anchor.diff:          let cutThreshPos = clamp (float model.cutThresh * scalingFactor) 0. 100.
           ctx.moveTo(0., 100. - float cutThreshPos)
           ctx.lineTo(255., 100. - float cutThreshPos)
  +        ctx.stroke()
  +
  +        let fadeThreshPos = clamp (float model.fadeThresh * scalingFactor) 0. 100.
  +        ctx.moveTo(0., 100. - float fadeThreshPos)
  +        ctx.lineTo(255., 100. - float fadeThreshPos)
           ctx.stroke()
   
           ctx.closePath () )
  
positive.code:                 R.Props.Min 1
                  R.Props.Max TMAX
                  R.Props.Value (string model.cutThresh)
                  R.Props.OnChange (fun e -> onThreshChange e dispatch )
              ]
          ]
          R.div [] [
  
negative.code:     Math.Abs (computeTotalLuma oldHist - computeTotalLuma newHist)
  
  let detectShot model currentHist =
      // TODO implement fading logic
      let difference =
          computeDifference model.lastShotHist currentHist
  
  