void save_as_png256(T1 & file, T2 const& image, const unsigned max_colors = 256, int trans_mode = -1)
{
// number of alpha ranges in png256 format; 2 results in smallest image with binary transparency
// 3 is minimum for semitransparency, 4 is recommended, anything else is worse
const unsigned TRANSPARENCY_LEVELS = (trans_mode==2||trans_mode<0)?MAX_OCTREE_LEVELS:2;
unsigned width = image.width();
unsigned height = image.height();
unsigned alphaHist[256];//transparency histogram
unsigned semiCount = 0;//sum of semitransparent pixels
unsigned meanAlpha = 0;
for(int i=0; i<256; i++){
alphaHist[i] = 0;
}
for (unsigned y = 0; y < height; ++y){
for (unsigned x = 0; x < width; ++x){
unsigned val = U2ALPHA((unsigned)image.getRow(y)[x]);
if (trans_mode==0)
val=255;
alphaHist[val]++;
meanAlpha += val;
if (val>0 && val<255)
semiCount++;
}
}
meanAlpha /= width*height;
// transparency ranges division points
unsigned limits[MAX_OCTREE_LEVELS+1];
limits[0] = 0;
limits[1] = (alphaHist[0]>0)?1:0;
limits[TRANSPARENCY_LEVELS] = 256;
unsigned alphaHistSum = 0;
for(unsigned j=1; j<TRANSPARENCY_LEVELS; j++)
limits[j] = limits[1];
for(unsigned i=1; i<256; i++){
alphaHistSum += alphaHist[i];
for(unsigned j=1; j<TRANSPARENCY_LEVELS; j++){
if (alphaHistSum<semiCount*(j)/4)
limits[j] = i;
}
}
// avoid too wide full transparent range
if (limits[1]>256/(TRANSPARENCY_LEVELS-1))
limits[1]=256/(TRANSPARENCY_LEVELS-1);
// avoid too wide full opaque range
if (limits[TRANSPARENCY_LEVELS-1]<212)
limits[TRANSPARENCY_LEVELS-1]=212;
if (TRANSPARENCY_LEVELS==2) {
limits[1]=127;
}
// estimated number of colors from palette assigned to chosen ranges
unsigned cols[MAX_OCTREE_LEVELS];
// count colors
for(unsigned j=1; j<=TRANSPARENCY_LEVELS; j++) {
cols[j-1] = 0;
for(unsigned i=limits[j-1]; i<limits[j]; i++){
cols[j-1] += alphaHist[i];
}
}
unsigned divCoef = width*height-cols[0];
if (divCoef==0) divCoef = 1;
cols[0] = cols[0]>0?1:0; // fully transparent color (one or not at all)
if (max_colors>=64) {
// give chance less populated but not empty cols to have at least few colors(12)
unsigned minCols = (12+1)*divCoef/(max_colors-cols[0]);
for(unsigned j=1; j<TRANSPARENCY_LEVELS; j++) if (cols[j]>12 && cols[j]<minCols) {
divCoef += minCols-cols[j];
cols[j] = minCols;
}
}
unsigned usedColors = cols[0];
for(unsigned j=1; j<TRANSPARENCY_LEVELS-1; j++){
cols[j] = cols[j]*(max_colors-cols[0])/divCoef;
usedColors += cols[j];
}
// use rest for most opaque group of pixels
cols[TRANSPARENCY_LEVELS-1] = max_colors-usedColors;
//no transparency
if (trans_mode == 0)
{
limits[1] = 0;
cols[0] = 0;
cols[1] = max_colors;
}
// octree table for separate alpha range with 1-based index (0 is fully transparent: no color)
octree<rgb> trees[MAX_OCTREE_LEVELS];
for(unsigned j=1; j<TRANSPARENCY_LEVELS; j++)
trees[j].setMaxColors(cols[j]);
for (unsigned y = 0; y < height; ++y)
{
typename T2::pixel_type const * row = image.getRow(y);
for (unsigned x = 0; x < width; ++x)
{
unsigned val = row[x];
// insert to proper tree based on alpha range
for(unsigned j=TRANSPARENCY_LEVELS-1; j>0; j--){
if (cols[j]>0 && U2ALPHA(val)>=limits[j]) {
trees[j].insert(mapnik::rgb(U2RED(val), U2GREEN(val), U2BLUE(val)));
break;
}
}
}
}
unsigned leftovers = 0;
std::vector<rgb> palette;
palette.reserve(max_colors);
if (cols[0])
palette.push_back(rgb(0,0,0));
for(unsigned j=1; j<TRANSPARENCY_LEVELS; j++) {
if (cols[j]>0) {
if (leftovers>0) {
cols[j] += leftovers;
trees[j].setMaxColors(cols[j]);
leftovers = 0;
}
std::vector<rgb> pal;
trees[j].setOffset(palette.size());
