在我的应用中，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's code来创建缩略图。问题是缩略图不是平方的，函数在设置kCGImageSourceThumbnailMaxPixelSize键后为90，似乎只调整图像的高度，据我所知，kCGImageSourceThumbnailMaxPixelSize键应该负责设置缩略图的高度和宽度。 / p>
以下是我的代码的一瞥：
- (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];
如果我没有设置imageView.contentMode = UIViewContentModeScaleAspectFit;，缩略图将会失真，因为它只是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平整？
答案 0 :(得分：53)
最简单的方法是将imageView上的contentMode设置为UIViewContentModeScaleAspectFill。但是，这可能并不理想，因为它会将整个图像保留在内存中。
以下是我用来调整图片大小的一些代码。
+ (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;
}
如果尺寸与图像的宽高比不同，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;
}
通常你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特定大小，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;
}
答案 1 :(得分：6)
以下是您可以参考的链接：
在这里你可以调整视图大小并添加比例填充，以便按比例增加宽高比和其他功能，如裁剪，缩放等。
您可以在参考链接UIImage + Resize下使用-(UIImage*)resizedImageToSize:(CGSize*)size方法来调整图像大小。
希望这会对你有所帮助。
如果您需要更多帮助，请与我们联系。
答案 2 :(得分：5)
Swift版本的Clever Error的答案如上： 更新为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!
}