a METHOD AND DEVICE FOR ADDING NOISE TO A VIDEO SIGNAL FOR IMPROVING A DISPLAY OF THE VIDEO SIGNAL

[0001] The invention relates to a method of and device for driving a display, more specifically a matrix display such as a plasma display panel, and to a display apparatus in which such a method is used

[0002] In plasma display panels a (Floyd-Steinberg) dithering method is used for reproducing true colors. However, especially in dark gray areas this dithering appeared to cause visible stable dither patterns.

[0003] It is, inter alia, an object of the invention to provide a display driving technique which causes less artifacts. To this end, a first aspect of the invention provides a display driving methods and device as defined in claims 1 and 4. A second aspect of the invention provides a display apparatus as defined in claim 5. Advantageous embodiments are defined in the dependent claims.

[0004] In a display driving method in accordance with a primary aspect of the invention, noise is added to a video signal before the video signal is subjected to a dithering operation.

[0005] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0006] The drawing shows an embodiment of a display apparatus in accordance with the present invention.

[0007] In the embodiment shown in the drawing, a television signal is picked up by an antenna A, down-converted to a base-band video signal by a tuner TUN, an subjected to various video signal processing operations by a video signal processor VSP to provide a first video signal. A digital versatile disk player DVD furnishes another possible signal for display. A personal computer PC furnishes a third possible video signal in VGA format Obviously, other video signal sources such as a laserdisc player, are possible as well. A switch SW selects one of the video signals. The selected signal is subjected to a gamma correction by a gamma correction circuit . In accordance with the present invention, a noise signal generated by a noise generator NG is added to the output signal of the gamma correction circuit by an adder AD. The output signal of the adder AD is applied to an A/D converter, whereafter the signal is subjected to a dithering operation by a dithering circuit DC. An output signal of the dithering circuit DC is displayed on a plasma display panel PDP.

[0008] The noise generator NG produces a small amount of noise, corresponding to about 0.5 least significant bit (LSB), obtained by a pseudo-random noise generator. The precise amount of added noise depends on the amount of noise already present in the signal and already added in preceding video signal operations. Preferably, only negative noise is added to ensure that black remains black. That only negative noise is added is accomplished by ensuring that during the measurement interval of a black level measurement loop the output signal of the noise generator NG is high. The A/D converter is adjusted to this high output level of the noise generator NG in that the lowest possible output signal of the A/D converter corresponds to a high output signal of the noise generator NG, so that when the noise generator NG starts to generates zeros again, these zeros result in that the video information becomes somewhat smaller while if ones are generated by the noise generator NG, the video information is unaffected. The noise is preferably added at a high-ohmic point in the circuit to allow for a simple noise insertion by means of a resistor.

[0009] As a result of the addition of this small amount of noise, the non-moving dither patterns have disappeared. Just above the black level, the noise is no longer perceivable; there are hardly any negative effects. The noise is only negative so that black remains black.

[0010] Advantageously, the gray-scale reproduction appeared to be improved as well by the addition of a small amount of noise. The noise results in that the bit transitions are obscured, without adding information. The result is a smoother image. This result could easily be obtained by adding noise in the analog domain, i.e. before the A/D converter

[0011] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. The invention can be applied with all dithering displays; a plasma display panel (PDP) is just one example of such a display. In the claims any reference signs placed between parentheses shall not be construed as limiting the claim. The word comprising does not exclude the presence of other elements or steps than those listed in a claim. The invention can be implemented by means of hardware comprising several distinct elements, and by means of a suitably programmed computer. In the device claim enumerating several means, several of these means can be embodied by one and the same item of hardware.