From adc784096f0e22ef7dd709c0bce3be5bbfaabb4d Mon Sep 17 00:00:00 2001
From: JustinLiang <justin.j.w.liang@gmail.com>
Date: Mon, 21 Mar 2016 00:07:38 -0700
Subject: [PATCH] Implemented difference of gaussian algorithm.

---
 SIFT/ComputeDifferenceOfGaussian.asv | 14 ++++++++++++++
 SIFT/ComputeDifferenceOfGaussian.m   | 14 ++++++++++++++
 SIFT/SIFT.m                          |  6 +++++-
 SIFT/ShowPyramid.m                   |  3 ++-
 4 files changed, 35 insertions(+), 2 deletions(-)
 create mode 100644 SIFT/ComputeDifferenceOfGaussian.asv
 create mode 100644 SIFT/ComputeDifferenceOfGaussian.m

diff --git a/SIFT/ComputeDifferenceOfGaussian.asv b/SIFT/ComputeDifferenceOfGaussian.asv
new file mode 100644
index 0000000..64aed5d
--- /dev/null
+++ b/SIFT/ComputeDifferenceOfGaussian.asv
@@ -0,0 +1,14 @@
+% This function computes the difference in gaussian and outputs a new pyramid
+function gaussianPyramid = ComputeDifferenceOfGaussian(pyramid)
+    if isempty(pyramid)
+        return
+    end
+    
+    gaussianPyramid = {};    % Initialize difference of gaussian cell array
+    
+    for i=1:size(pyramid,2)     % Iterate through the octaves
+        for j=1:size(pyramid{1},2)-1  % Iterate through the scales
+            gaussianPyramid{i}{j} = pyramid{i}{j} - pyramid{i;
+        end
+    end 
+end
\ No newline at end of file
diff --git a/SIFT/ComputeDifferenceOfGaussian.m b/SIFT/ComputeDifferenceOfGaussian.m
new file mode 100644
index 0000000..4b55dea
--- /dev/null
+++ b/SIFT/ComputeDifferenceOfGaussian.m
@@ -0,0 +1,14 @@
+% This function computes the difference in gaussian and outputs a new pyramid
+function gaussianPyramid = ComputeDifferenceOfGaussian(pyramid)
+    if isempty(pyramid)
+        return
+    end
+    
+    gaussianPyramid = {};    % Initialize difference of gaussian cell array
+    
+    for i=1:size(pyramid,2)     % Iterate through the octaves
+        for j=1:size(pyramid{1},2)-1  % Iterate through the scales
+            gaussianPyramid{i}{j} = pyramid{i}{j+1} - pyramid{i}{j};
+        end
+    end 
+end
\ No newline at end of file
diff --git a/SIFT/SIFT.m b/SIFT/SIFT.m
index 9bba8d2..ec47d43 100644
--- a/SIFT/SIFT.m
+++ b/SIFT/SIFT.m
@@ -1,7 +1,7 @@
 % Perform edge detection with interpolation during non maximum suppression
 function CannyEdgeDetector()
     close all;  % Close figures
-    OCTAVES = 4;
+    OCTAVES = 3;
     
     % Change the current folder to the folder of this m-file.
     % Courtesy of Brett Shoelson
@@ -15,4 +15,8 @@ function CannyEdgeDetector()
     
     pyramid = MakePyramid(im,OCTAVES);
     ShowPyramid(pyramid);
+    
+    pyramid = ComputeDifferenceOfGaussian(pyramid);
+    ShowPyramid(pyramid);
+
 end
diff --git a/SIFT/ShowPyramid.m b/SIFT/ShowPyramid.m
index 0de66ba..76ad723 100644
--- a/SIFT/ShowPyramid.m
+++ b/SIFT/ShowPyramid.m
@@ -15,8 +15,9 @@ function ShowPyramid(pyramid)
         end
     end 
     
+    figure;
     for i=1:length(pyramidImage)
-        figure;
+        subplot(length(pyramidImage),1,i);
         imshow(pyramidImage{i});
     end
 end
\ No newline at end of file