如何在Swift中调整图片大小？

Question

我正在使用Swift和Parse.com 为iOS制作一个应用程序我试图让用户从图像选择器中选择一张图片，然后将所选图像的大小调整为200x200像素，然后再上传到我的后端。Parse.com有一个名为“ AnyPic”的Instagram复制应用程序的教程，该教程提供了用于调整图像大小的代码，但它位于Objective-C中。// Resize the image to be square (what is shown in the preview)UIImage *resizedImage = [anImage resizedImageWithContentMode:UIViewContentModeScaleAspectFit        bounds:CGSizeMake(560.0f, 560.0f)        interpolationQuality:kCGInterpolationHigh];// Create a thumbnail and add a corner radius for use in table viewsUIImage *thumbnailImage = [anImage thumbnailImage:86.0f        transparentBorder:0.0f        cornerRadius:10.0f        interpolationQuality:kCGInterpolationDefault];如何在Swift中为所选图片创建200x200px版本（然后上传）？而且，thumbnailImage函数在做什么？

Answer 1

有关更多详细信息，请参阅我的博客文章，快速且客观地C调整图像大小。

快速调整图像尺寸的功能如下。

func resizeImage(image: UIImage, targetSize: CGSize) -> UIImage {

    let size = image.size

    let widthRatio  = targetSize.width  / size.width

    let heightRatio = targetSize.height / size.height

    // Figure out what our orientation is, and use that to form the rectangle

    var newSize: CGSize

    if(widthRatio > heightRatio) {

        newSize = CGSizeMake(size.width * heightRatio, size.height * heightRatio)

    } else {

        newSize = CGSizeMake(size.width * widthRatio,  size.height * widthRatio)

    }

    // This is the rect that we've calculated out and this is what is actually used below

    let rect = CGRectMake(0, 0, newSize.width, newSize.height)

    // Actually do the resizing to the rect using the ImageContext stuff

    UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)

    image.drawInRect(rect)

    let newImage = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()

    return newImage

}

使用上面的功能并使用200 * 200调整图像大小，如下代码

self.resizeImage(UIImage(named: "yourImageName")!, targetSize: CGSizeMake(200.0, 200.0))

swift3更新

 func resizeImage(image: UIImage, targetSize: CGSize) -> UIImage {

    let size = image.size

    let widthRatio  = targetSize.width  / size.width

    let heightRatio = targetSize.height / size.height

    // Figure out what our orientation is, and use that to form the rectangle

    var newSize: CGSize

    if(widthRatio > heightRatio) {

        newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)

    } else {

        newSize = CGSize(width: size.width * widthRatio,  height: size.height * widthRatio)

    }

    // This is the rect that we've calculated out and this is what is actually used below

    let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)

    // Actually do the resizing to the rect using the ImageContext stuff

    UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)

    image.draw(in: rect)

    let newImage = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()

    return newImage!

}

Answer 2

由于@KiritModi的答案来自2015年，因此这是Swift 3.0的版本：

func resizeImage(image: UIImage, targetSize: CGSize) -> UIImage {

    let size = image.size

    let widthRatio  = targetSize.width  / image.size.width

    let heightRatio = targetSize.height / image.size.height

    // Figure out what our orientation is, and use that to form the rectangle

    var newSize: CGSize

    if(widthRatio > heightRatio) {

        newSize = CGSize(width: size.width * heightRatio, height: size.height * heightRatio)

    } else {

        newSize = CGSize(width: size.width * widthRatio,  height: size.height * widthRatio)

    }

    // This is the rect that we've calculated out and this is what is actually used below

    let rect = CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height)

    // Actually do the resizing to the rect using the ImageContext stuff

    UIGraphicsBeginImageContextWithOptions(newSize, false, 1.0)

    image.draw(in: rect)

    let newImage = UIGraphicsGetImageFromCurrentImageContext()

    UIGraphicsEndImageContext()

    return newImage!

}

Answer 3

对于Swift 4.0和iOS 10

    extension UIImage {

        func resizeImage(_ dimension: CGFloat, opaque: Bool, contentMode: UIViewContentMode = .scaleAspectFit) -> UIImage {

            var width: CGFloat

            var height: CGFloat

            var newImage: UIImage

            let size = self.size

            let aspectRatio =  size.width/size.height

            switch contentMode {

                case .scaleAspectFit:

                    if aspectRatio > 1 {                            // Landscape image

                        width = dimension

                        height = dimension / aspectRatio

                    } else {                                        // Portrait image

                        height = dimension

                        width = dimension * aspectRatio

                    }

            default:

                fatalError("UIIMage.resizeToFit(): FATAL: Unimplemented ContentMode")

            }

            if #available(iOS 10.0, *) {

                let renderFormat = UIGraphicsImageRendererFormat.default()

                renderFormat.opaque = opaque

                let renderer = UIGraphicsImageRenderer(size: CGSize(width: width, height: height), format: renderFormat)

                newImage = renderer.image {

                    (context) in

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

                }

            } else {

                UIGraphicsBeginImageContextWithOptions(CGSize(width: width, height: height), opaque, 0)

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

                    newImage = UIGraphicsGetImageFromCurrentImageContext()!

                UIGraphicsEndImageContext()

            }

            return newImage

        }

    }