Image processing

• US 20070116354A1
• Filed: 12/01/2004
• Published: 05/24/2007
• Est. Priority Date: 12/05/2003
• Status: Active Grant

• Current Assignee: British Telecommunications PLC (BT Group PLC)
• Original Assignee: British Telecommunications PLC (BT Group PLC)
• Inventors: Stentiford, Frederick
• Granted Patent: US 7,653,238 B2
• Time in Patent Office: Days
• US Class Current: 382/166
• CPC Class Codes: G06T 2207/10024 Color image
• CPC Class Codes: G06T 2207/20012 Locally adaptive
• CPC Class Codes: G06T 5/70 Denoising; Smoothing

Abstract

Picture elements of a digitally coded image are each represented by a colour value. The value of an element is adjusted by firstly making a number of comparisons between the element and elements y elsewhere in the image. This comparison involves comparing a first picture element group (which comprises the picture element x under consideration and at least one further picture element in the vicinity thereof) with a second picture element group. The second picture element group comprises a base picture element y and at least one further picture element, the number of picture elements in the second group being the same as the number of picture elements in the first group and the position of the or each further element of the second group relative to the base picture element of the second group being the same as the position of the or a respective further element of the first group relative to the picture element under consideration. The comparison determines (114) whether the two groups match in the sense that they meet a criterion of similarity. When at least one comparison results in a match, a replacement colour value for the picture element under consideration is generated (116), as a function of the colour value for the base picture element of the or each second group for which a match was obtained

Claims

1. A method of processing a digitally coded image in which picture elements are each represented by a colour value, comprising, for each of a plurality of said picture elements:

(a) performing a plurality of comparisons, each comparison comprising comparing a first picture element group which comprises the picture element under consideration and at least one further picture element in the vicinity thereof with a second picture element group which comprises a base picture element and at least one further picture element, the number of picture elements in the second group being the same as the number of picture elements in the first group and the position of the or each further element of the second group relative to the base picture element of the second group being the same as the position of the or a respective further element of the first group relative to the picture element under consideration, wherein each comparison determines whether the two groups match in the sense that they meet a criterion of similarity; and

(b) when at least one comparison results in a match, computing a replacement colour value for the picture element under consideration, the replacement colour value being a function of the colour value for the base picture element of the or each second group for which a match was obtained.

2. A method according to claim 1 including identifying picture elements which meet a criterion of distinctiveness, and computing a replacement colour value only for picture elements not meeting the distinctiveness criterion.

3. A method according to claim 2 wherein the step of identifying picture elements which meet a criterion of distinctiveness is performed in advance, and said comparisons are performed only for picture elements not meeting the distinctiveness criterion.

4. A method according to claim 2 wherein the criterion of distinctiveness for a picture element is that the number of matches obtained for that picture element exceeds a threshold.

5. A method according to claim 1 wherein the selection of the or each further picture element of the first group is selected in a random or pseudo-random manner.

6. A method according to claim 1 wherein the selection of the or each further picture element of the first group is selected in a random or pseudo-random manner from picture elements lying within a predetermined distance of the element under consideration.

7. A method according to claim 1 wherein the further elements are selected afresh following a match.

8. A method according to claim 1 wherein the selection of the base picture element of the second group is selected in a random or pseudo-random manner.

9. A method according to claim 1 wherein the selection of the base picture element of the second group is selected in a random or pseudo-random manner from picture elements lying within a predetermined distance of the element under consideration.

10. A method according to claim 1 wherein the base picture element for the second group is selected afresh for each comparison.

11. A method according to claim 1 wherein the image is a monochrome image and the colour value is a single, luminance component.

12. A method according to claim 1 wherein the image is a colour image and the colour value has three components.

13. A method according to claim 11 wherein the match criterion is that no component of any picture element of the first group differs from the corresponding component of the spatially corresponding element of the second group by more than a threshold amount.

14. A method according to claim 1 wherein the replacement colour value for a pixel is a function also of its existing colour value.

15. A method according to claim 14 wherein the replacement colour value is the average of the colour value for the picture element under consideration and the colour value for the base picture element of the or each second group for which a match was obtained.

16. A method according to claim 14 wherein the replacement colour value is that one of a predetermined set of colour values which is closest to the average of the colour value for the picture element under consideration and the colour value for the base picture element of the or each second group for a match was obtained.

17. A method according to claim 1 including the step of processing the processed image again.

18. A method according to claim 1 including the step of applying spatial filtering to the processed image.

19. A method according to claim 1 including the step of encoding the processed image using a compression algorithm.

20. An image processing apparatus comprising means (603) for storing an image and means (2, 602) arranged in operation to perform the steps of claim 1.

21. A computer program comprising a data carrier having stored thereon a set of instructions for performing the method of claim 1.