UIImage를 축소하고 흐릿하게 만드는 대신 동시에 파삭 파삭하고 선명하게 만드는 방법은 무엇입니까?

UIImage를 축소하고 흐릿하게 만드는 대신 동시에 파삭 파삭하고 선명하게 만드는 방법은 무엇입니까?

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이미지의 크기를 줄여야하지만 선명하게해야합니다. 예를 들어 Photoshop에는 이미지 크기 축소 옵션 "Bicubic Smoother"(흐리게) 및 "Bicubic Sharper"가 있습니다.

이 이미지 축소 알고리즘이 오픈 소스이거나 어딘가에 문서화되어 있습니까? 아니면 SDK가이를 수행하는 방법을 제공합니까?

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단순히 사용하는 것만으로 imageWithCGImage는 충분하지 않습니다. 확장되지만 결과는 확대 또는 축소 여부에 관계없이 흐릿하고 차선책입니다.

앨리어싱을 올바르게하고 "재기"를 제거하려면 다음과 같은 것이 필요합니다. http://vocaro.com/trevor/blog/2009/10/12/resize-a-uiimage-the-right- 방법 / .

내 작업 테스트 코드는 다음과 같이 보입니다. 투명한 PNG로 작업하기 위해 약간의 조정이있는 Trevor의 솔루션입니다.

- (UIImage *)resizeImage:(UIImage*)image newSize:(CGSize)newSize {
    CGRect newRect = CGRectIntegral(CGRectMake(0, 0, newSize.width, newSize.height));
    CGImageRef imageRef = image.CGImage;

    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0);
    CGContextRef context = UIGraphicsGetCurrentContext();

    // Set the quality level to use when rescaling
    CGContextSetInterpolationQuality(context, kCGInterpolationHigh);
    CGAffineTransform flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, newSize.height);

    CGContextConcatCTM(context, flipVertical);  
    // Draw into the context; this scales the image
    CGContextDrawImage(context, newRect, imageRef);

    // Get the resized image from the context and a UIImage
    CGImageRef newImageRef = CGBitmapContextCreateImage(context);
    UIImage *newImage = [UIImage imageWithCGImage:newImageRef];

    CGImageRelease(newImageRef);
    UIGraphicsEndImageContext();    

    return newImage;
}

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Swift를 사용하는 사람들에게는 Swift에서 허용되는 답변이 있습니다.

func resizeImage(image: UIImage, newSize: CGSize) -> (UIImage) {
    let newRect = CGRectIntegral(CGRectMake(0,0, newSize.width, newSize.height))
    let imageRef = image.CGImage

    UIGraphicsBeginImageContextWithOptions(newSize, false, 0)
    let context = UIGraphicsGetCurrentContext()

    // Set the quality level to use when rescaling
    CGContextSetInterpolationQuality(context, kCGInterpolationHigh)
    let flipVertical = CGAffineTransformMake(1, 0, 0, -1, 0, newSize.height)

    CGContextConcatCTM(context, flipVertical)
    // Draw into the context; this scales the image
    CGContextDrawImage(context, newRect, imageRef)

    let newImageRef = CGBitmapContextCreateImage(context) as CGImage
    let newImage = UIImage(CGImage: newImageRef)

    // Get the resized image from the context and a UIImage
    UIGraphicsEndImageContext()

    return newImage
}

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누군가 Swift 버전을 찾고 있다면 @Dan Rosenstark의 수락 된 답변의 Swift 버전은 다음과 같습니다.

func resizeImage(image: UIImage, newHeight: CGFloat) -> UIImage {
    let scale = newHeight / image.size.height
    let newWidth = image.size.width * scale
    UIGraphicsBeginImageContext(CGSizeMake(newWidth, newHeight))
    image.drawInRect(CGRectMake(0, 0, newWidth, newHeight))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return newImage
}

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크기를 조정하는 동안 이미지의 원래 종횡비를 유지하면 아무리 축소해도 항상 선명한 이미지가됩니다.

다음 방법을 사용하여 확장 할 수 있습니다.

