Write more efficient dithered pngs using palettes
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2 changed files with 134 additions and 15 deletions
143
src/image.cc
143
src/image.cc
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@ -1,23 +1,49 @@
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#include "image.h"
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#include <array>
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#include <cassert>
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#include <cmath>
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#include <cstdio>
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#include <ctime>
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#include <fstream>
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#include <iostream>
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#include <png.h>
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const char *Image::opencl_grayscale_kernel_ = nullptr;
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const char *Image::opencl_color_kernel_ = nullptr;
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Image::Image() : data_(), width_(0), height_(0), is_grayscale_(true) {}
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const std::array<png_color, 2> Image::dither_bw_palette_ = {
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png_color{0, 0, 0}, // black
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png_color{255, 255, 255} // white
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};
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const std::array<png_color, 8> Image::dither_color_palette_ = {
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png_color{0, 0, 0}, // black
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png_color{255, 255, 255}, // white
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png_color{255, 0, 0}, // red
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png_color{0, 255, 0}, // green
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png_color{0, 0, 255}, // blue
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png_color{255, 255, 0}, // yellow
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png_color{255, 0, 255}, // magenta
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png_color{0, 255, 255}, // cyan
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};
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Image::Image()
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: data_(),
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width_(0),
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height_(0),
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is_grayscale_(true),
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is_dithered_grayscale_(false),
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is_dithered_color_(false) {}
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Image::Image(const char *filename) : Image(std::string(filename)) {}
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Image::Image(const std::string &filename)
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: data_(), width_(0), height_(0), is_grayscale_(true) {
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: data_(),
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width_(0),
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height_(0),
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is_grayscale_(true),
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is_dithered_grayscale_(false),
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is_dithered_color_(false) {
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if (filename.compare(filename.size() - 4, filename.size(), ".png") == 0) {
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// filename expected to be .png
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std::cout << "INFO: PNG filename extension detected, decoding..."
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@ -115,24 +141,109 @@ bool Image::SaveAsPNG(const std::string &filename, bool overwrite) {
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// set image information
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if (is_grayscale_) {
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png_set_IHDR(png_ptr, png_info_ptr, width_, height_, 8, PNG_COLOR_TYPE_GRAY,
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PNG_INTERLACE_NONE, PNG_COMPRESSION_TYPE_DEFAULT,
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PNG_FILTER_TYPE_DEFAULT);
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if (is_dithered_grayscale_) {
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png_set_IHDR(png_ptr, png_info_ptr, width_, height_, 1,
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PNG_COLOR_TYPE_PALETTE, PNG_INTERLACE_NONE,
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PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
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png_set_PLTE(png_ptr, png_info_ptr, dither_bw_palette_.data(),
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dither_bw_palette_.size());
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} else {
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png_set_IHDR(png_ptr, png_info_ptr, width_, height_, 8,
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PNG_COLOR_TYPE_GRAY, PNG_INTERLACE_NONE,
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PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
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}
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} else {
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png_set_IHDR(png_ptr, png_info_ptr, width_, height_, 8,
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PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
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PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
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if (is_dithered_color_) {
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png_set_IHDR(png_ptr, png_info_ptr, width_, height_, 4,
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PNG_COLOR_TYPE_PALETTE, PNG_INTERLACE_NONE,
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PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
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png_set_PLTE(png_ptr, png_info_ptr, dither_color_palette_.data(),
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dither_color_palette_.size());
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} else {
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png_set_IHDR(png_ptr, png_info_ptr, width_, height_, 8,
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PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
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PNG_COMPRESSION_TYPE_DEFAULT, PNG_FILTER_TYPE_DEFAULT);
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}
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}
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// write png info
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png_write_info(png_ptr, png_info_ptr);
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// write rows of image data
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for (unsigned int y = 0; y < height_; ++y) {
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if (is_grayscale_) {
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png_write_row(png_ptr, &data_.at(y * width_));
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} else {
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png_write_row(png_ptr, &data_.at(y * width_ * 4));
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if (is_dithered_grayscale_) {
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// using 1-bit palette in 1-bit color depth
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std::vector<unsigned char> row;
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unsigned char temp;
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unsigned int bidx;
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for (unsigned int y = 0; y < height_; ++y) {
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row.clear();
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temp = 0;
