c - 如何在C上使用libpng编写调色板图像？

Question

如何在C上使用libpng编写调色板图像？我的代码:

FILE *fp = fopen(file_name, "wb");
png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
info_ptr = png_create_info_struct(png_ptr);
png_init_io(png_ptr, fp);
png_set_strip_alpha(png_ptr);
png_read_update_info(png_ptr, info_ptr);

png_set_IHDR(png_ptr, info_ptr, width, height,
         8, PNG_COLOR_TYPE_PALETTE, PNG_INTERLACE_NONE,
         PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);


png_set_PLTE(png_ptr, info_ptr, palette, num_palette);
png_write_info(png_ptr, info_ptr);
png_write_image(png_ptr, row_pointers);
png_write_end(png_ptr, NULL);

fclose(fp);

我的结果:

http://rghost.ru/35558350/image.png

Answer 1

这是我今天为此编写的一些代码的缩写:

unsigned paletteSize = ...;

assert(paletteSize <= PNG_MAX_PALETTE_LENGTH);

png_color* palette = (png_color*)png_malloc(png_ptr, paletteSize*sizeof(png_color));

for (unsigned p = 0; p < paletteSize; p++)
{
  png_color* col = &palette[p];
  col->red = ...;
  col->green = ...;
  col->blue = ...;
}

png_set_PLTE(png_ptr, info_ptr, palette, paletteSize);

png_write_info(png_ptr, info_ptr);

// ... png_write_image, png_write_end

png_free(png_ptr, palette);


png_destroy_write_struct(&png_ptr, &info_ptr);