6 614 414

6,614,414 Title:

Method of and unit for displaying an image in sub-fields

A display unit displays an image on a display screen like a plasma display panel in a number of sub-fields. The display unit is arranged to control the intensity values of one of the color values of a pixel, in particular to control whether the highest weighted sub-field is switched on or off, by changing that color signal. The effect of this change on the luminance of the pixel is compensated by a change to one or both of the other color signals.

What is claimed is:

1. A display unit for displaying an image on a display device, wherein a plurality of sub-fields are defined, each sub-field having a respective illumination level which isapplied to the display device, the display unit comprising: an input for receiving respective input intensity values for sub-pixels of a particular pixel of the image; a control unit for comparing at least one of the input intensity values with apredetermined value, conditionally modifying, on the basis of said comparing, the at least one of the input intensity values to a desired value, and modifying at least a further one of the input intensity values to compensate the effect on a property ofthe pixel caused by the modifying, if any, of the at least one of the input intensity values; an output for sending respective output intensity values on the basis of the respective input intensity values potentially modified by the control unit; and acoding unit for coding the output intensity levels into combinations of sub-fields for the respective sub-pixels.

2. The display unit as claimed in claim 1, wherein the property of the pixel is the luminance of the pixel.

3. The display unit as claimed in claim 1, wherein the input receives the input intensity values for red, green and blue, respectively, and wherein the control unit conditionally modifies at least one of the 3 input intensity values to controlits value, and modifies at least one of the other 2 input intensity values to compensate the effect on the luminance according to the equation:

4. The display unit as claimed in claim 1, wherein the predetermined value corresponds with the illumination level of the highest weighted sub-field.

5. The display unit as claimed in claim 1, wherein the control unit modifies the at least one of the input intensity values if it falls in a range with a lower boundary equal to the predetermined value minus .DELTA..sub.in and an upper boundaryequal to the predetermined value plus .DELTA..sub.in, .DELTA..sub.in being equal to 5% of the maximum intensity level.

6. The display unit as claimed in claim 1, wherein the control unit compares the modification of the further one of the input intensity values with a limit and, if the further one of the input intensity values exceeds the limit, the control unitdisregards the modifications and outputs the input intensity values as the output intensity values.

7. An image display apparatus for displaying an image, comprising: receiving means for receiving a signal representing the image; a display unit as claimed in any one of the claims 1-6; and a display device for displaying the image.

8. A method of displaying an image on a display device, wherein a plurality of sub-fields are defined, each sub-field having a respective illumination level which is applied to the display device, the method comprising the steps: receivingrespective input intensity values for sub-pixels of a particular pixel of the image; comparing at least one of the input intensity values with at least one predetermined value; conditionally modifying, on the basis of said comparing the at least one ofthe input intensity values to a desired value; modifying at least a further one of the input intensity values to compensate the effect on a property of the pixel caused by the modifying, if any, of the at least one of the input intensity values; outputting respective output intensity values on the basis of the respective input intensity values potentially modified by the control unit; and coding the output intensity levels into combinations of sub-fields for the respective sub-pixels.

9. The method as claimed in claim 8, wherein the input intensity values relate to red, green and blue, respectively, and wherein at least one of the 3 input intensity values is modified to control its value, and at least one of the other 2 inputintensity values is modified to compensate the effect on the luminance according to the following equation:

10. The method as claimed in claim 8, wherein the predetermined value corresponds with the illumination level of the highest weighted sub-field.