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.

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()
}

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)

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
}
}

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)!


}

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.

Resize the UIImage using .resizeToMaximumBytes

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)

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.

Swift4.2

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

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
}

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

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)

Swift 5 & Xcode 14

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
}
}

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.

iOS 15+ Swift 5

Part of the solutions here doesn’t answer the question because they are not producing an image that has smaller file size to upload it to backend. It is very important to not uploading big image files to backend when it is not really needed. It will take much more space, will be more expensive to store and take more time to download causing UI to wait for content.

Lots of answers is using either

UIGraphicsImageRenderer(size: canvas).image {
_ in draw(in: CGRect(origin: .zero, size: canvas))
}

Or older

UIGraphicsGetImageFromCurrentImageContext()

The problem with these solutions is they generate smaller UIImage, but are not changing underlying CGImage so when you try to send image as DATA with .jpegData(compressionQuality:) you will note upload UIImage but data from underlying CGImage which is not resized and has large file size.

The other solutions are forcing compression of jpedData to smallest available which produce very large compression and quality loss.

To actually resize image with all underlying stuff and send it as really small best quality jpeg use method preparingThumbnail(of:) and set .jpegData(compressionQuality:) to 8 or 9.

extension UIImage {
func thumbnail(width: CGFloat) -> UIImage? {
guard size.width > width else { return self }
let imageSize = CGSize(
width: width,
height: CGFloat(ceil(width/size.width * size.height))
)
return preparingThumbnail(of: imageSize)
}
}

Here is documentation preparingThumbnail(of:)

In case someone needed, here is an async version modified from Ali Pacman's answer:

import UIKit


extension UIImage {
func compress(to maxByte: Int) async -> UIImage? {
let compressTask = Task(priority: .userInitiated) { () -> UIImage? in
guard let currentImageSize = jpegData(compressionQuality: 1.0)?.count else {
return nil
}


var iterationImage: UIImage? = self
var iterationImageSize = currentImageSize
var iterationCompression: CGFloat = 1.0
            

while iterationImageSize > maxByte && iterationCompression > 0.01 {
let percentageDecrease = getPercentageToDecreaseTo(forDataCount: iterationImageSize)
let canvasSize = CGSize(width: size.width * iterationCompression, height: size.height * iterationCompression)
                

UIGraphicsBeginImageContextWithOptions(canvasSize, false, scale)
defer { UIGraphicsEndImageContext() }
draw(in: CGRect(origin: .zero, size: canvasSize))
iterationImage = UIGraphicsGetImageFromCurrentImageContext()
                

guard let newImageSize = iterationImage?.jpegData(compressionQuality: 1.0)?.count else {
return nil
}
iterationImageSize = newImageSize
iterationCompression -= percentageDecrease
}
            

return iterationImage
}
return await compressTask.value
}
    

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