swift - 在上传到 Google Cloud 存储之前调整图像大小并压缩图像

Question

我创建了一个函数，可以在保持纵横比的同时将图像大小调整为最大宽度和高度。此外，我还根据压缩质量来压缩图像 - 我已经使用 11.7 mb 的 3024x4032 jpeg 图像对此进行了测试。

maxWidth = 800px
maxHeight = 1200px
compressionQuality = 0.5

该函数确实将图像大小从 11.7mb 减小到 0.51mb，但宽度和高度并未正确减小。上传到 Firebase 后，图像大小为 1600 x 2134px 两倍...但应该为 800x1066px(一半)

你能看出哪里出了问题吗？

import UIKit
import Foundation

class ImageEdit {
        static let instance = ImageEdit()

    func resizeAndCompressImageWith(image: UIImage, maxWidth: CGFloat, maxHeight: CGFloat, compressionQuality: CGFloat) -> Data? {

    let horizontalRatio = maxWidth / image.size.width
    let verticalRatio = maxHeight / image.size.height


    let ratio = min(horizontalRatio, verticalRatio)

    let newSize = CGSize(width: image.size.width * ratio, height: image.size.height * ratio)
    var newImage: UIImage

    if #available(iOS 10.0, *) {
        let renderFormat = UIGraphicsImageRendererFormat.default()
        renderFormat.opaque = false
        let renderer = UIGraphicsImageRenderer(size: CGSize(width: newSize.width, height: newSize.height), format: renderFormat)
        newImage = renderer.image {
            (context) in
            image.draw(in: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height))
        }
    } else {
        UIGraphicsBeginImageContextWithOptions(CGSize(width: newSize.width, height: newSize.height), true, 0)
        image.draw(in: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height))
        newImage = UIGraphicsGetImageFromCurrentImageContext()!
        UIGraphicsEndImageContext()
    }

            let data = UIImageJPEGRepresentation(newImage, compressionQuality)



    return data

}

}

这是将图像上传到 firebase 的代码。

func uploadImageToFirebaseAndReturnImageURL(directory: String, image: UIImage!, maxWidth: CGFloat, maxHeight: CGFloat, compressionQuality: CGFloat, handler: @escaping(_ imageURL: String)  -> ()) {
        let imageName = NSUUID().uuidString // create unique image name

        if let uploadData = ImageEdit.instance.resizeAndCompressImageWith(image: image, maxWidth: maxWidth, maxHeight: maxHeight, compressionQuality: compressionQuality) {

            DB_STORE.child(directory).child(imageName).putData(uploadData, metadata: nil, completion: { (metadata, error) in

                if error != nil {
                    print(error ?? "Image upload failed for unknown reason")
                    return
                }

                // if URL exist, then return imageURL
                if let imageURL = metadata?.downloadURL()?.absoluteString {
                  handler (imageURL)


                }
                return

            })
        }



    }

Answer 1

我将您的代码复制到测试项目中，并添加了一些打印语句，并尝试调整原始尺寸为 3360x2108 的图像大小。 (注意:我在此测试代码中使用强制展开，但不建议将其用于任何生产代码)。

这是我调用调整大小代码的函数:

func resizeImage() {
    guard let image = UIImage.init(named: "landscape") else {
        return
    }
    print("Original Image Size: width: \(image.size.width) height: \(image.size.height)")

    let _ = ImageEdit.instance.resizeAndCompressImageWith(image: image, maxWidth: 800.0, maxHeight: 1200.0, compressionQuality: 0.5)
}

这是我调整大小代码的更新版本。我只是在最后添加一些代码来实例化一些图像实例，以在转换后注销它们的实际大小:

import UIKit

class ImageEdit {
    static let instance = ImageEdit()

    func resizeAndCompressImageWith(image: UIImage, maxWidth: CGFloat, maxHeight: CGFloat, compressionQuality: CGFloat) -> Data? {

        let horizontalRatio = maxWidth / image.size.width
        let verticalRatio = maxHeight / image.size.height


        let ratio = min(horizontalRatio, verticalRatio)
        print("Image Ratio: \(ratio)")

        let newSize = CGSize(width: image.size.width * ratio, height: image.size.height * ratio)
        print("NewSize: \(String(describing: newSize))")
        var newImage: UIImage

        if #available(iOS 10.0, *) {
            print("UIGraphicsImageRendererFormat")
            let renderFormat = UIGraphicsImageRendererFormat.default()
            renderFormat.opaque = false
            let renderer = UIGraphicsImageRenderer(size: CGSize(width: newSize.width, height: newSize.height), format: renderFormat)
            newImage = renderer.image {
                (context) in
                image.draw(in: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height))
            }
        } else {
            print("UIGraphicsBeginImageContextWithOptions")
            UIGraphicsBeginImageContextWithOptions(CGSize(width: newSize.width, height: newSize.height), true, 0)
            image.draw(in: CGRect(x: 0, y: 0, width: newSize.width, height: newSize.height))
            newImage = UIGraphicsGetImageFromCurrentImageContext()!
            UIGraphicsEndImageContext()
        }
        print("NewImageSize: width: \(newImage.size.width) height: \(newImage.size.height)")

        let png = UIImagePNGRepresentation(newImage)
        let pngImg = UIImage.init(data: png!)!
        print("PNG - width: \(pngImg.size.width) - height: \(pngImg.size.height)")

        let data = UIImageJPEGRepresentation(newImage, compressionQuality)
        let jpgImg = UIImage.init(data: data!)!
        print("JPG - width: \(jpgImg.size.width) - height: \(jpgImg.size.height)")

        let fullData = UIImageJPEGRepresentation(newImage, 1.0)
        let jpgFull = UIImage.init(data: fullData!)!
        print("JPG FULL - width: \(jpgFull.size.width) - height: \(jpgFull.size.height)")

        return data

    }
}

当在 iOS 11 的模拟器上运行它时，我将其记录到调试器中:

Original Image Size: width: 3360.0 height: 2108.0
Image Ratio: 0.238095238095238
NewSize: (800.0, 501.904761904762)
UIGraphicsImageRendererFormat
NewImageSize: width: 800.0 height: 502.0
PNG - width: 2400.0 - height: 1506.0
JPG - width: 2400.0 - height: 1506.0
JPG FULL - width: 2400.0 - height: 1506.0

如果我注释掉你的

if #available(iOS 10.0, *) {

block 我仍然看到相同的测量结果。

看来newImage是直接生成的

UIGraphicsImageRendererFormat 
or 
UIGraphicsBeginImageContextWithOptions 

生成具有您指定大小的图像。但是，由于某种原因，通过

运行该图像

UIImagePNGRepresentation(newImage)
or
UIImageJPEGRepresentation(newImage, compressionQuality)

生成的图像尺寸比原始图像大 3 倍。即使我更新了

UIGraphicsBeginImageContextWithOptions(size, false, 0.0)
to
UIGraphicsBeginImageContextWithOptions(size, false, UIScreen.main.scale)

这似乎并不重要。

在我的测试用例中 UIScreen.main.scale = 3.0。

看来，通过 PNG 或 JPEG 表示方法转换图像会将其乘以这些函数生成的最终图像大小的 UIScreen.main.scale 值。