Image restoration method and associated apparatus

A signal processing method for estimating luminance for use with matrix array colour image sensors in which elected luminance-sensing pixels (G) capable of producing signals representative of luminance are arranged in a chequerboard pattern with colour sensing pixels (R, B) which are capable of producing signals representative of colour, the method comprising the steps of:

• ranking the signal values (G1, G2, G3, G4) representative of luminance obtained from a cluster of four luminance-sensing pixels (Gn, Ge, Gs, Gw) surrounding a first colour-sensing pixel (Hc), analysing the spatial distribution of said ranked signal values (G1, G2, G3, G4) so as to detect the presence of any diagonal luminance contour edge, horizontal luminance contour stripe or vertical luminance contour stripe at said first colour-sensing pixel (Hc), and determining an estimated discrete signal value representative of luminance for said first colour-sensing pixel based on one or more middle ranked signal values (G2, G3) in a contour-enhancing fashion dependent upon, firstly, whether any diagonal luminance contour edge is detected and, secondly, whether any horizontal or vertical luminance contour stripe which is detected is interpreted as a dark stripe on a light background or a light stripe on a dark background, wherein when the horizontal or vertical luminance contour stripe is detected the signal values representative of colour obtained from a plurality of said colour-sensing pixels (R, B) in the vicinity of said cluster of four luminance-sensing pixels (Gn, Ge, Gs, Gw) are compared so as to determine whether said detected horizontal or vertical luminance contour stripe is interpreted as a dark stripe on a light background or a light stripe on a dark background.

A signal processing method for estimating luminance, for use with matrix patterned sensors where elected sensor pixels (P) from which luminance-representative signals are taken only occupy alternate horizontal and vertical matrix element positions in the matrix pattern, the method comprising

• identifying each matrix element site (C) which is at the centre of both a row and a column of seven matrix elements and which is not the site of a said elected sensor pixel (P), and for each such identified site (C) processing the signals output from the immediately adjacent four pixels (Yn, Ye, Ys, Yw) in said row and column to establish both signal amplitude and pixel position and evaluating a luminance value for the matrix element of the identified site (C) from the amplitude values of the median pair (Y2, Y3) of said signal amplitudes in accordance with an algorithm where decision taking is based upon the location of the pixels from which the two signals (Y1, Y2) of highest amplitude emanate, the algorithm being such that when the two signals (Y1, Y2) of highest amplitude emanate from pixels in the same row or column a further signal processing step is undertaken to identify outputs (X1, X4) in said row and column from the two pixels respectively next adjacent to the pixels having the highest and lowest signal amplitudes (Y1, Y4), and to identify the mean (M) of signal outputs from the eight pixels (Xc) diagonally adjacent to, and arranged around, said four pixels (Yn, Ye, Ys, Yw) in said row and column, to enable an amplitude comparison to be made according to the result of which one of the said median pair (Y2, Y3) is selected.

A signal processing method for estimating luminance for use in a matrix array monochrome image sensor in which elected luminance-sensing pixels (P) capable of producing signals representative of luminance are arranged in a chequerboard pattern with non-luminance-representative matrix array elements (N) which do not produce signals, the method comprising the steps of:

• ranking the signal values (Y1, Y2, Y3, Y4) representative of luminance obtained from a cluster of four luminance-sensing pixels (Yn, Ye, Ys, Yw) surrounding a first non-luminance-representative matrix element (C), analysing the spatial distribution of said ranked signal values so as to detect the presence of any diagonal luminance contour edge, horizontal luminance contour stripe or vertical luminance contour stripe at said first non-luminance-representative matrix element (C), and determining an estimated discrete signal value representative of luminance for said non-luminance-representative matrix element (C) based on one or more middle ranked signal values (Y2, Y3) in a contour-enhancing fashion dependent upon, firstly, whether any diagonal luminance contour edge is detected and, secondly, whether any horizontal or vertical luminance contour stripe which is detected is interpreted as a dark stripe on a light background or a light stripe on a dark background, wherein when a horizontal or vertical luminance contour stripe is detected the signal values representative of luminance obtained from at least second and third luminance-sensing pixels (XI, X4) disposed respectively within and outwith the detected horizontal or vertical luminance contour stripe are compared with the mean (M) of the signal values obtained from a plurality of further luminance-sensing pixels (Xc) in the vicinity of said cluster of four luminance-sensing pixels (Yn, Ye, Ys, Yw) so as to determine whether said horizontal or vertical luminance contour stripe is interpreted as a dark stripe on a light background or a light stripe on a dark background.