UIImage initWithContentsOfFile:... -只需获取尺寸

Question

我只需要从PNG文件中获取宽度和高度。有没有可能使用UIImage？原因是有时(在极少数情况下，某些图像具有奇数宽度和RGB8格式) UIImage返回的尺寸与libpng不同)。

Answer 1

我在这里找到了答案：http://oleb.net/blog/2011/09/accessing-image-properties-without-loading-the-image-into-memory/

#import <ImageIO/ImageIO.h>

NSURL *imageFileURL = [NSURL fileURLWithPath:...];
CGImageSourceRef imageSource = CGImageSourceCreateWithURL((CFURLRef)imageFileURL, NULL);
if (imageSource == NULL) {
    // Error loading image
    ...
    return;
}

NSDictionary *options = [NSDictionary dictionaryWithObjectsAndKeys:
                         [NSNumber numberWithBool:NO], (NSString *)kCGImageSourceShouldCache, 
                         nil];
CFDictionaryRef imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, (CFDictionaryRef)options);
if (imageProperties) {
    NSNumber *width = (NSNumber *)CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelWidth);
    NSNumber *height = (NSNumber *)CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelHeight);
    NSLog(@"Image dimensions: %@ x %@ px", width, height);
    CFRelease(imageProperties);
}

我们可以从文件中访问任何元数据，而无需加载图像。