Cropping image with Swift and put it on center position

You can try this answer. It is written in swift 3.

extension UIImage {
  func crop(to:CGSize) -> UIImage {
    guard let cgimage = self.cgImage else { return self }

    let contextImage: UIImage = UIImage(cgImage: cgimage)

    let contextSize: CGSize = contextImage.size

    //Set to square
    var posX: CGFloat = 0.0
    var posY: CGFloat = 0.0
    let cropAspect: CGFloat = to.width / to.height

    var cropWidth: CGFloat = to.width
    var cropHeight: CGFloat = to.height

    if to.width > to.height { //Landscape
        cropWidth = contextSize.width
        cropHeight = contextSize.width / cropAspect
        posY = (contextSize.height - cropHeight) / 2
    } else if to.width < to.height { //Portrait
        cropHeight = contextSize.height
        cropWidth = contextSize.height * cropAspect
        posX = (contextSize.width - cropWidth) / 2
    } else { //Square
        if contextSize.width >= contextSize.height { //Square on landscape (or square)
            cropHeight = contextSize.height
            cropWidth = contextSize.height * cropAspect
            posX = (contextSize.width - cropWidth) / 2
        }else{ //Square on portrait
            cropWidth = contextSize.width
            cropHeight = contextSize.width / cropAspect
            posY = (contextSize.height - cropHeight) / 2
        }
    }

    let rect: CGRect = CGRect(x : posX, y : posY, width : cropWidth, height : cropHeight)

    // Create bitmap image from context using the rect
    let imageRef: CGImage = contextImage.cgImage!.cropping(to: rect)!

    // Create a new image based on the imageRef and rotate back to the original orientation
    let cropped: UIImage = UIImage(cgImage: imageRef, scale: self.scale, orientation: self.imageOrientation)

    cropped.draw(in: CGRect(x : 0, y : 0, width : to.width, height : to.height))

    return cropped
  }
}

The accepted answer only does squares for me. I needed a bit more flexible cropping mechanism so I wrote an extension as follows:

import UIKit

extension UIImage {

func crop(to:CGSize) -> UIImage {

    guard let cgimage = self.cgImage else { return self }

    let contextImage: UIImage = UIImage(cgImage: cgimage)

    guard let newCgImage = contextImage.cgImage else { return self }

    let contextSize: CGSize = contextImage.size

    //Set to square
    var posX: CGFloat = 0.0
    var posY: CGFloat = 0.0
    let cropAspect: CGFloat = to.width / to.height

    var cropWidth: CGFloat = to.width
    var cropHeight: CGFloat = to.height

    if to.width > to.height { //Landscape
        cropWidth = contextSize.width
        cropHeight = contextSize.width / cropAspect
        posY = (contextSize.height - cropHeight) / 2
    } else if to.width < to.height { //Portrait
        cropHeight = contextSize.height
        cropWidth = contextSize.height * cropAspect
        posX = (contextSize.width - cropWidth) / 2
    } else { //Square
        if contextSize.width >= contextSize.height { //Square on landscape (or square)
            cropHeight = contextSize.height
            cropWidth = contextSize.height * cropAspect
            posX = (contextSize.width - cropWidth) / 2
        }else{ //Square on portrait
            cropWidth = contextSize.width
            cropHeight = contextSize.width / cropAspect
            posY = (contextSize.height - cropHeight) / 2
        }
    }

    let rect: CGRect = CGRect(x: posX, y: posY, width: cropWidth, height: cropHeight)

    // Create bitmap image from context using the rect
    guard let imageRef: CGImage = newCgImage.cropping(to: rect) else { return self}

    // Create a new image based on the imageRef and rotate back to the original orientation
    let cropped: UIImage = UIImage(cgImage: imageRef, scale: self.scale, orientation: self.imageOrientation)

    UIGraphicsBeginImageContextWithOptions(to, false, self.scale)
    cropped.draw(in: CGRect(x: 0, y: 0, width: to.width, height: to.height))
    let resized = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return resized ?? self
  }
}

You can use it so:

let size = CGSize(width: 300, height: 200)
let image = UIImage(named: "my_great_photo")?.crop(size)

If anyone has ideas how to make the landscape, portrait and square handling a bit better let me know.

