15

在我的应用程序中，用户使用 UIImagePickerViewController 选择图像或拍照。选择图像后，我想在方形 UIImageView (90x90) 上显示其缩略图。

我正在使用Apple 的代码来创建缩略图。问题是缩略图不是平方的，该函数在将 kCGImageSourceThumbnailMaxPixelSize 键设置为 90 后，似乎只是调整图像的高度，据我所知 kCGImageSourceThumbnailMaxPixelSize 键应该负责设置缩略图的高度和宽度。

这是我的代码的一瞥：

- (void)imagePickerController:(UIImagePickerController *)picker
    didFinishPickingMediaWithInfo:(NSDictionary *)info {

    UIImage *image = [info objectForKey:UIImagePickerControllerOriginalImage];

    NSData *imageData = UIImageJPEGRepresentation (image, 0.5);

    // My image view is 90x90
    UIImage *thumbImage = MyCreateThumbnailImageFromData(imageData, 90);

    [myImageView setImage:thumbImage];

    if (picker.sourceType == UIImagePickerControllerSourceTypeCamera) {

        UIImageWriteToSavedPhotosAlbum(image, self, @selector(image:didFinishSavingWithError:contextInfo:), nil);
    }

    [picker dismissViewControllerAnimated:YES completion:nil];
}

UIImage* MyCreateThumbnailImageFromData (NSData * data, int imageSize) {

    CGImageRef        myThumbnailImage = NULL;
    CGImageSourceRef  myImageSource;
    CFDictionaryRef   myOptions = NULL;
    CFStringRef       myKeys[3];
    CFTypeRef         myValues[3];
    CFNumberRef       thumbnailSize;

    // Create an image source from NSData; no options.
    myImageSource = CGImageSourceCreateWithData((__bridge CFDataRef)data,
                                                NULL);

    // Make sure the image source exists before continuing.
    if (myImageSource == NULL){
        fprintf(stderr, "Image source is NULL.");
        return  NULL;
    }

    // Package the integer as a  CFNumber object. Using CFTypes allows you
    // to more easily create the options dictionary later.
    thumbnailSize = CFNumberCreate(NULL, kCFNumberIntType, &imageSize);

    // Set up the thumbnail options.
    myKeys[0] = kCGImageSourceCreateThumbnailWithTransform;
    myValues[0] = (CFTypeRef)kCFBooleanTrue;
    myKeys[1] = kCGImageSourceCreateThumbnailFromImageIfAbsent;
    myValues[1] = (CFTypeRef)kCFBooleanTrue;
    myKeys[2] = kCGImageSourceThumbnailMaxPixelSize;
    myValues[2] = thumbnailSize;

    myOptions = CFDictionaryCreate(NULL, (const void **) myKeys,
                                   (const void **) myValues, 2,
                                   &kCFTypeDictionaryKeyCallBacks,
                                   & kCFTypeDictionaryValueCallBacks);

    // Create the thumbnail image using the specified options.
    myThumbnailImage = CGImageSourceCreateThumbnailAtIndex(myImageSource,
                                                           0,
                                                           myOptions);

    UIImage* scaled = [UIImage imageWithCGImage:myThumbnailImage];

    // Release the options dictionary and the image source
    // when you no longer need them.

    CFRelease(thumbnailSize);
    CFRelease(myOptions);
    CFRelease(myImageSource);

    // Make sure the thumbnail image exists before continuing.
    if (myThumbnailImage == NULL) {
        fprintf(stderr, "Thumbnail image not created from image source.");
        return NULL;
    }
    return scaled;
}

这就是我的图像视图的实例化方式：

myImageView = [[UIImageView alloc] init];
imageView.contentMode = UIViewContentModeScaleAspectFit;

CGRect rect = imageView.frame;
rect.size.height = 90;
rect.size.width = 90;

imageView.frame = rect;
[imageView setUserInteractionEnabled:YES];

如果我不设置imageView.contentMode = UIViewContentModeScaleAspectFit;缩略图会失真，因为它只是我原始图像的一个版本，高度为 90 像素。

