ios - UIImageOrientation 到 CIDetectorImageOrientation

Question

使用CIDetector检测图片中的人脸，需要指定图片方向，根据文档，TIFF和EXIF规范中恰好指定了方向，这意味着它不同于UIImageOrientation。谷歌为我找到了以下功能，我试过了但发现它似乎不正确，或者我可能错过了其他东西，因为有时方向不对。有人知道发生了什么事吗？似乎一旦照片从 iDevice 导出，然后导入到另一个 iDevice，方向信息就会丢失/更改，从而导致一些方向不匹配。

- (int) metadataOrientationForUIImageOrientation:(UIImageOrientation)orientation
{
    switch (orientation) {
        case UIImageOrientationUp: // the picture was taken with the home button is placed right
            return 1;
        case UIImageOrientationRight: // bottom (portrait)
            return 6;
        case UIImageOrientationDown: // left
            return 3;
        case UIImageOrientationLeft: // top
            return 8;
        default:
            return 1;
    }
}

Answer 1

为了涵盖所有这些，并且在没有魔数(Magic Number)分配的情况下这样做(CGImagePropertyOrientation 的原始值可能在未来改变，虽然这不太可能......仍然是一个很好的做法)你应该包括 ImageIO 框架并使用实际常量:

#import <ImageIO/ImageIO.h>
- (CGImagePropertyOrientation)CGImagePropertyOrientation:(UIImageOrientation)orientation
{
    switch (orientation) {
        case UIImageOrientationUp:
            return kCGImagePropertyOrientationUp;
        case UIImageOrientationUpMirrored:
            return kCGImagePropertyOrientationUpMirrored;
        case UIImageOrientationDown:
            return kCGImagePropertyOrientationDown;
        case UIImageOrientationDownMirrored:
            return kCGImagePropertyOrientationDownMirrored;
        case UIImageOrientationLeftMirrored:
            return kCGImagePropertyOrientationLeftMirrored;
        case UIImageOrientationRight:
            return kCGImagePropertyOrientationRight;
        case UIImageOrientationRightMirrored:
            return kCGImagePropertyOrientationRightMirrored;
        case UIImageOrientationLeft:
            return kCGImagePropertyOrientationLeft;
    }
}