如何在上传到 Parse as PFFile 之前压缩或减小图像的大小？（迅速）答案

【问题标题】：How to compress of reduce the size of an image before uploading to Parse as PFFile? (Swift)如何在上传到 Parse as PFFile 之前压缩或减小图像的大小？（迅速）
【发布时间】：2015-06-25 22:11:27
【问题描述】：

直接在手机上拍照后，我试图将图像文件上传到 Parse。但它抛出了一个异常：

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
    }
}

在上传图片的视图控制器中：

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。有什么办法可以减小图片的大小或分辨率？

【问题讨论】：

我尝试了 gbk 的最后一个命题，最后发现如果我调用 let newData = UIImageJPEGRepresentation(UIImage(data: data), 1) newData.count 不等于 data.count 并且是真的更大，系数超过 2。这对我来说真的很令人惊讶！无论如何，谢谢你的代码！

标签： ios swift parse-platform uiimage

【解决方案1】：

是的，您可以使用UIImageJPEGRepresentation 而不是UIImagePNGRepresentation 来减小图像文件的大小。你可以创建一个扩展 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 Swift 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)
}

【讨论】：

使用未声明类型的 UIImage。这是我得到的错误
我返回的图像大小为 22-25MB，现在只是其中的一小部分。太感谢了！很棒的扩展！
除了语法没有区别。当然，您可以手动编写代码UIImageJPEGRepresentation(yourImage, 1.0) 而不是只输入.jp 并让xcode 为您自动完成该方法。压缩枚举 .whatever 也是如此。
@Umitk 你应该导入 UIKit
'jpegData(compressionQuality:)' 已重命名为 'UIImageJPEGRepresentation(::)'

【解决方案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
    } 
}

【讨论】：

这是更全面的解决方案。
swift 3.1 if let data = bits.representation(using: .jpeg, properties: [.compressionFactor:compressingValue])
这非常昂贵，您每次都在 while 循环中执行如此繁重的任务！没有限制条件..
全面但真的很难记忆。这会使旧设备因内存问题而崩溃。必须有更便宜的方法来做到这一点。
这是一个非常糟糕的主意，它充满了可怕的边缘情况。 1) 它从 compressingValue 1.0 开始，这意味着几乎没有任何压缩。如果图像尺寸很小，那么图像最终会比它们需要的多得多。 2）如果图像很大，它会很慢，因为它可能会重新压缩多次以低于目标大小。 3）如果图像非常大，那么它可能会压缩到图像看起来很垃圾的程度。在这些情况下，最好不要保存图像并告诉用户它太大了。

【解决方案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!)!
}

【讨论】：

【解决方案4】：

Xcode 7 的 Jus Fixing，于 2015 年 9 月 21 日测试并且工作正常：

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)! }
}

那么你可以这样使用它：

let imageData = imagePassed.lowestQualityJPEGNSData

【讨论】：

核心感谢答案所有者Thiago先生和编辑kuldeep先生

【解决方案5】：

如果您不需要压缩到特定大小，则使用func jpegData(compressionQuality: CGFloat) -> Data? 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停滞（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骤乘数，以加快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()
    }
}

及用法：

let data = image.compress(to: 300)

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

【讨论】：

【解决方案6】：

Swift 4 Binary Approach 压缩图像

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 二分搜索 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，*二分搜索** 方法将在最大 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，我们可以看到图像在浮点值 > 0.995 后停止压缩.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)!
    }
}

【讨论】：

为什么要使用 While 循环并手动递增变量？只需使用for i in 0...13。

【解决方案7】：

使用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)!)
    }
}

SWIFT 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)")
}

【讨论】：

非常慢且同步
可能会发生您调整大小的图像永远不会小于 300kB 并且您在这种情况下没有任何回退
至少 (compressQuality >= 0) 可能会作为额外的 && 条件添加到 while 循环中

【解决方案8】：

Swift 4.2 更新。我创建了这个扩展来减少 UIImage 的大小。
这里你有两种方法，第一种取百分比，第二种将图像缩小到 1MB。
当然你可以把第二种方法改成 1KB 或者你想要的任何大小。

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
    }
}

【讨论】：

【解决方案9】：

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

【讨论】：

【解决方案10】：

在 Swift 中

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!
    }

【讨论】：

【解决方案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)  }
}

【讨论】：

【解决方案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")
        }

【讨论】：

【解决方案13】：

我发现最简单的方法是

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)
    }
 
}

【讨论】：