如何旋转CGImageRef？

Question

我有一台UIImage，当我的iPad处于纵向时，它的方向看起来是正确的，但当我获得与它相关的CGImageRef时，CGImageRef逆时针旋转了90度。经过一些谷歌搜索，我了解到这是因为与UIImage不同，CGImageRef没有方向数据。我需要查看和修改图像中的一些像素，目前我正在通过直接访问rawData变量( CGImageRef是一个UIImage*)来执行此操作：

CGImageRef imageRef = [image CGImage];

CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB(); //maybe make ...Gray();
unsigned char *rawData = (unsigned char*) calloc(height * width * 4, sizeof(unsigned char));
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpaceRef, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);

CGContextDrawImage(context, CGRectMake(0, 0, width, height), imageRef);

但是，为了正确地修改存储在rawData中的像素数据，我需要CGImageRef处于正确的方向。如何将CGImageRef顺时针旋转90度，然后访问rawData (像素信息)？

Answer 1

试试这个：

CGImageRef imageRef = [sourceImage CGImage];
CGColorSpaceRef colorSpaceInfo = CGImageGetColorSpace(imageRef);


CGContextRef bitmap;

if (sourceImage.imageOrientation == UIImageOrientationUp || sourceImage.imageOrientation == UIImageOrientationDown) {
    bitmap = CGBitmapContextCreate(NULL, targetWidth, targetHeight, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

} else {
    bitmap = CGBitmapContextCreate(NULL, targetHeight, targetWidth, CGImageGetBitsPerComponent(imageRef), CGImageGetBytesPerRow(imageRef), colorSpaceInfo, bitmapInfo);

}   

if (sourceImage.imageOrientation == UIImageOrientationLeft) {
    CGContextRotateCTM (bitmap, radians(90));
    CGContextTranslateCTM (bitmap, 0, -targetHeight);

} else if (sourceImage.imageOrientation == UIImageOrientationRight) {
    CGContextRotateCTM (bitmap, radians(-90));
    CGContextTranslateCTM (bitmap, -targetWidth, 0);

} else if (sourceImage.imageOrientation == UIImageOrientationUp) {
    // NOTHING
} else if (sourceImage.imageOrientation == UIImageOrientationDown) {
    CGContextTranslateCTM (bitmap, targetWidth, targetHeight);
    CGContextRotateCTM (bitmap, radians(-180.));
}

CGContextDrawImage(bitmap, CGRectMake(0, 0, targetWidth, targetHeight), imageRef);
CGImageRef ref = CGBitmapContextCreateImage(bitmap);