通过面部检测进行裁剪

Question

我正在修改Apple SquareCam示例人脸检测应用程序，以便在写入相机胶卷之前裁剪出面部，而不是在脸部周围绘制红色正方形。 我正在使用相同的CGRect进行裁剪，就像用于绘制红色正方形一样。 然而，行为是不同的。 在纵向模式下，如果面部位于屏幕的水平中心，则会按预期裁剪面部（红色正方形所在的位置）。 如果脸部偏向左侧或右侧，则作物似乎总是从屏幕中间拍摄，而不是红色正方形。

这是苹果原始代码：

- (CGImageRef)newSquareOverlayedImageForFeatures:(NSArray *)features 
                                            inCGImage:(CGImageRef)backgroundImage 
                                      withOrientation:(UIDeviceOrientation)orientation 
                                          frontFacing:(BOOL)isFrontFacing
{
    CGImageRef returnImage = NULL;
    CGRect backgroundImageRect = CGRectMake(0., 0., CGImageGetWidth(backgroundImage), CGImageGetHeight(backgroundImage));
    CGContextRef bitmapContext = CreateCGBitmapContextForSize(backgroundImageRect.size);
    CGContextClearRect(bitmapContext, backgroundImageRect);
    CGContextDrawImage(bitmapContext, backgroundImageRect, backgroundImage);
    CGFloat rotationDegrees = 0.;

    switch (orientation) {
        case UIDeviceOrientationPortrait:
            rotationDegrees = -90.;
            break;
        case UIDeviceOrientationPortraitUpsideDown:
            rotationDegrees = 90.;
            break;
        case UIDeviceOrientationLandscapeLeft:
            if (isFrontFacing) rotationDegrees = 180.;
            else rotationDegrees = 0.;
            break;
        case UIDeviceOrientationLandscapeRight:
            if (isFrontFacing) rotationDegrees = 0.;
            else rotationDegrees = 180.;
            break;
        case UIDeviceOrientationFaceUp:
        case UIDeviceOrientationFaceDown:
        default:
            break; // leave the layer in its last known orientation
    }
    UIImage *rotatedSquareImage = [square imageRotatedByDegrees:rotationDegrees];

    // features found by the face detector
    for ( CIFaceFeature *ff in features ) {
        CGRect faceRect = [ff bounds];
        NSLog(@"faceRect=%@", NSStringFromCGRect(faceRect));
        CGContextDrawImage(bitmapContext, faceRect, [rotatedSquareImage CGImage]);
    }
    returnImage = CGBitmapContextCreateImage(bitmapContext);
    CGContextRelease (bitmapContext);

    return returnImage;
}

我的替代品：

- (CGImageRef)newSquareOverlayedImageForFeatures:(NSArray *)features 
                                            inCGImage:(CGImageRef)backgroundImage 
                                      withOrientation:(UIDeviceOrientation)orientation 
                                          frontFacing:(BOOL)isFrontFacing
{
    CGImageRef returnImage = NULL;

    //I'm only taking pics with one face. This is just for testing
    for ( CIFaceFeature *ff in features ) {
        CGRect faceRect = [ff bounds];
        returnImage = CGImageCreateWithImageInRect(backgroundImage, faceRect);
    }

    return returnImage;
}

更新*

基于Wains输入，我试图使我的代码更像原始，但结果是相同的：

- (NSArray*)extractFaceImages:(NSArray *)features
              fromCGImage:(CGImageRef)sourceImage
          withOrientation:(UIDeviceOrientation)orientation
              frontFacing:(BOOL)isFrontFacing
{
 NSMutableArray *faceImages = [[[NSMutableArray alloc] initWithCapacity:1] autorelease];


CGImageRef returnImage = NULL;
CGRect backgroundImageRect = CGRectMake(0., 0., CGImageGetWidth(sourceImage), CGImageGetHeight(sourceImage));
CGContextRef bitmapContext = CreateCGBitmapContextForSize(backgroundImageRect.size);
CGContextClearRect(bitmapContext, backgroundImageRect);
CGContextDrawImage(bitmapContext, backgroundImageRect, sourceImage);
CGFloat rotationDegrees = 0.;

switch (orientation) {
    case UIDeviceOrientationPortrait:
        rotationDegrees = -90.;
        break;
    case UIDeviceOrientationPortraitUpsideDown:
        rotationDegrees = 90.;
        break;
    case UIDeviceOrientationLandscapeLeft:
        if (isFrontFacing) rotationDegrees = 180.;
        else rotationDegrees = 0.;
        break;
    case UIDeviceOrientationLandscapeRight:
        if (isFrontFacing) rotationDegrees = 0.;
        else rotationDegrees = 180.;
        break;
    case UIDeviceOrientationFaceUp:
    case UIDeviceOrientationFaceDown:
    default:
        break; // leave the layer in its last known orientation
}

// features found by the face detector
for ( CIFaceFeature *ff in features ) {
    CGRect faceRect = [ff bounds];

    NSLog(@"faceRect=%@", NSStringFromCGRect(faceRect));

    returnImage = CGBitmapContextCreateImage(bitmapContext);
    returnImage = CGImageCreateWithImageInRect(returnImage, faceRect);
    UIImage *clippedFace = [UIImage imageWithCGImage:returnImage];
    [faceImages addObject:clippedFace];
}

CGContextRelease (bitmapContext);

return faceImages;

}

我拍了三张照片并用这些结果记录了faceRect;

拍摄的脸部位于设备左边缘附近。 捕捉图像完全错过了右边的脸：faceRect = {{972,43.0312}，{673.312,673.312}}

用脸定位在设备中间的Pic拍摄。 捕获图像很好：faceRect = {{1060.59,536.625}，{668.25,668.25}}

拍摄的脸部位于设备右边缘附近。 捕获图像完全错过了左侧的脸：faceRect = {{982.125,999.844}，{804.938,804.938}}

因此看起来“x”和“y”是相反的。 我正在拿着设备的肖像，但faceRect似乎是基于风景的。 但是，我无法弄清楚苹果原始代码的哪一部分可以解释这一点。 该方法中的方向代码似乎仅影响红色方块叠加图像本身。

Answer 1

您应该保留所有原始代码，并在返回之前添加一行（通过调整将图像生成放在循环中，因为您只裁剪第一个面）：

returnImage = CGImageCreateWithImageInRect(returnImage, faceRect);

这允许以正确的方向渲染图像，这意味着面部矩形将位于正确的位置。

Answer 2

您正面临这个问题，因为保存图像时，它会被垂直翻转保存。 而faceRect的位置与脸部并不完全吻合。 您可以通过修改解决这个问题faceRect在于它是在垂直翻转内这样的poistion returnImage 。

    for ( CIFaceFeature *ff in features ) {
        faceRect  = [ff bounds];
        CGRect modifiedRect = CGRectFlipVertical(faceRect,CGRectMake(0,0,CGImageGetWidth(returnImage),CGImageGetHeight(returnImage)));
        returnImage = CGImageCreateWithImageInRect(returnImage, modifiedRect);
        UIImage *clippedFace = [UIImage imageWithCGImage:returnImage];
        [faceImages addObject:clippedFace];
    }

CGRectFlipVertical(CGRect innerRect, CGRect outerRect)可以像这样定义，

    CGRect CGRectFlipVertical(CGRect innerRect, CGRect outerRect)
    {
      CGRect rect = innerRect;
      rect.origin.y = outerRect.origin.y + outerRect.size.height - (rect.origin.y + rect.size.height);
      return rect;
    }