Highlighting gray scale video display terminal

Apparatus for displaying image information consisting of pixels having digitally encoded intensities, comprising:

• (a) a source of digitized intensity information for each pixel, said intensity information being in the form of a first predetermined number of information levels;
• (b) display means capable of displaying pixels at a second predetermined number of discrete intensity levels in response to digitized display control signals, said display intensity levels corresponding to said information levels in accordance with a predetermined correspondence function;
• (c) first transfer means for converting each of a first range of said information levels into a corresponding display level in accordance with a first transfer function;
• (d) second transfer means for converting each of a second range of said information levels into a corresponding display level in accordance with a second transfer function;
• and
• (e) means for defining a highlight area within said image wherein pixels outside said highlight area are displayed in accordance with the conversion produced by said first transfer means, and wherein pixels inside said highlight area are displayed in accordance with the conversion produced by said second transfer means, said first and second transfer functions being such that level changes in a constant direction in said information level produce level changes in a constant direction in said display intensity level so as to change the brightness and/or contrast of said display but not its informational content.

Apparatus for displaying image information consisting of pixels having digitally encoded intensities, comprising:

• (a) a source of digitized intensity information for each pixel, said intensity information being in the form of a first predetermined number of information levels;
• (b) display means capable of displaying pixels at a second predetermined number of discrete intensity levels in response to digitized display control signals, said display intensity levels corresponding to said information levels in accordance with a predetermined correspondence function;
• (c) first transfer means for converting each of a first range of said information levels into a corresponding digital display level in accordance with a first transfer function within a first area of said display;
• (d) second transfer means for converting each of a second range of said information levels into a corresponding digital display level in accordance with a second transfer function distinct from said first transfer function within a selectable second area of said display;
• (e) said first and second transfer functions being such that changes in a constant direction in said information levels produce changes in a constant direction in said display intensity levels both in said first area and in said second area so as to change the brightness and/or contrast of said display but not its informational content;
• (f) highlighting means for selecting said second transfer function in said second area of said display;
• (g) converter means for converting digital display level data produced by said transfer means into an analog signal;
• and
• (h) amplifying means for amplifying said analog signal;
• (i) said display means being arranged to display image pixels with a brightness proportional to said amplified analog signal.

A method of eliminating contouring effect and reducing gray scale inversion round-off errors in a CRT display having a predetermined number of equally spaced discrete display intensity levels, said display being a display of digitized image information having a lesser number of equally spaced information levels, comprising the steps of:

• (a) providing a display control signal having a number of control signal levels equal to the number of display intensity levels to be displayed;
• and
• (b) converting each of said information levels to a corresponding display control signal level by a transfer function such that no step from one information level to the next causes more than a predetermined percentage change in said display intensity level;
• whereby display intensity percentage changes when going from one information level to the next that are large enough to cause contouring and/or round-off errors are avoided in the display.