如何从ALAsset对象获取全景图
如何从ALAsset对象获取全景图
提问于 2014-07-01 20:55:15
我们有大约2k个对象，它们是ALAsset类的实例，我们需要知道哪些文件是全景图像。我们已经尝试从ALAsset实例中获取CGImageRef，并检查宽高比。
ALAsset *alasset = ...
CFImageRef = alasset.thumbnail; // return square thumbnail and not suitable for me
CFImageRef = alasset.aspectRationThumbnail; //return aspect ration thumbnail, but very slowly它不适合我们，因为它对许多文件的运行速度很慢。
此外，我们还尝试从defaultRepresentation获取元数据并检查图像EXIF，但它的工作速度很慢。
NSDictionary *dictionary = [alasset defaultRepresentation] metadata]; //very slowly to有没有办法让它变得更好？
谢谢
回答 1
Stack Overflow用户
发布于 2015-01-21 19:00:05
最后，我为ALAsset找到了这个解决方案：
ALAssetsLibrary *assetsLibrary = ...;
NSOperation *queue = [NSoperationQueue alloc] init];
static NSString * const kAssetQueueName = ...;
static NSUInteger const kAssetConcurrentOperationCount = ...; //I use 5
queue.maxConcurrentOperationCount = kAssetConcurrentOperationCount;
queue.name = kAssetQueueName;
dispatch_async(dispatch_get_main_queue(), ^{
[assetsLibrary enumerateGroupsWithTypes:ALAssetsGroupAll usingBlock:^(ALAssetsGroup *group, BOOL *stop) {
/*You must check the group is not nil */
if (!group)
return;
/*Then you need to select group where you will search panoramas: for iPhone-Simulator it's @"Saved Photos" and "Camera Roll" for iPhone. It's actuality only for iOS 7 or early. */
static NSString * const kAssetGroupName = ...;
if ([[group valueForProperty:ALAssetsGroupPropertyName] kAssetGroupName]) {
[group enumerateAssetsUsingBlock:^(ALAsset *asset, NSUInteger index, BOOL *stop) {
if (!asset)
return;
[queue addOperationWithBlock:^{
//I use @autoreleasepool for instant memory release, after I find panoramas asset url
@autoreleasepool {
ALAssetRepresentation *defaultRepresentation = asset.defaultRepresentation;
if ([defaultRepresentation.UTI isEqualToString:@"public.jpeg"]) {
NSDictionary *metadata = defaultRepresentation.metadata;
if (!metadata)
return;
if (metadata[@"PixelWidth"] && metadata[@"PixelHeight"]) {
NSInteger pixelWidth = [metadata[@"PixelWidth"] integerValue];
NSInteger pixelHeight = [metadata[@"PixelHeight"] integerValue];
static NSUInteger const kSidesRelationshipConstant = ...; //I use 2
static NSUInteger const kMinimalPanoramaHeight = ...; //I use 600
if (pixelHeight >= kMinimalPanoramaHeight && pixelWidth/pixelHeight >= kSidesRelationshipConstant) {/*So, that is panorama.*/}
}
}];
}];
}
} failureBlock:^(NSError *error) {
//Some failing action, you know.
}];
};那是。所以，我认为这不是最好的解决方案。然而，对于今天，我没有找到更好的。
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原文链接：
https://stackoverflow.com/questions/24510857
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