Refresh rate

The refresh rate is a term used in film, television and computer technology. It denotes the number of frames per second that are projected, for example, on a movie screen or written on a TV screen or monitor of its lamp. They are usually in a in units of hertz (Hz ), or equivalent, as fps (frames per second = frames per second). When digital media is between the frame rate of the movie and those representing the projector, distinguished.

Effect

In the video or moving image reproduction, the physiological characteristic of the human visual system is used that mix changes in the image content with the continued existing in the millisecond range afterimage of the previous screen contents from the visual impression of her. [ Evidence ?]

Here a distinction between frame rate and refresh rate is important because it does not have to be identical. The frame rate should not fall below a value of about 30 frames / second in order to provide the human eye with a liquid moving image content image impression can. The limit for the performance of a flowing movement of man is slightly different to person. Today in the cinema usual frame rate of 24 Hz limits the display of moving pictures, which leads to the fact that objects that move with less favorable medium speed on the picture, as are " jerky " perceived. A good director knows to avoid, for example, be done by camera pans slowly or quickly enough. The recording studio cameras or camcorders used interlacing, which offers per second due to the higher frame rate of 50 or 60 phases of motion distinct advantages such as sports shots.

The refresh rate of a screen, is crucial to Flimmereindruck. However, this also depends on the display technology being used. Thus, each of the 24 images is per second ( = 24 Hz frame rate) projected twice with a shutter, so with a refresh rate of 48 Hz alternately switched on and dark, for example in the cinema. In liquid crystal displays, however, the refresh rate has little effect on the Flimmereindruck because of principle, the brightness of each pixel remains almost constant between picture what light-dark change avoids. It is noteworthy that the human visual system responds in the outdoor areas through the sensitive rods with brightness changes. Fibrillation is therefore more likely to be perceived if you have a CRT monitor viewed from a corner of the eye, for example.

For fast- moving images ( sports, video games, etc.) display technologies have advantages that have a high enough refresh rate with a minimum of 50 Hz and as short as possible pixel light duration. CRT screens are here basically against LCD technology at an advantage, since each pixel only briefly flashes in the picture period ( = 1/Bildwiederholfrequenz ) and thus leave movements a very sharp image impression on the viewer. Also OLEDs ( PMOLED / AMOLED ) technology, with a particularly short response time for this effect, the latest S- AMOLED have a response time of less than 0.1 ms, so it was hardly possible to determine so-called " ghosting" on these screens. In the human visual system arises from this brief flashing single frames a fluid movement. Research in the field of LCD technology tries to improve it by techniques such as "scanning backlight" or "black stripe insertion" ( Liquid Crystal Display ), which causes an effective shortening of the pixel illumination time (as in the cathode ray tube screen). Of course, this may again arise as flickering, but this is not perceived by a sufficiently high frame rate greater than about 80 Hz. One approach the display industry to improve the display of moving pictures by shortening the LCD switching time, brings in LCD switching times of less than about 10 ms no visible improvement more.

Some filmmakers, such as the American director James Cameron, pleading for several years for the introduction of a higher frame rate.

Standards

When displaying interlaced as it is used in PAL or NTSC ( analog TV ), the field frequency is as refresh rate generally called, so in PAL 50 Hz and approximately 59.94 Hz ( exactly 60000/1001 Hz) for NTSC. The frame frequency is only half as high. The image produced as with CRTs is perceived by most people to be flickering. With modern instruments, the repetition will therefore be increased with the help of an image memory to 100 Hz.

Some display devices (LCD, projectors) are not refreshed with the output from the graphics card frequency, which presupposes an image memory in the unit for frequency conversion. While these devices cope with various refresh rates in the input signal, the best picture is achieved by adjusting the input frequency to the actual refresh rate - with almost all of today's devices is 60 Hz

Typical frame rates

  • PC CRT monitors (about 1982 ... 1987): 50 ... 60 frames / second
  • PC CRT monitors (from about 1990): 60 ... 200 frames / second
  • PC -LC - Display: 60 frames / second

Calculation

The refresh rate of computer monitors can be approximately calculated as follows:

Where the horizontal frequency (number of rows per second) and the number of lines (vertical resolution).

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