WO2010074408A2

WO2010074408A2 - Method for reverse-gamma compensation of plasma display panel

Info

Publication number: WO2010074408A2
Application number: PCT/KR2009/006814
Authority: WO
Inventors: Su Sam Choi; Young Jun Lee; Yoon Jeong Lee
Original assignee: Orion Pdp Co., Ltd
Priority date: 2008-12-22
Filing date: 2009-11-19
Publication date: 2010-07-01
Also published as: KR20100072742A; CN102257552B; KR101431620B1; WO2010074408A3; CN102257552A

Abstract

A method for reverse-gamma compensation of a plasma display panel capable of preventing a phenomenon in which a reverse-gamma curve is distorted at an average picture level (APL) by calculating a reverse-gamma value of each APL and applying a subfield mapping table based thereon, thereby improving image quality particularly in a low gray scale region is disclosed. The method for reverse-gamma compensation of a plasma display panel includes: calculating the ratio of the number of the total sustain pulses of a reference APL to the number of the total sustain pulses of a specific APL; calculating the number of sustain pulses of each subfield adjusted by multiplying the calculated ratio by the number of sustain pulses of each subfield of the specific APL; performing subfield mapping on the adjusted number of sustain pulses of each subfield using a subfield mapping comparison value as a comparison value; and tracing a subfield mapping value matched with the subfield mapping value calculated through the subfield mapping on a subfield mapping table, and confirming the actual gray scale of the matched subfield mapping value as the integer part of a compensated reverse-gamma value.

Description

METHOD FOR REVERSE-GAMMA COMPENSATION OF PLASMA DISPLAY PANEL

This disclosure relates to a method for reverse-gamma compensation of a plasma display panel, and more particularly, to a method for reverse-gamma compensation of a plasma display panel capable of improving image quality in a low gray scale region by calculating a reverse-gamma value of each average picture level (APL) and applying a subfield mapping table based thereon.

A plasma display panel (PDP) is a device for displaying an image using visible light generated from a phosphor when ultraviolet light emitted by gas discharge excites the phosphor. Such a PDP has a configuration in which an upper substrate and a lower substrate are sealed. As illustrated in Fig. 1, scan electrodes Y1 to Yn and sustain electrodes Z are provided in the upper substrate, and address electrodes X1 to Xm are provided in the lower substrate. In addition, discharge cells 1 are provided at the intersections of the scan electrodes and the sustain electrodes.

The PDP employs a time-division driving method of dividing a single frame into subfields having different emissions in order to implement a gray scale of an image. Each subfield is split into a reset period for uniformly generating a discharge, an addressing period for selecting a discharge cell, and a sustain period for implementing a gray scale according to the frequency of discharge. For example, in the case of displaying an image at 256 gray levels, a frame period 16.67 ms corresponding to 1/60 second is divided into 8 subfields. In addition, each of the 8 subfields (SF1, SF2, ..., SF8) is split into a reset period, an address period, and a sustain period as illustrated in Fig. 2. Here, the reset period and the address period of each subfield are the same as those of other subfields, however, the sustain period and the frequency of discharge increase at the rate of 2ⁿ(n = 0,1,2,3,4,5,6,7) in proportion to the number of sustain pulses in the subfields. As described above, since the sustain periods of the subfields are different, the gray scale of an image can be implemented.

In order to lower power consumption, an average picture level (APL) curve as illustrated in Fig. 3 is used. In the APL curve, the number of sustain pulses increases as the APL decreases. That is, as the power consumption approaches its maximum (the maximum brightness, the minimum APL, and the minimum display area), the number of sustain pulses increases. On the contrary, as the APL increases, that is, as the power consumption approaches its minimum (the minimum brightness, the maximum APL, and the maximum display area), the number of sustain pulses decreases. In this method, in the case where an image is displayed on a relatively large portion of the PDP, the number of sustain pulses applied to a single discharge cell is reduced, and in the case where an image is displayed on a relatively small portion, the number of sustain pulses applied to a single discharge cell is increased, thereby preventing the reduction in the absolute brightness of the image displayed on the screen and reducing power consumption.

