Picture signal contrast control

• US 20030063221A1
• Filed: 04/08/2002
• Published: 04/03/2003
• Est. Priority Date: 04/11/2001
• Status: Active Grant

• Current Assignee: Dynamic Data Technologies LLC
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Stessen, Jeroen Hubert Christoffel Jacobus, Van Dalfsen, Age Jochem
• Granted Patent: US 7,050,114 B2
• Time in Patent Office: Days
• US Class Current: 348/678
• CPC Class Codes: H04N 9/68 for controlling the amplitude of colour signals, e.g. automatic chroma control circuits H04N9/71, H04N9/73 take precedence; camera processing pipelines for controlling the colour saturation of colour signals H04N23/86

Abstract

The present invention relates to controlling contrast in at least part of a picture. The contrast control is performed by reducing the saturation (2-4) of the picture during contrast increase (1).

Claims

1. A method of controlling contrast in a first part of a picture, said picture being represented by a picture signal, said picture signal comprising a number of sub signals each holding color information for different areas of the picture, said color information being represented by a first set of basic colors, each of said basic colors having an amplitude, the method comprising:

increasing (1) contrast by increasing the amplitudes of all basic colors in a selected sub signal representing that part of the picture to be contrast increased,

determining (2-4) if an amplitude of one of said basic colors exceeds a predefined value, and

reducing (2-4) saturation of said color information if an amplitude of one of said basic colors exceeds the predefined value.

2. A method according to claim 1, further comprising:

reducing (6) contrast by reducing the amplitudes of all the basic colors in that sub signal representing the part of the picture to be contrast increased.

3. A method according to claim 2,

wherein the reducing saturation step (2-4) comprises:

splitting (2) the selected sub signal into at least two groups of color information, a first group of which representing both contrast and saturation, and a second group of which representing only contrast, and

reducing (4) the signals of the first group of sub signals with a first value, and wherein the reducing contrast step (6) comprises;

reducing all basic colors with a second value.

4. A method according to claim 3, wherein the step of splitting the selected sub signal into at least two groups of color information comprises the step (2) of transforming the selected sub signal from being represented by the first set of basic colors to a second set of basic colors.

5. A method according to claim 3, wherein

the first value is determined (4) by multiplying the reciprocal of the amplitude of that basic color having the highest amplitude and being above the predefined value with the predefined value, and wherein the reduction of saturation is performed by multiplying the amplitudes of the signals of the first group of sub signals with the first value, and

the second value is determined (6) by multiplying the reciprocal of the amplitude of that basic color having the highest amplitude and being above the predefined value with the predefined value, and wherein the reduction of all basic colors is performed by multiplying the amplitudes of the signals of both the first and second group of sub signals with the second value.

6. A method according to claim 5, wherein the reciprocal of the amplitude of the basic color having the highest amplitude and/or the first value and/or the second value is/are are defined in lookup tables (LUT UV, LUT RGB).

7. A method according to claim 6, wherein the lookup table is implemented as a combination of at least one sparse table and at least one linear interpolator.

8. A method according to claim 1, wherein the steps of performing the reduction of saturation and performing the reduction of all basic colors are performed in a small insignificant part of the picture in which at least one amplitude of the basic colors exceeds the predefined value.

9. A method according to claim 8, further comprising contrast reduction of a large significant part of the picture in which at least one amplitude of the basic colors exceeds the predefined value.

10. A method according to claim 1, wherein the step of reducing saturation is performed by linearly reducing the amplitude of all basic color until at least one amplitude equals a predetermined amplitude value.

12. A display apparatus (31) comprising a display (35) and a signal processing device (33), the signal processing device being adapted to perform the method according to claim 1.

13. A computer program comprising a computer program code enabling a programmable device to perform the method according to claim 1.

14. A computer readable medium comprising a computer program according to claim 13.

11. A signal processing device (33) for controlling contrast in a first part of a picture, said picture being represented by a picture signal, said picture signal comprising a number of sub signals each holding color information for different areas of the picture, said color information being represented by a first set of basic colors, each basic color having an amplitude, said signal processor comprising:

means (1) for increasing the contrast by increasing the amplitudes of the basic colors in the sub signal representing that part of the picture to be contrast increased,

means (4) for determining if an amplitude of one of said basic colors exceeds a predefined value, and

means (4) for reducing saturation of said color information if an amplitude of one of said basic colors exceeds the predefined value.