SwiftHeartRate

Use video in cell phone camera to determine a user's heart rate (pulse)

Coded in Swift using Accelerate Library

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How are these values calculated?

Hi there,

First of all thanks for your code. I appreciate if you can have the time to explain the part when you calculate the heartbeat.

You have this function:

        // find peak power and bin
        var power = 0.0 as Float
        var bin = 0 as vDSP_Length
        
        // calculate heart rate, ie pulse
        // course bandwidth filter --- skip hr under/over unreasonable amounts
        let minHeartRate = 20                                       // skip anything lower ~35 bpm
        let maxHeartRate = Double(windowSizeOverTwo) / 4            // skip anything over ~225 bpm
        vDSP_maxvi(&powerVector+minHeartRate, 1, &power, &bin, vDSP_Length(maxHeartRate))
        bin += vDSP_Length(minHeartRate)        
        
        // push heart rate data to the user
        let timeElapsed = NSDate().timeIntervalSinceDate(timeElapsedStart)
        timeLabel.text = NSString(format: "Seconds: %d", Int(timeElapsed)) as String
        
        let binSize = fps * 60.0 / Float(windowSize)
        let errorSize = fps * 60.0 / Float(windowSize)
        
        let bpm = Float(bin) / Float(windowSize) * (fps * 60.0)
        pulseLabel.text = ("\(Int(bpm))")

First of all, I think the values you get there for minHeartRate and maxHeartRate depends on the FPS you are using that is 30 FPS, right? How do you get these values? In my case I am using 60 FPS and still using 512 samples when the app gets there.
power will contain the maximum value coming from the fourier transform and bin its index. You calculate these values but you just use bin.
you do not use either binSize and errorSize. What these variables represent?
what shows on the pulseLabel is the result of bpm that is the division of bin by some number.

I do not understand this.

bin is the Fourier Transform bin that has the highest intensity. A bin in the Fourier Transform is a frequency. I do not understand the relation between a bin and the heartbeat..

thanks.

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