US 6,307,980 B1Granted

Method and apparatus for introducing reference impairments into video signals

AssigneeCSELT - Centro Studi e Laboratori Telecomunicazioni S.p.A.

InventorMarco Quacchia

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Abstract

A method and an apparatus are provided for introducing reference impairments into pictures to be used in subjective tests on digital video signals, in compliance with ITU-T Recommendation P.930. The method generates blockiness distortion and/or edge busyness distortion. For the first distortion, areas close to picture edges are selected and, through a movement characteristics analysis, blocks are identified that belong to said areas and that are concerned only by the actual movement of the subject and, for blocks chosen among the identified ones, the luminance value is replaced by a value linked to the individual pixel luminance and to the average block luminance value. For the second distortion, echoes are applied that are randomly chosen in a prearranged set and that alternate at random.

Claims15

Dependent claims

Method of introducing reference impairments into digital video pictures, wherein at least a first distortion is introduced into a test picture, said first distortion being represented by a value modification at least of luminance pixels of pixel blocks located next to picture edges and affected by a movement of the picture, and wherein for said modification, in every picture frame:

a) picture edges are identified;
b) areas adjacent to said edges and including said pixel blocks are selected, and blocks potentially distortable are identified among the blocks belonging to said areas through an analysis of movement characteristics;
c) the pixel luminance value for each block to which distortion is actually to be applied is replaced by a value linked to the individual pixel luminance and to the average block luminance;
characterised in that, for said identification of blocks that are potentially distortable, blocks with a number of edge pixels lying within an upper range and blocks with a number of edge pixels lying within a lower range are detected and, for the blocks detected, at every frame an indicator of displacement with respect to a group of corresponding blocks in a previous frame is determined;
said displacement indicator is compared with a first threshold, and the distortion is applied only to blocks for which the displacement indicator is not less than said first threshold, to prevent application of distortion to blocks in which movement is only due to displacements of a camera picking up the picture.

2 more elements

Apparatus for introducing reference impairments into sequences of digital video pictures, comprising:

first memory means (8) for the temporary storage of subsequent frames of a picture to be distorted and of frames resulting from distortion application;
a processing unit (7) that accesses said first memory means to read picture parts, to identify areas where to introduce one or more of said distortions, to modify said areas as required by the specific distortions, and to write the modified picture to be supplied to display means (6);
second memory means (9) arranged to store operating information necessary to apply the distortions;
and
a control unit (10) arranged to select operating apparatus modes and values of parameters to be used and to store execution modes and values of parameters being used,
characterised in that said processing unit (7) is programmed in order to introduce into a sequence of pictures at least a first distortion, represented by a value modification at least of luminance pixels in a number of pixel blocks located next to picture edges and affected by a movement of the picture, through the following operations:
a) identification of picture edges in every frame;
b) identification of pixel blocks having a number of edges pixels lying within an upper value range and of pixel blocks having a number of edge pixels lying within a lower value range;
c) computation, for each pixel block identified in step b), of the displacement with respect to every block of a pre-set group of pixel blocks in a previous frame, generation of a respective displacement indicator and detection of the minimum displacement indicator for the current block;
d) selection of pixel blocks having a minimum displacement indicator higher than a threshold;
e) ordering of the pixel blocks selected in step d) according to the displacement indicator value;
f) computation of the maximum number of blocks to which frame distortion can be applied;
g) modification of the luminance value for the pixels in a block by replacing the original value with an average between said original value and an average block luminance value, said values being weighed with respective weighing factors, and addition to said average of a random value selected within a range that can be pre-set by means of said control unit (10), the modification operations being carried out for all blocks selected in step d), if their number does not exceed said maximum number, or only for those with greater displacement indicators, in a number equal to said maximum number, if the number of blocks selected in step d) exceeds said maximum number.

10 more elements

Dependencies are inferred from the claim text.