| 摘要 |
<p>In the reproduction of coloured images, the «white point», that is to say a point which determines which areas are to be printed with zero-ink, is a critical adjustement. In this invention, signals representing the three colour components derived from the original are applied to a NAND gate (14) and when all of these signals simultaneously represent a zero printing colour condition, the NAND gate generates a zero-ink signal. This is used to modify the zero-ink or white display on the monitor tube, for example by inhibiting passage of red and blue signals (18R, 188) to the display tube while allowing the passage of green signals. The green signal to the monitor tube may be periodically interrupted, so that zero-ink areas are shown in pulsating green. The operator then adjusts the white point until the pulsating green areas correspond to the areas of the original which are to be reproduced with zero-ink.</p> |