In addition, as the APL is changed, the number of the total sustain pulses is changed, and the number of sustain pulses of each subfield is changed. Here, since the number of sustain pulses of each sustain field is only an integer, although the number of the total sustain pulses is increased as the APL is decreased, the number of sustain pulses is not continuously increased with the subfield but is increased at specific APL. In the PDP which implements an image using the APL method described above, the same gamma value for each APL is used, so that a phenomenon occurs in which the gamma curve is distorted at each APL.

For example, referring to Table 1, when comparing the APL 103 with the APL 102, the difference between the numbers of the total sustain pulses is 10. However, the numbers of sustain pulses of the first subfields SF1 are the same and the numbers of sustain pulses of the second subfields SF2 are different. Accordingly, in a screen using the APL 103 and a screen using the APL 102, the brightnesses of the screens are the same at 0 gray scale up to a gray scale expressing the brightness only with the SF1, but are different from each other at a gray scale using the SF2. Referring to the brightness curve, the brightnesses of the APL 103 and the APL 102 are the same at 0 gray scale up to 20 gray scale, but at 21 gray scale, the brightness of the APL 102 is greater than the brightness of the APL 103. For this reason, it can be seen that the brightness is not smoothly increased or decreased according to the change in the APL, but the gray level is increased or changed at a specific APL. That is, in a low gray level region, a gray level section occurs in which the brightness does not change, and a phenomenon occurs in which the brightness is high at a specific APL, causing tiredness during watching. If the number of sustain pulses of the SF1 is changed from 1 to 2, at that APL, the brightness of the gray scale obtained by discharging only the SF1 becomes twice. Accordingly, a different gamma table may be applied for each APL. However, there is a problem in that applying a different gamma table for each APL requires a huge size of memory.

This disclosure provides a method for reverse-gamma compensation of a plasma display panel capable of improving image quality in all gray scale regions by calculating a reverse-gamma value of each average picture level (APL) and applying a subfield mapping table based thereon.

In one aspect, there is provided a method for reverse-gamma compensation of a plasma display panel, including: calculating the ratio of the number of the total sustain pulses of a reference average picture level (APL) to the number of the total sustain pulses of a specific APL; calculating the number of sustain pulses of each subfield adjusted by multiplying the calculated ratio by the number of sustain pulses of each subfield of the specific APL; performing subfield mapping on the adjusted number of sustain pulses of each subfield using a subfield mapping comparison value as a comparison value; and tracing a subfield mapping value matched with the subfield mapping value calculated through the subfield mapping on a subfield mapping table, and confirming the actual gray scale of the matched subfield mapping value as the integer part of a compensated reverse-gamma value.

In the performing of the subfield mapping, an initial subfield mapping comparison value among the subfield mapping comparison values may be confirmed as a reverse-gamma value of an input gray scale, the subfield mapping comparison value may be sequentially compared with the adjusted number of sustain pulses of each subfield from the highest subfield (which is a subfield having the highest adjusted number of sustain pulses) to lower subfields, in the case where the subfield mapping comparison value is smaller than the adjusted number of sustain pulses in a specific subfield, the mapping value of the corresponding subfield is 0 and the same subfield mapping comparison value is confirmed as the subfield mapping comparison value in the next subfield, and in the case where the subfield mapping comparison value is greater than the adjusted number of sustain pulses in the specific subfield, the mapping value of the corresponding subfield is 1 and a value obtained by subtracting the adjusted number of sustain pulses of the corresponding subfield from the corresponding subfield mapping comparison value is confirmed as the subfield mapping comparison value to be compared with the adjusted number of sustain pulses in the next subfield.

In addition, in the case where the subfield mapping comparison value is greater than the adjusted number of sustain pulses in the lowest subfield, a value obtained by subtracting the adjusted number of sustain pulses from the subfield mapping comparison value may be confirmed as the decimal of the compensated reverse-gamma value.

