カメラロールの画像を縮小していますが、アーティファクトが表示されています。
サンプル画像:
CGSize s = CGSizeMake(320, 320);
UIImage *scaledImage = [picture resizedImageWithContentMode:contentMode
bounds:s
interpolationQuality:kCGInterpolationHigh];
画像は 720x960 です。これは、比率が関係ないために発生しているのでしょうか。
ここに私のUIImageカテゴリクラスがあります:
/**
* Returns a copy of this image that is cropped to the given bounds.
* The bounds will be adjusted using CGRectIntegral.
* This method ignores the image's imageOrientation setting.
*/
- (UIImage *)croppedImage:(CGRect)bounds {
CGImageRef imageRef = CGImageCreateWithImageInRect([self CGImage], bounds);
UIImage *croppedImage = [UIImage imageWithCGImage:imageRef];
CGImageRelease(imageRef);
return croppedImage;
}
/**
* Returns a rescaled copy of the image, taking into account its orientation
* The image will be scaled disproportionately if necessary to fit the bounds specified by the parameter
*/
- (UIImage *)resizedImage:(CGSize)newSize interpolationQuality:(CGInterpolationQuality)quality {
BOOL drawTransposed;
CGAffineTransform transform = CGAffineTransformIdentity;
switch (self.imageOrientation) {
case UIImageOrientationLeft:
case UIImageOrientationLeftMirrored:
case UIImageOrientationRight:
case UIImageOrientationRightMirrored:
drawTransposed = YES;
break;
default:
drawTransposed = NO;
}
transform = [self transformForOrientation:newSize];
return [self resizedImage:newSize
transform:transform
drawTransposed:drawTransposed
interpolationQuality:quality];
}
/**
* Resizes the image according to the given content mode, taking into account
* the image's orientation
*/
- (UIImage *)resizedImageWithContentMode:(UIViewContentMode)contentMode
bounds:(CGSize)bounds
interpolationQuality:(CGInterpolationQuality)quality {
CGFloat horizontalRatio = bounds.width / self.size.width;
CGFloat verticalRatio = bounds.height / self.size.height;
CGFloat ratio;
switch (contentMode) {
case UIViewContentModeScaleAspectFill:
ratio = MAX(horizontalRatio, verticalRatio);
break;
case UIViewContentModeScaleAspectFit:
ratio = MIN(horizontalRatio, verticalRatio);
break;
default:
[NSException raise:NSInvalidArgumentException format:@"Unsupported content mode: %d", contentMode];
}
ratio = MIN(horizontalRatio, verticalRatio);
CGSize newSize = CGSizeMake(self.size.width * ratio, self.size.height * ratio);
return [self resizedImage:newSize interpolationQuality:quality];
}
#pragma mark - Private helper methods
/**
* Returns a copy of the image that has been transformed using the given affine transform and scaled to the new size
* The new image's orientation will be UIImageOrientationUp, regardless of the current image's orientation
* If the new size is not integral, it will be rounded up
*/
- (UIImage *)resizedImage:(CGSize)newSize
transform:(CGAffineTransform)transform
drawTransposed:(BOOL)transpose
interpolationQuality:(CGInterpolationQuality)quality {
CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
CGRect transposedRect = CGRectMake(0, 0, newRect.size.height, newRect.size.width);
CGImageRef imageRef = self.CGImage;
/**
* Fix for a colorspace / transparency issue that affects some types of
* images. See here: http://vocaro.com/trevor/blog/2009/10/12/resize-a-uiimage-the-right-way/comment-page-2/#comment-39951
*/
CGContextRef bitmap =CGBitmapContextCreate( NULL,
newRect.size.width,
newRect.size.height,
8,
0,
CGImageGetColorSpace( imageRef ),
kCGImageAlphaNoneSkipLast );
// Rotate and/or flip the image if required by its orientation
CGContextConcatCTM(bitmap, transform);
// CGContextSetShouldAntialias(bitmap,YES);
// Set the quality level to use when rescaling
CGContextSetInterpolationQuality(bitmap, quality);
// Draw into the context; this scales the image
CGContextDrawImage(bitmap, transpose ? transposedRect : newRect, imageRef);
// Get the resized image from the context and a UIImage
CGImageRef newImageRef = CGBitmapContextCreateImage(bitmap);
UIImage *newImage = [UIImage imageWithCGImage:newImageRef];
// Clean up
CGContextRelease(bitmap);
CGImageRelease(newImageRef);
return newImage;
}
/**
* Returns an affine transform that takes into account the image orientation
* when drawing a scaled image
*/
- (CGAffineTransform)transformForOrientation:(CGSize)newSize {
CGAffineTransform transform = CGAffineTransformIdentity;
switch (self.imageOrientation) {
case UIImageOrientationDown: // EXIF = 3
case UIImageOrientationDownMirrored: // EXIF = 4
transform = CGAffineTransformTranslate(transform, newSize.width, newSize.height);
transform = CGAffineTransformRotate(transform, M_PI);
break;
case UIImageOrientationLeft: // EXIF = 6
case UIImageOrientationLeftMirrored: // EXIF = 5
transform = CGAffineTransformTranslate(transform, newSize.width, 0);
transform = CGAffineTransformRotate(transform, M_PI_2);
break;
case UIImageOrientationRight: // EXIF = 8
case UIImageOrientationRightMirrored: // EXIF = 7
transform = CGAffineTransformTranslate(transform, 0, newSize.height);
transform = CGAffineTransformRotate(transform, -M_PI_2);
break;
default:
break;
}
switch (self.imageOrientation) {
case UIImageOrientationUpMirrored: // EXIF = 2
case UIImageOrientationDownMirrored: // EXIF = 4
transform = CGAffineTransformTranslate(transform, newSize.width, 0);
transform = CGAffineTransformScale(transform, -1, 1);
break;
case UIImageOrientationLeftMirrored: // EXIF = 5
case UIImageOrientationRightMirrored: // EXIF = 7
transform = CGAffineTransformTranslate(transform, newSize.height, 0);
transform = CGAffineTransformScale(transform, -1, 1);
break;
default:
break;
}
return transform;
}