Android Question How can i apply grayscale effect to camera preview data before send to detect function

Public Sub GreyScale (bmp As B4XBitmap) As B4XBitmap
    Dim bc As BitmapCreator = CreateBC(bmp)
    Dim argb As ARGBColor
    For x = 0 To bc.mWidth - 1
        For y = 0 To bc.mHeight - 1
            bc.GetARGB(x, y, argb)
            Dim c As Int = argb.r * 0.21 + argb.g * 0.72 + 0.07 * argb.b
            argb.r = c
            argb.g = c
            argb.b = c
            bc.SetARGB(x, y, argb)
        Next
    Next
    Return bc.Bitmap
End Sub