libpng用法，读写PNG图像

//file:pngtest.c
//changed from the libpng,对照libpng中源码阅读
//myers
#include "png.h"
#include <stdio.h>
#include "zlib.h"
#include "png.h"
#include <stdlib.h>
#include <string.h>
#include <stdio.h>

int main(int argc,char* argv[])
{
    static png_FILE_p fpin;
      static png_FILE_p fpout;
    //输入文件名
    char *inname = "/home/mingming/graph/1.png";
    char *outname = "/home/mingming/graph/1_like.png";
    //读：
    png_structp read_ptr;
      png_infop read_info_ptr, end_info_ptr;
    //写
    png_structp write_ptr;
    png_infop write_info_ptr,write_end_info_ptr;
    //
    png_bytep row_buf;
    png_uint_32 y;
    int num_pass, pass;
    png_uint_32 width, height;//宽度，高度
    int bit_depth, color_type;//位深，颜色类型
    int interlace_type, compression_type, filter_type;//扫描方式，压缩方式，滤波方式
    //读
    row_buf = NULL;
    //打开读文件
    if ((fpin = fopen(inname, "rb")) == NULL)
    {
        fprintf(stderr,"Could not find input file %s\n", inname);
        return (1);
    }
    //打开写文件
    if ((fpout = fopen(outname, "wb")) == NULL)
    {
        printf("Could not open output file %s\n", outname);
        fclose(fpin);
        return (1);
    }
    //我们这里不处理未知的块unknown chunk
    //初始化1
    read_ptr =
              png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    write_ptr =
          png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    read_info_ptr = png_create_info_struct(read_ptr);
       end_info_ptr = png_create_info_struct(read_ptr);
    write_info_ptr = png_create_info_struct(write_ptr);
       write_end_info_ptr = png_create_info_struct(write_ptr);
    //初始化2
    png_init_io(read_ptr, fpin);
    png_init_io(write_ptr, fpout);
    //读文件有high level(高层）和low level两种，我们选择从底层具体信息中读取。
    //这里我们读取所有可选。
    png_read_info(read_ptr, read_info_ptr);    
    //（1）IHDR
      //读取图像宽度(width)，高度(height)，位深(bit_depth)，颜色类型(color_type)，压缩方法(compression_type)
    //滤波器方法(filter_type),隔行扫描方式(interlace_type)
    if (png_get_IHDR(read_ptr, read_info_ptr, &width, &height, &bit_depth,
      &color_type, &interlace_type, &compression_type, &filter_type))
    {
    //我们采用默认扫描方式
     png_set_IHDR(write_ptr, write_info_ptr, width, height, bit_depth,
        color_type, PNG_INTERLACE_NONE, compression_type, filter_type);
    }
    //（2）cHRM
    //读取白色度信息  白/红/绿/蓝 点的x,y坐标，这里采用整形，不采用浮点数
    png_fixed_point white_x, white_y, red_x, red_y, green_x, green_y, blue_x,blue_y;

    if (png_get_cHRM_fixed(read_ptr, read_info_ptr, &white_x, &white_y,
     &red_x, &red_y, &green_x, &green_y, &blue_x, &blue_y))
    {
     png_set_cHRM_fixed(write_ptr, write_info_ptr, white_x, white_y, red_x,
        red_y, green_x, green_y, blue_x, blue_y);
    }
        //（3）gAMA
      png_fixed_point gamma;

      if (png_get_gAMA_fixed(read_ptr, read_info_ptr, &gamma))
         png_set_gAMA_fixed(write_ptr, write_info_ptr, gamma);
        //（4）iCCP
    png_charp name;
    png_bytep profile;
    png_uint_32 proflen;

    if (png_get_iCCP(read_ptr, read_info_ptr, &name, &compression_type,
              &profile, &proflen))
    {
     png_set_iCCP(write_ptr, write_info_ptr, name, compression_type,
              profile, proflen);
    }
    //(5)sRGB
      int intent;
      if (png_get_sRGB(read_ptr, read_info_ptr, &intent))
         png_set_sRGB(write_ptr, write_info_ptr, intent);
    //(7)PLTE
      png_colorp palette;
      int num_palette;

      if (png_get_PLTE(read_ptr, read_info_ptr, &palette, &num_palette))
         png_set_PLTE(write_ptr, write_info_ptr, palette, num_palette);
    //(8)bKGD
      png_color_16p background;

      if (png_get_bKGD(read_ptr, read_info_ptr, &background))
      {
         png_set_bKGD(write_ptr, write_info_ptr, background);
      }
    //(9)hist
 
      png_uint_16p hist;

      if (png_get_hIST(read_ptr, read_info_ptr, &hist))
         png_set_hIST(write_ptr, write_info_ptr, hist);
       //(10)oFFs
      png_int_32 offset_x, offset_y;
      int unit_type;

      if (png_get_oFFs(read_ptr, read_info_ptr, &offset_x, &offset_y,
          &unit_type))
      {
         png_set_oFFs(write_ptr, write_info_ptr, offset_x, offset_y, unit_type);
      }
    //(11)pCAL
      png_charp purpose, units;
      png_charpp params;
      png_int_32 X0, X1;
      int type, nparams;

