Resize Image without losing quality

Question

I'm using the functions below to resize my images width & height but I noticed that it ruins the image quality.

class func imageWithSize(image: UIImage,size: CGSize)->UIImage{
    if UIScreen.mainScreen().respondsToSelector("scale"){
        UIGraphicsBeginImageContextWithOptions(size,false,UIScreen.mainScreen().scale);
    }
    else
    {
        UIGraphicsBeginImageContext(size);
    }

    image.drawInRect(CGRectMake(0, 0, size.width, size.height));
    var newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return newImage;
}

class func resizeImageWithAspect(image: UIImage,scaledToMaxWidth width:CGFloat,maxHeight height :CGFloat)->UIImage
{


    let scaleFactor =  width / height;


    let newSize = CGSizeMake(width, height);

    return imageWithSize(image, size: newSize);
}

Is there another way to resize images without ruining the quality? Or how can I fix my functions below so it doesn't ruin the image quality after resizing?

@Mats It resizes the images correctly to whatever width and height I pass to the function. The problem is that the image becomes blurry — , Sep 16 '15 at 15:30
FYI - the `UIGraphicsBeginImageContextWithOptions` function was added in iOS 4. Checking to see if you should use it or not in this day and age is pointless. — rmaddy, Sep 16 '15 at 15:35
@rmaddy any idea on what I should use for iOS 8? I just want to resize the height and width without having the output become blurry — , Sep 16 '15 at 16:01
What you are doing looks correct as long as the newSize maintains the original aspect ratio and you are making the image smaller. — rmaddy, Sep 16 '15 at 16:04

Henry Declety · Answer 1 · 2018-04-05T11:02:19.587

51

Here is my code in swift. For squared images, it works really well and without any loss of quality!

extension UIImage {

    func resize(targetSize: CGSize) -> UIImage {
        return UIGraphicsImageRenderer(size:targetSize).image { _ in
            self.draw(in: CGRect(origin: .zero, size: targetSize))
        }
    }

}

edited Apr 05 '18 at 11:02

answered Mar 01 '18 at 23:56

Henry Declety

531
6
8

6

This should be the accepted answer for iOS 10.0 and above. – Josh O'Connor Apr 04 '18 at 23:16
3

It's unbelievable that this isn't the answer that's everywhere. Nearly every answer out there is long, convoluted, and distorts the image, but this doesn't. – Gabriel Garrett May 21 '18 at 18:09
3

It works for squared image but what about other images which are not squared ? – Birju Jan 28 '19 at 07:00
Thanks, you are safe me – IvanovDeveloper Apr 02 '19 at 13:29
Perfect! So much cleaner than the others. Of course, I'm working exclusively with square pics. But I expect if the aspect ratio is the same it should work for rectangular ones as well... – rattletrap99 Nov 14 '19 at 19:26
All above answers decrease the quality. Only this answer kept the video quality. – AsifHabib Mar 16 '21 at 20:56
Thank you for saving my time. This solution worked on first attempt. – Ankit Jain Nov 30 '22 at 14:04

Long Pham · Answer 2 · 2015-09-17T07:53:49.173

Here is my Objective-C code. It's work for me.

+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)newSize isAspectRation:(BOOL)aspect {
    if (!image) {
        return nil;
    }
    //UIGraphicsBeginImageContext(newSize);
    // In next line, pass 0.0 to use the current device's pixel scaling factor (and thus account for Retina resolution).
    // Pass 1.0 to force exact pixel size.
    CGFloat originRatio = image.size.width / image.size.height;
    CGFloat newRatio = newSize.width / newSize.height;

    CGSize sz;

    if (!aspect) {
        sz = newSize;
    }else {
        if (originRatio < newRatio) {
            sz.height = newSize.height;
            sz.width = newSize.height * originRatio;
        }else {
            sz.width = newSize.width;
            sz.height = newSize.width / originRatio;
        }
    }
    CGFloat scale = 1.0;
    //    if([[UIScreen mainScreen]respondsToSelector:@selector(scale)]) {
    //        CGFloat tmp = [[UIScreen mainScreen]scale];
    //        if (tmp > 1.5) {
    //            scale = 2.0;
    //        }
    //    }
    sz.width /= scale;
    sz.height /= scale;
    UIGraphicsBeginImageContextWithOptions(sz, NO, scale);
    [image drawInRect:CGRectMake(0, 0, sz.width, sz.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return newImage;
}

I saw your code in Swift. I just convert my Objective-C to Swift without test. Can you try it and let's me know. Thanks!

struct CommonUtils {
    static func imageWithImage(image: UIImage, scaleToSize newSize: CGSize, isAspectRation aspect: Bool) -> UIImage{

        let originRatio = image.size.width / image.size.height;//CGFloat
        let newRatio = newSize.width / newSize.height;

        var sz: CGSize = CGSizeZero

        if (!aspect) {
            sz = newSize
        }else {
            if (originRatio < newRatio) {
                sz.height = newSize.height
                sz.width = newSize.height * originRatio
            }else {
                sz.width = newSize.width
                sz.height = newSize.width / originRatio
            }
        }
        let scale: CGFloat = 1.0

        sz.width /= scale
        sz.height /= scale
        UIGraphicsBeginImageContextWithOptions(sz, false, scale)
        image.drawInRect(CGRectMake(0, 0, sz.width, sz.height))
        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage
    }
}

score 5 · Answer 3 · answered Apr 16 '20 at 10:26

I just created this useful UIImage extension with swift 5. You can use it to resize your UIImages without losing quality.

I added a couple of methods in order to be able to resize an image to a width or a height keeping the aspect ratio.


extension UIImage {

    func resize(targetSize: CGSize) -> UIImage {
        return UIGraphicsImageRenderer(size:targetSize).image { _ in
            self.draw(in: CGRect(origin: .zero, size: targetSize))
        }
    }

    func resize(scaledToWidth desiredWidth: CGFloat) -> UIImage {
        let oldWidth = size.width
        let scaleFactor = desiredWidth / oldWidth

        let newHeight = size.height * scaleFactor
        let newWidth = oldWidth * scaleFactor
        let newSize = CGSize(width: newWidth, height: newHeight)

        return resize(targetSize: newSize)
    }

    func resize(scaledToHeight desiredHeight: CGFloat) -> UIImage {
        let scaleFactor = desiredHeight / size.height
        let newWidth = size.width * scaleFactor
        let newSize = CGSize(width: newWidth, height: desiredHeight)

        return resize(targetSize: newSize)
    }

}

shan · Answer 4 · 2016-10-03T11:23:25.370

3

func image(image:UIImage,imageSize:CGSize)->UIImage
{
    UIGraphicsBeginImageContextWithOptions(imageSize, false, 0.0)
    [image .drawInRect(CGRectMake(0, 3, imageSize.width, imageSize.height))]
    let newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext()
    return newImage;
}

edited Oct 03 '16 at 11:23

answered Oct 03 '16 at 10:53

shan

136
7

3

Consider adding some context / explanation of the main points, so that your answer can be more helpful. – lfurini Oct 03 '16 at 11:14
- Decrease the video quality. Henry's Answer is good. – AsifHabib Mar 16 '21 at 20:57

Resize Image without losing quality

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