How do I resize the UIImage to reduce upload image size

I've been searching google, and have only come across libraries that either reduce the height/width or some how edit the UIImage appearance via CoreImage. But I have not seen or found one library, post that explains how to reduce image size so when it uploads, it's not the full image size.

so far I have this:

        if image != nil {
        //let data = NSData(data: UIImagePNGRepresentation(image))
        let data = UIImagePNGRepresentation(image)
        body.appendString("--\(boundary)\r\n")
        body.appendString("Content-Disposition: form-data; name=\"image\"; filename=\"randomName\"\r\n")
        body.appendString("Content-Type: image/png\r\n\r\n")
        body.appendData(data)
        body.appendString("\r\n")
    }

and it's sending 12MB photos. How can I reduce this to 1mb? thanks!

Xcode 9 • Swift 4 or later

edit/update: For iOS10+ We can use UIGraphicsImageRenderer. For older Swift syntax check edit history.

extension UIImage {
    func resized(withPercentage percentage: CGFloat, isOpaque: Bool = true) -> UIImage? {
        let canvas = CGSize(width: size.width * percentage, height: size.height * percentage)
        let format = imageRendererFormat
        format.opaque = isOpaque
        return UIGraphicsImageRenderer(size: canvas, format: format).image {
            _ in draw(in: CGRect(origin: .zero, size: canvas))
        }
    }
    func resized(toWidth width: CGFloat, isOpaque: Bool = true) -> UIImage? {
        let canvas = CGSize(width: width, height: CGFloat(ceil(width/size.width * size.height)))
        let format = imageRendererFormat
        format.opaque = isOpaque
        return UIGraphicsImageRenderer(size: canvas, format: format).image {
            _ in draw(in: CGRect(origin: .zero, size: canvas))
        }
    }
}

Usage:

let image = UIImage(data: try! Data(contentsOf: URL(string:"http://i.stack.imgur.com/Xs4RX.jpg")!))!

let thumb1 = image.resized(withPercentage: 0.1)
let thumb2 = image.resized(toWidth: 72.0)

This is the way which i followed to resize image.

 -(UIImage *)resizeImage:(UIImage *)image
{
   float actualHeight = image.size.height;
   float actualWidth = image.size.width;
   float maxHeight = 300.0;
   float maxWidth = 400.0;
   float imgRatio = actualWidth/actualHeight;
   float maxRatio = maxWidth/maxHeight;
   float compressionQuality = 0.5;//50 percent compression

   if (actualHeight > maxHeight || actualWidth > maxWidth)
   {
    if(imgRatio < maxRatio)
    {
        //adjust width according to maxHeight
        imgRatio = maxHeight / actualHeight;
        actualWidth = imgRatio * actualWidth;
        actualHeight = maxHeight;
    }
    else if(imgRatio > maxRatio)
    {
        //adjust height according to maxWidth
        imgRatio = maxWidth / actualWidth;
        actualHeight = imgRatio * actualHeight;
        actualWidth = maxWidth;
    }
    else
    {
        actualHeight = maxHeight;
        actualWidth = maxWidth;
    }
   }

   CGRect rect = CGRectMake(0.0, 0.0, actualWidth, actualHeight);
   UIGraphicsBeginImageContext(rect.size);
   [image drawInRect:rect];
   UIImage *img = UIGraphicsGetImageFromCurrentImageContext();
   NSData *imageData = UIImageJPEGRepresentation(img, compressionQuality);
   UIGraphicsEndImageContext();

   return [UIImage imageWithData:imageData];

}

Using this method my image having 6.5 MB reduced to 104 KB.

