NSData 到 UIImage 质量

Question

我用UIImage *image = [UIImage imageWithData: data]，但是图片大小大了四倍。原来data.length=100 KB，但是这个image现在多了400 KB。你可能会说用压缩完成。但我比压缩后通过以下方法data.length=200 KB。

以下是我的方式

压缩方式

 // spend is size (KB)
    - (NSData *)compressionImageData:(NSData *)data spend:(CGFloat)spend {

        if (data.length < spend) {
            return data;    //no compression
        }
        UIImage *sourceImg = [UIImage imageWithData:data];

        CGFloat compression = 0.9f;
        CGFloat maxCompression = 0.1f;
        NSData *imageData = UIImageJPEGRepresentation(sourceImg, compression);

        while ([imageData length] > spend && compression > maxCompression) {
            compression -= 0.1;
            imageData = UIImageJPEGRepresentation(sourceImg, compression);
        }
        return imageData; 
    }

图片下载方法：

- (void)loadPosterImage:(NSString *)imgURL {
    weakSelf();
    [[SDWebImageDownloader sharedDownloader] downloadImageWithURL:[NSURL URLWithString:imgURL]
            options:SDWebImageDownloaderLowPriority
            progress:^(NSInteger receivedSize, NSInteger expectedSize) {}
            completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
                strongSelf();
                //  image is through [UIImage imageWithData: data]
                self.posterImage = image;
                self.posterData = data;

            }];
}

图片大小超过 500 KB

data.lenght = 100KB

这是图片的data.length

这是图片的图片

Answer 1

我不知道为什么，但是你可以像这样重绘图像：

+(NSData *)compressDataWithImage:(UIImage *)image toMaxFIleSize:(NSInteger)maxFileSize {
UIImage *comImage;

comImage = image;
CGFloat compression = 1.0;
NSData *imageData = UIImageJPEGRepresentation(comImage, compression);
NSData *newData;
while (imageData.length > maxFileSize) {
    compression *= 0.5;
    newData = UIImageJPEGRepresentation(comImage, compression);
    if (newData.length == imageData.length) {
        CGSize newSize = CGSizeMake(comImage.size.width * 0.5, comImage.size.height * 0.5);
        UIGraphicsBeginImageContext(newSize);
        [comImage drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];
        comImage = UIGraphicsGetImageFromCurrentImageContext();
        newData = UIImageJPEGRepresentation(comImage, compression);
    }
    imageData = newData;
  }

return imageData;

}