2001
From: Pavel Krajcevski <pavel@cs.unc.edu>
Date: Thu, 10 Oct 2013 19:36:19 -0400
Subject: [PATCH] Add filtering operation.

---
 Base/include/Image.h    |  7 +++++
 Base/src/Image.cpp      | 59 +++++++++++++++++++++++++++++++++++++++++
 Base/test/TestImage.cpp | 30 +++++++++++++++++++++
 3 files changed, 96 insertions(+)

diff --git a/Base/include/Image.h b/Base/include/Image.h
index 0c0eaec..0d93ef6 100644
--- a/Base/include/Image.h
+++ b/Base/include/Image.h
@@ -49,6 +49,8 @@
 
 namespace FasTC {
 
+  class IPixel;
+
   template<typename U, typename V>
   extern double ComputePSNR(Image<U> *img1, Image<V> *img2);
 
@@ -105,6 +107,11 @@ namespace FasTC {
     // appropriate pixels.
     virtual void ComputePixels() { }
 
+    // Filters the image with a given set of kernel values. The values
+    // are normalized before they are used (i.e. we make sure that they
+    // sum up to one).
+    void Filter(const Image<IPixel> &kernel);
+
    private:
     uint32 m_Width;
     uint32 m_Height;
diff --git a/Base/src/Image.cpp b/Base/src/Image.cpp
index fd842d7..43b21cd 100644
--- a/Base/src/Image.cpp
+++ b/Base/src/Image.cpp
@@ -43,6 +43,7 @@
 
 #include "Image.h"
 
+#include <algorithm>
 #include <cstdlib>
 #include <cstdio>
 #include <cstring>
@@ -289,6 +290,64 @@ void Image<PixelType>::SetImageData(uint32 width, uint32 height, PixelType *data
   }
 }
 
+  template<typename T>
+  static inline T Clamp(const T &v, const T &a, const T &b) {
+    return ::std::min(::std::max(a, v), b);
+  }
+
+template<typename PixelType>
+void Image<PixelType>::Filter(const Image<IPixel> &kernel) {
+  Image<IPixel> k(kernel);
+
+  // Only odd sized filters make sense....
+  assert(k.GetWidth() % 2);
+  assert(k.GetHeight() % 2);
+
+  double sum = 0.0;
+  for(uint32 j = 0; j < k.GetHeight(); j++) {
+    for(uint32 i = 0; i < k.GetWidth(); i++) {
+      sum += static_cast<float>(k(i, j));
+    }
+  }
+
+  for(uint32 j = 0; j < k.GetHeight(); j++) {
+    for(uint32 i = 0; i < k.GetWidth(); i++) {
+      k(i, j) = static_cast<float>(k(i, j)) / sum;
+    }
+  }
+
+  int32 ih = static_cast<int32>(GetHeight());
+  int32 iw = static_cast<int32>(GetWidth());
+
+  int32 kh = static_cast<int32>(k.GetHeight());
+  int32 kw = static_cast<int32>(k.GetWidth());
+
+  Image<PixelType> filtered(iw, ih);
+
+  for(int32 j = 0; j < ih; j++) {
+    for(int32 i = 0; i < iw; i++) {
+      int32 yoffset = j - (k.GetHeight() / 2);
+      int32 xoffset = i - (k.GetWidth() / 2);
+
+      Color newPixel;
+      for(int32 y = 0; y < kh; y++) {
+        for(int32 x = 0; x < kw; x++) {
+          PixelType pixel = ((*this)(
+            Clamp<int32>(x + xoffset, 0, GetWidth() - 1),
+            Clamp<int32>(y + yoffset, 0, GetHeight() - 1)));
+          Color c; c.Unpack(pixel.Pack());
+          Color scaled = c * static_cast<float>(k(x, y));
+          newPixel += scaled;
+        }
+      }
+
+      filtered(i, j).Unpack(newPixel.Pack());
+    }
+  }
+
+  *this = filtered;
+}
+
 template class Image<Pixel>;
 template class Image<IPixel>;
 template class Image<Color>;
diff --git a/Base/test/TestImage.cpp b/Base/test/TestImage.cpp
index df1ffc7..1e0c012 100644
--- a/Base/test/TestImage.cpp
+++ b/Base/test/TestImage.cpp
@@ -52,6 +52,7 @@
 
 #include "gtest/gtest.h"
 #include "Image.h"
+#include "IPixel.h"
 #include "Pixel.h"
 #include "Utils.h"
 
@@ -119,3 +120,32 @@ TEST(Image, AssignmentOperator) {
     }
   }
 }
+
+TEST(Image, Filter) {
+  const uint32 w = 16;
+  const uint32 h = 16;
+
+  // Make a black and white image...
+  FasTC::Image<FasTC::IPixel> img(w, h);
+  for(uint32 j = 0; j < h; j++) {
+    for(uint32 i = 0; i < w; i++) {
+      if((i ^ j) % 2)
+        img(i, j) = 1.0f;
+      else
+        img(i, j) = 0.0f;
+    }
+  }
+
+  // Make a weird averaging kernel...
+  FasTC::Image<FasTC::IPixel> kernel(3, 3);
+  kernel(0, 1) = kernel(1, 0) = kernel(1, 2) = kernel(2, 1) = 0.125f;
+  kernel(1, 1) = 0.5f;
+
+  img.Filter(kernel);
+
+  for(uint32 j = 1; j < h-1; j++) {
+    for(uint32 i = 1; i < w-1; i++) {
+      EXPECT_NEAR(static_cast<float>(img(i, j)), 0.5f, 0.01);
+    }
+  }
+}