초록 ▼

Disclosed is a method of processing image signals from a first and a second image sensor, both of a document scanner unit, where the first image sensor provides a first image, and the second image sensor provides a second image. The first and the second image are two-dimensional images wherein said

Disclosed is a method of processing image signals from a first and a second image sensor, both of a document scanner unit, where the first image sensor provides a first image, and the second image sensor provides a second image. The first and the second image are two-dimensional images wherein said first and second image are recorded at respective areas of a scanned medium, where a portion of the respective areas is recorded also by the other of the respective image sensors. Thereby image data from overlapping and non-overlapping areas are present in the first and the second image. The method comprises: correlating the first image with the second image, creating a correlation image and processing the correlation image to determine a displacement between the first and the second image. Consequently, a versatile calibration method is provided that can determine a displacement between the first and the second image in two dimensions.

대표청구항 ▼

1. A method of processing image signals from a first and a second image sensor arranged as staggered linear arrays along an x-direction, both of a document scanner unit, where said first image sensor provides a first image, and said second image sensor provides a second image, said first and second

1. A method of processing image signals from a first and a second image sensor arranged as staggered linear arrays along an x-direction, both of a document scanner unit, where said first image sensor provides a first image, and said second image sensor provides a second image, said first and second images being two-dimensional images wherein said first and second image are recorded at respective areas of a scanned document, where the document is scanned by relative movement in a y-direction between the image sensors and the document, and where a portion of each respective area is recorded by the staggered first and second image sensors, whereby image data from overlapping and non-overlapping areas are present in the first and the second image; the method comprising: selecting a first two-dimensional sub image at a location in the overlapping area of the first image, and a second two-dimensional sub image at a location in the overlapping area of the second image, wherein the first and the second sub image both comprise image data from the same area of the scanned document;correlating said first sub image with said second sub image, creating a first correlation image indicative of correlations at various displacements between said first and second sub images;wherein the method further comprises repeating the above steps with sub images taken from different locations than the first and the second sub image, thus creating a second correlation image, and processing the first and second correlation image to determine first and second displacements between the sub-images of the first and the second image thereby registering time-varying relative displacements in the y-direction between scanning lines of the first and the second image sensors; andwherein the first and second displacements in the y-direction are used to combine the first and the second image into a third image by re-sampling one or both of the first and second image in at least the y-direction using the determined first and second displacements. 2. A method according to claim 1, where the first and the second image are combined to form a third image by selecting a part of the first image to be combined with a part of the second image by using the determined displacement between the first and the second image. 3. A method according to claim 1, where a guess of the displacement between the first and the second image is used to select the second sub image, so that the central part of the second sub image comprises image data from the same part of the scanned document as the central part of the first sub image, if the guess is correct. 4. A method according to claim 1, where the method further comprises the step of examining the sub images to determine if they are suitable for correlation and if the method determines that the sub images are unsuitable for correlation, a new set of sub images is selected at a new position in the first and the second image. 5. A method according to claim 1, where the method further comprises the step of examining a correlation image to determine if the correlation image is valid, and if the method determines that the correlation image is invalid, the correlation image is not used to determine a displacement between the first and the second image. 6. A method according to claim 5, where the correlation images are processed together by creating a two dimensional histogram image over the location/index of the pixel in the correlation images representing the highest correlation. 7. A calibrating method for a large format scanner comprising a first and a second image sensor, where a physical displacement between the first and the second image sensor is estimated by determining a displacement between a first image provided by the first image sensor and a second image provided by the second image sensor using a method according to claim 1. 8. A calibration method for a large format scanner according to claim 7, where the large format scanner is only recalibrated if the estimated change in the displacement between the first and the second image is above a predetermined threshold. 9. A data processing system having a non-transitory computer readable storage medium having stored thereon program code adapted to cause the data processing system to perform the steps of the method according to claim 1, when said program code is executed on the data processing system. 10. A non-transitory computer program product comprising program code adapted to cause a data processing system to perform the steps of the method according to claim 1, when said program code is executed on the data processing system. 11. A non-transitory computer program product according to claim 10, comprising a computer-readable medium having stored thereon the program code. 12. A non-transitory computer readable storage medium having stored thereon computer executable code which, when executed by a processor, causes the processor to perform the steps of the method according to claim 1. 13. An apparatus for scanning comprising a first and a second image sensor arranged as staggered linear arrays along an x-direction where said first image sensor provides a first image, and said second image sensor provides a second image, said first and second image being two-dimensional images wherein said first and second image are recorded at respective areas of a scanned document, where the document is scanned by relative movement in a y-direction between the image sensors and the document, and, where a portion of each respective area is recorded by the staggered first and second image sensors, whereby image data from overlapping and non-overlapping areas are present in the first and the second image, the apparatus further comprising a processing unit configured to perform the following steps: select a first two-dimensional sub image at a location in the overlapping area of the first image, and a second two-dimensional sub image at a location in the overlapping area of the second image, wherein the first and the second sub image both comprise image data from the same area of the scanned document;correlate said first sub image with said second sub image, creating a first correlation image indicative of correlations at various displacements between said first and second sub images; andrepeat the above steps with sub images taken from different locations than the first and the second sub image, thus creating a second correlation image, and processing the first and second correlation image to determine first and second displacements between sub-images of the first and the second image thereby registering time-varying relative displacements in the y-direction between scanning lines of the first and the second image sensors, andwherein the first and second displacements in the y-direction are used to combine the first and the second image into a third image by re-sampling one or both of the first and second image in at least the y-direction using the determined first and second displacements.