Puts quantization in another namespace and adds non-linear quantization out of the box.

wavelet/jcmp.cpp

@@ -7,40 +7,29 @@
 #include "jcmp.hpp"
 #include "wavelet.hpp"
 
-using namespace wvlt::V2;
-
-// Can be any functions from R+ -> R
-// as long as backward is its inverse
-static double forward(double x){
-	//return std::log(1 + std::log(1 + x));
-	return std::log(x);
-}
-
-static double backward(double x){
-	//return std::exp(std::exp(x) - 1) - 1;
-	return std::exp(x);
-}
+using namespace wvlt;
+using namespace jcmp;
 
 // note: we take a copy, because we will modify it in place
-static jcmp::image compress(std::vector<double> image, jcmp::uint width, double threshold, unsigned int& nzeros){
-	jcmp::uint height = image.size() / width;
+static image compress(std::vector<double> img, uint width, double threshold, unsigned int& nzeros){
+	uint height = img.size() / width;
 	assert(is_pow_of_two(width));
 	assert(is_pow_of_two(height));
 
 	// wavelet transform in x-direction
 	for(unsigned int i = 0; i < height; ++i){
-		wavelet(&image[i*width], width, 1);
+		wavelet(&img[i*width], width, 1);
 	}
 
 	// wavelet transform in y-direction
 	for(unsigned int i = 0; i < width; ++i){
-		wavelet(&image[i], height, width);
+		wavelet(&img[i], height, width);
 	}
 
 	double min_abs = 10000.0;
 	double max_abs = 0.0;
 
-	for(auto& el : image){
+	for(auto& el : img){
 		auto absel = std::abs(el);
 		if(absel > threshold) {
 			min_abs = std::min(min_abs, absel);
@@ -50,28 +39,28 @@ static jcmp::image compress(std::vector<double> image, jcmp::uint width, double
 		}
 	}
 
-	jcmp::quantization q(&forward, &backward, max_abs, min_abs);
+	auto q = quantization::get(quantization::type::logarithmic, max_abs, min_abs);
 
 	// save the principal coefficients
 	std::vector<jcmp::coefficient> v;
 	for(unsigned int y = 0; y < height; ++y){
 		for(unsigned int x = 0; x < width; ++x){
-			auto&& el = image[x + width*y];
-			if(el != 0) v.push_back({q.forwards(el), jcmp::uint(x), jcmp::uint(y)});
+			auto&& el = img[x + width*y];
+			if(el != 0) v.push_back({q.forwards(el), uint(x), uint(y)});
 		}
 	}
 
 	nzeros = v.size();
-	return jcmp::image(width, height, q.p, std::move(v));
+	return image(width, height, q.p, std::move(v));
 }
 
-static std::vector<double> decompress(jcmp::image in){
+static std::vector<double> decompress(image in){
 	auto width = in.header.width;
 	auto height = in.header.height;
 	assert(is_pow_of_two(width));
 	assert(is_pow_of_two(height));
 
-	auto q = in.header.get_quantization(&forward, &backward);
+	auto q = in.header.get_quantization(quantization::type::logarithmic);
 
 	std::vector<double> image(width * height, 0.0);
 
@@ -120,7 +109,7 @@ int main(){
 
 		// compress and decompress to see how we lost information
 		unsigned int nzeros = 0;
-		auto compressed_vec = decompress(compress(image_vec, width, 0.1, nzeros));
+		auto compressed_vec = decompress(compress(image_vec, width, 0.5, nzeros));
 
 		// output some information
 		std::cout << field("raw") << human_string(sizeof(uint8_t) * image_vec.size(), "b") << std::endl;

wavelet/jcmp_image.hpp

@@ -13,10 +13,10 @@ namespace jcmp {
 		uint width;
 		uint height;
 		uint length;
-		quantize_params qp;
+		quantization::parameters qp;
 
 		header() = default;
-		header(uint width_, uint height_, uint length_, quantize_params const & p)
+		header(uint width_, uint height_, uint length_, quantization::parameters const & p)
 		: signature{'J', 'C', 'M', 'P'}
 		, width(width_)
 		, height(height_)
@@ -24,13 +24,8 @@ namespace jcmp {
 		, qp(p)
 		{}
 