      if (png_get_pCAL(read_ptr, read_info_ptr, &purpose, &X0, &X1, &type,
         &nparams, &units, &params))
      {
         png_set_pCAL(write_ptr, write_info_ptr, purpose, X0, X1, type,
            nparams, units, params);
      }
       //(12)pHYs
   
      png_uint_32 res_x, res_y;

      if (png_get_pHYs(read_ptr, read_info_ptr, &res_x, &res_y, &unit_type))
         png_set_pHYs(write_ptr, write_info_ptr, res_x, res_y, unit_type);
   //(13)sBIT
      png_color_8p sig_bit;

      if (png_get_sBIT(read_ptr, read_info_ptr, &sig_bit))
         png_set_sBIT(write_ptr, write_info_ptr, sig_bit);
    //（14）sCAL
      int unit;
      png_charp scal_width, scal_height;

      if (png_get_sCAL_s(read_ptr, read_info_ptr, &unit, &scal_width,
          &scal_height))
      {
         png_set_sCAL_s(write_ptr, write_info_ptr, unit, scal_width,
             scal_height);
      }
        //(15)iTXt
      png_textp text_ptr;
      int num_text;

      if (png_get_text(read_ptr, read_info_ptr, &text_ptr, &num_text) > 0)
      {
         png_set_text(write_ptr, write_info_ptr, text_ptr, num_text);
      }
    //(16)tIME,这里我们不支持RFC1123
      png_timep mod_time;

      if (png_get_tIME(read_ptr, read_info_ptr, &mod_time))
      {
         png_set_tIME(write_ptr, write_info_ptr, mod_time);
      }
    //(17)tRNS
      png_bytep trans_alpha;
      int num_trans;
      png_color_16p trans_color;

      if (png_get_tRNS(read_ptr, read_info_ptr, &trans_alpha, &num_trans,
         &trans_color))
      {
         int sample_max = (1 << bit_depth);
         /* libpng doesn't reject a tRNS chunk with out-of-range samples */
         if (!((color_type == PNG_COLOR_TYPE_GRAY &&
             (int)trans_color->gray > sample_max) ||
             (color_type == PNG_COLOR_TYPE_RGB &&
             ((int)trans_color->red > sample_max ||
             (int)trans_color->green > sample_max ||
             (int)trans_color->blue > sample_max))))
            png_set_tRNS(write_ptr, write_info_ptr, trans_alpha, num_trans,
               trans_color);
      }
    
    //写进新的png文件中
    png_write_info(write_ptr, write_info_ptr);
    //读真正的图像数据
    num_pass = 1;
   for (pass = 0; pass < num_pass; pass++)
   {
      for (y = 0; y < height; y++)
      {
    //分配内存
         row_buf = (png_bytep)png_malloc(read_ptr,
            png_get_rowbytes(read_ptr, read_info_ptr));
    png_read_rows(read_ptr, (png_bytepp)&row_buf, NULL, 1);
    png_write_rows(write_ptr, (png_bytepp)&row_buf, 1);
         png_free(read_ptr, row_buf);
         row_buf = NULL;
      }
   }
    //结束
   png_read_end(read_ptr, end_info_ptr);
    //
    //tTXt
      if (png_get_text(read_ptr, end_info_ptr, &text_ptr, &num_text) > 0)
      {
         png_set_text(write_ptr, write_end_info_ptr, text_ptr, num_text);
      }
    //tIME
      if (png_get_tIME(read_ptr, end_info_ptr, &mod_time))
      {
         png_set_tIME(write_ptr, write_end_info_ptr, mod_time);
      }
    //
    png_write_end(write_ptr, write_end_info_ptr);
    //回收
    png_free(read_ptr, row_buf);
    row_buf = NULL;
    png_destroy_read_struct(&read_ptr, &read_info_ptr, &end_info_ptr);
    png_destroy_info_struct(write_ptr, &write_end_info_ptr);
    png_destroy_write_struct(&write_ptr, &write_info_ptr);
    //
   fclose(fpin);
   fclose(fpout);
    //测试，比较两个PNG文件是否相同
   if ((fpin = fopen(inname, "rb")) == NULL)
   {
      printf("Could not find file %s\n", inname);
      return (1);
   }

   if ((fpout = fopen(outname, "rb")) == NULL)
   {
      printf("Could not find file %s\n", outname);
      fclose(fpin);
      return (1);
   }
   char inbuf[256], outbuf[256];
   for (;;)
   {
      png_size_t num_in, num_out;

         num_in = fread(inbuf, 1, 1, fpin);
         num_out = fread(outbuf, 1, 1, fpout);

      if (num_in != num_out)
      {
         printf("\nFiles %s and %s 大小不同\n",
                 inname, outname);

         fclose(fpin);
         fclose(fpout);
         return (0);
      }

      if (!num_in)
         break;

      if (memcmp(inbuf, outbuf, num_in))
      {
         printf("\nFiles %s and %s 内容不同\n", inname, outname);
         fclose(fpin);
         fclose(fpout);
         return (0);
      }
   }

   fclose(fpin);
   fclose(fpout);

   return (0);

}