如何旋转CGImageRef？

Question

我有一个UIImage，当我的iPad保持纵向显示时，它看起来是正确的方式，但是当我得到CGImageRef与之关联时，CGImageRef逆时针旋转90度。谷歌搜索后，我知道这是因为CGImageRef没有方向数据，不像UIImage。我需要查看和修改一些像素在CGImageRef，目前我在做这个通过直接访问RAWDATA变量（图像是一个UIImage *）：

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，为了让我正常修改rawData中存储的像素数据，我需要CGImageRef处于正确的方向。如何顺时针旋转CGImageRef 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);