-		template <typename F>
-		quantization get_quantization(F const & f, F const & f_inv){
-			quantization q;
-			q.p = qp;
-			q.f = f;
-			q.f_inv = f_inv;
-			return q;
+		quantization::base get_quantization(quantization::type t){
+			return quantization::get(t, qp.f_max_abs, qp.f_min_abs, false);
 		}
 	};
 
@@ -46,7 +41,7 @@ namespace jcmp {
 
 		image() = default;
 
-		image(uint width, uint height, quantize_params const & p, std::vector<coefficient> const & data_in)
+		image(uint width, uint height, quantization::parameters const & p, std::vector<coefficient> const & data_in)
 		: header(width, height, data_in.size(), p)
 		, data(data_in)
 		{}

wavelet/jcmp_quantization.hpp

@@ -1,6 +1,12 @@
 #pragma once
 
+#include <functional>
+
 namespace jcmp {
+	// Will quantize a double such that it fits in a uint8_t
+	// Also support non-linear quantization (which is usefull
+	// when the data is non-uniformly distributed)
+	namespace quantization {
 		// input in [0, 1], output [0, 255]
 		inline uint8_t clamp_round(double x){
 			if(x <= 0.0) return 0;
@@ -10,25 +16,19 @@ namespace jcmp {
 
 		// parameters which need to be stored in the file
 		// to be able to dequantize
-	struct quantize_params {
+		// TODO: add type of quantization
+		struct parameters {
 			double f_max_abs;
 			double f_min_abs;
 		};
 
-	// Quantization may be non linear (given by f and f_inv)
-	struct quantization {
+		// the basic struct doing the quantization
+		struct base {
+			// f needs to be of type R+ -> R
+			// and F-inv should be its inverse
 			std::function<double(double)> f;
 			std::function<double(double)> f_inv;
-		quantize_params p;
-
-		quantization() = default;
-
-		template <typename F>
-		quantization(F const & f_, F const & f_inv_, double max_abs, double min_abs)
-		: f(f_)
-		, f_inv(f_inv_)
-		, p{f(max_abs), f(min_abs)}
-		{}
+			parameters p;
 
 			uint8_t forwards(double x){
 				double y = std::abs(x);
@@ -45,5 +45,47 @@ namespace jcmp {
 			}
 		};
 
-	static_assert(sizeof(quantize_params) == 16, "struct not propery packed");
+		// kinds of quantization which come out of the
+		// box with get(...)
+		enum class type {
+			linear,
+			logarithmic,
+			square_root
+		};
+
+		// non-overloaded versions
+		double id(double x) { return x; }
+		double log(double x) { return std::log(x); }
+		double exp(double x) { return std::exp(x); }
+		double sqrt(double x) { return std::sqrt(x); }
+		double sqr(double x) { return x*x; }
+
+		base get(type t, double max_abs, double min_abs, bool apply = true){
+			base b;
+			switch (t) {
+				case type::linear:
+					b.f = &id;
+					b.f_inv = &id;
+					break;
+				case type::logarithmic:
+					b.f = &log;
+					b.f_inv = &exp;
+					break;
+				case type::square_root:
+					b.f = &sqrt;
+					b.f_inv = &sqr;
+					break;
+			}
+			if(apply){
+				b.p.f_max_abs = b.f(max_abs);
+				b.p.f_min_abs = b.f(min_abs);
+			} else {
+				b.p.f_max_abs = max_abs;
+				b.p.f_min_abs = min_abs;
+			}
+			return b;
+		}
+
+		static_assert(sizeof(parameters) == 16, "struct not propery packed");
+	}
 }