arithmetic coding for images

Author: sundeshgupta

arithmetic_decode_image.cpp

@@ -0,0 +1,135 @@
+#include <bits/stdc++.h>
+using namespace std;
+#define STB_IMAGE_WRITE_IMPLEMENTATION
+#include "stb_image_write.h"
+#define ll long long
+
+const ll MIN = 0;
+const ll MAX = 65535;
+
+ll lower[257];
+vector <ll> _low, _high;
+
+string write_bits(bool bit, int bit_to_fall){
+	string tmp;
+	tmp += to_string(bit);
+	while(bit_to_fall){
+		tmp += to_string(!bit);
+		bit_to_fall -= 1;
+	}
+	return tmp;
+}
+
+int to_int(int _pos, string &encode){
+	int n = 0;
+	for (int i = _pos; i < sizeof(short) * 8 + _pos; i++)
+	{
+		n <<= 1;
+		n |= encode[i] - '0';
+	}
+	return n;
+}
+
+ll add_bit(ll value, int count_taken, bool &flag, string &encode){
+	bitset<16> a(value);
+
+	if(flag == 1){
+		a.reset(0);
+	}
+	else if(count_taken > encode.length()){
+		a.set(0);
+		flag = 1;
+	}
+	else if(encode[count_taken] == '1'){
+		a.set(0);
+	}
+	else if(encode[count_taken] == '0'){
+		a.reset(0);
+	}
+
+	value = (ll)(a.to_ulong());
+	return value;
+}
+
+uint8_t* rgb_image;
+string code;
+
+int main()
+{
+	auto start = chrono::high_resolution_clock::now(); 
+
+	ifstream in("arithmetic_encoded.txt");
+
+	const ll ONE_QTR = MAX / 4 + 1;
+	const ll HALF = 2 * ONE_QTR;
+	const ll THREE_QTR = 3 * ONE_QTR;
+
+	ll len;
+	in >> len;
+	for(int i=0; i<=256; i++)	in >> lower[i];
+
+
+	in >> code;
+	cout<<code.size()<<"\n";
+	int height, width, num_channel;
+
+	in>>height>>width>>num_channel;
+
+	cout<<height<<" "<<width<<" "<<num_channel<<"\n";
+
+    rgb_image = (uint8_t*) malloc(width*height*num_channel);
+    
+    int itr = 0;
+
+    _low.resize(len);
+    _high.resize(len);
+
+	_low[0] = MIN;
+	_high[0] = MAX;
+
+	ll value = to_int(0, code);
+	int count_taken = 16;
+	bool flag = 0;
+	for(int i=1;i<len;i++){
+		ll range = (_high[i-1] - _low[i-1] + 1);
+		ll nxt = (((value - _low[i-1]) + 1) * len - 1) / range;
+
+		int symbol;
+		for(symbol = 1; lower[symbol] <= nxt; symbol++);
+		
+		_low[i] = _low[i-1] + (range * lower[symbol-1]) / len;
+		_high[i] = _low[i-1] + (range * lower[symbol]) / len - 1;
+
+		if(symbol == 256)
+			break;
+
+		rgb_image[itr++] = symbol;
+
+		for(;;){
+			if(_high[i] >= HALF){
+				if(_low[i] >= HALF){
+					value -= HALF;
+					_low[i] -= HALF;
+					_high[i] -= HALF;
+				}
+				else if (_low[i] >= ONE_QTR && _high[i] < THREE_QTR)
+				{
+					value -= ONE_QTR;
+					_low[i] -= ONE_QTR;
+					_high[i] -= ONE_QTR;
+				}
+				else
+				{
+					break;
+				}
+			}
+			_low[i] = 2 * _low[i];
+			_high[i] = 2 * _high[i] + 1;
+			value = add_bit(2 * value, count_taken, flag, code);
+			count_taken++;
+		}
+	}
+
+	stbi_write_png("ac_image.png", width, height, num_channel, rgb_image, width*num_channel);
+
+}

