Method and apparatus for increasing the gamut of an additive display driven from a digital source

• US 4,994,901 A
• Filed: 12/23/1988
• Issued: 02/19/1991
• Est. Priority Date: 12/23/1988
• Status: Expired due to Fees

• Current Assignee: Eastman Kodak Company
• Original Assignee: Eastman Kodak Company
• Inventors: Parulski, Kenneth A., Bellis, Donald C. Jr.
• Primary Examiner(s): Groody, James J.
• Assistant Examiner(s): Harvey, David E.
• Application Number:
  US07/289,107
• Time in Patent Office: 788 Days
• Field of Search: 358/76, 358/75, 358/80, 358/13, 358/21 R, 358/32, 340/701
• US Class Current: 358/530
• CPC Class Codes: H04N 1/6058 Reduction of colour to a range of reproducible colours, e.g. to ink- reproducible colour gamut

Abstract

An additive display is driven from a digital source, such as a frame memory, to produce red and blue luminances that exceed the respective white point luminances of the display, thus producing saturated colors including red and blue and accordingly extending the gamut of the display system. The signals input to the frame memory are initially processed by a circuit, such as a color matrix, that is capable of corrections exceeding the white point of the image source. The processed signals are then encoded with more "headroom" for exceeding the respective white points of red and blue color values than for green color values. In one embodiment, the full red and blue bit resolution is bit-shifted and stored in the frame memory, with the red and blue white points stored as lesser code values than the green white point. The display drive signals produced from the encoded color values are then equalized for a common white point signal value before being applied to the additive display, such as a color CRT monitor.

Claims

1. Apparatus for driving an additive display with color signals from a digital source, the display having a characteristic white point comprised of predetermined signal values in each of several color components, said apparatus comprising:

means for digitally encoding the color component signals according to code values specifying predetermined ranges of color values, whereby the range of color values exceeding the white point of at least one color component is greater than the range of color values exceeding the white point of at least one remaining color component;

means for generating a display drive signal based on the values of the encoded color components, said drive signal including color drive component signals that are processed to produce a peak white according to the characteristic white point of the display; and

means for applying the color drive component signals to the display, thereby driving the display beyond the white point of said one color component and accordingly producing saturated colors including that component.

2. Apparatus as claimed in claim 1 in which the additive display is a CRT display.

3. Apparatus for driving an additive display with color signals from a digital source, the display having a characteristic white point comprised of predetermined color signal values, said apparatus comprising:

means for generating a set of digital color signals corresponding to red, green and blue components;

digital means for separately storing the red, green and blue components according to code values specifying predetermined ranges of color values, whereby the range of color values exceeding the white point luminance of at least a first color component is greater than the range of color values exceeding the white point luminance of at least one other color component;

means for generating a display drive signal based on the values of the stored color signals, said drive signal including analog red, green and blue drive component signals that are processed in view of the aforesaid unequal ranges to produce a peak white according to the characteristic white point of the display; and

means for applying the drive signal to the display, thereby driving the display beyond the white point of said first color component and accordingly producing saturated display colors including that component.

4. Apparatus as claimed in claim 3 in which said coded color values comprise bit strings of defined lengths and said color signal generating means generates said first color component with a range exceeding its white point by one or more additional bits of resolution.

5. Apparatus as claimed in claim 4 in which said color signal generating means further comprises means for shifting said one or more additional bits of said first component so that the coded values of all color components are equalized to the same bit length, and the processing provided by said drive signal generating means provides additional amplification of said first color component to substantially equalize the analog white point levels of the red, green and blue drive component signals.

6. Apparatus as claimed in claim 4 in which said storing means provides sufficient capacity for storing said first color component including said additional bits of resolution and said drive signal generating means includes a digital-to-analog converter with sufficient bit resolution to process said first color component including said additional bits.

7. Apparatus as claimed in claim 3 wherein said color signal generating means quantizes said first color component with at least one less bit of amplitude resolution whereby the code value specifying the white point of said first color component is less than the code value specifying the white point of said other component.

8. Apparatus as claimed in claim 3 in which the additive display is a CRT display.

9. Apparatus for driving an additive display with color signals from a digital source, the display having a characteristic white point comprised of predetermined red, green and blue signal values, said apparatus comprising:

means for generating digital code values for color signals obtained from a source that provides an unequal range of code assignments for color values exceeding the respective red, green and blue white points;

means for generating a display drive signal based on the coded red, green and blue colors, said drive signal including red, green, and blue voltage signals that are adjusted in view of the unequal ranges to produce a peak white according to the characteristic white point of the display; and

means for applying the drive signal to the display, thereby driving the display beyond the white point for certain of the colors and accordingly producing saturated colors including those certain colors.

