GB1523352A - Digital apparatus for treatment of information representative on image to be displayed on the screen of a visual display system - Google Patents

Abstract

1523352 Television picture processing systems COMPAGNIE INDUSTRIELLE DES TELECOMMUNICATIONS CIT-ALCATEL 24 July 1975 [31 July 1974] 30966/75 Heading H4F An arrangement for displaying on a cathode-ray tube an image derived from image-representing data includes means for processing the data in such a way that a data item having a value falling within a preselected range of values is converted to another value prior to display. The arrangement allows selected ranges of values, e.g. of luminance or colour, to be reduced to a single value or to be expanded to occupy the maximum range of values that the display can accommodate, so reducing or increasing the prominence of areas of the image. In one embodiment, Fig. 1 (not shown), the image-representing data is digital and held in a store (1). The data may have been obtained from satellite and each data word represents the value d of the luminance of a corresponding point of the image. The range of possible values of d extends from O to M, as indicated in Fig. 2. Words are read in succession from the store and are processed for control of a television-type display. Each word read is compared (3) with a reference value R, Fig. 2, to determine whether d is less than, equal to, or greater than R. Means (15) are provided to select one of three modes of operation. In a first mode, all image points having a value d= R are displayed with a chosen luminance and all other points are displayed with a luminance value 0, i.e. the display shows points of equal luminance in the stored image. In a second mode, all points having a value less than R are multiplied (8) by a factor kl so that the range O-R is expanded to fill the range O-M, points having values in the range R-M being displayed with a luminance 0. In the third mode the range R-M is expanded to O-M, points in the range O-R being displayed with a luminance 0. The luminance range O-M may be divided into more than two zones, e.g. O-R1, R1-R2, R2-M, Fig. 5 (not shown), and the zone boundaries, e.g. Rl, R2, may be variable. Data values falling within a selected zone or zones may be assigned the same luminance value, e.g. I1, which may be adjustable. Similar adjustments may be made in respect of further stored data representing the colour of the image points, Fig. 6 (not shown), so that points having a selected colour value or lying within a selected range of values can have reduced or increased prominence in the displayed image. Digital masking techniques may be employed in the processing of the data, Fig. 4 (not shown), and calibration marks, &c. may be added to the displayed image.