Method and arrangement for objective assessment of video quality

• US 6,704,451 B1
• Filed: 10/17/2000
• Issued: 03/09/2004
• Est. Priority Date: 03/02/1998
• Status: Expired due to Term

• Current Assignee: Koninklijke KPN NV
• Original Assignee: Koninklijke KPN NV
• Inventors: Beerends, John Gerard, Hekstra, Andries Pieter, De Caluwe, Franciscus Elisabeth, Koenen, Robert Hendrik
• Primary Examiner(s): MARIAM, DANIEL G
• Application Number:
  US09/601,901
• Time in Patent Office: 1,239 Days
• Field of Search: 382/112, 382/199, 382/206, 382/228, 382/254, 382/266, 382/269, 382/272, 348/180, 348/181, 348/184, 348/192, 348/193, 358/504, 714/712
• US Class Current: 382/199
• CPC Class Codes: G06T 9/00 Image coding bandwidth or redundancy reduction for static pictures H04N1/41; coding or decoding of static colour picture signals H04N1/64; methods or arrangements for coding, decoding, compressing or decompressing digital video signals H04N19/00
• CPC Class Codes: H04N 17/00 Diagnosis, testing or measuring for television systems or their details

Abstract

A method of and an arrangement for obtaining quality indicators for an objective assessment of a degraded or output video signal with respect to a reference or input video signal. The strength of edges or signal transitions in both the input and the output video signals are calculated to provide input and output edge signals. By processing the edge signals, introduced edges and omitted edges in the output edge signal are established. For each of the luminance and chrominance signals of a color video signal first and second quality indicators are obtained from normalized values of the introduced edges and omitted edges, relative to the output edge signal and the input edge signal normalized by first and second normalization factors, respectively. By using smeared Sobel filtering, correlation of calculated MOS and observed MOS by human test persons reaches a value of above 0.9.

Claims

1. A method of obtaining quality indicators for an objective assessment of a degraded or output video signal with respect to a reference or input video signal by quantifying the strength of edges or signal transitions in both the input and the output video signals using edge or signal transition detection, said method comprising:

a first main step of generating image features of the input and output video signals, the image features including edge information, and

a second main step of determining quality indicators from the generated image features, characterised in that the first main step includes the steps of;

a) detecting edges in the input and the output video signals, respectively (25, 27), and

b) calculating the edginess of the input and the output video signals, providing input and output edge signals (26, 28); and

the second main step includes the steps of;

c) establishing introduced edges in the output edge signal by comparing the input and output edge signals of corresponding parts of the input and output video signals (29), introduced edges being edges which are present in the output edge signal and are absent at corresponding positions in the input edge signal;

d) establishing omitted edges in the output edge signal by comparing the input and output edge signals of corresponding parts of the input and output video signals (33), omitted edges being edges which are present in the input edge signal and are absent at corresponding positions in the output edge signal;

e) obtaining normalised values of the introduced edges relative to the output edge signal adjusted by a first normalisation factor (30);

f) obtaining normalised values of the omitted edges relative to the input edge signal adjusted by a second normalisation factor (34);

g) calculating a first quality indicator by averaging the values obtained in step e) (31, 32); and

h) calculating a second quality indicator by averaging the values obtained in step f) (35, 36).

2. A method according to claim 1, characterised in that

i) the input and output edge signals are provided as corresponding unipolar signals;

j) the input and output edge signals of corresponding parts of the input and output video signals are aligned;

k) a bipolar distortion signal is established by difference building of the aligned input and output edge signals, and

l) the introduced and omitted edges are established from the respective polarities of the distortion signal.

3. A method according to claim 1, characterised in that the first and second normalisation factors are set in accordance with the characteristics of the video signals.

4. A method according to claim 3, characterised in that the first and second normalisation factors comprise a constant part set in accordance with luminance and chrominance values of the video signals.

5. A method according to claim 3 characterised in that the first normalisation factor comprises a variable part obtained from maximum characteristic edge values of the video signals.

6. A method according to claim 1, characterised in that the input and output edge signals are provided from Sobel filtering.

7. A method according to claim 6, characterised in that the input and output edge signals are provided from improved or smeared Sobel filtering.

8. A method according to claim 1, characterised in that the first and second quality indicators are obtained for either luminance and/or chrominance signals of the input and output video signals.

9. A method according to claim 8, characterised in that for the luminance signals a constant part of the first normalisation factor is in a range between 15 and 30, preferably 20, a constant part of the second normalisation factor is in a range between 5 and 15, preferably 10, and a variable part of the first normalisation factor is in a range between 0.3 and 1, preferably 0.6, times a maximum value of the luminance signal of the input and output video signals.

10. A method according to claim 9, characterised in that for the chrominance signals the constant part of the first and second normalisation factors is in a range between 5 and 15, preferably 10.

11. A method according to claim 8, a weighted quality indicator is obtained from the first and second quality indicators of each of the luminance and chrominance signals, and a Mean Opinion Score (MOS) is calculated from the obtained weighted quality indicators.

12. A method according to claim 11, characterised in that multiple linear regression techniques are used for weighing of the respective first and second quality indicators.

13. A method according to claim 1, characterised in that the normalisation factors and/or weighing of the quality indicators are set from quality indicators obtained from subjective quality data and calculated quality data.

14. An Application Specific Integrated Circuit (ASIC) adapted to include means for performing all the method steps of claim 1.

15. The method according to claim 1 wherein the method is adapted in measuring the quality of video codecs.

16. The method according to claim 1 wherein the method is adapted in measuring the quality of video transmissions.

17. An arrangement for obtaining quality indicators for an objective assessment of a degraded or output video signal with respect to a reference or input video signal by quantizing the strength of edges or signal transitions in both the input and the output video signals using edge or signal transition detection, said arrangement comprising:

means for generating image features of the input and output video signals, the image features including edge information, and

means for determining quality indicators from the generated image features, characterised in that the means for generating image features include;

a) means (42, 43) for detecting edges in the input and the output video signals, respectively, and

b) means (42, 43) for calculating the edginess of the input and the output video signals, providing input and output edge signals;

and the means for determining quality indicators include;

c) means (45) for establishing introduced edges in the output edge signal by comparing the input and output edge signals of corresponding parts of the input and output video signals, introduced edges being edges which are present in the output edge signal and are absent at corresponding positions in the input edge signal;

d) means (46) for establishing omitted edges in the output edge signal by comparing the input and output edge signals of corresponding parts of the input and output video signals, omitted edges being edges which are present in the input edge signal and are absent at corresponding positions in the output edge signal;

e) means (47) for obtaining normalised values of the introduced edges relative to the output edge signal adjusted by a first normalisation factor;

f) means (48) for obtaining normalised values of the omitted edges relative to the input edge signal adjusted by a second normalisation factor;

g) means (49) for calculating a first quality indicator (51) by averaging the values obtained in step e); and

h) means (50) for calculating a second quality indicator (52) by averaging the values obtained in step f).

18. An arrangement according to claim 17, characterised in that the edge detection and calculation means comprise Sobel filter means.

19. An arrangement according to claim 17, characterised in that the edge detection and calculation means comprise improved or smeared Sobel filter means.

20. An arrangement according to claim 17, implemented in digital processor means.

21. An Application Specific Integrated Circuit (ASIC) adapted to include the arrangement of claim 17.