1. Field of the Invention
The present invention relates to an image display method and device for a plasma display panel (PDP). More specifically, the present invention relates to a PDP image display method and device for reducing flicker and dynamic false contour (DFC) generated when inputting 50 Hz PAL (phase alternating by line) video signals to realize images.
2. Description of the Related Art
A PDP is a display device for restoring image data input as electrical signals by arranging a plurality of discharge cells in a matrix pattern and selectively allowing the discharge cells to emit light.
Gray displaying is needed so that the PDP may operate as a color display device, and a gray realization method for dividing a single field into a plurality of subfields and performing time-division control on the subfields is used to realize the gray display.
Flickers are closely related to the quality of images perceived by humans, as flickers tend to degrade the quality of human visual experience. The flickers are more frequently detected by human eyes as a screen becomes bigger or a frequency lowers.
When images generated using PAL video signals are displayed on a large PDP, both of the above-noted conditions are met, thereby causing a lot of flickers. Therefore, when the PDP is driven at 50 Hz using a minimum incremental arrangement or a minimum decrement arrangement which is a general arrangement of subfields used for the PDP, a lot of flickers are generated.
Since the screen cannot be controlled in the above-noted two conditions that cause flicker, a method for controlling the frequency is used to reduce the flicker.
Korean published application No. 2000-16955 discloses a conventional method for reducing flicker generation by control of the frequency. In order to reduce large screen flickers generated when inputting 50 Hz video signals to drive a PDP, subfields in a single frame are divided into two groups G1 and G2, and the subfields of the groups except the least significant bit (LSB) subfield are established to have the same configuration. In other words, luminance weights are similarly allocated to the subfields of the respective groups, as shown in FIG. 1. The above-described method is much more effective than the conventional subfield arrangement, such as the minimum incremental arrangement or the minimum decrement arrangement.
Referring to FIG. 1, a total interval of a single frame is 20 ms, and the intervals of the respective groups G1 and G2 are fixed as 10 ms. Two suspension intervals are provided, one of which is positioned at the end of the frame, that is, at the end of the second group G2, and the other of which is positioned between the two groups G1 and G2, that is, at the end of the first group G1.
FIG. 2, for example, shows a partial realization of low gray by using a conventional subfield arrangement.
As shown, in the case of displaying low gray such as a low gray of from 0 to 11 by using a conventional subfield arrangement, a time difference between the subfields corresponding to the LSB and the LSB+1 is several ms.
For example, in the case of low gray 3, the lowest subfield SF1 of the first group G1 is turned on, and the lowest subfield SF1 of the second group G2 is turned on. In this instance, the subfield of the first group G1 is a subfield of the LSB, the subfield of the second group G2 is a subfield of the LSB+1, and the time difference between the subfields is 10 ms, a very big difference.
When the subfield arrangement of the Korean published application No. 2000-16955 is used and error diffusion is applied to display low gray, the time difference between the subfields corresponding to the LSB and the LSB+1 is as big as several ms, and a light emission sustain time having the above-noted time difference is short. Therefore, a severe DFC can occur in a boundary of grays when an image sensed by eyes moves.
For example, FIG. 3 shows a concept diagram of a DFC that would be generated when using the disclosure of the above-noted published application, when an image moves in the case where adjacent grays are 4 and 3. As shown in FIG. 3, the DFC occurs at a total of five points when the image moves in the case adjacent grays are 4 and 3, and difference values between the highest gray 4 and a distorted gray from among original grays are respectively 2, 1, 3, 2, and 1.5 depending on the generation points. These difference values show generation intensities of the generated DFC. The distorted gray while moving the image is displayed as color distortion, and it is displayed as color distortion in the DFC pattern.
Since the PDP has high power consumption because of its driving features, an automatic power control (APC) for controlling the power consumption according to a load ratio (or an average signal level (ASL)) of a frame to be displayed is provided. The APC method controls the APC levels according to the load ratio of the input video data, and varies a number of sustain pulses for each APC level to control the power consumption to be below a predetermined level.
Following the APC method, the number of sustain pulses applied to each subfield according to the load ratio is varied. That is, the total number of sustain pulses applied to the respective groups G1 and G2 is varied according to the load ratio, and since each subfield has a number of sustain pulses of as many as luminance weights that the corresponding subfield has, the number of sustain pulses applied to each subfield is also varied.
FIGS. 4A through 4C show positions of the subfields and central positions of light emission for each APC in the conventional PDP subfield structure, FIG. 4A showing a case when the APC is the minimum, FIG. 4B showing a case when the APC is the maximum, and FIG. 4C showing a case when a time of the first group G1 is greater than that of the second group G2.
As shown in FIGS. 4A and 4B, time gaps TIME G1G2 and TIME G2G1 between the central positions of light emission of the groups G1 and G2 are the same when the APC is the minimum and the maximum, and hence, the central positions of light emission of the first and second groups G1 and G2 have periodicity in many gray regions. Therefore, the conventional PDP subfield structure generates fewer flickers.
However, as shown in FIG. 4C, when a subfield occupation time of the first group G1 is longer than that of the second group G2 in the case of forming partial gray irrespective of the APC level, the positions of the top subfields of the first and second groups that are turned on become different. Referring to FIG. 4C, the time gap TIME G1G2 between the light emission centers of the first and second groups G1 and G2 is less than the time gap TIME G2G1 between the light emission centers of the second group G2 and a next frame's first group G1, and as a result, the light emission centers of the groups G1 and G2 lose periodicity, thereby generating flicker.