+ (UIImage *)imageWithCGImage:(CGImageRef)imageRef scale:(CGFloat)scale orientation:(UIImageOrientation)orientation

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Swift 3의 경우

func resizeImage(image: UIImage, newSize: CGSize) -> (UIImage) {

    let newRect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height).integral
    UIGraphicsBeginImageContextWithOptions(newSize, false, 0)
    let context = UIGraphicsGetCurrentContext()

    // Set the quality level to use when rescaling
    context!.interpolationQuality = CGInterpolationQuality.default
    let flipVertical = CGAffineTransform(a: 1, b: 0, c: 0, d: -1, tx: 0, ty: newSize.height)

    context!.concatenate(flipVertical)
    // Draw into the context; this scales the image
    context?.draw(image.cgImage!, in: CGRect(x: 0.0,y: 0.0, width: newRect.width, height: newRect.height))

    let newImageRef = context!.makeImage()! as CGImage
    let newImage = UIImage(cgImage: newImageRef)

    // Get the resized image from the context and a UIImage
    UIGraphicsEndImageContext()

    return newImage
 }

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@YAR 솔루션이 제대로 작동하고 있습니다.

내 요구 사항에 맞지 않는 한 가지가 있습니다. 전체 이미지의 크기가 조정됩니다. 나는 photos app on iphone. 이것은 "긴면"을 계산하고 "오버레이"를 잘라내어 이미지 품질과 관련하여 훨씬 더 나은 결과를 얻습니다.

- (UIImage *)resizeImageProportionallyIntoNewSize:(CGSize)newSize;
{
    CGFloat scaleWidth = 1.0f;
    CGFloat scaleHeight = 1.0f;

    if (CGSizeEqualToSize(self.size, newSize) == NO) {

        //calculate "the longer side"
        if(self.size.width > self.size.height) {
            scaleWidth = self.size.width / self.size.height;
        } else {
            scaleHeight = self.size.height / self.size.width;
        }
    }    

    //prepare source and target image
    UIImage *sourceImage = self;
    UIImage *newImage = nil;

    // Now we create a context in newSize and draw the image out of the bounds of the context to get
    // A proportionally scaled image by cutting of the image overlay
    UIGraphicsBeginImageContext(newSize);

    //Center image point so that on each egde is a little cutoff
    CGRect thumbnailRect = CGRectZero;
    thumbnailRect.size.width  = newSize.width * scaleWidth;
    thumbnailRect.size.height = newSize.height * scaleHeight;
    thumbnailRect.origin.x = (int) (newSize.width - thumbnailRect.size.width) * 0.5;
    thumbnailRect.origin.y = (int) (newSize.height - thumbnailRect.size.height) * 0.5;

    [sourceImage drawInRect:thumbnailRect];

    newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    if(newImage == nil) NSLog(@"could not scale image");

    return newImage ;
}

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This extension should scale the image while keeping original aspect ratio. The rest of the image is cropped. (Swift 3)

extension UIImage {    
    func thumbnail(ofSize proposedSize: CGSize) -> UIImage? {

        let scale = min(size.width/proposedSize.width, size.height/proposedSize.height)

        let newSize = CGSize(width: size.width/scale, height: size.height/scale)
        let newOrigin = CGPoint(x: (proposedSize.width - newSize.width)/2, y: (proposedSize.height - newSize.height)/2)

        let thumbRect = CGRect(origin: newOrigin, size: newSize).integral

        UIGraphicsBeginImageContextWithOptions(proposedSize, false, 0)

        draw(in: thumbRect)

        let result = UIGraphicsGetImageFromCurrentImageContext()

        UIGraphicsEndImageContext()

        return result
    }
}

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For swift 4.2:

extension UIImage {

    func resized(By coefficient:CGFloat) -> UIImage? {

        guard coefficient >= 0 && coefficient <= 1 else {

            print("The coefficient must be a floating point number between 0 and 1")
            return nil
        }

        let newWidth = size.width * coefficient
        let newHeight = size.height * coefficient

        UIGraphicsBeginImageContext(CGSize(width: newWidth, height: newHeight))

        draw(in: CGRect(x: 0, y: 0, width: newWidth, height: newHeight))

        let newImage = UIGraphicsGetImageFromCurrentImageContext()

        UIGraphicsEndImageContext()

        return newImage
    }
}

참고URL : https://stackoverflow.com/questions/6141298/how-to-scale-down-a-uiimage-and-make-it-crispy-sharp-at-the-same-time-instead