Platenless book scanner with line buffering to compensate for image skew

A method for scanning a bound document on a support defining a support plane, the bound document having non-planar page contours spaced a distance from the support plane, and the bound document having a spine skewed relative to the reference line in the support plane, comprising the steps of:

• recording pre-scan data during a first scan of the bound document, the pre-scan data providing a three dimensional geometrical contour map of a page of the bound document relative to the support plane;
• calculating from the geometrical contour map an angular offset, the angular offset providing a measure of document skew between the spine of the bound document relative to the reference line in the support plane;
• identifying a set of scan line buffers for storing a scan line of image data, the number of scan line buffers in the set of scan line buffers being a function of the calculated angular offset;
• recording image data during a second scan of the bound document, the image data filling each scan line buffer in the set of scan line buffers;
• and
• polling pixels in the set of scan line buffers in accordance with the geometrical contour map to correct distortions caused by the measure of document skew of the spine of the bound document relative to the reference line in the support plane, and the non-planar page contours of the bound document, said polling step identifying pixel locations in the set of scan line buffers to provide a corrected scan line of image data.

An apparatus for scanning a bound document, comprising:

• a support for supporting the bound document in an open condition in a support plane with a reference line defined therein;
• means for recording geometrical image data of the bound document, the geometrical image data providing a non-planar map of the bound document in three-dimensions relative to the support plane;
• means for analyzing the geometrical image data to identify an angular offset between a reference axis of the bound document and the reference line in the support plane, the angular offset providing a measure of document skew between the reference axis of the bound document and the reference line in the support plane;
• means for identifying a set of scan line buffers for storing multiple scan lines of image data, the set of scan line buffers being a function of the angular offset determined by said analyzing means;
• means for scanning the bound document to record a set of scan lines of image data sufficient to fill the set of scan line buffers, each scan line in the set of scan lines of image data being aligned along an axis parallel to the reference line in the support plane;
• and
• an output scan line generator for correcting image data stored in said set of scan line buffers, said output scan line generator polling the image data stored in the set of scan line buffers in accordance with the geometrical contour map to correct distortion caused by the measure of document skew of the spine of the bound document relative to the reference line in the support plane, and the non-planar page contours of the bound document, said output scan line generator identifying locations in the set of scan line buffers to provide a corrected scan line of image data aligned parallel to the reference axis of the bound document.