Get pixels value from png file. which is right & why? - ios

Question

I need pixel value from png file. so I searched SO and got two methods as follows:
Method 1
- (void)GeneratePixelArray {
UIImage *cImage = [UIImage imageNamed:#"ball.png"];
int width = (int)cImage.size.width;
int height = (int)cImage.size.height;
unsigned char *cMap = (unsigned char *)malloc(width * height);
memset(cMap, 0, width * height);
CFDataRef imageData = CGDataProviderCopyData(CGImageGetDataProvider(cImage.CGImage));
const UInt32 *pixels = (const UInt32*)CFDataGetBytePtr(imageData);
//0xff 0x00 is guard for this demo
for (int j = 0; j < (width * height); j++)
{
printf("0x%x\n", (unsigned int)pixels[j]);
}
CFRelease(imageData);
}
Method 2
- (void *)GeneratePixelArray//: (UIImage *) image
{
UIImage *cImage = [[UIImage alloc] imageNamed:#"ball.png"];
//UIImage *cImage = [UIImage imageNamed:#"ball.png"];
int pixelsWidth = (int)cImage.size.width;
int pixelsHeight = (int)cImage.size.height;
CGRect rect = {{0,0}, {pixelsWidth, pixelsHeight}};
// Use RCG color space without Alpha, just RGB
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
if(colorSpace == NULL)
{
NSLog(#"Error allocating color space! \n");
return NULL;
}
unsigned int bitmapBytesPerRow = pixelsWidth*4;
unsigned int bitmapByteCount = bitmapBytesPerRow*pixelsHeight;
void * bitmapData = malloc(bitmapByteCount);
if (bitmapData == NULL) {
NSLog(#"Memory not allocated!\n");
CGColorSpaceRelease(colorSpace);
return NULL;
}
// create bitmap context ,8 bits per component
CGContextRef context = CGBitmapContextCreate(bitmapData,
pixelsWidth,
pixelsHeight,
8,//bits per component
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedLast);
// Make sure release colorspace before returning
CGColorSpaceRelease(colorSpace);
if (context == NULL)
{
free(bitmapData);
NSLog(#"Context not be created!");
return NULL;
}
// Draw the image to the bitmap context
CGContextDrawImage(context, rect, cImage.CGImage);
// Now we can get a pointer to the image data associated with context
unsigned char *bitsData;
bitsData = CGBitmapContextGetData(context);
if (!bitsData)
{
NSLog(#"Failed");
return;
}
void *data = CGBitmapContextGetData(context);
unsigned char* bitmapData2 = malloc(bitmapByteCount);
if (bitmapData2 == NULL)
{
NSLog(#"Memory not be allocated!\n");
return NULL;
}
unsigned char* rcdata = (unsigned char *)data;
unsigned char* wcdata = bitmapData2;
// remove ARGB's fourth value, it is Alpha
for (int i = 0; i < bitmapByteCount / 4; ++i, rcdata += 4)
{
printf("%x\n", (unsigned int)*(unsigned int*)rcdata);
*(wcdata + 0) = *(rcdata + 0);
*(wcdata + 1) = *(rcdata + 1);
*(wcdata + 2) = *(rcdata + 2);
*(wcdata + 3) = *(rcdata + 3);
if (*(wcdata+3)<20) {
printf("alpha...\n");
}
// if ( (*(wcdata + 0)==255) &&(*(wcdata + 1)==0) && (*(wcdata + 2)==0) ) {
// printf("red\n");
// }
wcdata += 4;// skip alpha
}
CGContextRelease(context);
return bitsData;
}
I logged output using:
printf("%x\n", (unsigned int)*(unsigned int*)rcdata);
Method 1 and Method 2 logs differ! Why? I am confused.
Thanks a lot!