用IOS app上传图片到服务器文件过大

Question

我正在使用 IOS 应用程序将照片上传到服务器。重要的是，照片上传时没有质量损失，并以 jpeg 格式上传。我目前的问题是照片上传没有质量损失，但文件大小比预期的要大。例如：我通过应用上传了一个文件，文件大小为 4.7 MB。当我将同一张照片通过电子邮件发送给自己并为电子邮件选择“实际照片”选项时，照片的大小仅为 1.7 MB。并排比较显示质量没有差异。

这是我上传文件的方式。

ALAssetsLibrary *library = [ALAssetsLibrary new];
[library getImageAtURL:orderImage.imageUrl with completionBlock:^(UIImage *image)

NSData *fileData = UIImageJPEGRepresentation(image, 1.0)

NSURLRequest *request = [self multipartFormRequestWithMethod:@"POST" path:path parameters:nil constructingBodyWithBlock:^(id<AFMultipartFormData> formData)
{
    [formData appendPartWithFileData:fileData name:@"uploadedfile" fileName:fileName mimeType:mimeType];
    [formData appendPartWithFormData:[extraInfo dataUsingEncoding:NSISOLatin2StringEncoding] name:@"extraInfo"];
}];

Answer 1

问题是UIImageJPEGRepresentation。它不会检索原始 JPEG，而是创建一个新的 JPEG。当您使用compressionQuality 或1 时（大概是为了避免进一步的图像质量损失），它会创建这种不压缩的新表示（通常会导致文件大于原始文件）。

我建议使用getBytes 来检索原始资产，而不是通过UIImage 往返并通过UIImageJPEGRepresentation 获取数据：

ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
[library assetForURL:assetsLibraryURL resultBlock:^(ALAsset *asset) {
    ALAssetRepresentation *representation = [asset defaultRepresentation];

    // I generally would write directly to a `NSOutputStream`, but if you want it in a
    // NSData, it would be something like:

    NSMutableData *data = [NSMutableData data];

    // now loop, reading data into buffer and writing that to our data stream

    NSError *error;
    long long bufferOffset = 0ll;
    NSInteger bufferSize = 10000;
    long long bytesRemaining = [representation size];
    uint8_t buffer[bufferSize];
    while (bytesRemaining > 0) {
        NSUInteger bytesRead = [representation getBytes:buffer fromOffset:bufferOffset length:bufferSize error:&error];
        if (bytesRead == 0) {
            NSLog(@"error reading asset representation: %@", error);
            return;
        }
        bytesRemaining -= bytesRead;
        bufferOffset   += bytesRead;
        [data appendBytes:buffer length:bytesRead];
    }

    // ok, successfully read original asset; 
    // do whatever you want with it here

} failureBlock:^(NSError *error) {
    NSLog(@"error=%@", error);
}];

--

如果你使用iOS 8引入的Photos框架，可以使用PHImageManager获取图片数据：

PHFetchResult *result = [PHAsset fetchAssetsWithALAssetURLs:@[assetsLibraryURL] options:nil];
PHAsset *asset = [result firstObject];
if (asset) {
    PHImageManager *manager = [PHImageManager defaultManager];
    [manager requestImageDataForAsset:asset options:nil resultHandler:^(NSData *imageData, NSString *dataUTI, UIImageOrientation orientation, NSDictionary *info) {
        // use `imageData` here
    }];
}