CGImageSource读取图像数据

文章目录

1. 创建CGImageSourceRef
2. 获取图像
3. 创建图像的缩略图
4. 获取图像的属性信息

CGImageSource是对图像数据读取任务的抽象，通过它可以获得图像对象、缩略图、图像的属性(包括Exif信息)。

创建CGImageSourceRef

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NSString *imagePath = [[NSBundle bundleForClass:self.class] pathForImageResource:@"test.png"];
CGImageSourceRef imageSource = CGImageSourceCreateWithURL((__bridge CFURLRef)[NSURL fileURLWithPath:imagePath],NULL);

获取图像

1	CGImageRef imageRef = CGImageSourceCreateImageAtIndex(imageSource, 0, NULL);

创建图像的缩略图

//缩略图的宽和高
double thumbnailWidth=xxx,thumbnailHeight=xxx;
if (imageSource != NULL) {
    //缩略图的信息的字典
    NSDictionary *options = @{
                           (id) kCGImageSourceCreateThumbnailWithTransform : @YES,
                           (id) kCGImageSourceCreateThumbnailFromImageAlways : @YES,
                           (id) kCGImageSourceThumbnailMaxPixelSize : [NSNumber numberWithInt:MAX(thumbnailWidth,thumbnailHeight)]
                           };
    //得到缩略图
    CGImageRef thumbnailRef = CGImageSourceCreateThumbnailAtIndex(imageSource, 0, (__bridge CFDictionaryRef)options);
    CFRelease(imageSource);
    
    if (thumbnailRef) {
        lastImage = [UIImage imageWithCGImage:thumbnailRef];
        CGImageRelease(thumbnailRef);
    }
}

CFDictionaryRef 字典规范的操作标识：

kCGImageSourceCreateThumbnailFromImageIfAbsent （如果有缩略图则使用，无则使用原图产生缩略图）默认值是kCFBooleanFalse
kCGImageSourceCreateThumbnailFromImageAlways （用原图产生缩略图）默认值是kCFBooleanFalse
kCGImageSourceThumbnailMaxPixelSize （缩略图长或宽最大尺寸）value为CFNumber类型
kCGImageSourceCreateThumbnailWithTransform （根据exif标记 自动旋转）默认值是kCFBooleanFalse

获取图像的属性信息

CFDictionaryRef imageInfo = CGImageSourceCopyPropertiesAtIndex(imageSource, 0,NULL);
//像素的宽
NSNumber *pixelWidthObj = (__bridge NSNumber *)CFDictionaryGetValue(imageInfo, kCGImagePropertyPixelWidth);
//像素的高
NSNumber *pixelHeightObj = (__bridge NSNumber *)CFDictionaryGetValue(imageInfo, kCGImagePropertyPixelHeight);
//图像的旋转方向
NSInteger orientation = [(__bridge NSNumber *)CFDictionaryGetValue(imageInfo, kCGImagePropertyOrientation) integerValue];
//Exif信息
NSDictionary *exifInfo = (__bridge NSDictionary *)CFDictionaryGetValue(imageInfo, kCGImagePropertyExifAuxDictionary);