[IOS]获取某一点的RGB值
unsignedchar pixel[4] = {0};
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef context = CGBitmapContextCreate(pixel, 1, 1, 8, 4, colorSpace, kCGBitmapAlphaInfoMask & kCGImageAlphaPremultipliedLast);
CGContextTranslateCTM(context, 0, 0);
[self.layerrenderInContext:context];
CGContextRelease(context);
CGColorSpaceRelease(colorSpace);
