Motion interpolation
Motion interpolation ( engl. For "motion interpolation") is a form of video processing, by means of mathematical in the algorithms , such as motion compensation are calculated intermediate images and inserted between the existing images. Motion interpolation is used to subsequently increase the frame rate of a film or video recording and thereby make movements appear smoother and more natural.
Working principle
Motion interpolation algorithms compare two successive individual images with one another (other previous and subsequent images may also be included in the calculation in order to be able to make a more precise prediction of the movement). The differences between the two images are used to analyze which parts of the image have moved in which direction. An attempt is then made to calculate where the moving image parts should have been after half the time that has passed between the two individual images. The background, any changes in perspective and the brightness are also taken into account. The image calculated in this way is inserted between the two individual images.
Many current television sets have a built-in motion interpolation function. Motion interpolation is also possible using software, for example with WinDVD or PowerDVD . Some professional video editing and compositing programs, such as B. Adobe After Effects , have motion interpolation functions. Here, the interframe calculation can also be used to create slow motion without any visible jerking.
Advantages disadvantages
For historical and technical reasons, feature films are recorded with a frame rate of 24 frames per second. Likewise, some digital cameras and most smartphones only record at frame rates of 24, 25 or 30 frames per second. However, these image frequencies are perceived by the human eye as being slightly “jerky” from medium-fast movements. This effect increases with the speed of the movements. In films, therefore, attempts are often made to avoid rapid camera pans and movements. In contrast, television and video productions that are recorded with video cameras usually have a higher frame rate of 50 or 60 frames per second (see television standard ). We perceive this frame rate as fluid and natural.
Using motion interpolation, recordings that were recorded with lower frame rates are extrapolated to these 50/60 frames per second and ideally look like a recording made with this frame rate. Movements are perceived more fluid, natural and detailed.
However, depending on the viewer, this is not always desirable. The low frame rate, which was technically feasible in the early days of cinema technology, has not changed for decades and has led to a strong familiarization effect on the part of the viewer. Paradoxically, the display of a film with a higher frame rate can lead to rejection among some of the viewers, although, as described above, it is more natural and theoretically more pleasant to watch. In computer games, however, a low refresh rate is unanimously considered undesirable.
Some people perceive the jerking as aesthetic, because it corresponds to the frame rate that has been used for decades in the cinema, and many viewers consider it an important part of the "film look". The interframe calculation removes the jerking and makes the movements smoother; this can lead to a so-called soap opera effect (possibly in connection with further measures for the intended image improvement) .
The quality of motion interpolation strongly depends on the image content. While calm, even and easily predictable movements can lead to almost perfect results, the intermediate image calculation is often difficult or even impossible in the case of sudden or very fast movements and those against a complex and finely structured background. Depending on the particular algorithm and the selected settings, the inter-frame calculation is either temporarily suspended altogether if no good result is to be expected in the latter case, or an attempt is still as good as possible to perform the calculation proceeds, resulting in visible unnatural distortions and artifacts lead can.
The calculation of the intermediate images in the television set results in a slight delay compared to the signal source. This can lead to asynchrony between the sound and the image when the sound is reproduced separately, which is why televisions delay the sound transfer to an external playback device (e.g. surround receiver ). For real-time critical applications such as computer or console games, the player's reaction time is longer.
Trivia
In 2000 , Faroudja Labs was the first manufacturer of a processor for entertainment electronics that could perform these complex calculations in real time .
See also
literature
- LS Brotman, AN Netravali: Motion interpolation by optimal control. In: Proceedings of the 15th Annual Conference on Computer Graphics and interactive Techniques. 1988, pp. 309-315, doi : 10.1145 / 54852.378531 .