Video Quality Measurement

• US 20080317111A1
• Filed: 11/07/2006
• Published: 12/25/2008
• Est. Priority Date: 12/05/2005
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Davis, Andrew G
• Granted Patent: US 8,254,438 B2
• Time in Patent Office: Days
• US Class Current: 375/227
• CPC Class Codes: H04N 17/004 for digital television systems
• CPC Class Codes: H04N 19/124 Quantisation
• CPC Class Codes: H04N 19/154 Measured or subjectively estimated visual quality after decoding, e.g. measurement of distortion use of rate-distortion criteria H04N19/147
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/61 in combination with predictive coding

Abstract

This application is concerned with a non-intrusive video quality measurement method, in particular where the video signal having: an original form; encoded form in which video signal has been encoded using a compression algorithm utilising a variable quantiser step size such that the encoded signal includes a quantiser step size parameter; and, a decoded form in which the encoded video signal has been at least in part reconverted to the original form. The method comprises the steps of: a) generating a first quality measure which is a function of said quantiser step size parameter; b) generating a second quality measure which is a function of the spatial complexity of the frames represented by the video signal in the decoded form; and, c) combining the first and second measures in order to obtain an estimate for the subjective visual quality of the decoded video.

Claims

1. A method of generating a measure of quality for a video signal representative of a plurality of frames, the video signal having:

an original form;

an encoded form in which the video signal has been encoded using a compression algorithm utilising a variable quantiser step size such that the encoded signal has a quantiser step size parameter associable therewith; and

, a decoded form in which the encoded video signal has been at least in part reconverted to the original form, the method comprising;

a) generating a first quality measure which is a function of said quantiser step size parameter;

b) generating a second quality measure which is a function of the spatial complexity of at least part of the frames represented by the video signal in the decoded form; and

c) combining the first and second measures.

2. A method as claimed in claim 1, wherein the spatial complexity is measured by determining a local contrast measure at a plurality of positions in a frame.

3. A method as claimed in claim 2, wherein each local contrast measure is obtained by performing a comparison function on the intensity of neighbouring regions of a frame.

4. A method as claimed in claim 3, wherein each frame includes plurality of pixels, and wherein for at least some of the pixels of a given frame, the comparison function is performed on neighbouring regions in the vicinity of a pixel, so as to obtain a comparison value in respect of that pixel.

5. A method as claimed in claim 1, wherein the neighbouring regions are elongate.

6. A method as claimed in claim 5, wherein the frames each include a plurality of pixels arranged in a grid fashion, the grid having a plurality of rows and a plurality of columns, and wherein each elongate region is formed by a plurality of pixels arranged along a row portion or a column portion.

7. A method as claimed in claim 1, wherein pairs of neighbouring regions elongate in a first direction are compared.

8. A method as claimed in claim 7, wherein pairs of neighbouring regions elongate in a second direction are compared.

9. A method as claimed in claim 8, wherein the first direction and the second direction are orthogonal to one another.

10. A method as claimed in claim 3, wherein the comparison function involves evaluating the difference in the intensity of a pair of neighbouring regions.

11. A method as claimed in claim 3, wherein for neighbouring regions in the vicinity of a pixel, the comparison function involves evaluating the difference in the intensity of a first pair of neighbouring regions elongate in a first direction, and, evaluating the difference in the intensities of a pair of neighbouring regions elongate in a second direction.

12. A method as claimed in claim 11, wherein the comparison function further involves choosing the greater of the differences in the first and second directions.

16. A method as claimed in claim 1, wherein the intensity of a neighbouring region is obtained from the average intensity of the pixels within that region.

17. A method as claimed in claim 2, wherein the spatial complexity of a frame is calculated using an average of the local contrast measure obtained at different positions in a frame.

18. A method as claimed in claim 2, wherein the spatial complexity of a plurality of frames is averaged.

19. A method as claimed in claim 1, wherein the spatial complexity is obtained by performing a comparison function on neighbouring regions in frame, which neighbouring regions are elongate so as to each have a long axis and a short axis, and wherein the long axis of each elongate region is between 0.5% and 2% of the frame dimension in the direction of the long axis.

20. A method as claimed in claim 19, wherein the short axis of each elongate region corresponds to the width of a single pixel.

13. A method as claimed in claims, wherein the frames each include a plurality of pixels, and for at least some of the pixels in a given frame, the spatial complexity is determined from a measure of the intensity gradient in a first direction at a given pixel, and the intensity gradient at that pixel in a second direction, the first and second directions being preferably orthogonal to one another.

14. A method as claimed in claim 13, wherein for a given pixel, the spatial complexity is calculated using the greater of the gradients in the first and second directions at that pixel.

15. A method as claimed in claim 13, wherein the measure of the intensity gradient is linearly related to the difference in the intensity of neighbouring regions of a frame.

21. A apparatus for generating a measure of quality for a video signal representative of a plurality of frames, the video signal having:

an original form;

an encoded form in which the video signal has been encoded using a compression algorithm utilising a variable quantiser step size such that the encoded signal has a quantiser step size parameter associable therewith; and

, a decoded form in which the encoded video signal has been at least in part reconverted to the original form, the apparatus comprising;

a) means for generating a first quality measure which is a function of said quantiser step size parameter;

b) means for generating a second quality measure which is a function of the spatial complexity of the frames represented by the video signal in the decoded form; and

c) means for combining the first and second measures so as to generate the measure of quality for the video signal.