iPhoneカメラの画像をアップロード用にリサイズ（縮小・ダウンスケール、または回転）する

参考サイト

iPhoneのカメラで撮影した画像は、1,600 x 1,200とそのままアップロードするには大きいので、リサイズする方法を調べました。
まだ自分でもよくわかっていませんが、メモとして載せておきます。

画像のサイズを取得

- (void)imagePickerController:(UIImagePickerController *)picker didFinishPickingImage:(UIImage *)image editingInfo:(NSDictionary *)editingInfo {
    CGImageRef ref = image.CGImage;
    int width = CGImageGetWidth(ref);
    int height = CGImageGetHeight(ref);
    NSLog(@"image size = %d x %d", width, height);
    
    UIImage *orig = [editingInfo objectForKey:UIImagePickerControllerOriginalImage];
    ref = orig.CGImage;
    width = CGImageGetWidth(ref);
    height = CGImageGetHeight(ref);
    NSLog(@"orig image size = %d x %d", width, height);
 
    CGRect origRect;
    [[editingInfo objectForKey:UIImagePickerControllerCropRect] getValue:&origRect];
    
    NSLog(@"Crop rect = %f %f %f %f", origRect.origin.x, origRect.origin.y, origRect.size.width, origRect.size.height);
}

縮小と回転

kMaxResolutionの値を変えると、縮小率が変化します。
縦と横の長い方の値がkMaxResolutionの値になるように、縮小されます。
はてな touchでは400です。

UIImage *scaleAndRotateImage(UIImage *image)
{
	int kMaxResolution = 320; // Or whatever
	
	CGImageRef imgRef = image.CGImage;
	
	CGFloat width = CGImageGetWidth(imgRef);
	CGFloat height = CGImageGetHeight(imgRef);
	
	
	CGAffineTransform transform = CGAffineTransformIdentity;
	CGRect bounds = CGRectMake(0, 0, width, height);
	if (width > kMaxResolution || height > kMaxResolution) {
		CGFloat ratio = width/height;
		if (ratio > 1) {
			bounds.size.width = kMaxResolution;
			bounds.size.height = bounds.size.width / ratio;
		}
		else {
			bounds.size.height = kMaxResolution;
			bounds.size.width = bounds.size.height * ratio;
		}
	}
	
	CGFloat scaleRatio = bounds.size.width / width;
	CGSize imageSize = CGSizeMake(CGImageGetWidth(imgRef), CGImageGetHeight(imgRef));
	CGFloat boundHeight;
	UIImageOrientation orient = image.imageOrientation;
	switch(orient) {
			
		case UIImageOrientationUp: //EXIF = 1
			transform = CGAffineTransformIdentity;
			break;
			
		case UIImageOrientationUpMirrored: //EXIF = 2
			transform = CGAffineTransformMakeTranslation(imageSize.width, 0.0);
			transform = CGAffineTransformScale(transform, -1.0, 1.0);
			break;
			
		case UIImageOrientationDown: //EXIF = 3
			transform = CGAffineTransformMakeTranslation(imageSize.width, imageSize.height);
			transform = CGAffineTransformRotate(transform, M_PI);
			break;
			
		case UIImageOrientationDownMirrored: //EXIF = 4
			transform = CGAffineTransformMakeTranslation(0.0, imageSize.height);
			transform = CGAffineTransformScale(transform, 1.0, -1.0);
			break;
			
		case UIImageOrientationLeftMirrored: //EXIF = 5
			boundHeight = bounds.size.height;
			bounds.size.height = bounds.size.width;
			bounds.size.width = boundHeight;
			transform = CGAffineTransformMakeTranslation(imageSize.height, imageSize.width);
			transform = CGAffineTransformScale(transform, -1.0, 1.0);
			transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
			break;
			
		case UIImageOrientationLeft: //EXIF = 6
			boundHeight = bounds.size.height;
			bounds.size.height = bounds.size.width;
			bounds.size.width = boundHeight;
			transform = CGAffineTransformMakeTranslation(0.0, imageSize.width);
			transform = CGAffineTransformRotate(transform, 3.0 * M_PI / 2.0);
			break;
			
		case UIImageOrientationRightMirrored: //EXIF = 7
			boundHeight = bounds.size.height;
			bounds.size.height = bounds.size.width;
			bounds.size.width = boundHeight;
			transform = CGAffineTransformMakeScale(-1.0, 1.0);
			transform = CGAffineTransformRotate(transform, M_PI / 2.0);
			break;
			
		case UIImageOrientationRight: //EXIF = 8
			boundHeight = bounds.size.height;
			bounds.size.height = bounds.size.width;
			bounds.size.width = boundHeight;
			transform = CGAffineTransformMakeTranslation(imageSize.height, 0.0);
			transform = CGAffineTransformRotate(transform, M_PI / 2.0);
			break;
			
		default:
			[NSException raise:NSInternalInconsistencyException format:@"Invalid image orientation"];
			
	}
	
	UIGraphicsBeginImageContext(bounds.size);
	
	CGContextRef context = UIGraphicsGetCurrentContext();
	
	if (orient == UIImageOrientationRight || orient == UIImageOrientationLeft) {
		CGContextScaleCTM(context, -scaleRatio, scaleRatio);
		CGContextTranslateCTM(context, -height, 0);
	}
	else {
		CGContextScaleCTM(context, scaleRatio, -scaleRatio);
		CGContextTranslateCTM(context, 0, -height);
	}
	
	CGContextConcatCTM(context, transform);
	
	CGContextDrawImage(UIGraphicsGetCurrentContext(), CGRectMake(0, 0, width, height), imgRef);
	UIImage *imageCopy = UIGraphicsGetImageFromCurrentImageContext();
	UIGraphicsEndImageContext();
	
	return imageCopy;
}