To generate a histogram matched image

1. A method to generate a histogram matched image, the method comprising:

partitioning a portion of a first reference image into a plurality of regions;

performing histogram matching separately on the plurality of regions of the first reference image and corresponding regions in a second image to generate a plurality of first histogram matched reference images;

performing histogram matching on the portion of the first reference image and a corresponding portion in the second image to generate a second histogram matched reference image; and

selecting an area from one of at least a first histogram matched reference image and the second histogram matched reference image, to generate a finalized histogram matched reference image.

2. A method as claimed in claim 1 , wherein the plurality of regions of the first reference image have uniform intensities.

3. A method as claimed in claim 1 , further comprising determining if the difference between a maximum intensity value and a minimum intensity value of the portion of the first reference image exceeds a threshold value, the portion of the first reference image being partitioned if the difference exceeds the threshold value.

4. A method as claimed in claim 1 , wherein the area selected is determined by:

comparing the similarity of the area in the first histogram matched reference image with the corresponding area in the second image;

comparing the similarity of the area in the second histogram matched reference image with the corresponding area in the second image; and

selecting the area that is most similar to the corresponding area in the second image.

5. A method as claimed in claim 1 , further comprising combining two or more adjacent regions that are uniform relative to one another.

6. A method as claimed in claim 1 , further comprising: partitioning a region into a plurality of sub-regions; performing histogram matching separately on the plurality of sub-regions of the first reference image and corresponding sub-regions in the second image to generate a plurality of third histogram matched reference images.

7. A method as claimed in claim 6 , wherein selecting an area includes selecting an area from one of at least a first histogram matched reference image, the second histogram matched reference image and a third histogram matched reference image.

8. A method as claimed in claim 1 , wherein the partitioning includes performing quad tree decomposition of the first reference image.

9. A method as claimed in claim 1 , further comprising performing similarity analysis using the finalized histogram matched reference image and the second image to detect printing defects in the second image.

10. An apparatus to generate a histogram matched image, the apparatus comprising a controller to:

partition a portion of a first reference image into a plurality of regions;

perform histogram matching separately on the plurality of regions of the first reference image and corresponding regions in a second image to generate a plurality of first histogram matched reference images;

perform histogram matching on the portion of the first reference image and a corresponding portion in the second image to generate a second histogram matched reference image; and

select an area from one of at least a first histogram matched reference image and the second histogram matched reference image, to generate a finalized histogram matched reference image.

11. An apparatus as claimed in claim 10 , wherein the plurality of regions of the first reference image have uniform intensities.

12. An apparatus as claimed in claim 10 , wherein the controller is arranged to determine if the difference between a maximum intensity value and a minimum intensity value of the portion of the first reference image exceeds a threshold value, the portion of the first reference image being partitioned if the difference exceeds the threshold value.

13. An apparatus as claimed in claim 10 , wherein the area selected is determined by:

comparing the similarity of the area in the first histogram matched reference image with the corresponding area in the second image;

comparing the similarity of the area in the second histogram matched reference image with the corresponding area in the second image; and

selecting the area that is most similar to the corresponding area in the second image.

14. An apparatus as claimed in claim 10 , wherein the apparatus is arranged to combine two or more adjacent regions that are uniform relative to one another.

15. An apparatus as claimed in claim 10 , wherein the controller is arranged to: partition a region into a plurality of sub-regions; perform histogram matching separately on the plurality of sub-regions of the first reference image and corresponding sub-regions in the second image to generate a plurality of third histogram matched reference images.

16. An apparatus as claimed in claim 15 , wherein selecting an area includes selecting an area from one of at least a first histogram matched reference image, the second histogram matched reference image and a third histogram matched reference image.

17. An apparatus as claimed in claim 10 , wherein the partitioning includes performing quad tree decomposition of the first reference image.

18. An apparatus as claimed in claim 10 , wherein the controller is arranged to perform similarity analysis using the finalized histogram matched reference image and the second image to detect printing defects in the second image.

19. Printer apparatus comprising:

a printer to print on media using a reference image;

a scanner to generate a scanned image of the printed media;

a controller to partition a portion of the reference image into a plurality of regions, and to perform histogram matching separately on the plurality of regions and corresponding regions of the scanned image to generate a plurality of first histogram matched reference images, and to perform histogram matching on the portion of the reference image and a corresponding portion in the scanned image to generate a second histogram matched reference image, and to select an area from one of at least a first histogram matched reference image and the second histogram matched reference image to generate a finalized histogram matched reference image, the controller being arranged to detect a printing defect in the printed media by comparing the scanned image with the finalized histogram matched reference image.

20. Printer apparatus as claimed in claim 19 , further comprising an alarm to indicate that a printing defect has been detected on the printed media.