Predict Card Magic Trick

Magician take out the JQK cards, and let audience choose one,
After audience choosed the card, you can let her watch your phone,
and wipe off the black screen rapidly.
In the end the card was chosen by audience will appear on the screen.
App feature:
1. Can predict any JQK card after audience choose
2. No need to setting before audience choose
3. The phone brightness will set to 0, when magic trick start
(that can avoid audience found flaws)
4. Set brightness = 0.5 when card is showing
5. The phone will not closed by screen saver