Question

如您所知，iphone指南不鼓励加载大于1024x1024的图像。

我必须加载的图像大小各不相同，我想检查我即将加载的图像的大小;但是使用uiimage的.size属性需要对图像进行加密...这正是我想要避免的。

我的推理是否有问题或是否有解决方法？

谢谢大家

Answer 1

从iOS 4.0开始，iOS SDK包含CGImageSource... functions（在ImageIO框架中）。它是一种非常灵活的API，用于查询元数据而无需将图像加载到内存中。获取图像的像素尺寸应该像这样工作（确保在目标中包含ImageIO.framework）：

#import <ImageIO/ImageIO.h>

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

CGFloat width = 0.0f, height = 0.0f;
CFDictionaryRef imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, NULL);

CFRelease(imageSource);

if (imageProperties != NULL) {

    CFNumberRef widthNum  = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelWidth);
    if (widthNum != NULL) {
        CFNumberGetValue(widthNum, kCFNumberCGFloatType, &width);
    }

    CFNumberRef heightNum = CFDictionaryGetValue(imageProperties, kCGImagePropertyPixelHeight);
    if (heightNum != NULL) {
        CFNumberGetValue(heightNum, kCFNumberCGFloatType, &height);
    }

    // Check orientation and flip size if required
    CFNumberRef orientationNum = CFDictionaryGetValue(imageProperties, kCGImagePropertyOrientation);
    if (orientationNum != NULL) {
        int orientation;
        CFNumberGetValue(orientationNum, kCFNumberIntType, &orientation);
        if (orientation > 4) {
            CGFloat temp = width;
            width = height;
            height = temp;
        }
    }

    CFRelease(imageProperties);
}

NSLog(@"Image dimensions: %.0f x %.0f px", width, height);

（改编自Gelphman和Laden的“Quartz编程”，第9.5页，第228页）

Answer 2

Swift 3 版本的答案：

import Foundation
import ImageIO

func sizeForImage(at url: URL) -> CGSize? {

    guard let imageSource = CGImageSourceCreateWithURL(url as CFURL, nil)
        , let imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) as? [AnyHashable: Any]
        , let pixelWidth = imageProperties[kCGImagePropertyPixelWidth as String]
        , let pixelHeight = imageProperties[kCGImagePropertyPixelHeight as String]
        , let orientationNumber = imageProperties[kCGImagePropertyOrientation as String]
        else {
            return nil
    }

    var width: CGFloat = 0, height: CGFloat = 0, orientation: Int = 0

    CFNumberGetValue(pixelWidth as! CFNumber, .cgFloatType, &width)
    CFNumberGetValue(pixelHeight as! CFNumber, .cgFloatType, &height)
    CFNumberGetValue(orientationNumber as! CFNumber, .intType, &orientation)

    // Check orientation and flip size if required
    if orientation > 4 { let temp = width; width = height; height = temp }

    return CGSize(width: width, height: height)
}

Answer 3

在 Swift 5 中，使用ImageIO，

extension URL{
    var sizeOfImage: CGSize?{
        guard let imageSource = CGImageSourceCreateWithURL(self as CFURL, nil)
            , let imageProperties = CGImageSourceCopyPropertiesAtIndex(imageSource, 0, nil) as? [AnyHashable: Any]
            , let pixelWidth = imageProperties[kCGImagePropertyPixelWidth as String] as! CFNumber?
            , let pixelHeight = imageProperties[kCGImagePropertyPixelHeight as String] as! CFNumber?
            else {
                return nil
        }
        var width: CGFloat = 0, height: CGFloat = 0
        CFNumberGetValue(pixelWidth, .cgFloatType, &width)
        CFNumberGetValue(pixelHeight, .cgFloatType, &height)
       }
       return CGSize(width: width, height: height)
    }
}

imageProperties[kCGImagePropertyOrientation as String]可能为空。

没有，我用png图片文件进行了测试

为Apple says

kCGImagePropertyOrientation

此键的数值根据TIFF和Exif规范编码图像的预期显示方向。

访问UIImage属性而不在内存中加载图像

3 个答案: