Abstract: A method for measuring the spatial frequency response (SFR) of an imaging system (299) including a display device (280) and an image capture device (290) is disclosed. The method displays a sequence of displayable test pattern images on the display device, the sequence comprising a first test pattern image and at least two subsequent test pattern images, each of the displayable test pattern images including a test pattern having at least one sinusoidal pattern at one or more spatial frequencies such that a phase shift of the sinusoidal pattern has a plurality of pre-determined values. The displayed images are captured with the image capture device to generate a corresponding sequence of captured test pattern images. The captured test pattern images are then compared with the displayable test pattern images to calculate the SFR at a plurality of image locations in the imaging system at the one or more spatial frequencies.

Abstract: Disclosed is a method of determining at least one three-dimensional (3D) geometric parameter of an imaging device. A two-dimensional (2D) target image is provided having a plurality of alignment patterns. The target image is imaged with an imaging device to form a captured image. At least one pattern of the captured image is compared with a corresponding pattern of the target image. From the comparison, the geometric parameter of the imaging device is then determined. The alignment patterns include at least one of (i) one or more patterns comprising a 2D scale and rotation invariant basis function, (ii) one or more patterns comprising a 1D scale invariant basis function, and (iii) one or more patterns having a plurality of grey levels and comprising a plurality of superimposed sinusoidal patterns, the plurality of sinusoidal patterns having a plurality of predetermined discrete orientations.

Abstract: A method of generating a matching key for an image is disclosed. The matching key is substantially invariant to rotation, scale and translation. The method starts by forming a spatial domain representation of the image that is substantially invariant to translation of the image. Rotation and/or scaling in the spatial domain representation is next transformed into translation to form a transformed image. A representation of the transformed image is then formed that is substantially invariant to translation of the transformed image. The representation of the transformed image is the matching key for the image.

Abstract: A method (400) is disclosed for estimating an affine relation between a first image and a second image. The first and second images each have at least 4 non-parallel lines therein. The method (400) starts by identifying (406) sets of intersection points of the lines appearing in each of the images. The method (400) then determines (412) whether a relation between intersection points exists. If the relation exists then the first and second images are affine related and the affine distortion may be inverted (418).

Abstract: A method (300) is described of determining characteristic of an ink jet printer (15). A chart containing multiple regions or patches is printed (320) on a print medium (115) using the ink jet print (15). The chart includes at least a first region printed using a first set of nozzles, and at least a second region printed using a second set of nozzles. The first and second sets of nozzles are a predetermined distance apart in the printer head of the printer (15). The printing of the first and second regions is also separated by a print medium advance operation equal to the predetermined distance. This causes the first and second regions to be aligned in the direction of the print medium advance operation. The chart is then imaged using scanner (16) chart to form a chart image. The positions of the regions appearing in the chart image are next determined (340).

Abstract: A method (300) is described of determining characteristic of an ink jet printer (15). A chart containing multiple regions or patches is printed (320) on a print medium (115) using the ink jet print (15). The chart includes at least a first region printed using a first set of nozzles, and at least a second region printed using a second set of nozzles. The first and second sets of nozzles are a predetermined distance apart in the printer head of the printer (15). The printing of the first and second regions is also separated by a print medium advance operation equal to the predetermined distance. This causes the first and second regions to be aligned in the direction of the print medium advance operation. The chart is then imaged using scanner (16) chart to form a chart image. The positions of the regions appearing in the chart image are next determined (340).

Abstract: A method and system is disclosed for authenticating a physical medium (1405). The method starts by retrieving (1406) a reference digital signature (1412) previously determined (1403) based upon visual characteristics of an area (1402) of a reference physical medium (1400). A candidate digital signature (1415) is determined based upon visual characteristics of an area (1408) of the physical medium (1405), the area (1408) of the physical medium (1405) being at least partly corresponding to the area (1402) of the reference physical medium (1400). Weight values associated with different parts of at least one of the areas (1402 and 1408) are determined (201). Finally, the candidate digital signature (1415) is compared (1420) with the reference digital signature (1412), wherein the contributing of the parts in the comparison (1420) is based upon the weight values.

Abstract: A method (100) of demodulating a real two-dimensional pattern (110) is disclosed. The method (100) estimates (120, 130) a quadrature two-dimensional pattern from the real two-dimensional pattern (110) using a smooth phase only transform having an anti-symmetric phase, such as a spiral phase filter (140). A demodulated image is created by combining (180) the real two-dimensional pattern (110) and the estimated quadrature two-dimensional pattern.

Abstract: A method (200) of enhanced peak detection in a correlation signal (g(x)) is disclosed. The method (200) comprises identifying (215) in the correlation signal (g(x)) positions where the modulus value of the correlation signal is above a first predetermined value. Each of the identified positions is then processed by forming (220) a sub-signal from the correlation signal by isolating a region of samples, the region comprising substantially equal numbers of samples on opposite sides of the identified position. The sub-signal is then up-sampled (221, 222, 225) to a higher resolution using Fourier interpolation. The up-sampled sub-signal is searched (230) for a peak value, and when the peak value is greater than a second predetermined value, parameters associated with the peak value is stored (236).

Abstract: A method (200) is disclosed of detecting one or more patterns embedded in an image. Each pattern embedded in the image has been formed from a one-dimensional basis function. The method (200) starts by calculating (210) a projective transform of the image. A 1-D correlation is then calculated (220) between the projective transform and the basis function for a selection of angles. Finally, one or more peaks of the correlation are found (230). The position of each of the peaks provides spatial parameters of one of the one or more embedded patterns.

