获取PNG图片的RGBA

http://www.cnblogs.com/mr-wid/archive/2013/04/19/3029842.html

先看这篇文章，关于pnglib的入门讲解

下面贴上源代码（在VC 6.0下编译通过）：

#include "stdafx.h"
#include <stdio.h>
#include "png.h"
#include <stdlib.h>


typedef struct {
    unsigned char* pixelData;
    int imageWidth;
    int imageHeight;
}ImageInfo; 


typedef struct {
    unsigned char* data;
    int size;
    int offset;
}ImageSource;


ImageInfo*  decodePNGFromFile(char* fileName)
{
    char png_header[8];
    png_structp png_ptr;
    png_infop info_ptr;
    int width, height, rowBytes;
    png_byte color_type; 
    png_byte bit_depth;
    png_colorp palette;


    /* open file and test for it being a png */
    FILE *file = fopen(fileName, "rb");
    fread(png_header, 1, 8, file);
    if(png_sig_cmp((png_bytep)png_header, 0, 8))
    {
        //TFC_DEBUG("Not a PNG file...");
        fclose(file);
    }
    /* initialise structures for reading a png file */
    png_ptr = png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
    info_ptr = png_create_info_struct(png_ptr);
    if (setjmp(png_jmpbuf(png_ptr)))
    {
        png_destroy_read_struct(&png_ptr, &info_ptr, 0);
        //TFC_DEBUG("ReadPngFile: Failed to read the PNG file");
        fclose(file);
    }
    //I/O initialisation methods
    png_init_io(png_ptr, file);
    png_set_sig_bytes(png_ptr, 8);  //Required!!!




    /* **************************************************
    * The high-level read interface in libpng (http://www.libpng.org/pub/png/libpng-1.2.5-manual.html)
    * **************************************************
    */
      png_read_png(png_ptr, info_ptr, PNG_TRANSFORM_EXPAND, 0);
      width = info_ptr->width;
      height = info_ptr->height;
      unsigned char* rgba = new unsigned char[width * height * 4];  //each pixel(RGBA) has 4 bytes
      png_bytep* row_pointers = png_get_rows(png_ptr, info_ptr);


      //Original PNG pixel data stored from top-left corner, BUT OGLES Texture drawing is from bottom-left corner
      //int pos = 0;
      //for(int row = 0; row < height; row++)
      //{
          //for(int col = 0; col < (4 * width); col += 4)
          //{
              //rgba[pos++] = row_pointers[row][col];    // red
              //rgba[pos++] = row_pointers[row][col + 1]; // green
              //rgba[pos++] = row_pointers[row][col + 2]; // blue
              //rgba[pos++] = row_pointers[row][col + 3]; // alpha
          //}
      //}




      //unlike store the pixel data from top-left corner, store them from bottom-left corner for OGLES Texture drawing...
      int pos = (width * height * 4) - (4 * width);
      for(int row = 0; row < height; row++)
      {
          for(int col = 0; col < (4 * width); col += 4)
          {
              rgba[pos++] = row_pointers[row][col];        // red
              rgba[pos++] = row_pointers[row][col + 1]; // green
              rgba[pos++] = row_pointers[row][col + 2]; // blue
              rgba[pos++] = row_pointers[row][col + 3]; // alpha
          }
          pos=(pos - (width * 4)*2); //move the pointer back two rows
      }


    ImageInfo* imageInfo = (ImageInfo*)malloc(sizeof(ImageInfo));
    imageInfo->pixelData = rgba;
    imageInfo->imageHeight = height;
    imageInfo->imageWidth = width;


    //clean up after the read, and free any memory allocated
    png_destroy_read_struct(&png_ptr, &info_ptr, NULL);
    fclose(file);
    return imageInfo;
}


int main(int argc,char* argv[]){
printf("start!\n");
ImageInfo* aaa;
aaa = decodePNGFromFile("test.png");
printf("imageInfo width:%d \n",aaa->imageWidth);
printf("imageInfo height:%d \n",aaa->imageHeight);
printf("imageInfo pixelData:%d \n",aaa->pixelData[0]);
printf("imageInfo pixelData:%d \n",aaa->pixelData[1]);
printf("imageInfo pixelData:%d \n",aaa->pixelData[2]);
printf("imageInfo pixelData:%d \n",aaa->pixelData[3]);


FILE *stream;
stream = fopen("test.txt","w+");

//这里i=3,i=i+4，因为我这里只需要用到alpha值，所以rgb被忽略掉
for(int i=3;i<aaa->imageWidth * aaa->imageHeight * 4;i=i+4){
printf("wade%d:%d \n",i,aaa->pixelData[i]);
fprintf(stream,"%d\n",aaa->pixelData[i]);
}


fclose(stream);


return 0;
}