-(id) initWithImage: (UIImage*) image //create BitmapContext with UIImage and use 'pixelData' as the pointer
{
CGContextRef context = NULL;
CGColorSpaceRef colorSpace;
int bitmapByteCount;
int bitmapBytesPerRow;
bitmapBytesPerRow = (image.size.width * 4);
bitmapByteCount = (bitmapBytesPerRow * image.size.height);
colorSpace = CGColorSpaceCreateDeviceRGB();
pixelData = malloc( bitmapByteCount ); //unsigned char* pixelData is defined in head file
context = CGBitmapContextCreate (pixelData,
image.size.width,
image.size.height,
8, // bits per component
bitmapBytesPerRow,
colorSpace,
kCGImageAlphaPremultipliedFirst
);
CGColorSpaceRelease( colorSpace );
CGContextDrawImage(context, CGRectMake(0, 0, image.size.width, image.size.height), image.CGImage);
pixelData = CGBitmapContextGetData(context);
return self;
}
-(float) alphaAtX:(int)x y:(int)y //get alpha component using the pointer 'pixelData'
{
return pixelData[(y *width + x) *4 + 3]; //+0 for red, +1 for green, +2 for blue, +3 for alpha
}
-(void)viewDidLoad { [super viewDidLoad]; //加载图片 UIImage *img = [UIImage imageNamed:@"MacDrive.png"]; }
[self initWithImage:img]; //create BitmapContext with UIImage
float alpha = [self alphaAtX:20 y:20]; //store alpha component
当我尝试存储红/绿/蓝色时,它们总是变成240。而alpha始终为255。
所以我认为指针可能有问题。它无法返回我想要的正确ARGB数据。对于代码有什么错误的想法吗?