在上传到 Parse 作为 PFFile 之前，如何压缩或减小图像的大小？ （迅速）

Question

直接在手机上拍照后，我试图将图像文件上传到 Parse。 但它抛出一个异常：

由于未捕获的异常“NSInvalidArgumentException”而终止应用程序，原因：“PFFile 不能大于 10485760 字节”

这是我的代码：

在第一个视图控制器中：

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if (segue.identifier == "getImage")
    {
        var svc = segue.destinationViewController as! ClothesDetail
        svc.imagePassed = imageView.image
    }
}

在上传图像的视图控制器中：

let imageData = UIImagePNGRepresentation(imagePassed)
let imageFile = PFFile(name: "\(picName).png", data: imageData)

var userpic = PFObject(className:"UserPic")
userpic["picImage"] = imageFile`

但我仍然需要将该照片上传到 Parse。 有没有办法减小图像的大小或分辨率？

Answer 1

是的，您可以使用UIImageJPEGRepresentation而不是UIImagePNGRepresentation来减小图像文件的大小。 您可以创建一个扩展 UIImage 如下：

Xcode 8.2 • Swift 3.0.2

extension UIImage {
    enum JPEGQuality: CGFloat {
        case lowest  = 0
        case low     = 0.25
        case medium  = 0.5
        case high    = 0.75
        case highest = 1
    }

    /// Returns the data for the specified image in JPEG format.
    /// If the image object’s underlying image data has been purged, calling this function forces that data to be reloaded into memory.
    /// - returns: A data object containing the JPEG data, or nil if there was a problem generating the data. This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format.
    func jpeg(_ quality: JPEGQuality) -> Data? {
        return UIImageJPEGRepresentation(self, quality.rawValue)
    }
}

---

编辑/更新：

Xcode 10 斯威夫特 4.2

extension UIImage {
    enum JPEGQuality: CGFloat {
        case lowest  = 0
        case low     = 0.25
        case medium  = 0.5
        case high    = 0.75
        case highest = 1
    }

    /// Returns the data for the specified image in JPEG format.
    /// If the image object’s underlying image data has been purged, calling this function forces that data to be reloaded into memory.
    /// - returns: A data object containing the JPEG data, or nil if there was a problem generating the data. This function may return nil if the image has no data or if the underlying CGImageRef contains data in an unsupported bitmap format.
    func jpeg(_ jpegQuality: JPEGQuality) -> Data? {
        return jpegData(compressionQuality: jpegQuality.rawValue)
    }
}

---

用法：

if let imageData = image.jpeg(.lowest) {
    print(imageData.count)
}

Answer 2

如果您想将图像的大小限制为某个具体值，您可以执行以下操作：

import UIKit

extension UIImage {
    // MARK: - UIImage+Resize
    func compressTo(_ expectedSizeInMb:Int) -> UIImage? {
        let sizeInBytes = expectedSizeInMb * 1024 * 1024
        var needCompress:Bool = true
        var imgData:Data?
        var compressingValue:CGFloat = 1.0
        while (needCompress && compressingValue > 0.0) {
        if let data:Data = UIImageJPEGRepresentation(self, compressingValue) {
            if data.count < sizeInBytes {
                needCompress = false
                imgData = data
            } else {
                compressingValue -= 0.1
            }
        }
    }

    if let data = imgData {
        if (data.count < sizeInBytes) {
            return UIImage(data: data)
        }
    }
        return nil
    } 
}

Answer 3

  //image compression
func resizeImage(image: UIImage) -> UIImage {
    var actualHeight: Float = Float(image.size.height)
    var actualWidth: Float = 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 = CGRectMake(0.0, 0.0, CGFloat(actualWidth), CGFloat(actualHeight))
    UIGraphicsBeginImageContext(rect.size)
    image.drawInRect(rect)
    let img = UIGraphicsGetImageFromCurrentImageContext()
    let imageData = UIImageJPEGRepresentation(img!,CGFloat(compressionQuality))
    UIGraphicsEndImageContext()
    return UIImage(data: imageData!)!
}