那么，为什么我的缩略图不是方形的？

4

4 回答 4

54

最简单的做法是将contentModeimageView 上的设置UIViewContentModeScaleAspectFill改为。但是，这可能并不理想，因为它会将整个图像保存在内存中。

这是我用来调整图像大小的一些代码。

+ (UIImage *)imageWithImage:(UIImage *)image scaledToSize:(CGSize)size
{
    UIGraphicsBeginImageContextWithOptions(size, NO, 0);
    [image drawInRect:CGRectMake(0, 0, size.width, size.height)];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();
    return newImage;
}

如果尺寸与图像的纵横比不同，此版本将防止图像失真。

+ (UIImage *)imageWithImage:(UIImage *)image scaledToFillSize:(CGSize)size
{
    CGFloat scale = MAX(size.width/image.size.width, size.height/image.size.height);
    CGFloat width = image.size.width * scale;
    CGFloat height = image.size.height * scale;
    CGRect imageRect = CGRectMake((size.width - width)/2.0f,
                                  (size.height - height)/2.0f,
                                  width,
                                  height);

    UIGraphicsBeginImageContextWithOptions(size, NO, 0);
    [image drawInRect:imageRect];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();
    return newImage;
}

通常您只需要图像的顶部正方形（而不是中心）。并且您希望最终图像具有一定的尺寸，例如 128x128，如下例所示。

- (UIImage *)squareAndSmall // as a category (so, 'self' is the input image)
{
    // fromCleverError's original
    // http://stackoverflow.com/questions/17884555
    CGSize finalsize = CGSizeMake(128,128);

    CGFloat scale = MAX(
        finalsize.width/self.size.width,
        finalsize.height/self.size.height);
    CGFloat width = self.size.width * scale;
    CGFloat height = self.size.height * scale;

    CGRect rr = CGRectMake( 0, 0, width, height);

    UIGraphicsBeginImageContextWithOptions(finalsize, NO, 0);
    [self drawInRect:rr];
    UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();    
    UIGraphicsEndImageContext();
    return newImage;
}
于 2013-07-26T15:04:19.017 回答
6

这是一个链接，您可以参考：

1) UIImage+调整大小

2) UIImage+ProportionalFill

在这里，您可以调整视图大小并添加比例填充，以便按比例调整纵横比和其他功能，如裁剪、缩放等。

您可以使用-(UIImage*)resizedImageToSize:(CGSize*)size上面的参考链接 UIImage+Resize 下的方法来重新调整图像。

希望这对您有所帮助。

如果您需要更多帮助，请告诉我。

于 2013-07-26T15:01:16.583 回答
6

上面聪明错误答案的 Swift 版本：更新到 swift 4.1

func resizeImageToCenter(image: UIImage) -> UIImage {
    let size = CGSize(width: 100, height: 100)

    // Define rect for thumbnail
    let scale = max(size.width/image.size.width, size.height/image.size.height)
    let width = image.size.width * scale
    let height = image.size.height * scale
    let x = (size.width - width) / CGFloat(2)
    let y = (size.height - height) / CGFloat(2)
    let thumbnailRect = CGRect.init(x: x, y: y, width: width, height: height)

    // Generate thumbnail from image
    UIGraphicsBeginImageContextWithOptions(size, false, 0)
    image.draw(in: thumbnailRect)
    let thumbnail = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()
    return thumbnail!
}
于 2016-04-16T00:53:14.313 回答
0

另一种方法 - 前几天遇到了一个问题，其他人在使用最适合大图像的苹果示例代码时可能会遇到同样的问题。

正如接受的答案中提到的，这有将整个图像加载到内存中的问题，如果它太大，iOS 可能会杀死你的应用程序。Apple 示例代码中的 CGImageSourceCreateThumbnailAtIndex 效率更高，但是示例中存在错误。CFDictionaryCreate 中的第三个参数是要复制的“numValues”。必须是3而不是 2。

myOptions = CFDictionaryCreate(NULL, (const void **) myKeys,  
                               (const void **) myValues, 
                               3, //Changed to 3  
                               &kCFTypeDictionaryKeyCallBacks,  
                               & kCFTypeDictionaryValueCallBacks);
于 2015-09-10T16:33:48.363 回答