Patent EP-0060220-A1 (EP)
Inventor: VUILLEME FREDY
IPC: H04N17/04
Filed: 1982-03-02
Abstract: 1. Arrangement for generating an alignment display on the screen of a video monitor in order to determine the exact position of an object the image of which also appears on said screen, said alignment display comprising at least one horizontal and one vertical line situated at a precisely predetermined position on the screen and the monitor being controlled by a composite signal formed in particular from a horizontal synchronization signal (SH), a vertical synchronization signal (SV) and a spot intensity signal for regulating the grey level at every point of the screen, characterized in that it comprises : - means (13) for developing in addition to said synchronization signals : - a vertical blanking signal (BV) defining for each complete screen scanning sequence the starting point of the screen lines reserved for the alignment display ; - a horizontal blanking signal (BH) defining for each line scanning sequence the end point of such line ; and - a clock signal (H) the frequency of which is a multiple of that of the synchronization signals ; - means (14) for generating an alignment display signal, i.e. a spot intensity signal controlling the visualisation of the alignment display, such means comprising : - for the visualisation of a horizontal line of the alignment display, a circuit adapted to furnish in response to a first enabling signal a spot intensity signal corresponding to the visualisation on the screen of a predetermined number of successive scanning lines ; and - for the visualisation of a vertical line formed by a vertical stacking of a series of elementary segments of successive lines on the screen, a circuit adapted to furnish in response to a second enabling signal a spot intensity signal corresponding to the visualisation on the screen of one of said elementary segments of predetermined length ; - memory means for storing : - a first digital reference value (21, 22) associated with the position of the horizontal line of the alignment display, this value corresponding to the number of the first scanning line of the screen forming the horizontal line of the alignment display such scanning lines starting from the first line defined by the vertical blanking signal ; and - a second digital reference value (30, 31) associated with the position of each elementary segment of the horizontal line provided to form the vertical line of the alignment display, this value corresponding for each scanning line to the number of clock pulses separating the beginning of the said elementary segment from the beginning of the portion of the line reserved for visualisation of the alignment display, - first means (17) for counting the number of lines scanned on the screen, such counting means being set to an initial count by the vertical blanking signal and incremented by the horizontal blanking signal ; - second means (25) for counting the clock pulses, such counting means being set to an initial value when the spot arrives at the beginning of the portion of each scanning line reserved for visualisation of the alignment display and incremented by the clock signal ; and - a first (20) and a second (29) comparison means to compare respectively the contents of the first and second counting means with the first and second digital reference values and to generate upon coincidence said first or second enabling signal for the circuits provided for the visualisation of a horizontal line or a vertical line.