ImageIO

在阅读有关gif编解码相关的内容时&＃xff0c;有见到使用ImageIO相关的内容

• iOS中ImageIO框架详解与应用分析
• Image I/O Programming Guide

参考Accessing Image Properties Without Loading the Image Into Memory提到其一些应用

比如说你想获取图片的一些属性&＃xff0c;比如图片的尺寸和一些其他的元数据&＃xff0c;但是这张图片你并不需要再屏幕上显示。最简单的方式就是使用UIImage&＃xff1a;

UIImage *image &＃61; [UIImage imageWithContentsOfFile:...];
CGSize imageSize &＃61; image.size;
...

这样做所带来的问题是整张图片都会被加载到内存中。由于在内存中是未压缩的&＃xff0c;所以一个512 × 512 的图片就有1M

此时就可以使用ImageIO.framework

如下的例子&＃xff0c;获取一张网络上的图片&＃xff0c;输出图片的大小&＃xff1a;

NSString *urlStr &＃61; &＃64;"https://timgsa.baidu.com/timg?image&quality&＃61;80&size&＃61;b9999_10000&sec&＃61;1524748621307&di&＃61;46209fd530717b3c1621468c5e22e063&imgtype&＃61;0&src&＃61;http%3A%2F%2Fa.hiphotos.baidu.com%2Fimage%2Fpic%2Fitem%2F0ff41bd5ad6eddc4c984b29335dbb6fd52663372.jpg";NSURL *imageFileURL &＃61; [NSURL URLWithString:urlStr];CGImageSourceRef imageSource &＃61; CGImageSourceCreateWithURL((CFURLRef)imageFileURL, NULL);if (imageSource &＃61;&＃61; NULL) {// Error loading imagereturn;}NSDictionary *options &＃61; [NSDictionary dictionaryWithObjectsAndKeys:[NSNumber numberWithBool:NO], (NSString *)kCGImageSourceShouldCache,nil];CFDictionaryRef imageProperties &＃61; CGImageSourceCopyPropertiesAtIndex(imageSource, 0, (CFDictionaryRef)options);if (imageProperties) {NSNumber *width &＃61; (NSNumber *)CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelWidth);NSNumber *height &＃61; (NSNumber *)CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelHeight);NSLog(&＃64;"Image dimensions: %&＃64; x %&＃64; px", width, height);CFRelease(imageProperties);}CFRelease(imageSource);

输出结果为&＃xff1a;

Image dimensions: 1280 x 1920 px

CGImageSourceCopyPropertiesAtIndex()返回的字典包含许多信息

如下可以获取拍摄的日期、相机的模式和GPS信息等&＃xff1a;

CFDictionaryRef exif &＃61; CFDictionaryGetValue(imageProperties, kCGImagePropertyExifDictionary);if (exif) {NSString *dateTakenString &＃61; (NSString *)CFDictionaryGetValue(exif, kCGImagePropertyExifDateTimeOriginal);NSLog(&＃64;"Date Taken: %&＃64;", dateTakenString);}CFDictionaryRef tiff &＃61; CFDictionaryGetValue(imageProperties, kCGImagePropertyTIFFDictionary);if (tiff) {NSString *cameraModel &＃61; (NSString *)CFDictionaryGetValue(tiff, kCGImagePropertyTIFFModel);NSLog(&＃64;"Camera Model: %&＃64;", cameraModel);}CFDictionaryRef gps &＃61; CFDictionaryGetValue(imageProperties, kCGImagePropertyGPSDictionary);if (gps) {NSString *latitudeString &＃61; (NSString *)CFDictionaryGetValue(gps, kCGImagePropertyGPSLatitude);NSString *latitudeRef &＃61; (NSString *)CFDictionaryGetValue(gps, kCGImagePropertyGPSLatitudeRef);NSString *longitudeString &＃61; (NSString *)CFDictionaryGetValue(gps, kCGImagePropertyGPSLongitude);NSString *longitudeRef &＃61; (NSString *)CFDictionaryGetValue(gps, kCGImagePropertyGPSLongitudeRef);NSLog(&＃64;"GPS Coordinates: %&＃64; %&＃64; / %&＃64; %&＃64;", longitudeString, longitudeRef, latitudeString, latitudeRef);}

在Programming iOS 10 Dive Deep into Views View Controllers and Frameworks一书中&＃xff0c;就有这样的使用形式&＃xff1a;

let url &＃61; Bundle.main.url(forResource:"colson", withExtension: "jpg")!let src &＃61; CGImageSourceCreateWithURL(url as CFURL, nil)!let result &＃61; CGImageSourceCopyPropertiesAtIndex(src, 0, nil)!let d &＃61; result as! [AnyHashable:Any] // :) works because CFString is now AnyHashableprint(d)// just proving it really is a dictionarylet width &＃61; d[kCGImagePropertyPixelWidth] as! CGFloatlet height &＃61; d[kCGImagePropertyPixelHeight] as! CGFloatprint("\(width) by \(height)")// another way; no one in his right mind would do this, thoughdo {let result &＃61; CGImageSourceCopyPropertiesAtIndex(src, 0, nil)!let key &＃61; kCGImagePropertyPixelWidth // CFStringlet p1 &＃61; Unmanaged.passUnretained(key).toOpaque() // UnsafeMutableRawPointerlet p2 &＃61; CFDictionaryGetValue(result, p1) // UnsafeRawPointerlet n &＃61; Unmanaged.fromOpaque(p2!).takeUnretainedValue() // CFNumbervar width : CGFloat &＃61; 0CFNumberGetValue(n, .cgFloatType, &width) // width is now 640.0print(width)}

缩略图
如果你在显示某个图片的时候&＃xff0c;不关心原始的图片数据&＃xff0c;缩率图thumbnail正是你所需要的

使用CGImageSourceCreateThumbnailAtIndex时传递一个字典。需要注意的是我们使用的CGImage是实际的像素&＃xff0c;所以要考虑到设备的scale

let url &＃61; Bundle.main.url(forResource:"colson", withExtension: "jpg")!let src &＃61; CGImageSourceCreateWithURL(url as CFURL, nil)!let scale &＃61; UIScreen.main.scalelet w &＃61; self.iv.bounds.width * scalelet d : [AnyHashable:Any] &＃61; [kCGImageSourceShouldAllowFloat : true,kCGImageSourceCreateThumbnailWithTransform : true,kCGImageSourceCreateThumbnailFromImageAlways : true,kCGImageSourceThumbnailMaxPixelSize : w]let imref &＃61; CGImageSourceCreateThumbnailAtIndex(src, 0, d as CFDictionary)!let im &＃61; UIImage(cgImage: imref, scale: scale, orientation: .up)self.iv.image &＃61; imprint(im)print(im.size)

保存图片为特定的格式

需要使用到image destination&＃xff0c;如下的例子&＃xff0c;保存为TIFF

let url &＃61; Bundle.main.url(forResource:"colson", withExtension: "jpg")!let src &＃61; CGImageSourceCreateWithURL(url as CFURL, nil)!let fm &＃61; FileManager.defaultlet suppurl &＃61; try! fm.url(for:.applicationSupportDirectory, in: .userDomainMask, appropriateFor: nil, create: true)let tiff &＃61; suppurl.appendingPathComponent("mytiff.tiff")let dest &＃61; CGImageDestinationCreateWithURL(tiff as CFURL, kUTTypeTIFF, 1, nil)!CGImageDestinationAddImageFromSource(dest, src, 0, nil)let ok &＃61; CGImageDestinationFinalize(dest)if ok {print("tiff image written to disk")} else {print("something went wrong")}