Perimeter detection

1. A computer-implemented method for identifying and processing a colour block area in an image, the method comprising:

a) scanning for border crossings in the image in a direction from a user-provided origin point within the colour block area;

b) on finding a border crossing, tracing a path of the border such that the colour block area is on a predetermined side of the traced path;

c) if the path encloses the origin point and is traced clockwise or counterclockwise according to the predetermined choice of keeping the colour block area to the right or left respectively, determining that the border is a perimeter for the colour block area; or if not, continuing to scan for border crossings in said direction;

d) if the border is determined to be the perimeter of the colour block area, scanning from the perimeter the image in the colour block area so as to detect further border crossings in the image; and

e) processing, based on the determined perimeter, the colour block area.

2. A method as claimed in claim 1 , wherein scanning the image in the colour block area comprises scanning in a series of directions inwards from the perimeter.

3. A method as claimed in claim 2 , wherein the series of directions comprise a first set of mutually parallel directions and a second set of mutually parallel directions orthogonal to the first set of mutually parallel directions.

4. A method as claimed in claim 2 , wherein in each step of scanning the image in a series of directions the available directions are the same.

5. A method as claimed in claim 1 , wherein the method comprises, on detecting each further border crossing in the image:

tracing a further border defined by that further crossing;

determining that the traced further border is within the perimeter for the colour block area and encloses a further area; and

scanning the image in a series of directions outwards from said further border so as to detect other border crossings in the image.

6. A method as claimed in claim 5 , comprising determining a region of the image (i) having as its perimeter the perimeter of the colour block area and (ii) excluding the further area defined by the further border.

7. A method as claimed in claim 6 , comprising:

processing the image to apply a transformation to the determined region, the remainder of the image remaining substantially unchanged under the transformation; and

displaying an image resulting from the transformation.

8. A method as claimed in claim 7 , wherein the transformation is a change of chrominance and/or luminance.

9. A method as claimed in claim 1 , wherein the method comprises, on detecting the perimeter of a colour block area containing the origin point:

determining whether said perimeter exceeds a predetermined threshold and/or the size of the area exceeds a predetermined threshold and/or the circumference of said perimeter that encloses the area exceeds a predetermined threshold; if not, discarding the detected perimeter and continuing to scan in the same direction.

10. A method as claimed in claim 1 , comprising:

displaying the image via a device; and

obtaining user input via said device indicating the origin point.

11. A method as claimed in claim 1 , wherein the image is a frame of a video stream.

12. A device comprising:

a memory storing non-transient program code; and

a processor configured to identify and process a colour block area, given an image and a user-provided origin point by executing the code to perform the steps of:

a) scanning for border crossings in the image in a direction from a user-provided origin point within the colour block area;

b) on finding a border crossing, tracing a path of the border such that the colour block area is on a predetermined side of the traced path;

c) if the path encloses the origin point and is traced clockwise or counterclockwise according to the predetermined choice of keeping the colour block area to the right or left respectively, determining that the border is a perimeter for the colour block area; or if not, continuing to scan for border crossings in said direction;

d) if the border is determined to be the perimeter of the colour block area, scanning from the perimeter the image in the colour block area so as to detect further border crossings in the image; and

e) processing, based on the determined perimeter, the colour block area.

13. A device as claimed in claim 12 , wherein the processor is further configured to scan the image in the colour block area by scanning in a series of directions inwards from the perimeter.

14. A device as claimed in claim 13 , wherein the series of directions comprise a first set of mutually parallel directions and a second set of mutually parallel directions orthogonal to the first set of mutually parallel directions.

15. A device as claimed in claim 12 , wherein the device comprises a display and the device is configured to:

determine a region of the image (i) having as its perimeter the perimeter of the colour block area and (ii) excluding an area defined by the further border that is within the perimeter of the colour block area;

process the image to apply a transformation to the determined region, the remainder of the image remaining substantially unchanged under the transformation; and

display the image resulting from the transformation on the display.

16. A device as claimed in claim 12 , wherein the device comprises a camera and the image is an image captured by the camera.

17. A device as claimed in claim 16 , wherein the image is a frame of a video stream captured by the camera.

18. A device as claimed in claim 17 , wherein the device is configured to perform the said steps in real time on successive frames of the video stream.

19. A device as claimed in claim 12 , wherein processor is further configured to, on detecting each further border crossing in the image:

trace a further border defined by that further crossing;

determine that the traced further border is within the perimeter for the colour block area and encloses a further area; and

scan the image in a series of directions outwards from said further border so as to detect other border crossings in the image.

20. A non-transitory computer readable storage medium having stored thereon computer readable instructions that, when executed at a computer system, cause the computer system to perform a method for identifying and processing a colour block area in an image, the method comprising:

a) scanning for border crossings in the image in a direction from a user-provided origin point within the colour block area;

b) on finding a border crossing, tracing a path of the border such that the colour block area is on a predetermined side of the traced path;

c) if the path encloses the origin point and is traced clockwise or counterclockwise according to the predetermined choice of keeping the colour block area to the right or left respectively, determining that the border is a perimeter for the colour block area; or if not, continuing to scan for border crossings in said direction;

d) if the border is determined to be the perimeter of the colour block area, scanning from the perimeter the image in the colour block area so as to detect further border crossings in the image; and

e) processing, based on the determined perimeter, the colour block area.