Answer 4

Jus Fixing for Xcode 7，于 2015 年 9 月 21 日测试，工作正常：

只需创建一个扩展UIImage如下：

extension UIImage
{
    var highestQualityJPEGNSData: NSData { return UIImageJPEGRepresentation(self, 1.0)! }
    var highQualityJPEGNSData: NSData    { return UIImageJPEGRepresentation(self, 0.75)!}
    var mediumQualityJPEGNSData: NSData  { return UIImageJPEGRepresentation(self, 0.5)! }
    var lowQualityJPEGNSData: NSData     { return UIImageJPEGRepresentation(self, 0.25)!}
    var lowestQualityJPEGNSData: NSData  { return UIImageJPEGRepresentation(self, 0.0)! }
}

然后你可以像这样使用它：

let imageData = imagePassed.lowestQualityJPEGNSData

Answer 5

使用func jpegData(compressionQuality: CGFloat) -> Data? 如果您不需要压缩到特定大小，则效果很好。 但是，对于某些图像，我发现能够压缩到特定文件大小以下很有用。 在这种情况下， jpegData是不可靠的，并且图像的迭代压缩会导致文件大小趋于平稳（并且可能非常昂贵）。 相反，我更喜欢减小 UIImage 本身的大小，然后转换为 jpegData 并检查减小的大小是否低于我选择的值（在我设置的误差范围内）。 我根据当前文件大小与所需文件大小的比率调整压缩步长乘数，以加速最昂贵的第一次迭代。

斯威夫特 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 {
        let bytes = kb * 1024
        var compression: CGFloat = 1.0
        let step: CGFloat = 0.05
        var holderImage = self
        var complete = false
        while(!complete) {
            if let data = holderImage.jpegData(compressionQuality: 1.0) {
                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()
    }
}

和用法：

let data = image.compress(to: 300)

UIImage resized扩展来自： How do I resize the UIImage to reduce upload image size

Answer 6

Swift 4 二进制压缩图像的方法

我相信现在回答这个问题已经很晚了，但这是我对优化问题的解决方案我正在使用二进制搜索来找到最佳值。 因此，例如，假设通过正常减法方法达到 62% 需要 38 次压缩尝试，*二元搜索**方法将在 max log(100) = 大约 7 次尝试中达到所需的解决方案。

但是，还要通知您UIImageJPEGRepresentation函数的行为不是线性的，尤其是当数字接近 1 时。这是屏幕截图，我们可以看到在浮点值 > 0.995 后图像停止压缩。 这种行为是非常不可预测的，所以最好有一个可以处理这种情况的增量缓冲区。

这是它的代码

extension UIImage {
    func resizeToApprox(sizeInMB: Double, deltaInMB: Double = 0.2) -> Data {
        let allowedSizeInBytes = Int(sizeInMB * 1024 * 1024)
        let deltaInBytes = Int(deltaInMB * 1024 * 1024)
        let fullResImage = UIImageJPEGRepresentation(self, 1.0)
        if (fullResImage?.count)! < Int(deltaInBytes + allowedSizeInBytes) {
            return fullResImage!
        }

        var i = 0

        var left:CGFloat = 0.0, right: CGFloat = 1.0
        var mid = (left + right) / 2.0
        var newResImage = UIImageJPEGRepresentation(self, mid)

        while (true) {
            i += 1
            if (i > 13) {
                print("Compression ran too many times ") // ideally max should be 7 times as  log(base 2) 100 = 6.6
                break
            }


            print("mid = \(mid)")

            if ((newResImage?.count)! < (allowedSizeInBytes - deltaInBytes)) {
                left = mid
            } else if ((newResImage?.count)! > (allowedSizeInBytes + deltaInBytes)) {
                right = mid
            } else {
                print("loop ran \(i) times")
                return newResImage!
            }
             mid = (left + right) / 2.0
            newResImage = UIImageJPEGRepresentation(self, mid)