arithmetic_encode_image.cpp

@@ -0,0 +1,170 @@
+#include <bits/stdc++.h>
+using namespace std;
+#define ll long long
+#define STB_IMAGE_IMPLEMENTATION
+#include "stb_image.h"
+
+const ll MIN = 0;
+const ll MAX = 65535;
+
+ll lower[257];
+vector <ll> low, high;
+
+string write_bits(bool bit, int bit_to_fall){
+	string tmp;
+	tmp += to_string(bit);
+	while(bit_to_fall){
+		tmp += to_string(!bit);
+		bit_to_fall -= 1;
+	}
+	return tmp;
+}
+
+int to_int(int _pos, string &encode){
+	int n = 0;
+	for (int i = _pos; i < sizeof(short) * 8 + _pos; i++)
+	{
+		n <<= 1;
+		n |= encode[i] - '0';
+	}
+	return n;
+}
+
+ll add_bit(ll value, int count_taken, bool &flag, string &encode){
+	bitset<16> a(value);
+
+	if(flag == 1){
+		a.reset(0);
+	}
+	else if(count_taken > encode.length()){
+		a.set(0);
+		flag = 1;
+	}
+	else if(encode[count_taken] == '1'){
+		a.set(0);
+	}
+	else if(encode[count_taken] == '0'){
+		a.reset(0);
+	}
+
+	value = (ll)(a.to_ulong());
+	return value;
+}
+
+ofstream out("arithmetic_encoded.txt");
+
+string image_pixels = "";
+string code = "";
+
+int main(int argc, char** argv)
+{
+
+	int width, height, bpp, num_channel = 1;
+
+
+	if (argc>2)
+	{
+		cout<<"Error: Too many arguments\n";
+		return 0;
+	}
+	if (argc==2)
+	{
+		if (string(argv[1])!="grey" && string(argv[1])!="rgb")
+		{
+			cout<<"Error: Invalid Argument\n";
+			return 0;
+		}
+		if (string(argv[1]) == "rgb")
+			num_channel = 3;
+	}
+	
+	// string filename;
+	// cin>>filename;
+
+	uint8_t* rgb_image = stbi_load("./images/2.bmp", &width, &height, &bpp, num_channel);
+
+	const ll ONE_QTR = MAX / 4 + 1;
+	const ll HALF = 2 * ONE_QTR;
+	const ll THREE_QTR = 3 * ONE_QTR;
+
+	int len = height*width*num_channel + 1;
+	cout<<height<<" "<<width<<" "<<num_channel<<"\n";
+	cout<<len<<"\n";
+
+	low.resize(len);
+	high.resize(len);
+	
+	low[0] = MIN;
+	high[0] = MAX;
+	
+	int current = 1;
+	int i = 0;
+	
+	int itr = 0;
+	for (int i = 0; i < height; ++i)
+		for (int j = 0; j < width; ++j)
+			for(int k = 0; k < num_channel; ++k){
+				if (int(rgb_image[itr])==0)
+					rgb_image[itr] = char(1);
+				lower[int(rgb_image[itr++])] += 1;
+			}
+
+	lower[256] = 1;
+
+	for(int i=1; i<=256; i++){
+		lower[i] += lower[i-1];
+	}
+
+	int bit_to_fall = 0;
+
+	while(i < len){
+		if(i == len-1)	current = 256;
+		else current = rgb_image[i];
+		i += 1;
+
+		ll range = high[i-1] - low[i-1] + 1;
+		low[i] = low[i-1] + (range * lower[current-1]) / len;
+		high[i] = low[i-1] + (range * lower[current]) / len - 1;
+
+		while(true){
+			if(high[i] < HALF){
+				code += write_bits(0, bit_to_fall);
+				bit_to_fall = 0;
+			}
+			else if(low[i] >= HALF){
+				code += write_bits(1, bit_to_fall);
+				bit_to_fall = 0;
+				low[i] -= HALF;
+				high[i] -= HALF;
+			}
+			else if(low[i] >= ONE_QTR and high[i] < THREE_QTR){
+				bit_to_fall += 1;
+				low[i] -= ONE_QTR;
+				high[i] -= ONE_QTR;
+			}
+			else
+				break;
+			low[i] = 2 * low[i];
+			high[i] = 2 * high[i] + 1;
+		}
+	}
+
+	ll p = low[i-1];
+
+	for(int j=15; j>=0; j--){
+		if((p & (1LL<<j)))	code += '1';
+		else code += '0';
+	}
+
+	out << len << " ";
+
+	for(int i=0; i<=256; i++)
+		out << lower[i] << " ";
+
+	out << code << "\n";
+
+	cout<<code.size()<<"\n";
+	
+	out << height << " " << width << " " << num_channel << "\n";	
+
+}