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bidx = 0;
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for (unsigned int x = 0; x < width_; ++x) {
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if (data_.at(x + y * width_) != 0) {
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temp |= 0x80 >> bidx;
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}
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++bidx;
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if (bidx >= 8) {
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row.push_back(temp);
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temp = 0;
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bidx = 0;
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}
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}
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row.push_back(temp);
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png_write_row(png_ptr, row.data());
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}
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} else if (is_dithered_color_) {
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// using 3-bit palette in 4-bit color depth
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std::vector<unsigned char> row;
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unsigned char temp;
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unsigned int bidx;
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unsigned char red, green, blue;
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for (unsigned int y = 0; y < height_; ++y) {
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row.clear();
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temp = 0;
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bidx = 0;
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for (unsigned int x = 0; x < width_; ++x) {
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red = data_.at(x * 4 + y * 4 * width_);
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green = data_.at(x * 4 + y * 4 * width_ + 1);
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blue = data_.at(x * 4 + y * 4 * width_ + 2);
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if (red == 0 && green == 0 && blue == 0) {
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// noop
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} else if (red != 0 && green != 0 && blue != 0) {
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temp |= 0x10 >> (bidx * 4);
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} else if (red != 0 && green == 0 && blue == 0) {
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temp |= 0x20 >> (bidx * 4);
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} else if (red == 0 && green != 0 && blue == 0) {
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temp |= 0x30 >> (bidx * 4);
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} else if (red == 0 && green == 0 && blue != 0) {
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temp |= 0x40 >> (bidx * 4);
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} else if (red != 0 && green != 0 && blue == 0) {
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temp |= 0x50 >> (bidx * 4);
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} else if (red != 0 && green == 0 && blue != 0) {
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temp |= 0x60 >> (bidx * 4);
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} else if (red == 0 && green != 0 && blue != 0) {
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temp |= 0x70 >> (bidx * 4);
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} else {
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assert(!"Unreachable");
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}
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++bidx;
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if (bidx >= 2) {
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bidx = 0;
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row.push_back(temp);
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temp = 0;
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}
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}
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row.push_back(temp);
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png_write_row(png_ptr, row.data());
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}
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} else {
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// using full 8-bit per-channel colors
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for (unsigned int y = 0; y < height_; ++y) {
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if (is_grayscale_) {
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png_write_row(png_ptr, &data_.at(y * width_));
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} else {
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png_write_row(png_ptr, &data_.at(y * width_ * 4));
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}
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}
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}
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@ -258,6 +369,7 @@ std::unique_ptr<Image> Image::ToGrayscaleDitheredWithBlueNoise(
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<< std::endl;
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return {};
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}
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grayscale_image->is_dithered_grayscale_ = true;
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auto opencl_handle = GetOpenCLHandle();
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if (!opencl_handle) {
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std::cout
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@ -594,6 +706,7 @@ std::unique_ptr<Image> Image::ToColorDitheredWithBlueNoise(Image *blue_noise) {
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std::unique_ptr<Image> result_image =
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std::unique_ptr<Image>(new Image(*this));
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result_image->is_dithered_color_ = true;
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if (!opencl_handle->GetBufferData(kid, output_buffer_id,
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result_image->GetSize(),
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@ -6,6 +6,8 @@
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#include <string>
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#include <vector>
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#include <png.h>
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#include "opencl_handle.h"
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class Image {
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@ -128,12 +130,16 @@ class Image {
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private:
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static const char *opencl_grayscale_kernel_;
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static const char *opencl_color_kernel_;
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static const std::array<png_color, 2> dither_bw_palette_;
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static const std::array<png_color, 8> dither_color_palette_;
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OpenCLHandle::Ptr opencl_handle_;
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/// Internally holds rgba
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std::vector<uint8_t> data_;
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unsigned int width_;
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unsigned int height_;
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bool is_grayscale_;
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bool is_dithered_grayscale_;
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bool is_dithered_color_;
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void DecodePNG(const std::string &filename);
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void DecodePGM(const std::string &filename);
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