The method for reverse-gamma compensation of a plasma display panel may provide the following advantages.

Since increments/decrements of the number of the total sustain pulses according to increases/decreases of the average picture level (APL) are uniformly distributed over the entire gray scales, the entire gray scales may be relatively uniformly increased or decreased.

The above and other aspects, features and advantages of the disclosed exemplary embodiments will be more apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a view illustrating the configuration of a general plasma display panel;

Fig. 2 is a reference showing the principle of implementing an image of the plasma display panel;

Fig. 3 is a view showing an average picture level (APL) curve;

Fig. 4 is a block diagram of a driver circuit for implementing a method for reverse-gamma compensation of a plasma display panel according to an embodiment;

Fig. 5 is a flowchart for explaining the method for reverse-gamma compensation of a plasma display panel according to an embodiment;

Fig. 6 is a reference showing a brightness curve according to a prior art;

Fig. 7 is a reference showing a brightness curve applying the method for reverse-gamma compensation of a plasma display panel according to an embodiment;

Fig. 8 is a reference showing a brightness gamma curve according to a prior art; and

Fig. 9 is a reference showing a brightness gamma curve applying the method for reverse-gamma compensation of a plasma display panel according to an embodiment.

Exemplary embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This disclosure may, however, be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth therein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art. In the description, details of well-known features and techniques may be omitted to avoid unnecessarily obscuring the presented embodiments.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of this disclosure. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. Furthermore, the use of the terms a, an, etc. does not denote a limitation of quantity, but rather denotes the presence of at least one of the referenced item. It will be further understood that the terms "comprises" and/or "comprising", or "includes" and/or "including" when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Hereinafter, a method for reverse-gamma compensation of a plasma display panel according to an embodiment will be described in detail with reference to the accompanying drawings. Fig. 4 is a block diagram of a driver circuit for implementing a method for reverse-gamma compensation of a plasma display panel according to an embodiment. Fig. 5 is a flowchart for explaining a method for reverse-gamma compensation of a plasma display panel according to an embodiment.

A driver circuit for implementing a method for reverse-gamma compensation of a plasma display panel according to an embodiment will now be described. As illustrated in Fig. 4, a driver circuit of a plasma display panel according to an embodiment includes a signal receiver 101, a frame buffer 102, a reverse-gamma calculator 103, an average picture level (APL) calculator 104, a reverse-gamma compensator 105, and a halftoning unit 106.

The signal receiver 101 has a function of receiving digital image data, i.e. R, G, and B data, inputted through a video board of the PDP. The reverse-gamma calculator 103 has a function of calculating the reverse-gamma values of the R, G, and B data inputted through the video board 101 using Equation 1 explained later.

The frame buffer 102 has a function of temporarily storing the digital image data inputted from the signal receiver 101 in order to obtain the APL value of the input image in advance. An image inputted first is delayed by a frame through the storing process of the frame buffer 102, and at the same time, the APL value of the corresponding inputted image is calculated by the APL calculator 104 described later. Thereafter, the image data inputted to the frame buffer 102 is read at the next frame, and the reverse-gamma value is compensated according to the APL value calculated in advance. In addition, the APL calculator 104 has a function of calculating the

APL using Equations

2 and 3 as follows:

[Math Figure 1]

where Input denotes R, G, and B data, SFM Level denotes a subfield mapping level, and 2.2 is a gamma value.

[Math Figure 2]

where Gamma Value is 2.2.

[Math Figure 3]

The reverse-gamma compensator 105 has a function of compensating the reverse-gamma value of a specific APL. Specifically, the reverse-gamma compensator 105 has a function of calculating the ratio of the number Ref_T_sus of the total sustain pulses of a reference APL to the number T_sus of the total sustain pulses of a specific APL, multiplying the ratio by the number of sustain pulses of each subfield of the specific APL, comparing the calculated number of sustain pulses of each subfield with the reverse-gamma value calculated by the reverse-gamma calculator 103 to calculate a subfield mapping value, and tracing the calculated subfield mapping value on a subfield mapping table to calculate the compensated reverse-gamma value. The function of the reverse-gamma compensator 105 corresponds to the method for reverse-gamma compensation of a plasma panel display according to an embodiment, and a detailed description thereof will be provided later.

