我需要计算UIImage中所有黑色像素的数量。我找到了一段可能能用的代码，但是它是用Objective-C编写的。我尝试将其转换为Swift，但是出现了许多错误，我找不到解决方法。
使用Swift做这件事的最佳方法是什么？
简单图像
Objective-C:
/**
* Structure to keep one pixel in RRRRRRRRGGGGGGGGBBBBBBBBAAAAAAAA format
*/
struct pixel {
unsigned char r, g, b, a;
};
/**
* Process the image and return the number of pure red pixels in it.
*/
- (NSUInteger) processImage: (UIImage*) image
{
NSUInteger numberOfRedPixels = 0;
// Allocate a buffer big enough to hold all the pixels
struct pixel* pixels = (struct pixel*) calloc(1, image.size.width * image.size.height * sizeof(struct pixel));
if (pixels != nil)
{
// Create a new bitmap
CGContextRef context = CGBitmapContextCreate(
(void*) pixels,
image.size.width,
image.size.height,
8,
image.size.width * 4,
CGImageGetColorSpace(image.CGImage),
kCGImageAlphaPremultipliedLast
);
if (context != NULL)
{
// Draw the image in the bitmap
CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), image.CGImage);
// Now that we have the image drawn in our own buffer, we can loop over the pixels to
// process it. This simple case simply counts all pixels that have a pure red component.
// There are probably more efficient and interesting ways to do this. But the important
// part is that the pixels buffer can be read directly.
NSUInteger numberOfPixels = image.size.width * image.size.height;
while (numberOfPixels > 0) {
if (pixels->r == 255) {
numberOfRedPixels++;
}
pixels++;
numberOfPixels--;
}
CGContextRelease(context);
}
free(pixels);
}
return numberOfRedPixels;
}