J-S on your chart the downtrend is over almost as soon as it starts. You don't know it is a downtrend until it has moved 4 points right? A point later price retraces 6+ ticks so its finished.
There are much better ways of determining trend imho that you can see instantly just using price action. Is price making higher highs higher lows and higher closes? Is it leaving higher swing highs and swing lows? etc. Thats just my opinion each to there own of course
You might want to check out Clyde Lee's website the swing machine he has a tradestation function called swingleeII (from memory) that is freely given and has many user inputs and options to determine swing points. It will plot a zigzag swing to swing I think too. Actually i believe most zigzag indicators will do what you require with little or no modification.
Cheers.