Abstract: A method (750) of encoding a value is disclosed. In one implementation the value is encoded into an image (700). The method (750) operates by defining (403) a first ordered set of positions; determining (405) a number of marks for encoding the value in the ordered set of positions; determining (409) a selection of the first ordered set of positions using combinatorial theory with the number of marks and the number of positions in the first ordered set of positions for encoding the value; and placing (411) marks at the selection of the first ordered set of positions. Preferably the value is encoded by encoding a base value and an offset value, the base value is encoded by the number of marks, and the offset value is encoded by the selection of positions. Preferably the marks are basis patterns forming a watermark (710).

Abstract: A method of utilising a two-dimensional code pattern is disclosed comprising the steps of encoding (5) the structure of phase perturbations (including singularities) on a continuous phase map structure as an encoded representation of the code information. The codes can then be impressed or printed on other media such labels, documents, envelopes etc. A method of demodulating (10) the aforementioned codes and determining a phase map structure for the code including the detection of embedded phase singularities and decoding the embedded information, is also disclosed.

Abstract: A method (400) of estimating an orientation angle (?0) of a pattern in an image (405) is described. A complex energy operator is applied to the image (405). The complex energy operator is defined as ?c{f}=(D{f})2?fD2{f}. A phase component of the result, which is defined as 2?0=arg(?c{f}) is determined, from which the orientation angle (?0) is calculated. A method (100,200) of demodulating a real two-dimensional pattern is also described. A two-dimensional spiral phase filter is applied to the pattern. The result is combined with the original pattern to provide a demodulated image. Furthermore, a method (600) of estimating a spatial phase of fringe pattern images in a sequence of fringe patterns is disclosed. The fringe pattern images are converted to pure AMFM patterns by removing offsets from each. Contingent analytic images are determined corresponding to each of said AMFM patterns, from which phase differences and phase shifts are determined from dependent pairs.

Abstract: Methods (450, 750) are disclosed for embedding a watermark into an image (400, 700). The watermark comprises at least one basis pattern. A real part of the basis pattern(s) (410, 710) is added to the image (400, 700) to form a watermarked image (420, 730). The basis pattern(s) has scale and rotation invariant properties. The pattern(s) is preferably added to the image at a low intensity to make the pattern(s) invisible or imperceptible to the human visual system under normal viewing conditions. Methods (800, 900) are also disclosed for detecting a watermark from a watermarked image (810, 910). The watermark image (810, 910) is correlated with the basis pattern to provide a result image (830, 950).

Abstract: A method and apparatus (9) for estimating the blur parameters of blurred images (g1, g2) are disclosed. The apparatus (9) has one or more image sensors (10) for capturing the blurred images (g1, g2), a plurality of correlators (20, 30) for performing autocorrelation of the blurred image (g1) and cross-correlation between the two images (g1, g2) respectively, and an error function calculator (40) for evaluating an error function over all possible displacements using the results from the correlators (20, 30). The apparatus (9) further includes an extreme locater (50) for finding the displacement with the minimum value for the error function.

Abstract: A method (200) is disclosed of detecting one or more patterns embedded in an image. Each pattern embedded in the image has been formed from a one-dimensional basis function. The method (200) starts by calculating (210) a projective transform of the image. A 1-D correlation is then calculated (220) between the projective transform and the basis function for a selection of angles. Finally, one or more peaks of the correlation are found (230). The position of each of the peaks provides spatial parameters of one of the one or more embedded patterns.

Abstract: A method (750) of encoding a value is disclosed. In one implementation the value is encoded into an image (700). The method (750) operates by defining (403) a first ordered set of positions; determining (405) a number of marks for encoding the value in the ordered set of positions; determining (409) a selection of the first ordered set of positions using combinatorial theory with the number of marks and the number of positions in the first ordered set of positions for encoding the value; and placing (411) marks at the selection of the first ordered set of positions. Preferably the value is encoded by encoding a base value and an offset value, the base value is encoded by the number of marks, and the offset value is encoded by the selection of positions. Preferably the marks are basis patterns forming a watermark (710).

Abstract: A method of encoding images such as fingerprint type images (FIG. 2) is disclosed. A phase map structure for the image is formed (FIG. 3) and any singularities (+1, 2, 0.5) in the phase map structure are removed to create a continuous phase map structure (FIG. 5). The structure of the singularities and the continuous phase map structure are then separately encoded to form an encoded representation (88) of the image (50). Preferably, the singularity encoding includes encoding a position of each singularity in addition to its order and orientation. The phase map structure can be of the form: ƒ(x,y)=a(x,y)+b(x,y)cos(&phgr;(x,y))+c(x,y)+n(x,y) The significance map can further include a separate encoding of phase map magnitude components.

Abstract: A method of halftoning input image data intended for reproduction on a display (114) having a plurality of pixels (23-27) and a limited pixel response time (see FIG. 1) is disclosed. In a first halftone cycle (K=n), the method comprises (first) halftoning an input value (30) to display an extreme representable (100% or 0%). In a second halftone cycle (K=n+1), (second) halftoning the input value (30) to display an intermediate value such that the average of the extreme representable value and the intermediate value is substantially equal to the input value.

Abstract: A method (400) of estimating an orientation angle (&bgr;0) of a pattern in an image (405) is described. A complex energy operator is applied to the image (405). The complex energy operator is defined as &PSgr;c{ƒ}=(D{ƒ})2−ƒD2{ƒ}. A phase component of the result, which is defined as 2&bgr;0=arg(&PSgr;c{ƒ}) is determined, from which the orientation angle (&bgr;0) is calculated. A method (100,200) of demodulating a real two-dimensional pattern is also described. A two-dimensional spiral phase filter is applied to the pattern. The result is combined with the original pattern to provide a demodulated image. Furthermore, a method (600) of estimating a spatial phase of fringe pattern images in a sequence of fringe patterns is disclosed. The fringe pattern images are converted to pure AMFM patterns by removing offsets from each.