Detection and suppression of flicker in a sequence of images

Abstract

The invention relates to a method, device and computer-program product for detection of undesired temporal variations (flicker) in a sequence of video frames. In one embodiment, frame-wise luminance means are compared with a reference level and the crossing frequency is compared with expected variation frequencies, such as frequencies associated with an illumination frequency through aliasing. The crossings count can be refined by introducing a latency zone around the reference level. In case of a positive detection of an undesired temporal variation, there is further provided a correction method, device and computer-program product using cumulated distribution functions. The visual detriment of flicker-induced saturation of pixels is alleviated either by brightening non-saturated pixels or by replacing the saturated pixels by randomly sampled values in accordance with a reference cumulated distribution function. The invention provides embodiments suitable for real-time processing of streamed video sequences.

Description

technical field [0001] The invention disclosed herein relates generally to video processing, and more precisely to the continuous detection of undesired transient changes in a sequence of video frames. In particular, the invention is suitable for detecting aliasing-related artefacts in a sequence of video frames streamed over a communication network. Advantageously, the present invention also provides methods and devices for the detection and suppression of undesired transiently altered binding. technical background [0002] During playback of moving images (that is, sequences of still images (frames) presented continuously at appropriate points in time), viewers sometimes observe undesired brightness variations, known as "flickers," which do not appear in the depicted in the scene. As used herein, a scene is a region of space that is visible or partially visible in the field of view of an imaging device recording a moving image. Although the entire scene may not be visib...

AI Technical Summary

Problems solved by technology

For example, a provider of video telephony services cannot assume that such a hardware feature is available, but instead has to accept image data from any device operated by a user of the service

Finally, the sheer complexity of some methods makes them unusable for video telephony

On a normally loaded PC, fairly accurate Fourier-based detection methods can take up most of the CPU performance; at the very least, computationally complex methods mean the risk of forcing ad hoc quality degradation on videotelephony systems, such as frame rate drops, Image size reduction, etc.

Images