Swift 4 code:

func resize(_ image: UIImage) -> UIImage {
    var actualHeight = Float(image.size.height)
    var actualWidth = Float(image.size.width)
    let maxHeight: Float = 300.0
    let maxWidth: Float = 400.0
    var imgRatio: Float = actualWidth / actualHeight
    let maxRatio: Float = maxWidth / maxHeight
    let compressionQuality: Float = 0.5
    //50 percent compression
    if actualHeight > maxHeight || actualWidth > maxWidth {
        if imgRatio < maxRatio {
            //adjust width according to maxHeight
            imgRatio = maxHeight / actualHeight
            actualWidth = imgRatio * actualWidth
            actualHeight = maxHeight
        }
        else if imgRatio > maxRatio {
            //adjust height according to maxWidth
            imgRatio = maxWidth / actualWidth
            actualHeight = imgRatio * actualHeight
            actualWidth = maxWidth
        }
        else {
            actualHeight = maxHeight
            actualWidth = maxWidth
        }
    }
    let rect = CGRect(x: 0.0, y: 0.0, width: CGFloat(actualWidth), height: CGFloat(actualHeight))
    UIGraphicsBeginImageContext(rect.size)
    image.draw(in: rect)
    let img = UIGraphicsGetImageFromCurrentImageContext()
    let imageData = img?.jpegData(compressionQuality: CGFloat(compressionQuality)) 
    UIGraphicsEndImageContext()
    return UIImage(data: imageData!) ?? UIImage()
}

Swift 5.4 & Xcode 13

I was not satisfied with the solutions here, which generate an image based on a given KB size, since most of them used .jpegData(compressionQuality: x). This method won't work with large images, since even with compression quality set to 0.0, the large image will remain large, e.g. a 10 MB produced by portrait mode of a newer iPhone still will be above 1 MB with compressionQuality set to 0.0.

Therefore I used some answers here and rewrote a Helper Struct which converts an image in a background que:

import UIKit

struct ImageCompressor {
    static func compress(image: UIImage, maxByte: Int,
                         completion: @escaping (UIImage?) -> ()) {
        DispatchQueue.global(qos: .userInitiated).async {
            guard let currentImageSize = image.jpegData(compressionQuality: 1.0)?.count else {
                return completion(nil)
            }
        
            var iterationImage: UIImage? = image
            var iterationImageSize = currentImageSize
            var iterationCompression: CGFloat = 1.0
        
            while iterationImageSize > maxByte && iterationCompression > 0.01 {
                let percantageDecrease = getPercantageToDecreaseTo(forDataCount: iterationImageSize)
            
                let canvasSize = CGSize(width: image.size.width * iterationCompression,
                                        height: image.size.height * iterationCompression)
                UIGraphicsBeginImageContextWithOptions(canvasSize, false, image.scale)
                defer { UIGraphicsEndImageContext() }
                image.draw(in: CGRect(origin: .zero, size: canvasSize))
                iterationImage = UIGraphicsGetImageFromCurrentImageContext()
            
                guard let newImageSize = iterationImage?.jpegData(compressionQuality: 1.0)?.count else {
                    return completion(nil)
                }
                iterationImageSize = newImageSize
                iterationCompression -= percantageDecrease
            }
            completion(iterationImage)
        }
    }

    private static func getPercantageToDecreaseTo(forDataCount dataCount: Int) -> CGFloat {
        switch dataCount {
        case 0..<3000000: return 0.05
        case 3000000..<10000000: return 0.1
        default: return 0.2
        }
    }
}

Compress an image to max 1 MB:

        ImageCompressor.compress(image: image, maxByte: 1000000) { image in
            guard let compressedImage = image else { return }
            // Use compressedImage
        }
    }

In case someone is looking for resizing image to less than 1MB with Swift 3 and 4.

