如何让简单的人脸检测工作？答案

【问题标题】：How to get simple face detection working?如何让简单的人脸检测工作？
【发布时间】：2019-03-31 20:21:39
【问题描述】：

我正在尝试获取一个在 iOS 上使用 ML Kit 进行人脸检测的简单示例。以下是 Objective C 代码的摘录：

    FIRVisionFaceDetectorOptions *faceDetectorOptions;
    FIRVision *vision;
    FIRVisionFaceDetector *faceDetector;

    faceDetectorOptions = [[FIRVisionFaceDetectorOptions alloc] init];
    faceDetectorOptions.performanceMode = FIRVisionFaceDetectorPerformanceModeAccurate;
    faceDetectorOptions.landmarkMode = FIRVisionFaceDetectorLandmarkModeAll;
    faceDetectorOptions.contourMode = FIRVisionFaceDetectorContourModeNone;
    faceDetectorOptions.classificationMode = FIRVisionFaceDetectorClassificationModeAll;
    faceDetectorOptions.minFaceSize = 0.1; // TODO: finalize this option value

    vision = [FIRVision vision];
    faceDetector = [vision faceDetectorWithOptions:faceDetectorOptions];

    UIImage *staticImg = [UIImage imageNamed:@"sample.jpg"];
    FIRVisionImage *visionImage = [[FIRVisionImage alloc] initWithImage:staticImg];

    NSError* error = Nil;
    NSArray<FIRVisionFace *> * faces = [faceDetector resultsInImage:visionImage error:&error];
    NSLog(@"Synchronous result. error = %@, face count = %lu", error, faces.count);

sample.jpg 文件是下载并作为资源添加到我的 Xcode 项目中的以下图像： http://chwb.org/wp-content/uploads/2014/01/Theo_Janssen-Face1.jpg

resultsInImage 没有返回错误，但也没有面孔。它记录：

Synchronous result. error = (null), face count = 0

我做错了吗？

【问题讨论】：

标签： firebase tensorflow-lite firebase-mlkit

【解决方案1】：

我想通了。问题是我需要像这样设置图像元数据：

    FIRVisionImageMetadata *imageMetadata = [FIRVisionImageMetadata new];
    imageMetadata.orientation = [FcFaceDetector visionImageOrientationFromImageOrientation:uiImage.imageOrientation];
    visionImage.metadata = imageMetadata;

+ (FIRVisionDetectorImageOrientation) visionImageOrientationFromImageOrientation:(UIImageOrientation)imageOrientation {
    switch (imageOrientation) {
            case UIImageOrientationUp:
            return FIRVisionDetectorImageOrientationTopLeft;
            case UIImageOrientationDown:
            return FIRVisionDetectorImageOrientationBottomRight;
            case UIImageOrientationLeft:
            return FIRVisionDetectorImageOrientationLeftBottom;
            case UIImageOrientationRight:
            return FIRVisionDetectorImageOrientationRightTop;
            case UIImageOrientationUpMirrored:
            return FIRVisionDetectorImageOrientationTopRight;
            case UIImageOrientationDownMirrored:
            return FIRVisionDetectorImageOrientationBottomLeft;
            case UIImageOrientationLeftMirrored:
            return FIRVisionDetectorImageOrientationLeftTop;
            case UIImageOrientationRightMirrored:
            return FIRVisionDetectorImageOrientationRightBottom;
    }
}

文档似乎并不清楚，因为它似乎建议不要设置它： https://firebase.google.com/docs/ml-kit/ios/detect-faces#2-run-the-face-detector

【讨论】：