Apparatus for calibrating an analogue screen display system

Claim 1

Apparatus for use in calibrating an analogue display system comprising: digital-to-analogue conversion (D.A.C.) means for converting digital color control signals to analogue colour component signals suitable for controlling an electronic display, and analogue signal modifying means for modifying the analogue colour component signals from the D.A.C. means and connected to a screen of the analogue display system; the apparatus further comprising: switch means connected to said D.A.C. means and said analogue signal modifying means said switch means including means for producing analogue calibration color component signals, said switch means being operable in a first simultaneous display mode to pass said analogue colour component signals from said D.A.C. means directly to said analogue signal modifying means and operable in a second simultaneous display mode to pass said analogue calibration colour component signals to said analogue signal modifying means such that an appearance of said analogue colour component signals from said D.A.C. means and an appearance of said analogue calibration colour component signals can be visually compared on the screen of the analogue display system to determine whether any reproduction errors are in said D.A.C. means or in said analogue signal modifying means.