10. Apparatus as claimed in claim 9 in which the source is a color matrixing circuit.

11. Apparatus as claimed in claim 9 in which the source is a graphics display generator.

12. Apparatus for driving a CRT display with color signals from a digital source, said CRT display having a characteristic white point comprised of predetermined red, green and blue signal values, said apparatus comprising:

means for generating red, green and blue input signals;

means for digitally encoding the input signals with a greater range of quantization levels provided for red and blue than for green for color values exceeding the respective red, green and blue white points;

means for generating a CRT drive signal based on the coded red, green and blue signals, said drive signal including red, green and blue voltage signals that are equalized to produce a peak white according to the characteristic white point of the CRT display; and

means for applying the CRT drive signal to the CRT display, thereby driving the CRT display beyond the red and blue white point values and accordingly producing saturated colors including red and blue.

13. Apparatus as claimed in claim 12 in which said means for digitally encoding the input signals represents the red, green and blue white points with substantially the same bit assignment and the red and blue color values exceeding the respective red and blue white points with additional bits.

14. Apparatus as claimed in claim 13 in which said means for generating a CRT drive signal includes a plurality of digital-to-analog converters for generating said voltage signals from the digitally coded signals, the digital-to-analog converters for the red and blue coded signals having additional bit resolution to render the color values exceeding the respective red and blue white points.

15. Apparatus as claimed in claim 12 in which said means for digitally encoding the input signals further comprises:

means for initially representing the red, green and blue input signals with bit assignments that render the white point of the CRT display by the same code value for each color; and

means for shifting the bit field for the red and blue bit assignments by at least one bit so that, after shifting, the red and blue white points are represented by lesser bit assignments than the green white point.

16. Apparatus as claimed in claim 15 in which said means for generating a CRT drive signal comprises:

means for converting the coded red, green and blue signals into said voltage signals; and

means for scaling the red and blue voltage signals relative to the green voltage signal so that the analog white points comprise substantially the same signal voltage for each color.

17. Apparatus for driving a CRT display with color signals from a digital source, said CRT display having characteristic white point comprised of predetermined color values, said apparatus comprising:

means for generating red, green and blue signals;

means for quantizing the red and blue signals at a relatively lower bit resolution than the green information signal so that peak white is achieved at a relatively lower code value for red and blue than for green;

digital-to-analog converters for generating analog red, green and blue signals from the quantized signals;

means for unequally amplifying the red, green and blue analog signals so that peak white is achieved at substantially the same signal voltages for each color; and

means for driving the CRT display with the amplified analog signals.

18. A method for driving an additive display with color signals from a digital source, said display having a characteristic white point comprised of predetermined signal values in each of several color components, said method comprising the steps of:

generating a set of color component signals;

digitally encoding the color component signals according to code values specifying unequal ranges of color values exceeding the respective white points of the color components;

generating a drive signal based on the encoded color component signals, said drive signal including analog color drive component signals equalized to produce a peak white according to the characteristic white point of the display; and

applying the equalized color drive component signals to the display.

19. A method for driving a CRT display with color signals from a digital source, said display having a characteristic white point comprised of predetermined red, green and blue white point values, said method comprising the steps of:

generating red, green and blue digital signals with unequal headroom for additional code values above the respective red, green and blue white point values;

generating a CRT drive signal from the red, green and blue digital signals, said digital signals processed in view of the unequal headroom to provide equalized analog red, green and blue drive signals; and

applying the red, green and blue drive signals to the CRT display, thereby driving the CRT display beyond the white point value of at least one of the colors and accordingly producing a saturated display including that color.

20. A method as claimed in claim 19 in which the step of generating digital signals with unequal headroom represents the additional headroom with additional bits of resolution and the step of generating a CRT drive signal includes converting the digital signals into analog signals with additional resolution to process the additional headroom.

21. A method as claimed in claim 19 in which the step of generating red, green and blue digital signals provides the additional headroom by lowering the bit resolution by one or more bits, and the step of generating a CRT drive signal comprises (a) converting the digital signals into analog voltage signals and (b) scaling the voltage signals so that the red, green and blue drive voltages are equal.

22. A method for driving a CRT display with color signals from a digital source, said method comprising the steps of:

generating red, green and blue digital signals;

bit-shifting the red and blue signals;

storing the red, green and blue digital signals as equal length code words;

converting the stored signals into analog voltage signals;

amplifying the red and blue voltage signals relatively more than the green signal; and

applying the amplified voltage signals to the CRT display.