Colour saturation correction device

SUBMISSION NUMBER

Internat, classif. Date of grant

09301061

H04N

August 1995

The Minister of Economic Affairs

Having regard to the Law of 28 March 1984 on inventive patents, in particular Article 22;

Having regard to the Royal Decree of 2 December 1986, concerning the filing, granting and maintenance of inventive patents, in particular article 28;

Having regard to the official report drawn up by the Industrial Property Office on 08 October 1993 in LOOO

DECISION:

ARTICLE 1.- The following will be awarded to: PHILIPS ELECTRONICS NV Groenewoudseweg 1, NL-5621 BA EINDHOVEN (THE NETHERLANDS) represented by: STEENBEEK L., INTERNATIONAL PATENT OFFICE, PO Box 220 NL 5600 AE EINDHOVEN.

an invention patent for a term of 20 years, subject to payment of the annual fees for: COLOR SATURATION CORRECTION DEVICE.

INVENTOR (S): Jaspers Cornells AM, Groenewoudseweg 1, NL-5621 BA Eindhoven (NL)

ARTICLE 2.- This patent has been granted without prior examination of its patentability, without warranty of its value or the correctness of the description of the invention and at the applicant's own risk.

Brussels. «Nuxu3L.ua

BY SPECIAL AUTHORIZATION:

August 1995

G.DE CUYPERE Board Secretary

0930106ÎA

Color saturation correction device.

The invention relates to a color saturation correction device for correcting the saturation of door signals when a corresponding luminance signal has been processed. The invention also relates to a display device provided with such a door saturation correction device.

A color saturation correction device of the type mentioned in the opening paragraph is known from US-A-4,831,434, in which luminance signals before (Y1) and after (Y2) are measured in a contrast operation, and both color difference signals are multiplied by the quotient (Y2 / Y1) of the luminance signal (Y2) after the contrast operation and the luminance signal (Y1) before the contrast operation. This automatically compensates for a decreasing color saturation occurring with brightness increase and an increasing color saturation occurring with brightness decrease. Small luminance input signals (Y1) appear to result in an undesired amplification of the color noise as well as chrominance signals and / or color signals exceeding their respective maximum values ​​as a result of the division by a small number (Y1). In addition, even with larger luminance input signals (Y1), the color signals may rise above their respective maximum values ​​due to the multiplication of the chrominance signals by an inversely proportional factor to the luminance input signal (Y1). Finally, a division with analog circuit elements is difficult to carry out.

It is an object of the invention, inter alia, to provide a color saturation correction device and a display device in which these drawbacks are reduced. To that end, a first aspect of the invention provides a color saturation correction device as defined in claim 1. Advantageous embodiments of

09301081 the invention are stated in the subclaims. A second aspect of the invention provides a display device as defined in claim 4.

In the color saturation correction device according to the invention, it is no longer divided by the luminance input signal, so that all disadvantageous consequences of such a division are avoided and, moreover, a simpler circuit is created.

These and other aspects of the invention will be apparent from and elucidated on the basis of the embodiments described below.

In the drawing shows:

Fig. 1 a display device comprising a first embodiment of a color saturation correction device according to the invention, and

Fig. 2 is a preferred embodiment of a color saturation correction device according to the invention.

In FIG. 1, a luminance input signal Yi is applied to a processing block 1 which performs some processing irrelevant to the present invention on the luminance input signal Yi. A luminance output signal Yo output by the processing block 1 is applied to a plus input of a subtractor 3, a minus input of which receives the luminance input signal. The luminance difference signal ΔΥ output by subtractor 3 is added to 1 in an adder 5 to obtain a chrominance correction factor C of the formula C = 1 + K * (Yo - Yi), where K may be a predetermined constant. In practice, the value K = 1 for skin tones was found to yield attractive results. Depending on the color properties of the display tube, however, a different value of K may be preferred. The correction factor C is then multiplied in multipliers 7 and 9 by chrominance input signals Ui and Vi, respectively, to obtain chrominance output signals Uo and Vo, respectively. A matrix circuit 11 supplies color signals R, G, B to a display device 13 on the basis of the luminance output signal Yo and the chrominance output signals Uo, Vo.

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Fig. 2 shows a preferred embodiment of a door saturation correction device according to the invention. The core of the device is formed by a multiplier 21 in which a chrominance signal UI (or VI) is multiplied by the luminance difference signal ΔΥ and the constant K; a black level reference signal Ybref is also applied to the multiplier 21 to obtain a desired output level. The output of the multiplier 21 is added to the chrominance signal UI (or VI) in an adder 23 to obtain a signal C * UI (or C * VI) according to the formula UI + K * ΔΥ * UI (or VI + K * ΔΥ * VI), which means multiplying the chrominance signal UI (or VI) by a correction factor C = 1 + Κ * ΔΥ. The value ΔΥ = (Yo - Yi) indicates the difference between a luminance output Yo and a luminance input Yi. The output of the adder 23 is output via a buffer 25 as a chrominance output signal Uo (orVo).

The others in FIG. 2 circuit elements shown serve to clamp the black level of the chrominance output signal Uo (or Vo) on the black level reference Ybref. For this purpose the chrominance output signal is applied via a buffer 27 and a switch 29 controlled by a clamping pulse Cl to a terminal of capacitor 31, the other terminal of which is grounded . The voltage present on the capacitor 31 is connected to a plus input of a differential amplifier 33, the minus input of which is fed the black level reference signal Ybref via a resistor 35. The differential amplifier 33 is counter-coupled by means of a capacitor 37. The output of the differential amplifier 33 is connected to the minus input of a differential amplifier 39, the plus input of which receives the chrominance input signal Ui (or Vi) via a capacitor 41 and the black level reference signal Ybref via a resistor 43. The output of the differential amplifier 39 provides the chrominance signal UI (or VI) discussed above.

It should be noted that the above-described embodiments illustrate but do not limit the invention, and that skilled practitioners will be able to design many alternative embodiments without departing from the scope of the following claims. For example, it is possible in FIG. 1 instead of a processing block 1 and a subtractor 3 for determining the difference

09301061

ΔY between input and output of the processing block 1, to have a (not shown) processing block Γ for determining a correction term ΔΥ to be added to the luminance input signal Yi as well as an adder (not shown) 3 'which is derived from the luminance input signal Yi and the correction term ΔΥ produces the luminance output signal Yo. The difference (Yo - Yi) indicated in the formula for the correction factor C = 1 + Κ * ΔΥ with ΔΥ = (Yo - Yi) does not therefore mean that this difference ΔΥ = (Yo - Yi) is actually deducted from the luminance input signal Yi and the luminance output signal Yo is determined; the difference ΔΥ = (Yo - Yi) can also be obtained directly from the luminance input signal Yi by the processing block ((not shown). The one shown in FIG. 2 indicated manner to multiply the chrominance signals by the correction factor C = ί + Κ * ΔΥ, namely by adding the term K * ΔΥ * UI to a chrominance signal UI, can of course also be included in the circuit of FIG. 1 be applied. Instead of a constant, the factor K can also be a function of, for example, the shade, so that a different correction is applied for skin tones than for other shades, such as, for example, the shade of grass.

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