        }

        return UIImageJPEGRepresentation(self, 0.5)!
    }
}

Answer 7

UIImage扩展非常简单

extension UIImage {

func resizeByByte(maxByte: Int, completion: @escaping (Data) -> Void) {
    var compressQuality: CGFloat = 1
    var imageData = Data()
    var imageByte = UIImageJPEGRepresentation(self, 1)?.count
    
    while imageByte! > maxByte {
        imageData = UIImageJPEGRepresentation(self, compressQuality)!
        imageByte = UIImageJPEGRepresentation(self, compressQuality)?.count
        compressQuality -= 0.1
    }
    
    if maxByte > imageByte! {
        completion(imageData)
    } else {
        completion(UIImageJPEGRepresentation(self, 1)!)
    }
}

快速 5

extension UIImage {
    
    func resizeByByte(maxByte: Int, completion: @escaping (Data) -> Void) {
        var compressQuality: CGFloat = 1
        var imageData = Data()
        var imageByte = self.jpegData(compressionQuality: 1)?.count
        
        while imageByte! > maxByte {
            imageData = self.jpegData(compressionQuality: compressQuality)!
            imageByte = self.jpegData(compressionQuality: compressQuality)?.count
            compressQuality -= 0.1
        }
        
        if maxByte > imageByte! {
            completion(imageData)
        } else {
            completion(self.jpegData(compressionQuality: 1)!)
        }
    }
}

使用

// max 300kb
image.resizeByByte(maxByte: 300000) { (resizedData) in
    print("image size: \(resizedData.count)")
}

Answer 8

在斯威夫特

func ResizeImageFromOriginalSize(targetSize: CGSize) -> UIImage {
        var actualHeight: Float = Float(self.size.height)
        var actualWidth: Float = Float(self.size.width)
        let maxHeight: Float = Float(targetSize.height)
        let maxWidth: Float = Float(targetSize.width)
        var imgRatio: Float = actualWidth / actualHeight
        let maxRatio: Float = maxWidth / maxHeight
        var 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
                compressionQuality = 1.0
            }
        }
        let rect = CGRect(x: 0.0, y: 0.0, width: CGFloat(actualWidth), height: CGFloat(actualHeight))
        UIGraphicsBeginImageContextWithOptions(rect.size, false, CGFloat(compressionQuality))
        self.draw(in: rect)
        let newImage = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()
        return newImage!
    }

Answer 9

斯威夫特 4.2更新。 我创建了这个扩展来减少 UIImage 的大小。
这里有两种方法，第一种是取百分比，第二种是将图像缩小到 1MB。
当然，您可以将第二种方法更改为 1KB 或您想要的任何大小。

import UIKit

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 = self.pngData() else { return nil }
        let megaByte = 1000.0

        var resizingImage = self
        var imageSizeKB = Double(imageData.count) / megaByte // ! Or devide for 1024 if you need KB but not kB

        while imageSizeKB > megaByte { // ! Or use 1024 if you need KB but not kB
            guard let resizedImage = resizingImage.resized(withPercentage: 0.5),
            let imageData = resizedImage.pngData() else { return nil }

            resizingImage = resizedImage
            imageSizeKB = Double(imageData.count) / megaByte // ! Or devide for 1024 if you need KB but not kB
        }

        return resizingImage
    }
}

Answer 10

在 Swift 5 中，@Thiago Arreguy 回答：

extension UIImage {

    var highestQualityJPEGNSData: Data { return self.jpegData(compressionQuality: 1.0)! }
    var highQualityJPEGNSData: Data    { return self.jpegData(compressionQuality: 0.75)!}
    var mediumQualityJPEGNSData: Data  { return self.jpegData(compressionQuality: 0.5)! }
    var lowQualityJPEGNSData: Data     { return self.jpegData(compressionQuality: 0.25)!}
    var lowestQualityJPEGNSData: Data  { return self.jpegData(compressionQuality: 0.0)! }