Just copy&paste this extension:

extension UIImage {

func resized(withPercentage percentage: CGFloat) -> UIImage? {
    let canvasSize = CGSize(width: size.width * percentage, height: size.height * percentage)
    UIGraphicsBeginImageContextWithOptions(canvasSize, false, scale)
    defer { UIGraphicsEndImageContext() }
    draw(in: CGRect(origin: .zero, size: canvasSize))
    return UIGraphicsGetImageFromCurrentImageContext()
}

func resizedTo1MB() -> UIImage? {
    guard let imageData = UIImagePNGRepresentation(self) else { return nil }

    var resizingImage = self
    var imageSizeKB = Double(imageData.count) / 1000.0 // ! Or devide for 1024 if you need KB but not kB

    while imageSizeKB > 1000 { // ! Or use 1024 if you need KB but not kB
        guard let resizedImage = resizingImage.resized(withPercentage: 0.9),
            let imageData = UIImagePNGRepresentation(resizedImage)
            else { return nil }

        resizingImage = resizedImage
        imageSizeKB = Double(imageData.count) / 1000.0 // ! Or devide for 1024 if you need KB but not kB
    }

    return resizingImage
}
}

And use:

let resizedImage = originalImage.resizedTo1MB()

Edit: Please note it's blocking UI, so move to background thread if you think it's the right way for your case.

same as Leo Answer but little edits for SWIFT 2.0

 extension UIImage {
    func resizeWithPercentage(percentage: CGFloat) -> UIImage? {
        let imageView = UIImageView(frame: CGRect(origin: .zero, size: CGSize(width: size.width * percentage, height: size.height * percentage)))
        imageView.contentMode = .ScaleAspectFit
        imageView.image = self
        UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, false, scale)
        guard let context = UIGraphicsGetCurrentContext() else { return nil }
        imageView.layer.renderInContext(context)
        guard let result = UIGraphicsGetImageFromCurrentImageContext() else { return nil }
        UIGraphicsEndImageContext()
        return result
    }

    func resizeWithWidth(width: CGFloat) -> UIImage? {
        let imageView = UIImageView(frame: CGRect(origin: .zero, size: CGSize(width: width, height: CGFloat(ceil(width/size.width * size.height)))))
        imageView.contentMode = .ScaleAspectFit
        imageView.image = self
        UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, false, scale)
        guard let context = UIGraphicsGetCurrentContext() else { return nil }
        imageView.layer.renderInContext(context)
        guard let result = UIGraphicsGetImageFromCurrentImageContext() else { return nil }
        UIGraphicsEndImageContext()
        return result
    }
}

Swift4.2

  let imagedata = yourImage.jpegData(compressionQuality: 0.1)!

Here is user4261201's answer but in swift, that I am currently using:

func compressImage (_ image: UIImage) -> UIImage {
    
    let actualHeight:CGFloat = image.size.height
    let actualWidth:CGFloat = image.size.width
    let imgRatio:CGFloat = actualWidth/actualHeight
    let maxWidth:CGFloat = 1024.0
    let resizedHeight:CGFloat = maxWidth/imgRatio
    let compressionQuality:CGFloat = 0.5
    
    let rect:CGRect = CGRect(x: 0, y: 0, width: maxWidth, height: resizedHeight)
    UIGraphicsBeginImageContext(rect.size)
    image.draw(in: rect)
    let img: UIImage = UIGraphicsGetImageFromCurrentImageContext()!
    let imageData:Data = UIImageJPEGRepresentation(img, compressionQuality)!
    UIGraphicsEndImageContext()
    
    return UIImage(data: imageData)!
    
}

I think the core of the question here is how to reliably shrink a UIImage's data to a certain size before uploading to a server, rather than just shrink the UIImage itself.

Using func jpegData(compressionQuality: CGFloat) -> Data? works well if you don't need to compress to a specific size. However, for certain cases, I find it useful to be able to compress below a certain specified file size. In that case, jpegData is unreliable, and iterative compressing of an image this way results in plateauing out on filesize (and can be really expensive). Instead, I prefer to reduce the size of the UIImage itself as in Leo's answer, then convert to jpegData and iteratively check to see if the reduced size is beneath the value I chose (within a margin that I set). I adjust the compression step multiplier based on the ratio of the current filesize to the desired filesize to speed up the first iterations which are the most expensive (since the filesize is the largest at that point).

