It fools your brain better into thinking there's smooth motion. Once again, however, there are a couple downsides. When the TV spends half of its time showing a black screen, its light output drops. In many cases this trade-off is acceptable, as modern TVs are exceptionally bright. In other cases, not as much. I have a front projector, for example, and the BFI mode can make the image look very dim. There's also the potential for visible flicker, as the TV essentially flashes on and off with the inserted black frames.
Like frame interpolation, black frame insertion has different implementations. Rarely would a TV with a BFI mode show a black frame for the same length of time it shows a real frame. It's also not necessarily a "frame" at all. All LCDs create light with a backlight. This backlight can also turn off for only a portion of the time the frame is on screen, which is one of the ways companies can claim their 60Hz TVs have a "motion rate" higher than Another method is a rolling or scanning backlight, where parts of the image go dark in sequence.
The backlight might darken first in the top quarter of the screen, then middle-top, middle-bottom and bottom quarter. Rinse and repeat. An illustration of what a rolling backlight would look like. You see the image on the left. Faster than you can see, sections of the backlight turn off, in sequence, down the screen. It would do this for every frame of video. There are also levels of how "black" the black frame is.
A Hz TV could insert a frame that's a duplicate of the previous frame, but darker. Not "black," just dimmer. There are pros and cons to this method, too.
Not as much light is lost, but perhaps the motion doesn't seem quite as sharp. As with frame interpolation, if your TV has different settings, it's definitely worth reading up on what they do and testing them out. However, there is still one display technology that doesn't: DLP. Currently only found in front projectors, Digital Light Processing uses millions of tiny mirrors that rapidly flash on and off to build an image on a screen.
Some movie theater projectors use this technology. At home they're not that expensive. You'll need a screen, too, but they're not that expensive either.
Many models are even cheaper. However, there are several trade-offs. While modern projectors are very bright compared to older models, they don't hold a foot-candle to the average television.
In a room with dark curtains, or if you watch TV mostly at night, this isn't an issue. I've used a projector as my main TV for over 15 years. I use blackout curtains in that room, however. Judder is an artifact of adjusting the framerate and it looks like a sort of stutter in movement that would otherwise be smooth a slow pan, for instance. Instead of showing a bright image the whole time, they display the frame, then a short frame of either darkness or a very dimmed picture.
This alleviates much of the issue with judder and motion blur as it allows your brain to fill in the gap faster than you can consciously notice. It is also an old technique, and is used in theaters. It provides the traditional cinema feel. With 30p content, the frames can be interlaced to create a 60i stream or displayed twice each to achieve the fields-per-second rate.
But if 24fps content were played at 30fps, the on-screen motion would appear 25 percent fasterand if the audio kept pace, everyone would sound like a helium addict. If frames were dropped to 20fps, which fits more nicely into 60, the video would look too choppy.
So instead, every four frames of 24p source content is turned into five frames using a process called pulldown. When this modified video is viewed on a TV, the content has been adjusted by creating two interlaced fields that combine adjacent frames in every five-field batch.
It essentially turns 24p video into 30fps video, which is more compatible with the way TVs and broadcast systems work. None of that is what causes the distracting too-smooth effect. This is especially true when comparing flagship-tier 60Hz panels to cheaper Hz displays. Overall quality is definitely more important than a slightly more fluid feeling user interface.
The frame rate of an app or game depends not just on the underlying hardware, but also the way that the application is coded to render and the way Android works. Google has published insights into how high refresh rate displays work with content on Android.
The first point worth noting is that frame rates are limited by rendering times, controlled by the Android Choreographer. Instead, games may stick to 90, 60, 45, or even 30fps. Phones with more processing power are more likely to hit high frame rate targets with lower latency, although some apps may even be optimized for specific platforms.
The situation is further complicated by using multiple apps and UI elements at once. Google notes that Hz displays are good for viewing 24, 30, 45, and 60fps content without judder, as these rates as easily divisible by Playing back a 24fps video on a Hz display avoids the pulldown algorithm required by a 60Hz display, for example.
However, conflicts can occur between software, such as a low frame rate video and high frame rate UI.
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