Psytechnics Limited

Benjamin Pernot

Quan Huynh-Thu

Ludovic Malfait

The present invention relates to an apparatus and method for normalization of an image signal, particularly for use in perceptual video and still image quality measurement when the quality measurement is achieved by making a comparison between a reference signal and a decoded signal. The invention provides a method for normalizing a decoded image signal in relation to a reference image signal to generate a normalized image signal comprising the steps of: generating a non-linear transformation vector in dependence upon at least one component of the decoded image signal and at least one component of the reference image signal; and applying said non-linear transformation vector to at least one component of the decoded image signal to generate a normalized image signal. Methods and apparatus for perceptual video and still image quality measurement using said method are also provided.

Method and apparatus for image signal normalisation

The present invention relates to an apparatus and method for processing images, in particular for determining the degree of blockiness in coded images. The invention comprises apparatus and methods for determining a degree of blockiness by performing the steps of: for each of a plurality of pixels determining a vertical gradient measure in dependence upon the values of said pixel and neighbouring pixels; comparing said vertical gradient measure with a vertical gradient threshold and defining said pixel as a potential horizontal boundary in dependence thereon determining a horizontal gradient measure in dependence upon the values of said pixel and neighbouring pixels; comparing said horizontal gradient measure with a horizontal gradient threshold and defining said pixel as a potential vertical boundary in dependence thereon; and determining said blocking artefact measure in dependence upon the vertical gradient measure of pixels defined as a potential horizontal boundary and upon the horizontal gradient measure of pixels defined as a potential vertical boundary. Method and apparatus for generating a quality measure in dependence upon the measure of blockiness are also provided.

Method and apparatus for measuring blockiness in video images

This invention relates to alignment of signals, particularly for use in a quality assessment system. The invention provides a method and apparatus for aligning a first signal comprising a sequence of frames with a second signal comprising a sequence of frames, the method comprising the steps of: determining a similarity measure between each of a plurality of frames of the first signal and each of a plurality of frames of the second signal; assigning a matching value to each frame of the first signal wherein the matching value indicates a relative position of a matching frame in the second signal, by repeating the sub-steps of: generating a relative delay histogram the histogram comprising a set of values corresponding to each of a set of relative delays by: selecting a subset of frames of the first signal and for each frame of said subset identifying the frame of the second signal having the greatest similarity with said frame; determining the relative delay between the identified frame of the second signal and said frame of the first signal; and incrementing the value of the histogram corresponding to said relative delay; identifying one or more peaks in the relative delay histogram; and assigning the matching value to each frame contributing to a peak in dependence upon said identified peaks.

Method and apparatus for aligning signals

This invention provides a parameter for use in assessing video quality based on temporal frame freezing for use in an apparatus and method for perceptual video quality measurement. The invention provides a method of generating a freeze frame parameter relating to the perceptual impact of frozen frames in a video signal comprising the steps of: identifying frozen frames; identifying a freeze event comprising a plurality of consecutive frozen frames, the freeze event having a duration in dependence upon the number of frozen frames in said sequence; defining a set of duration ranges; and generating a freeze frame parameter in dependence upon the number of freeze events having a duration falling within each duration range. Methods and apparatus for perceptual video quality measurement using the method are also provided.

Method and apparatus for generation of a video quality parameter

The present invention relates to an apparatus and method for processing images, in particular for determining the degree of blockiness in coded images. The invention comprises apparatus and methods for determining a degree of blockiness in a digital image comprising blocks each block comprising a plurality of rows and a plurality of columns of pixels each pixel having a value by performing the steps of: for each block determining an intra block measure in dependence upon the values of a set of pixels within said block; and determining said measure in dependence upon a plurality of said intra block measures corresponding to each block. Method and apparatus for generating a quality measure in dependence upon the measure of blockiness are also provided.

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Ipswich, United Kingdom

Benjamin Pernot