Swift 5

extension UIImage {
    func resized(withPercentage percentage: CGFloat, isOpaque: Bool = true) -> UIImage? {
        let canvas = CGSize(width: size.width * percentage, height: size.height * percentage)
        let format = imageRendererFormat
        format.opaque = isOpaque
        return UIGraphicsImageRenderer(size: canvas, format: format).image {
            _ in draw(in: CGRect(origin: .zero, size: canvas))
        }
    }
    
    func compress(to kb: Int, allowedMargin: CGFloat = 0.2) -> Data {
        guard kb > 10 else { return Data() } // Prevents user from compressing below a limit (10kb in this case).
        let bytes = kb * 1024
        var compression: CGFloat = 1.0
        let step: CGFloat = 0.05
        var holderImage = self
        var complete = false
        while(!complete) {
            guard let data = holderImage.jpegData(compressionQuality: 1.0) else { break }
            let ratio = data.count / bytes
            if data.count < Int(CGFloat(bytes) * (1 + allowedMargin)) {
                complete = true
                return data
            } else {
                let multiplier:CGFloat = CGFloat((ratio / 5) + 1)
                compression -= (step * multiplier)
            }
            guard let newImage = holderImage.resized(withPercentage: compression) else { break }
            holderImage = newImage
        }
        
        return Data()
    }
}
 

And usage:

let data = image.compress(to: 1000)

If you are uploading image in NSData format, use this :

NSData *imageData = UIImageJPEGRepresentation(yourImage, floatValue);

yourImage is your UIImage. floatvalue is compression value(0.0 to 1.0)

The above is to convert image to JPEG.

For PNGuse : UIImagePNGRepresentation

Note : Above code is in Objective-C. Please check how to define NSData in Swift.

Based on the answer of Tung Fam. To resize to a specific file size. Like 0.7 MB you can use this code.

extension UIImage {

func resize(withPercentage percentage: CGFloat) -> UIImage? {
    var newRect = CGRect(origin: .zero, size: CGSize(width: size.width*percentage, height: size.height*percentage))
    UIGraphicsBeginImageContextWithOptions(newRect.size, true, 1)
    self.draw(in: newRect)
    defer {UIGraphicsEndImageContext()}
    return UIGraphicsGetImageFromCurrentImageContext()
}

func resizeTo(MB: Double) -> UIImage? {
    guard let fileSize = self.pngData()?.count else {return nil}
    let fileSizeInMB = CGFloat(fileSize)/(1024.0*1024.0)//form bytes to MB
    let percentage = 1/fileSizeInMB
    return resize(withPercentage: percentage)
}
}

Using this you can control the size that you want:

func jpegImage(image: UIImage, maxSize: Int, minSize: Int, times: Int) -> Data? {
    var maxQuality: CGFloat = 1.0
    var minQuality: CGFloat = 0.0
    var bestData: Data?
    for _ in 1...times {
        let thisQuality = (maxQuality + minQuality) / 2
        guard let data = image.jpegData(compressionQuality: thisQuality) else { return nil }
        let thisSize = data.count
        if thisSize > maxSize {
            maxQuality = thisQuality
        } else {
            minQuality = thisQuality
            bestData = data
            if thisSize > minSize {
                return bestData
            }
        }
    }
    return bestData
}

Method call example:

jpegImage(image: image, maxSize: 500000, minSize: 400000, times: 10)  

It will try to get a file between a maximum and minimum size of maxSize and minSize, but only try times times. If it fails within that time, it will return nil.

I think the easiest way is provided by swift itself to compress the image into compressed data below is the code in swift 4.2

let imageData = yourImageTobeCompressed.jpegData(compressionQuality: 0.5)

and you can send this imageData to upload to server.