The halftoning unit 106 has a function of halftoning the decimal fractions of the compensated reverse-gamma value calculated by the reverse-gamma compensator 105 using error diffusion or dithering.

The driver circuit for implementing the method for reverse-gamma compensation of a plasma display panel according to an embodiment has been described. Hereinafter, a method for reverse-gamma compensation of a plasma display panel according to an embodiment will be described in detail.

As described above, the base of the method for reverse-gamma compensation of a plasma display panel according to an embodiment is to compensate the reverse-gamma value of a specific APL, and the details thereof are to compensate the reverse-gamma value of each APL and compensate the number of sustain pulses of each subfield of the APL based thereon to implement an image having a brightness close to an actual brightness.

Calculation the ratio of the number of the total sustain pulses of a reference APL to the number of the total sustain pulses of a specific APL

In order to implement this, as illustrated in Fig. 5, the reference APL is set (S501), and the ratio of the number of the total sustain pulses of the reference APL to that of the specific APL to be compensated is calculated (S502). The reference APL may be one of a plurality of APLs, and for example, the reference APL may be set an APL at the highest APL of the plurality of APLs. The number of the total sustain pulses with APL and the number of sustain pulses of each subfield (SF1, SF2, SF3, SF4, SF5, SF6, SF7, and SF8) may be represented by Table 1 as follows. Table 1 is an APL table showing 128 APLs (level 0 to level 127). In Table 1, the highest APL is the level 127, and the number (Ref._-T_sus) of the total sustain pulses in this case is 255.

[Table 1]

If the specific APL to be compensated is the level 115, the number T_sus of to total sustain pulses at this level is 311, and the ratio (Ref._-T_sus/T_sus= 255/311) of the number of the total sustain pulses of the reference APL to that of the specific APL is 0.82 (see Equation 4).

[Math Figure 4]

where Ref._-T_susdenotes the number of the total sustain pulses of the reference APL, and T_susis the number of the total sustain pulses of the specific APL.

Adjustment of the Number of Sustain Pulses of Each Subfield

As described above, in the state where the ratio of the number of the total sustain pulses of the reference APL to that of the specific APL is calculated, the adjusted number of sustain pulses of each subfield of the specific APL by multiplying the calculated ratio (Ref._-T_sus/T_sus) by the number of sustain pulses of each subfield of the specific APL, is calculated (S503). Table 2 shows the number of sustain pulses of each subfield of the specific APL (level 115) and the value calculated by multiplying this by the ratio.

[Table 2]

Subfield Mapping and Reverse-gamma Compensation

Thereafter, a process for adding a weight to each subfield by comparing the adjusted number of sustain pulses of each subfield of the calculated specific APL with the reverse-gamma value corresponded to a specific input gray scale, that is, a subfield mapping process is performed (S504). For example, in the case where the input gray scale is 40, the reverse-gamma value for this is 4.33 (see Table 3), the reverse-gamma value in this case is compared with the adjusted number of sustain pulses of each subfield of the calculated specific APL, and by means of this, the process of adding a weight to each subfield is performed.

[Table 3]

Reverse-gamma Value per Input Gray Scale

Specifically, in the subfield mapping process, when the subfield mapping comparison value is greater than the adjusted number of sustain pulses of each subfield, the mapping value is 1, and when it is smaller, the mapping value is 0. Here, the initial subfield mapping comparison value is the reverse-gamma value of an input gray scale. The subfield mapping comparison value is sequentially compared with the adjusted number of sustain pulses of each subfield from the highest subfield (which is a subfield having the highest adjusted number of sustain pulses) to lower subfields. In the case where the subfield mapping comparison value is smaller than the adjusted number of sustain pulses in a specific subfield, the mapping value of the corresponding subfield is 0, and the same subfield mapping comparison value is used as the subfield mapping comparison value in the next subfield. In the case where the corresponding subfield mapping comparison value is greater than the adjusted number of sustain pulses in the specific subfield, the mapping value of the corresponding subfield is 1, and a value obtained by subtracting the adjusted number of sustain pulses from the corresponding subfield mapping comparison value is used as the subfield mapping comparison value to be compared with the adjusted number of sustain pulses in the next subfield.