}

你可以这样调用：

let imageData = imagePassed.lowestQualityJPEGNSData

Answer 11

斯威夫特 3

@leo-dabus 为 swift 3 修改了答案

    extension UIImage {
    var uncompressedPNGData: Data?      { return UIImagePNGRepresentation(self)        }
    var highestQualityJPEGNSData: Data? { return UIImageJPEGRepresentation(self, 1.0)  }
    var highQualityJPEGNSData: Data?    { return UIImageJPEGRepresentation(self, 0.75) }
    var mediumQualityJPEGNSData: Data?  { return UIImageJPEGRepresentation(self, 0.5)  }
    var lowQualityJPEGNSData: Data?     { return UIImageJPEGRepresentation(self, 0.25) }
    var lowestQualityJPEGNSData:Data?   { return UIImageJPEGRepresentation(self, 0.0)  }
}

Answer 12

在 Swift 4 中，我创建了这个扩展，它将接收预期的大小并尝试达到它。

extension UIImage {

    enum CompressImageErrors: Error {
        case invalidExSize
        case sizeImpossibleToReach
    }
    func compressImage(_ expectedSizeKb: Int, completion : (UIImage,CGFloat) -> Void ) throws {

        let minimalCompressRate :CGFloat = 0.4 // min compressRate to be checked later

        if expectedSizeKb == 0 {
            throw CompressImageErrors.invalidExSize // if the size is equal to zero throws
        }

        let expectedSizeBytes = expectedSizeKb * 1024
        let imageToBeHandled: UIImage = self
        var actualHeight : CGFloat = self.size.height
        var actualWidth : CGFloat = self.size.width
        var maxHeight : CGFloat = 841 //A4 default size I'm thinking about a document
        var maxWidth : CGFloat = 594
        var imgRatio : CGFloat = actualWidth/actualHeight
        let maxRatio : CGFloat = maxWidth/maxHeight
        var compressionQuality : CGFloat = 1
        var imageData:Data = UIImageJPEGRepresentation(imageToBeHandled, compressionQuality)!
        while imageData.count > expectedSizeBytes {

            if (actualHeight > maxHeight || actualWidth > maxWidth){
                if(imgRatio < maxRatio){
                    imgRatio = maxHeight / actualHeight;
                    actualWidth = imgRatio * actualWidth;
                    actualHeight = maxHeight;
                }
                else if(imgRatio > maxRatio){
                    imgRatio = maxWidth / actualWidth;
                    actualHeight = imgRatio * actualHeight;
                    actualWidth = maxWidth;
                }
                else{
                    actualHeight = maxHeight;
                    actualWidth = maxWidth;
                    compressionQuality = 1;
                }
            }
            let rect = CGRect(x: 0.0, y: 0.0, width: actualWidth, height: actualHeight)
            UIGraphicsBeginImageContext(rect.size);
            imageToBeHandled.draw(in: rect)
            let img = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
                if let imgData = UIImageJPEGRepresentation(img!, compressionQuality) {
                if imgData.count > expectedSizeBytes {
                    if compressionQuality > minimalCompressRate {
                        compressionQuality -= 0.1
                    } else {
                        maxHeight = maxHeight * 0.9
                        maxWidth = maxWidth * 0.9
                    }
                }
                imageData = imgData
            }


        }

        completion(UIImage(data: imageData)!, compressionQuality)
    }


}

使用

        do {
            try UiImageView.image?.compressImage(100, completion: { (image, compressRatio) in
                print(image.size) 
                imageData = UIImageJPEGRepresentation(image, compressRatio)
                base64data = imageData?.base64EncodedString()

            })
        } catch {
                 print("Error")
        }

Answer 13

我发现的最简单的方法是

extension UIImage {

    func compressImage(with maxSizeInBytes: Int ) -> UIImage? {
        if maxSizeInBytes < 0 {
            return nil
        }
        var currentImage:UIImage? = self
        var divideQuality:CGFloat = 1.0
        var imageData = self.jpegData(compressionQuality:divideQuality )
        while imageData!.count > maxSizeInBytes {
            divideQuality = divideQuality/2
            imageData = currentImage?.jpegData(compressionQuality: divideQuality)
        }
        guard let data = imageData else {
            return nil
        }
        currentImage = UIImage(data: data)
        return UIImage(data: (currentImage?.jpegData(compressionQuality: divideQuality)) as! Data)
    }
 
}