trees[j].create_palette(pal);
assert(pal.size() <= max_colors);
leftovers = cols[j]-pal.size();
cols[j] = pal.size();
for(unsigned i=0; i<pal.size(); i++){
palette.push_back(pal[i]);
}
assert(palette.size() <= 256);
}
}
//transparency values per palette index
std::vector<unsigned> alphaTable;
//alphaTable.resize(palette.size());//allow semitransparency also in almost opaque range
if (trans_mode != 0)
alphaTable.resize(palette.size() - cols[TRANSPARENCY_LEVELS-1]);
if (palette.size() > 16 )
{
// >16 && <=256 colors -> write 8-bit color depth
image_data_8 reduced_image(width,height);
reduce_8(image, reduced_image, trees, limits, TRANSPARENCY_LEVELS, alphaTable);
save_as_png(file,palette,reduced_image,width,height,8,alphaTable);
}
else if (palette.size() == 1)
{
// 1 color image -> write 1-bit color depth PNG
unsigned image_width = (int(0.125*width) + 7)&~7;
unsigned image_height = height;
image_data_8 reduced_image(image_width,image_height);
reduce_1(image,reduced_image,trees, limits, alphaTable);
if (meanAlpha<255 && cols[0]==0) {
alphaTable.resize(1);
alphaTable[0] = meanAlpha;
}
save_as_png(file,palette,reduced_image,width,height,1,alphaTable);
}
else
{
// <=16 colors -> write 4-bit color depth PNG
unsigned image_width = (int(0.5*width) + 3)&~3;
unsigned image_height = height;
image_data_8 reduced_image(image_width,image_height);
reduce_4(image, reduced_image, trees, limits, TRANSPARENCY_LEVELS, alphaTable);
save_as_png(file,palette,reduced_image,width,height,4,alphaTable);
}
}
void save_as_png(T1 & file,
T2 const& image,
png_options const& opts)
{
if (opts.use_miniz)
{
MiniZ::PNGWriter writer(opts.compression,opts.strategy);
if (opts.trans_mode == 0)
{
writer.writeIHDR(image.width(), image.height(), 24);
writer.writeIDATStripAlpha(image);
}
else
{
writer.writeIHDR(image.width(), image.height(), 32);
writer.writeIDAT(image);
}
writer.writeIEND();
writer.toStream(file);
return;
}
png_voidp error_ptr=0;
png_structp png_ptr=png_create_write_struct(PNG_LIBPNG_VER_STRING,
error_ptr,0, 0);
if (!png_ptr) return;
// switch on optimization only if supported
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200) && defined(PNG_MMX_CODE_SUPPORTED)
png_uint_32 mask, flags;
flags = png_get_asm_flags(png_ptr);
mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
png_set_asm_flags(png_ptr, flags | mask);
#endif
png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE, PNG_FILTER_NONE);
png_infop info_ptr = png_create_info_struct(png_ptr);
if (!info_ptr)
{
png_destroy_write_struct(&png_ptr,(png_infopp)0);
return;
}
jmp_buf* jmp_context = (jmp_buf*) png_get_error_ptr(png_ptr);
if (jmp_context)
{
png_destroy_write_struct(&png_ptr, &info_ptr);
return;
}
png_set_write_fn (png_ptr, &file, &write_data<T1>, &flush_data<T1>);
png_set_compression_level(png_ptr, opts.compression);
png_set_compression_strategy(png_ptr, opts.strategy);
png_set_compression_buffer_size(png_ptr, 32768);
png_set_IHDR(png_ptr, info_ptr,image.width(),image.height(),8,
(opts.trans_mode == 0) ? PNG_COLOR_TYPE_RGB : PNG_COLOR_TYPE_RGB_ALPHA,PNG_INTERLACE_NONE,
PNG_COMPRESSION_TYPE_DEFAULT,PNG_FILTER_TYPE_DEFAULT);
const std::unique_ptr<png_bytep[]> row_pointers(new png_bytep[image.height()]);
for (unsigned int i = 0; i < image.height(); i++)
{
row_pointers[i] = (png_bytep)image.getRow(i);
}
png_set_rows(png_ptr, info_ptr, row_pointers.get());
png_write_png(png_ptr, info_ptr, (opts.trans_mode == 0) ? PNG_TRANSFORM_STRIP_FILLER_AFTER : PNG_TRANSFORM_IDENTITY, nullptr);
png_destroy_write_struct(&png_ptr, &info_ptr);
}