To get a centered position for your crop, you can halve the difference of the height and width. Then you can assign the bounds for the new width and height after checking the orientation of the image (which part is longer)

func cropToBounds(image: UIImage, width: Double, height: Double) -> UIImage {

    let contextImage: UIImage = UIImage(CGImage: image.CGImage)!

    let contextSize: CGSize = contextImage.size

    var posX: CGFloat = 0.0
    var posY: CGFloat = 0.0
    var cgwidth: CGFloat = CGFloat(width)
    var cgheight: CGFloat = CGFloat(height)

    // See what size is longer and create the center off of that
    if contextSize.width > contextSize.height {
        posX = ((contextSize.width - contextSize.height) / 2)
        posY = 0
        cgwidth = contextSize.height
        cgheight = contextSize.height
    } else {
        posX = 0
        posY = ((contextSize.height - contextSize.width) / 2)
        cgwidth = contextSize.width
        cgheight = contextSize.width
    }

    let rect: CGRect = CGRectMake(posX, posY, cgwidth, cgheight)

    // Create bitmap image from context using the rect
    let imageRef: CGImageRef = CGImageCreateWithImageInRect(contextImage.CGImage, rect)

    // Create a new image based on the imageRef and rotate back to the original orientation
    let image: UIImage = UIImage(CGImage: imageRef, scale: image.scale, orientation: image.imageOrientation)!

    return image
}

I found most of this info over at this website in case you wanted to read further.

Updated for Swift 4

func cropToBounds(image: UIImage, width: Double, height: Double) -> UIImage {

        let cgimage = image.cgImage!
        let contextImage: UIImage = UIImage(cgImage: cgimage)
        let contextSize: CGSize = contextImage.size
        var posX: CGFloat = 0.0
        var posY: CGFloat = 0.0
        var cgwidth: CGFloat = CGFloat(width)
        var cgheight: CGFloat = CGFloat(height)

        // See what size is longer and create the center off of that
        if contextSize.width > contextSize.height {
            posX = ((contextSize.width - contextSize.height) / 2)
            posY = 0
            cgwidth = contextSize.height
            cgheight = contextSize.height
        } else {
            posX = 0
            posY = ((contextSize.height - contextSize.width) / 2)
            cgwidth = contextSize.width
            cgheight = contextSize.width
        }

        let rect: CGRect = CGRect(x: posX, y: posY, width: cgwidth, height: cgheight)

        // Create bitmap image from context using the rect
        let imageRef: CGImage = cgimage.cropping(to: rect)!

        // Create a new image based on the imageRef and rotate back to the original orientation
        let image: UIImage = UIImage(cgImage: imageRef, scale: image.scale, orientation: image.imageOrientation)

        return image
    }

This is THE answer, credit to @awolf (Cropping an UIImage). Handles scale and orientation perfectly. Just call this method on the image you want to crop, and pass in the cropping CGRect without worrying about scale or orientation. Feel free to check whether cgImage is nil instead of force unwrapping it like I did here.

extension UIImage {
    func croppedInRect(rect: CGRect) -> UIImage {
        func rad(_ degree: Double) -> CGFloat {
            return CGFloat(degree / 180.0 * .pi)
        }

        var rectTransform: CGAffineTransform
        switch imageOrientation {
        case .left:
            rectTransform = CGAffineTransform(rotationAngle: rad(90)).translatedBy(x: 0, y: -self.size.height)
        case .right:
            rectTransform = CGAffineTransform(rotationAngle: rad(-90)).translatedBy(x: -self.size.width, y: 0)
        case .down:
            rectTransform = CGAffineTransform(rotationAngle: rad(-180)).translatedBy(x: -self.size.width, y: -self.size.height)
        default:
            rectTransform = .identity
        }
        rectTransform = rectTransform.scaledBy(x: self.scale, y: self.scale)

        let imageRef = self.cgImage!.cropping(to: rect.applying(rectTransform))
        let result = UIImage(cgImage: imageRef!, scale: self.scale, orientation: self.imageOrientation)
        return result
    }
}

If you want the cropping rect to be centered, just do simple math. Along the lines of

let x = (image.width - croppingFrame.width) / 2

Another note: if you are working with imageView embedded in a scrollView, there is one additional step, you have to take the zoom factor into account. Assuming your imageView spans the entire content view of the scrollView, and you use the bounds of the scrollView as the cropping frame, the cropped image can be obtained as

let ratio = imageView.image!.size.height / scrollView.contentSize.height
let origin = CGPoint(x: scrollView.contentOffset.x * ratio, y: scrollView.contentOffset.y * ratio)
let size = CGSize(width: scrollView.bounds.size.width * ratio, let height: scrollView.bounds.size.height * ratio)
let cropFrame = CGRect(origin: origin, size: size)
let croppedImage = imageView.image!.croppedInRect(rect: cropFrame)