Referring to Table 4, the mapping process is performed from the highest subfield SF8. Since the adjusted number 129.55 of sustain pulses of the SF8 is greater than the reverse-gamma value 4.33 of the input gray scale which is the initial subfield mapping comparison value, the mapping value of the SF8 is 0. In the next subfield SF7, the subfield mapping comparison value 4.33 of the previous subfield SF8 is used as the subfield mapping comparison value again, and since the adjusted number 64.77 of sustain pulses of the SF7 is greater than the comparison value, the mapping value is 0. When the mapping process is sequentially performed in this manner, since the adjusted numbers (129.55 = SF8, 64.77 = SF7, 31.98 = SF6, 15.58 = SF5, and 7.38 = SF4) of sustain pulses of the subfields from SF8 to SF4 are greater than the reverse-gamma value 4.33 of the input gray scale that is the subfield mapping comparison value, the mapping values of the SF8 to SF4 are 0. In the SF3, since the subfield mapping comparison value which is the reverse-gamma value 4.33 of the input gray scale is larger than the adjusted number 3.28 of sustain pulses, the mapping value of the SF3 is 1, and a value 1.05 (= 4.33 - 3.28) obtained by subtracting the adjusted number 3.28 of sustain pulses from the subfield mapping comparison value 4.33 is used as the subfield mapping comparison value of the next subfield, that is, the SF2. In the SF2, since the subfield mapping comparison value 1.05 is smaller than the adjusted number 1.64 of sustain pulses, the mapping value is 0, and the comparison value 1.05 is used as the subfield mapping comparison value of the next SF1.

Last, in the SF1, since the subfield mapping comparison value 1.05 is greater than the adjusted number 0.82 of sustain pulses, the mapping value of the SF1 is 1, and the value 0.23 (= 1.05 - 0.82) which is obtained by subtracting the adjusted number 0.82 of sustain pulses from the subfield mapping comparison value 1.05 means the decimal of the compensated reverse-gamma value, which will be described later.

[Table 4]

Subfield Mapping Process

Through the aforementioned process of extracting the mapping value of each subfield, that is, the subfield mapping process, the subfield mapping values (1 0 1 0 0 0 0 0) of the total subfields for the adjusted number of sustain pulses of the specific APL are derived as shown in Table 4. When the derived subfield mapping value is traced on the subfield mapping table (see Table 5) (S505), the actual gray scale of the matched subfield mapping value is traced, and it can be seen that the derived subfield mapping value is the weight (1 0 1 0 0 0 0 0) of each subfield of the actual gray scale level 5 (S506).

[Table 5]

Subfield Mapping Table

The actual gray scale level 5 having a weight which is the same as the derived subfield mapping value is the reverse-gamma value of the input gray scale 40 of the specific APL (level 115), that is, the integer part 5 of the compensated reverse-gamma value, and the decimal 0.23 obtained by the subfield mapping process is the decimal part of the compensated reverse-gamma value (S507). In the APL 115, the reverse-gamma value of the input gray scale 40 is compensated from 4.33 to 5.23. Here, the decimal obtained by the subfield mapping process is halftoned by the halftoning unit 105 using error diffusion or dithering.

It can be seen that the compensated reverse-gamma value calculated by the above-mentioned method approaches the actual brightness through the followings. Specifically, the reverse-gamma value 4.33 of the input gray scale 40 of the APL 115 has to be brighter by 1.22 (= 311/255) times which is the ratio of the total sustain pulses of the reference APL to that of the specific APL (level 115). Here, since the compensated reverse-gamma value calculated by the above-mentioned method is 5.23, it can be checked that the brightness approaches the theoretical actual brightness.

