Hi, I’m Cedric from Rtings.com This video is part of a series about Motion
and today’s subject is flickering, either via Black Frame Insertion or PWM dimming.
And we are going to talk about how does these things affect motion blur. First we will look
at it from a theory standpoint, and then we’re going to test some TVs to see how it is in
real life. In the previous video, we saw that when we
follow a moving object with our eyes, it results in a blur due to the frame rate. This is assuming
the frame is displayed for the whole duration. Or in other words, that the screen is using
a sample-and-hold method liked OLED TVs. But this is not true for all screens. Some
of them flickers, which reduces the perceived motion blur. Here is a demonstration of a
screen that displays a frame for a very short time. It the field of view of the moving eye,
you can see that the logo is quite clear since it always appears at the same spot, so you
don’t have the blur caused by the shift of the movement. This technique is called
Black Frame Insertion since it is like if you inserted a black frame in between each
frames. Now let’s talk about a real-life example
of a Black Frame Insertion. I am going to use the Sony X750D for this in our test room.
By default, it doesn’t flicker at all. So if I take a picture. It looks like what you
would expect. Now let’s turn on the ‘Clearness’ feature,
which is the Black Frame Insertion. You can see that the screen starts to flicker
and if we take a picture. It looks a lot more clear now. It is slightly blurry though, that’s
because the TV still needs to display the frame for a little bit in order for us to
see a picture. You will notice though that the overall screen brightness is a lot darker,
that’s because the backlight is turned off most of the time. Also, the constant flickering
can be bothering for some people and cause headaches.
We can even see even more what the backlight does by looking at the oscilloscope. You can
see that it flickers at a frequency of about 60Hz and that the pulse last about 2ms.
Now let’s look at an example of a different kind of flickering: PWM dimming. PWM stands
for Pulse Width Modulation, which is a way to control the power by flickering the voltage
instead of simply reducing it. That Sony TV doesn’t use PWM Diming, so if I reduce the
backlight. You can see that it simply reduces the light instead of flickering.
Let’s try this on a Samsung TV KS8000 which uses the PWM dimming. At max backlight, you
can see that it doesn’t flicker. But if I reduce the backlight, it starts to flicker,
but not as much as the Black Frame Insertion. The frequency in this case is 120Hz which
is twice as fast as a real Black Frame Insertion at 60Hz. The bad thing about it is like Black
Frame Insertion, it can give you a little bit of a headache. But the good thing is that
it helps clarify the movement a little bit. Let’s take a picture to see how it looks
like. What is interesting here is you can see a duplication of the logo. That’s because
the frequency of the PWM dimming is 120Hz, so each frame is displayed twice. Back to
our illustration of a Black Frame Insertion. In the case of a PWM Dimming at 120Hz. When
the content is 60 frames per second content, each frame will flicker twice. In your field
of view of your moving eye, that means the logo will appear twice per frame, but at a
different position, which is what creates the duplication of the logo. So you will see
a duplication each time the frame rate of the content doesn’t match the flickering
of the TV. So overall, a flickering of the screen can
reduce the perceived motion blur when following a moving object. But it comes at the cost
of a dimmer screen and it can be tiring for the eye. In our reviews, a perfect TV is a
TV that doesn’t flicker at all by default, but that has the options to add the flickering
if the user wants it. If you want to check out all our measurements
of which TV flickers and at which frequency, on the link in the description below. If you
like this video, subscribe to our channel, and see you next time time!