This is what I done in swift 3 for resizing an UIImage. It reduces the image size to less than 100kb. It works proportionally!

extension UIImage {
    class func scaleImageWithDivisor(img: UIImage, divisor: CGFloat) -> UIImage {
        let size = CGSize(width: img.size.width/divisor, height: img.size.height/divisor)
        UIGraphicsBeginImageContext(size)
        img.draw(in: CGRect(x: 0, y: 0, width: size.width, height: size.height))
        let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return scaledImage!
    }
}

Usage:

let scaledImage = UIImage.scaleImageWithDivisor(img: capturedImage!, divisor: 3)

Same in Objective-C :

interface :

@interface UIImage (Resize)

- (UIImage *)resizedWithPercentage:(CGFloat)percentage;
- (UIImage *)resizeTo:(CGFloat)weight isPng:(BOOL)isPng jpegCompressionQuality:(CGFloat)compressionQuality;

@end

implementation :

#import "UIImage+Resize.h"

@implementation UIImage (Resize)

- (UIImage *)resizedWithPercentage:(CGFloat)percentage {
    CGSize canvasSize = CGSizeMake(self.size.width * percentage, self.size.height * percentage);
    UIGraphicsBeginImageContextWithOptions(canvasSize, false, self.scale);
    [self drawInRect:CGRectMake(0, 0, canvasSize.width, canvasSize.height)];
    UIImage *sizedImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return sizedImage;
}

- (UIImage *)resizeTo:(CGFloat)weight isPng:(BOOL)isPng jpegCompressionQuality:(CGFloat)compressionQuality {
    NSData *imageData = isPng ? UIImagePNGRepresentation(self) : UIImageJPEGRepresentation(self, compressionQuality);
    if (imageData && [imageData length] > 0) {
        UIImage *resizingImage = self;
        double imageSizeKB = [imageData length] / weight;
    
        while (imageSizeKB > weight) {
            UIImage *resizedImage = [resizingImage resizedWithPercentage:0.9];
            imageData = isPng ? UIImagePNGRepresentation(resizedImage) : UIImageJPEGRepresentation(resizedImage, compressionQuality);
            resizingImage = resizedImage;
            imageSizeKB = (double)(imageData.length / weight);
        }
    
        return resizingImage;
    }
    return nil;
}

Usage :

#import "UIImage+Resize.h"

UIImage *resizedImage = [self.picture resizeTo:2048 isPng:NO jpegCompressionQuality:1.0];

When I try to use the accepted answer to resize an image for use in my project it comes out very pixelated and blurry. I ended up with this piece of code to resize images without adding pixelation or blur:

func scale(withPercentage percentage: CGFloat)-> UIImage? {
        let cgSize = CGSize(width: size.width * percentage, height: size.height * percentage)

        let hasAlpha = true
        let scale: CGFloat = 0.0 // Use scale factor of main screen

        UIGraphicsBeginImageContextWithOptions(cgSize, !hasAlpha, scale)
        self.draw(in: CGRect(origin: CGPoint.zero, size: cgSize))

        let scaledImage = UIGraphicsGetImageFromCurrentImageContext()
        return scaledImage
    }

I came across this question while investigating image compression and export in Swift, and used it as a starting point to understand the problem better & derive a better technique.

The UIGraphicsBeginImageContext(), UIGraphicsGetImageFromCurrentImageContext(), UIGraphicsEndImageContext() process is an older technique which has been superseded by UIGraphicsImageRenderer, as used by iron_john_bonney and leo-dabus. Their examples were written as extensions on UIImage, whereas I chose to write an independent function. The required differences in approach can be identified by comparison (look at and near the UIGraphicsImageRenderer call), and could easily be ported back into a UIImage extension.

