Question

我使用这个从服务器获取图像：

- (void)downloadImageWithURL:(NSURL *)url completionBlock:(void (^)(BOOL succeeded, NSData *data))completionBlock
{
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse *response, NSData *data, NSError *error)
     {
         if (!error)
         {
             completionBlock(YES, data);
         }
         else
         {
             completionBlock(NO, nil);
         }
     }];
}

哪个提供NSData。现在为了获得更好的性能，我想在jpeg中显示图像。

我知道如何使用NSData to UIImag转换UIImage *image=[UIImage imageWithData:data]; e 以及如何从图像NSData *imageData = UIImagePNGRepresentation(image);

创建NSData

但两者都没有做我需要的，我想从服务器获取NSData，并创建它的JPEG图像。我该怎么办？（我是否必须首先使用jpeg创建新数据，而不是使用此数据中的图像？）

Answer 1

要将从服务器获取的数据转换为jpeg，请使用：

UIImage *image = [UIImage imageWithData:serverData];
NSData *jpegData = UIImageJPEGRepresentation(image, 0.75f);

Answer 2

你可能需要这样做：

CGDataProviderRef imgProvider = CGDataProviderCreateWithCFData((CFDataRef) data);
CGImageRef imgRef = CGImageCreateWithJPEGDataProvider(imgProvider, NULL, true, kCGRenderingIntentDefault);

确保释放imgRef和imgProvider

Answer 3

在Swift 5和iOS 12中，您可以使用CGImage，CGImageDestination和CGDataProvider以便将某些JPEG图像数据写入给定的URL。以下函数实现显示了如何执行此操作：

import Foundation
import ImageIO
import MobileCoreServices

func saveImageData(_ data: Data, to fileUrl: URL) {
    guard let provider = CGDataProvider(data: data as CFData) else {
        print("Could not create data provider from data")
        return
    }

    guard let cgImage = CGImage(jpegDataProviderSource: provider, decode: nil, shouldInterpolate: true, intent: CGColorRenderingIntent.defaultIntent) else {
        print("Could not create cgImage from provider")
        return
    }

    guard let imageDestination = CGImageDestinationCreateWithURL(fileUrl as CFURL, kUTTypeJPEG, 1, nil) else {
        print("Could not create an image destination from url")
        return
    }

    let options = [
        kCGImageDestinationLossyCompressionQuality: 0.75, // Compress quality (if required)
        kCGImagePropertyOrientation: CGImagePropertyOrientation.right.rawValue // Rotate image to the right (if required)
    ] as CFDictionary

    CGImageDestinationAddImage(imageDestination, cgImage, options)
    let imageIsWritten = CGImageDestinationFinalize(imageDestination)

    if !imageIsWritten {
        print("Image could not be written")
    }
}

用法：

let data: Data = …
let documentDirectoryUrl = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
let fileUrl = documentDirectoryUrl.appendingPathComponent("image.jpeg")
saveImageData(data, to: fileUrl)

来源： -Image I/O Programming Guide - Working with Image Destinations

从NSData创建Jpeg

3 个答案: