检测来自相机的光脉冲

Question

我正在尝试为 iPhone 实现心跳检测器算法 这是出于教育目的，考虑到已经有几个应用程序在这样做...

我有这个函数来获取帧中颜色的变化...

- (void)processNewCameraFrame:(CVImageBufferRef)cameraFrame; {
CVPixelBufferLockBaseAddress(cameraFrame, 0);
int bufferHeight = CVPixelBufferGetHeight(cameraFrame);
int bufferWidth = CVPixelBufferGetWidth(cameraFrame);

// Create a new texture from the camera frame data, display that using the shaders
glGenTextures(1, &videoFrameTexture);
glBindTexture(GL_TEXTURE_2D, videoFrameTexture);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
// This is necessary for non-power-of-two textures
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

/*Create a CGImageRef from the CVImageBufferRef*/

uint8_t *baseAddress = (uint8_t *)CVPixelBufferGetBaseAddress(cameraFrame);
size_t bytesPerRow = CVPixelBufferGetBytesPerRow(cameraFrame);
size_t width = CVPixelBufferGetWidth(cameraFrame); 
size_t height = CVPixelBufferGetHeight(cameraFrame); 

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGContextRef newContext = CGBitmapContextCreate(baseAddress, width, height, 8, bytesPerRow, colorSpace, kCGBitmapByteOrder32Little | kCGImageAlphaPremultipliedFirst); 
CGImageRef newImage = CGBitmapContextCreateImage(newContext);

UIImage *image = [UIImage imageWithCGImage:newImage];

image = [image imageByApplyingDiagonalMotionBlur5x5];

[self processData:image];

CGImageRelease(newImage);
CGContextRelease(newContext);
CGColorSpaceRelease(colorSpace);

// Using BGRA extension to pull in video frame data directly
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, bufferWidth, bufferHeight, 0, GL_BGRA, GL_UNSIGNED_BYTE, CVPixelBufferGetBaseAddress(cameraFrame));

[self drawFrame];

glDeleteTextures(1, &videoFrameTexture);

CVPixelBufferUnlockBaseAddress(cameraFrame, 0);

以及以下函数来获取图像中的主色

- (UIColor *)getDominantColor:(UIImage*)image {
NSUInteger red = 0;
NSUInteger green = 0;
NSUInteger blue = 0;

// Allocate a buffer big enough to hold all the pixels

struct pixel* pixels = (struct pixel*) calloc(1, image.size.width * image.size.height * sizeof(struct pixel));
if (pixels != nil) {

    CGContextRef context = CGBitmapContextCreate(
                                                 (void*) pixels,
                                                 image.size.width,
                                                 image.size.height,
                                                 8,
                                                 image.size.width * 4,
                                                 CGImageGetColorSpace(image.CGImage),
                                                 kCGImageAlphaPremultipliedLast
                                                 );

    if (context != NULL) {
        // Draw the image in the bitmap

        CGContextDrawImage(context, CGRectMake(0.0f, 0.0f, image.size.width, image.size.height), image.CGImage);

        // Now that we have the image drawn in our own buffer, we can loop over the pixels to
        // process it. This simple case simply counts all pixels that have a pure red component.

        // There are probably more efficient and interesting ways to do this. But the important
        // part is that the pixels buffer can be read directly.

        NSUInteger numberOfPixels = image.size.width * image.size.height;
        for (int i=0; i<numberOfPixels; i++) {
            red += pixels[i].r;
            green += pixels[i].g;
            blue += pixels[i].b;
        }


        red /= numberOfPixels;
        green /= numberOfPixels;
        blue /= numberOfPixels;

        CGContextRelease(context);
    }

    free(pixels);
}

return [UIColor colorWithRed:red/255.0f green:green/255.0f blue:blue/255.0f alpha:1.0f];
}

，但绘制每帧的红色分量序列并没有给我提供可靠的心跳图......

这是正确的方法吗？我正在使用 FFT，但我认为处理信号频谱以计算峰值是没有用的...也许我可以使用 FFT 来应用低通滤波器的卷积，而不是逆 FFT 来检查这些新数据达到峰值...