I thought there was potential for improvement on the compression algorithms used here, so I took an approach that started by adjusting the image to have a given total number of pixels, and then compressing it by adjusting the jpeg compression to achieve a specified final file size. The intent of specifying a total number of pixels was to avoid getting tied up in issues with image aspect ratios. Although I haven't done an exhaustive investigation, I suspect scaling an image to a specified total number of pixels will put the final jpeg image file size in a general range, and then jpeg compression can then be used to ensure that a file size limit is achieved with acceptable image quality, providing the initial pixel count isn't too high.

When using UIGraphicsImageRenderer, the CGRect is specified in logical pixels on a host Apple device, which is different to the actual pixels in the output jpeg. Look up device pixel ratios to understand this. To obtain the device pixel ratio, I tried extracting it from the environment, but these techniques caused the playground to crash, so I used a less efficient technique that worked.

If you paste this code into an Xcode playround and place an appropriate .jpg file in the Resources folder, the output file will be placed in the Playground output folder (use Quick Look in the Live View to find this location).

import UIKit

func compressUIImage(_ image: UIImage?, numPixels: Int, fileSizeLimitKB: Double, exportImage: Bool) -> Data {
    var returnData: Data
    if let origWidth = image?.size.width,
       let origHeight = image?.size.height {
        print("Original image size =", origWidth, "*", origHeight, "pixels")

        let imgMult = min(sqrt(CGFloat(numPixels)/(origWidth * origHeight)), 1) // This multiplier scales the image to have the desired number of pixels
        print("imageMultiplier =", imgMult)

        let cgRect = CGRect(origin: .zero, size: CGSize(width: origWidth * imgMult, height: origHeight * imgMult)) // This is in *logical* pixels
        let renderer = UIGraphicsImageRenderer(size: cgRect.size)
        
        let img = renderer.image { ctx in
            image?.draw(in: cgRect)
        }
        
        // Now get the device pixel ratio if needed...
        var img_scale: CGFloat = 1
        if exportImage {
            img_scale = img.scale
        }
        print("Image scaling factor =", img_scale)

        // ...and use to ensure *output* image has desired number of pixels
        let cgRect_scaled = CGRect(origin: .zero, size: CGSize(width: origWidth * imgMult/img_scale, height: origHeight * imgMult/img_scale)) // This is in *logical* pixels
        print("New image size (in logical pixels) =", cgRect_scaled.width, "*", cgRect_scaled.height, "pixels") // Due to device pixel ratios, can have fractional pixel dimensions

        let renderer_scaled = UIGraphicsImageRenderer(size: cgRect_scaled.size)

        let img_scaled = renderer_scaled.image { ctx in
            image?.draw(in: cgRect_scaled)
        }

        var compQual = CGFloat(1.0)

        returnData = img_scaled.jpegData(compressionQuality: 1.0)!
        var imageSizeKB = Double(returnData.count) / 1000.0
        
        print("compressionQuality =", compQual, "=> imageSizeKB =", imageSizeKB, "KB")
        while imageSizeKB > fileSizeLimitKB {
            compQual *= 0.9
            returnData = img_scaled.jpegData(compressionQuality: compQual)!
            imageSizeKB = Double(returnData.count) / 1000.0
            print("compressionQuality =", compQual, "=> imageSizeKB =", imageSizeKB, "KB")
        }
    } else {
        returnData = Data()
    }
    return returnData
}

let image_orig = UIImage(named: "input.jpg")

let image_comp_data = compressUIImage(image_orig, numPixels: Int(4e6), fileSizeLimitKB: 1300, exportImage: true)

func getDocumentsDirectory() -> URL {
    let paths = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask)
    return paths[0]
}

let filename = getDocumentsDirectory().appendingPathComponent("output.jpg")

try? image_comp_data.write(to: filename)

Sources included Jordan Morgan, and Hacking with Swift.

extension UIImage {
func resized(toValue value: CGFloat) -> UIImage {
    if size.width > size.height {
        return self.resize(toWidth: value)!
    } else {
        return self.resize(toHeight: value)!
    }
}

Resize the UIImage using .resizeToMaximumBytes