In addition, in the method for reverse-gamma compensation of a plasma display panel according to the embodiment, since increments/decrements of the number of the total sustain pulses according to increases/decreases of the APL are uniformly distributed over the entire gray scales, even when the APL is changed, the brightness is changed at a constant rate over the entire gray scales, thereby improving the reliability image quality. Figs. 6 and 7 illustrate brightness curves according to the prior art and brightness curves applying the method for reverse-gamma compensation of a plasma display panel according to an embodiment. According to the prior art, it can be seen that when the APL is changed to 127, 103, and 102, the brightness is significantly changed at specific gray scales. According to the embodiment, as illustrated in Fig. 7, it can be seen that although the APL is changed, the brightness is smoothly increased/decreased over the entire gray scales.

In addition, according to the prior art, when the APL is changed, the brightness gamma curves displayed on the actual panel are slightly different from each other (see Fig. 8). However, according to the embodiment, as illustrated in Fig. 9, although the APL is changed, substantially the same brightness gamma curves are attained. Here, the brightness gamma curve means a curve obtained by dividing the brightness of each gray scale at a specific APL by the brightness of the maximum gray scale at the APL and multiplying it by 255, that is, a gamma curve expressed as the actual brightness at the specific APL.

While the exemplary embodiments have been shown and described, it will be understood by those skilled in the art that various changes in form and details may be made thereto without departing from the spirit and scope of this disclosure as defined by the appended claims.

In addition, many modifications can be made to adapt a particular situation or material to the teachings of this disclosure without departing from the essential scope thereof. Therefore, it is intended that this disclosure not be limited to the particular exemplary embodiments disclosed as the best mode contemplated for carrying out this disclosure, but that this disclosure will include all embodiments falling within the scope of the appended claims.

Claims

A method for reverse-gamma compensation of a plasma display panel, including:

calculating the ratio of the number of the total sustain pulses of a reference average picture level (APL) to the number of the total sustain pulses of a specific APL;

calculating the number of sustain pulses of each subfield adjusted by multiplying the calculated ratio by the number of sustain pulses of each subfield of the specific APL;

performing subfield mapping on the adjusted number of sustain pulses of each subfield using a subfield mapping comparison value as a comparison value; and

tracing a subfield mapping value matched with the subfield mapping value calculated through the subfield mapping on a subfield mapping table, and confirming the actual gray scale of the matched subfield mapping value as the integer part of a compensated reverse-gamma value.
The method according to claim 1,

wherein, in the performing of the subfield mapping,

confirming an initial subfield mapping comparison value among the subfield mapping comparison values as a reverse-gamma value of an input gray scale,

comparing the subfield mapping comparison value with the adjusted number of sustain pulses of each subfield from the highest subfield to lower subfields sequentially,

in the case where the subfield mapping comparison value is smaller than the adjusted number of sustain pulses in a specific subfield, using the mapping value of the corresponding subfield as 0, and confirming the same subfield mapping comparison value as the subfield mapping comparison value in the next subfield, and

in the case where the subfield mapping comparison value is greater than the adjusted number of sustain pulses in the specific subfield, using the mapping value of the corresponding subfield as 1, and confirming a value obtained by subtracting the adjusted number of sustain pulses of the corresponding subfield from the corresponding subfield mapping comparison value as the subfield mapping comparison value to be compared with the adjusted number of sustain pulses in the next subfield.
The method according to claim 2, wherein, in the case where the subfield mapping comparison value is greater than the adjusted number of sustain pulses in the lowest subfield, confirming a value obtained by subtracting the adjusted number of sustain pulses from the subfield mapping comparison value as the decimal of the compensated reverse-gamma value.
The method according to claim 3, further including halftoning the decimal.
The method according to claim 1, wherein the reference APL is one of a plurality APLs.
The method according to claim 5, wherein the reference APL is an APL at the highest APL of the plurality of APLs.