如何在不模糊的情况下保存/共享缩小的图像

Question

我有一个真心的问题。我使用了以下算法来调整图像大小和共享图像。

func resizeImageWith(newSize: CGSize) -> UIImage {

    let horizontalRatio = newSize.width / size.width
    let verticalRatio = newSize.height / size.height

    let ratio = max(horizontalRatio, verticalRatio)
    let newSize = CGSize(width: size.width * ratio, height: size.height * ratio)
    UIGraphicsBeginImageContextWithOptions(newSize, true, 0)
    draw(in: CGRect(origin: CGPoint(x: 0, y: 0), size: newSize))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return newImage!
}

func shareImageToSM(image : UIImage) {

    let imageToShare = [ image ]

    let activityVC = UIActivityViewController(activityItems: imageToShare, applicationActivities: nil)

    //New Excluded Activities Code
    if #available(iOS 9.0, *) {
        activityVC.excludedActivityTypes = [UIActivityType.airDrop, UIActivityType.addToReadingList, UIActivityType.openInIBooks]
    } else {
        activityVC.excludedActivityTypes = [UIActivityType.airDrop, UIActivityType.addToReadingList]
    }
    //

    activityVC.popoverPresentationController?.sourceView = self.view
    self.present(activityVC, animated: true, completion: nil)
}

它可以正确地调整图像大小。例如，它将我的600x600图像缩小到150x150，但当我尝试保存或分享缩小后的图像时，它的大小与实际图像相同，但变得模糊。请看下面的图片。

​

上面是600x600的实际图像大小和尺寸

​

这是保存/共享的已调整大小的图片(150x150)。

我希望这张图片以150x150的尺寸保存/共享，但实际的像素质量更高，如下图所示。请帮帮我，这对我来说是一个严重的问题和令人头疼的问题。

​

Answer 1

 enum ImageQuality:CGFloat {
    case iq_50 = 50, iq_100 = 100 ,iq_320 = 320, iq_480 = 480 , iq_640 = 640 , iq_720 = 720 , iq_1024 = 1024
}
static func scaleImage(sourceImage: UIImage, imageQuality:ImageQuality) -> UIImage{
    let finalSize:CGSize = getNewsize(sourceSize: sourceImage.size, targetSize: imageQuality.rawValue)
    UIGraphicsBeginImageContextWithOptions(finalSize, false, 0)
    sourceImage.draw(in: CGRect(origin: .zero, size: finalSize))
    let newImage = UIGraphicsGetImageFromCurrentImageContext()!
    UIGraphicsEndImageContext()
    return newImage
}
static func getNewsize(sourceSize:CGSize, targetSize:CGFloat) -> CGSize{
    let width: CGFloat = sourceSize.width
    let height: CGFloat = sourceSize.height
    var scaleFactor: CGFloat = 0.0
    var scaledWidth: CGFloat = targetSize
    var scaledHeight: CGFloat = targetSize

    let widthFactor: CGFloat = targetSize / width
    let heightFactor: CGFloat = targetSize / height

    if widthFactor > heightFactor {
        scaleFactor = widthFactor
    }
    else {
        scaleFactor = heightFactor
    }
    scaledWidth = width * scaleFactor
    scaledHeight = height * scaleFactor
    return CGSize(width: scaledWidth, height: scaledHeight)
}