A Swift version of this SO answer: http://stackoverflow.com/questions/603907/uiimage-resize-then-crop#605385

scale-and-crop-image.swift

// credit: http://stackoverflow.com/questions/603907/uiimage-resize-then-crop#605385
func scaleAndCropImage(_ image:UIImage, toSize size: CGSize) -> UIImage {
    // Make sure the image isn't already sized.
    guard !image.size.equalTo(size) else {
        return image
    }

    let widthFactor = size.width / image.size.width
    let heightFactor = size.height / image.size.height
    var scaleFactor: CGFloat = 0.0

    scaleFactor = heightFactor

    if widthFactor > heightFactor {
        scaleFactor = widthFactor
    }

    var thumbnailOrigin = CGPoint.zero
    let scaledWidth  = image.size.width * scaleFactor
    let scaledHeight = image.size.height * scaleFactor

    if widthFactor > heightFactor {
        thumbnailOrigin.y = (size.height - scaledHeight) / 2.0
    }

    else if widthFactor < heightFactor {
        thumbnailOrigin.x = (size.width - scaledWidth) / 2.0
    }

    var thumbnailRect = CGRect.zero
    thumbnailRect.origin = thumbnailOrigin
    thumbnailRect.size.width  = scaledWidth
    thumbnailRect.size.height = scaledHeight

    // Why use `UIGraphicsBeginImageContextWithOptions` over `UIGraphicsBeginImageContext`?
    // see: http://stackoverflow.com/questions/4334233/how-to-capture-uiview-to-uiimage-without-loss-of-quality-on-retina-display#4334902
    UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
    image.draw(in: thumbnailRect)
    let scaledImage = UIGraphicsGetImageFromCurrentImageContext()!
    UIGraphicsEndImageContext()

    return scaledImage
}

Description

This resizes and then crops an image to fit within a specified rect.

The image is drawn off-screen in a buffer, that is done with UIGraphicsBeginImageContextWithOptions. See the Drawing and Printing Guide for iOS

Performance

Although this is the most efficient way to resize an image it still is an expensive procedure, hence, it ought to be run a few times as possible. Execute this routine on a background thread and then cache the result.

Thanks man! it solved my big problem!