Abstract: A method and a circuit for determining the orientation of ridges of a digital image representing a fingerprint or the like, including for each image pixel, calculating a quantity taking into account the neighboring pixels in all directions, and of bidirectionally scanning the image line by line.

Abstract: The invention concerns a method for locating, in a digital image, a circle centre comprising the following steps: a) predefining a set of potential radii of the circle; b) dimensioning (303) two accumulators to a dimension in the form of a column matrix not larger than the size of the image in x-axis and a line matrix not larger than the size of the image in y-axis; c) sequentially, for each pixel image of the image: (i) selecting successively each potential radius; (ii) evaluating the position of the potential center of a circle of the selected radius and whereof the pixel concerned is on the periphery; and (iii) incrementing accumulators at the x-axis and the y axis of the potential center; and d) selecting (304) as coordinates of the located centre, the x-axis and the y-axis corresponding to the maximum of accumulators.

Abstract: A method and a system for evaluating the definition of the image of an eye iris or the like, including approximately localizing the pupil in the image, defining, from the approximate position of the pupil, an examination window centered on this position, and applying a gradient accumulation operation to the luminance values of the pixels of the examination window, the running total being proportional to the definition score of the image.

Abstract: A band-pass filter with at least one passband, which is real, bidimensional, oriented along the phase axis and resulting from the product of two identical one-dimensional Hamming windows, the transfer function of each of these windows being: X i ? ( f ) = ? i + ( 1 - ? i ) ? cos ? ? ? ( f - f ? ? q i ) f0 i , w ? ? h ? ? e ? ? r ? ? e f is a current frequency; ?i is a real number, included between and excluding 0 and 1; fqi is a central frequency of the passband; and f0i defines half of the passband centered on fqi.

Abstract: A method for coding in frequency, module and phase a digital representation, in the space field, of a ring-shaped element, including the steps of: applying to any point of the element a polar conversion at constant angle, whereby the element is unfolded in rectangular form; transferring, to the frequency field, any point of the converted rectangular shape by means of a Fourier transform; filtering the discrete data resulting from the transfer by means of at least one real, bidimensional, band-pass filter, oriented along the phase axis; applying a Hilbert transform to the filtering results; applying an inverse Fourier transform to the results of the Hilbert transform; and extracting phase and module information in the space field.

Abstract: The invention concerns a method for locating, in a digital image, a circle centre, comprising the following steps: a) predefining a set of potential radii of the circle; b) dimensioning (303) two accumulators to a dimension in the form of a column matrix not larger than the size of the image in x-axis and a line matrix not larger than the size of the image in y-axis; c) sequentially, for each pixel of the image: (i) selecting successively each potential radius; (ii) evaluating the position of the potential centre of a circle of the selected radius and whereof the pixel concerned is on the periphery; and (iii) incrementing said accumulators at the x-axis and the y-axis of the potential centre; and d) selecting (304), as coordinates of the located centre, the x-axis and the y-axis corresponding to the maximum of accumulators.

Abstract: A method for generating a typical image including at least three values per pixel, based on a set of binary images all showing a same element, including: summing up the binary values of the pixels of same coordinates in the set of binary images; generating a first state in the typical image if the sum of the pixels of same coordinates of the binary images provides a value smaller than a first threshold; and generating a second state in the typical image if the sum of the pixels of same coordinates of the binary images provides a value greater than a second threshold.

Abstract: A method and a system for evaluating the definition of the image of an eye iris or the like, consisting of approximately localizing the pupil in the image, defining, from the approximate position of the pupil, an examination window centered on this position, and applying a gradient accumulation operation to the luminance values of the pixels of the examination window, the running total being proportional to the definition score of the image.

Abstract: A method and a system determine a score characteristic of the definition of a digital imageby cumulating the quadratic norm of horizontal and vertical gradients of luminance values of pixels of the image, the pixels being chosen at least according to a first maximum luminance threshold of other pixels in the concerned direction.

Abstract: A method and a circuit for determining the orientation of ridges of a digital image representing a fingerprint or the like, consisting for each image pixel of calculating a quantity taking into account the neighboring pixels in all directions, and of bidirectionally scanning the image line by line.

Abstract: A method for coding in frequency, module and phase a digital representation, in the space field, of a ring-shaped element, including the steps of: applying to any point of the element a polar conversion at constant angle, whereby the element is unfolded in rectangular form; transferring, to the frequency field, any point of the converted rectangular shape by means of a Fourier transform; filtering the discrete data resulting from the transfer by means of at least one real, bidimensional, band-pass filter, oriented along the phase axis; applying a Hilbert transform to the filtering results; applying an inverse Fourier transform to the results of the Hilbert transform; and extracting phase and module information in the space field.

Abstract: A band-pass filter with at least one passband, which is real, bidimensional, oriented along the phase axis and resulting from the product of two identical one-dimensional Hamming windows, the transfer function of each of these windows being: 1 X i ⁡ ( f ) = α i + ( 1 - α i ) ⁢ cos ⁢ π ⁡ ( f - f ⁢   ⁢ q i ) f0 i , w ⁢   ⁢ h ⁢   ⁢ e ⁢   ⁢ r ⁢   ⁢ e