added improved huffman for image

Author: sundeshgupta

improved-huffman_image.cpp

@@ -0,0 +1,145 @@
+#include <bits/stdc++.h>
+using namespace std;
+#define STB_IMAGE_IMPLEMENTATION
+#include "stb_image.h"
+
+struct pixel{
+	float freq;
+	int label;
+	pixel* left, *right;
+
+	pixel(int x, float y):	label(x), freq(y){
+		left = NULL;
+		right = NULL;
+	}
+
+	void print(){
+		cout << label << " " << freq << endl;
+	}
+};
+
+struct huffcode{
+	int label;
+	int parent;
+	string code;
+};
+
+struct compare{
+	bool operator() (pixel* a, pixel* b){
+		return a->freq > b->freq;
+	}
+};
+
+huffcode codes[256];
+
+void preoder(pixel* root, string s, int level, int parent){
+	if(root->label < 256){
+		codes[root->label].parent = parent;
+		codes[root->label].code = s;
+		cout << setfill(' ') << setw(3) << root->label 
+			<< " -> " << setw(20) << s << setw(4) << codes[root->label].parent << setw(20)<< fixed << setprecision(10) << root->freq << endl; 
+		return;
+	}
+	// out << root->label << " -> " << root->left->label << " [ label = \"" << s+'0' << "\"];"<<endl;
+	// out << root->label << " -> " << root->right->label << " [ label = \"" << s+'1' << "\"];" << endl; 
+	
+	if(level == 3)
+		parent = root->label;
+
+	preoder(root->left , s + '0', level+1, parent);
+	preoder(root->right, s + '1', level+1, parent);
+
+	return;
+}
+
+
+
+int main()
+{
+	int width, height, bpp;
+
+	uint8_t* rgb_image = stbi_load("colombia.jpg", &width, &height, &bpp, 1);
+
+	int image[height][width];
+	int itr = 0;
+	for (int i = 0; i < height; ++i)
+		for (int j = 0; j < width; ++j)
+			image[i][j] = rgb_image[itr++];
+
+	stbi_image_free(rgb_image);	
+
+	int hist[256] = {0}; 
+	  
+	for (int i = 0; i < height; i++) 
+	    for (int j = 0; j < width; j++) 
+	        hist[image[i][j]] += 1;
+
+	int totpix = height*width;
+
+	float freq[256] = {0};
+	
+	for (int i = 0; i < 256; ++i)
+		freq[i] = ((float)hist[i])/totpix;
+
+
+
+	priority_queue<pixel*, vector<pixel*>, compare> pq;
+
+	for(int i = 0; i < 256; i++){
+		if (freq[i] > 0){
+			pixel* tmp = new pixel(i, freq[i]);
+			pq.push(tmp);
+		}
+	}
+
+	int cnt = 256;
+	while(pq.size() > 1){
+		pixel* first = pq.top();
+		pq.pop();
+		pixel* second = pq.top();
+		pq.pop();
+		pixel* tmp = new pixel(cnt++, first->freq + second->freq);
+		tmp->left = first;
+		tmp->right = second;
+		pq.push(tmp);
+	}
+
+	pixel* root = pq.top();
+
+	preoder(root, "", 0, -1);
+	
+
+	int compression_size = 0;
+	int last = -1;
+	bool f = 0;
+	for (int i = 0; i < height; ++i)
+	{
+		for (int j = 0; j < width; ++j)
+		{
+			if(f == 0){
+				compression_size += codes[image[i][j]].code.size();
+			}
+			else if(codes[image[i][j]].parent == codes[last].parent){
+				compression_size += 1;
+				string code = codes[image[i][j]].code;
+				compression_size += code.substr(3, code.length()).size();
+			}
+			else{
+				compression_size += 1;
+				compression_size += codes[image[i][j]].code.size();
+			}
+			if(codes[image[i][j]].parent == -1)
+				f = 0;
+			else{
+				last = image[i][j];
+				f = 1;
+			}
+		}
+	}
+
+	cout << compression_size << " " << 256*256*8 << endl;
+
+
+	return 0;
+}
+