Question

我有从图库中访问过的图片。我想将此图像存储在数据库中，然后重新调整大小并将其POST到服务器。如果图像被压缩，是否可以告诉我是否会丢失EXIF数据？我的原始图片有EXIF数据。如果数据没有丢失。请指导我如何压缩和重新调整图像大小

Answer 1

图片大小调整

此区域的答案很多，例如：The simplest way to resize an UIImage?或https://stackoverflow.com/questions/1282830/uiimagepickercontroller-uiimage-memory-and-more处的更多详情

图片压缩

您可以使用UIImageJPEGRepresentation C函数，该函数声明为...

NSData * UIImageJPEGRepresentation (
   UIImage *image,
   CGFloat compressionQuality
);

...您可以传递UIImage对象并将压缩质量设置在0.0（最大压缩）范围内，达到1.0（最佳质量）。

EXIF损失

查看https://stackoverflow.com/questions/1282830/uiimagepickercontroller-uiimage-memory-and-more

上的答案

Answer 2

如果你想在不丢失exif的情况下压缩图像，首先你应该得到图像的属性，而你得到的数据UIImageJPEGRepresentation不包含exif。

1：getoritatinal图像数据 2：压缩providerData 3：wite exif压缩数据

- (void)setImagePropertyWith:(ALAsset *)asset

 {
        //get full imageData
        ALAssetRepresentation * defaultRep = [asset defaultRepresentation];
        Byte *buffer = (Byte*)malloc(defaultRep.size);
        NSUInteger buffered = [defaultRep getBytes:buffer fromOffset:0.0 length:defaultRep.size error:nil];
        NSData * data = [NSData dataWithBytesNoCopy:buffer length:buffered freeWhenDone:YES];

        // compressData providerData 
        CGDataProviderRef jpegdata = CGDataProviderCreateWithCFData((CFDataRef)data);
        CGImageRef imageRef = CGImageCreateWithJPEGDataProvider(jpegdata, NULL, YES, kCGRenderingIntentDefault);
        UIImage * image = [UIImage imageWithCGImage:imageRef];
        NSData* finaldata = UIImageJPEGRepresentation(image, 0.5);

        //compressData with exif
        finaldata =  [self writeExif:(NSDictionary *)[self getPropertyOfdata:data] intoImage:finaldata];

    }
    - (CFDictionaryRef )getPropertyOfdata:(NSData *)data
    {
        CGImageSourceRef imageSource = CGImageSourceCreateWithData((CFDataRef)data, NULL);
        if (imageSource == NULL) {
            // Error loading image
            return nil;
        }
        NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                                 [NSNumber numberWithBool:NO], (NSString *)kCGImageSourceShouldCache,
                                 nil];
        CFDictionaryRef imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, (CFDictionaryRef)options);
        NSLog(@"ori:%@",imageProperties);
        return imageProperties;
    //    [self writeExif: (NSDictionary *)imageSource intoImageData:data];
    }

iphone用exif数据减小图像的大小（以字节为单位）

2 个答案: