Frame rate, or frame frequency, is the frequency (rate) at which an imaging device produces unique consecutive images called frames. The term applies equally well to computer graphics, video cameras, film cameras, and motion capture systems. Frame rate is most often expressed in frames per second (FPS), (fps) and in progressive scan monitors as hertz (Hz).
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There are currently (2010) three main frame rate standards in the TV and movie-making business: 24p, 25p and 30p. However there are many variations on these as well as newer emerging standards.
Higher frame rates including 300 Hz have been tested by BBC R&D over concerns with sports and other broadcasts where fast motion with large HD displays could have a disorientating effect on viewers.[6] 300 FPS can be converted to both 50 and 60 Hz transmission formats without major issues.
Owing to their flexibility, software-based video formats can specify arbitrarily high frame rates, and many (cathode ray tube) consumer PC monitors operate at hundreds of frames per second, depending on selected video mode. LCD screens are usually 24 , 25, 50 , 60 or 120 FPS.
Frame rate is also a term used in real-time computing. In a fashion somewhat comparable to the moving-picture definition presented above, a real-time frame is the time it takes to complete a full round of the system's processing tasks. If the frame rate of a real-time system is 60 hertz, the system reevaluates all necessary inputs and updates the necessary outputs 60 times per second under all circumstances.
The designed frame rates of real-time systems vary depending on the equipment. For a real-time system that is steering an oil tanker, a frame rate of 1 Hz may be sufficient, while a rate of even 100 Hz may not be adequate for steering a guided missile. The designer must choose a frame rate appropriate to the application's requirements.
Frame rates in video games refer to the speed at which the image is refreshed (typically in frames per second, or FPS). Many underlying processes, such as collision detection and network processing, run at different or inconsistent frequencies or in different physical components of a computer. FPS affect the experience in two ways: low FPS does not give the illusion of motion effectively and affects the user's capacity to interact with the game, while FPS that vary substantially from one second to the next depending on computational load produce uneven, “choppy” animation. Many games lock their frame rate at lower but more sustainable levels to give consistently smooth motion.
The first 3D first-person shooter game for a personal computer, 3D Monster Maze, had a frame rate of approximately 6 FPS, and was still a success. In modern action-oriented games where players must visually track animated objects and react quickly, frame rates of between 30 to 100+ FPS are considered acceptable by most, though this can vary significantly from game to game. Modern action games, including popular console shooters such as Halo 3, are locked at 30 FPS maximum, while others, such as Unreal Tournament 3, can run well in excess of 100 FPS on sufficient hardware. The frame rate within games varies considerably depending upon what is currently happening at a given moment, or with the hardware configuration (especially in PC games.) When the computation of a frame consumes more time than is alloted between frames, the frame rate decreases.
A culture of competition has arisen among game enthusiasts with regard to frame rates, with players striving to obtain the highest FPS possible, due to their utility in demonstrating a system's power and efficiency. Indeed, many benchmarks (such as 3DMark) released by the marketing departments of hardware manufacturers and published in hardware reviews focus on the FPS measurement. Even though the typical LCD monitors of today are locked at 60 FPS, making extremely high frame rates impossible to see in realtime, playthroughs of game “timedemos” at hundreds or thousands of FPS for benchmarking purposes are still common.
Beyond measurement and bragging rights, such exercises do have practical bearing in some cases. A certain amount of discarded “headroom” frames are beneficial for the elimination of uneven (“choppy” or “jumpy”) output, and to prevent FPS from plummeting during the intense sequences when players need smooth feedback most.
Aside from frame rate, a separate but related factor unique to interactive applications such as gaming is latency. Excessive preprocessing can result in a noticeable delay between player commands and computer feedback, even when a full frame rate is maintained, often referred to as input lag.
Without realistic motion blurring, video games and computer animations do not look as fluid as film, even with the same frame rate. When a fast moving object is present on two consecutive frames, a gap between the images on the two frames contributes to a noticeable separation of the object and its afterimage in the eye. Motion blurring mitigates this effect, since it tends to reduce the image gap when the two frames are strung together The effect of motion blurring is essentially superimposing multiple images of the fast-moving object on a single frame. Motion blurring makes the motion more fluid to the human eye, even as the image of the object becomes blurry on each individual frame.
A high frame rate still doesn't guarantee fluid movements, especially on hardware with more than one GPU. The Effect is known as micro stuttering.
The human visual system does not see in terms of frames; it works with a continuous flow of light information. A related question is, “how many frames per second are needed for an observer to not see artifacts?” However, this question also does not have a single straight-forward answer. If the image switches between black and white each frame, the image appears to flicker at frame rates slower than 30 FPS. In other words, the flicker-fusion point, where the eyes see gray instead of flickering tends to be around 60 Hz. However, fast moving objects may require higher frame rates to avoid judder (non-smooth motion) artifacts—and the retinal fusion point can vary in different people, as in different lighting conditions. The flicker-fusion point can only be applied to digital images of absolute values, such as black and white. Where as a more analogous representation can run at lower frame rates, and still be perceived by a viewer. For example, motion blurring in digital games allows the frame rate to be lowered, while the human perception of motion remains unaffected. This would be the equivalent of introducing shades of gray into the black–white flicker.
Although human vision has no “frame rate”, it may be possible to investigate the consequences of changes in frame rate for human observers. The most famous example may be the wagon-wheel effect, a form of aliasing in the time domain; in which a spinning wheel suddenly appears to change direction when its speed approaches the frame rate of the image capture/reproduction system.
Different capture/playback systems may operate at the same frame rate, and still give a different level of "realism" or artifacts attributed to frame rate. One reason for this may be the temporal characteristics of the camera and display device.
Judder is a real problem in this day where 46 and 52 inch television sets have become the norm. The amount an object moves between frames physically on screen is now of such a magnitude that objects and backgrounds can no longer be classed as "clear" . Letters cannot be read and looking at vertical objects like trees and lamp posts while the camera is panning sideways have even been known cause headaches. The actual amount of motion blur needed to make 24 frames per second smooth eliminates every remnant of detail from the frames. Where adding the right amount of motion blur eliminates the uncomfortable side effects , it is more than often simply not done. It requires extra processing to turn the extra frames of a 120 FPS source (which is the current recording "standard") into adequate motion blur for a 24 FPS target. It would also potentially remove the detail and clarity of background advertising . Today , devices are up to the task of displaying 60 frames per second , using them all on the source media is very much possible. For example , the amount of data that can be stored on blu-ray and the processing power to decode it is more than adequate. Though the extra frames when not filtered correctly , can produce a somewhat video-esque quality to the whole, the improvement to motion heavy sequences is undeniable. Televisions these days often have an option to do some kind of frame interpolation (what would be a frame between 2 real frames gets calculated to some degree) , where for frames that are almost identical this can give some manner of improvement in judder , it comes nowhere close to a source having a higher number of frames, it is merely a trick to compensate for sources not having a high enough FPS rate. This interpolation creates artifacts on screen that are clearly noticeable also.