KR101431620B1 - Method for reverse-gamma compensation of plasma display panel - Google Patents

Abstract

In the present invention, an inverse gamma value for each APL is calculated and a sub-field mapping table based on the inverse gamma value is applied to prevent the inverse gamma curve from being distorted for each APL step. In particular, A method of inverse gamma correction of a plasma display panel according to the present invention includes calculating a ratio of the number of sustain pulses of a reference APL to a total number of sustain pulses of a specific APL, A step of calculating the number of sustain pulses for each subfield adjusted by multiplying the number of sustain pulses for each subfield by a number of sustain pulses per subfield, Field mapping and a sub-field mapping value calculated through the sub-field mapping, And tracking the matching subfield mapping value on the subfield mapping table and determining the actual gradation of the matching subfield mapping value as an integer part of the corrected inverse gamma value.

Reverse gamma, APL, sustain pulse

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a plasma display panel,

The present invention relates to a method of inverse gamma correction of a plasma display panel, and more particularly, to a plasma display apparatus capable of improving image quality in a low gradation region by calculating an inverse gamma value according to each APL and applying a sub- Gamma correction method of the panel.

A plasma display panel (PDP) is an apparatus for displaying an image using visible light generated from a phosphor when ultraviolet rays generated by gas discharge excite the phosphor. 1, the PDP includes a scan electrode Y1 to Yn and a sustain electrode Z on the upper substrate and an address electrode X1 to Xn on the lower substrate. Xm. In addition, the discharge cells 1 are provided at the intersection of the scan electrode and the sustain electrode.

In order to realize a gray scale of an image, such a PDP employs a method of dividing one frame into several subfields having different emission counts for time division driving. Each subfield is divided into a reset period for uniformly generating a discharge, an address period for selecting a discharge cell, and a sustain period for implementing gradation according to the number of discharges. For example, in the case of displaying an image at 256 gradations, a frame period (16.67 ms) corresponding to 1/60 second is divided into 8 subfields. Each of the eight subfields SF1, SF2, ..., SF8 is again divided into a reset period, an address period, and a sustain period as shown in Fig. Here, the reset period and the address period of each subfield are the same for each subfield, while the sustain period and the number of discharges thereof are 2 ⁿ (n = 0, 1, 2, 3, 4, 5, 6, 7). As described above, since the sustain period is different in each subfield, the gray level of the image can be realized.

On the other hand, an average picture level (APL) curve as shown in Fig. 3 is generally used to reduce power consumption. In the APL curve, the number of sustain pulses increases as the APL decreases. That is, the number of sustain pulses increases as the power reaches the maximum (maximum luminance, minimum APL, minimum display area). On the contrary, the number of sustain pulses decreases as the APL increases, that is, as the power decreases to the lowest (luminance minimum, APL maximum, maximum display area). In this manner, when an image is displayed on a relatively large portion of the PDP, the number of sustain pulses applied to one discharge cell is reduced, and when an image is displayed on a relatively small portion, It is possible to prevent the decrease of the absolute luminance of the image displayed on the screen and reduce the power consumption by increasing the number of the sustain pulses.

Also, as the APL varies, the total number of sustain pulses changes, and thus the number of sustain pulses for each subfield also changes. At this time, since the number of sustain pulses can only have a constant value, even if the APL decreases and the total number of sustain pulses increases, the number of sustain pulses for each subfield does not increase continuously but becomes a specific APL level Increase. In the PDP that implements an image using the APL method, a gamma curve is distorted in each APL step by using the same gamma value for the APL step.

For example, when comparing APL 103 and APL 102 with reference to Table 1, the number of sustain pulses in the first subfield SF1 is equal to the number of sustain pulses in the second subfield SF1, The number of sustain pulses in the field SF2 is different. Accordingly, in the screen using the APL 103 step and the screen using the APL 102 step, the brightness is the same from the 0th gradation to the gradation expressing brightness only in SF1, but the brightness is different in the gradation using SF2. In the luminance curve, the brightnesses of the APL 103 and APL 102 stages are the same from the 0th gradation to the 20th gradation but the brightness of the APL 102 stage is brighter than that of the 103th stage in the 21st gradation. For this reason, it can be confirmed that the gradation increases or decreases when passing the specific APL step without increasing or decreasing smoothly according to the APL change. That is, in the low gradation region, a gradation period in which the brightness does not change occurs, and a phenomenon in which the brightness becomes bright at a certain APL level occurs, which causes fatigue during viewing. If the number of sustain pulses in SF1 changes from 1 to 2, the brightness of the discharge in SF1 only becomes twice as bright as that in the APL stage. Accordingly, although gamma tables can be applied to different APL steps, if a gamma table is applied to each APL step, a large memory size is required.

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is an object of the present invention to provide a plasma display panel capable of improving the image quality in all gradation areas by calculating inverse gamma values according to APLs, It is an object of the present invention to provide a correction method.

According to another aspect of the present invention, there is provided a method of correcting an inverse gamma of a plasma display panel, the method comprising: calculating a ratio of a reference APL and a total number of sustain pulses of a specific APL; Calculating a number of sustain pulses for each subfield, which is adjusted by multiplying the number of sustain pulses by the number of sustain pulses per subfield, using the subfield mapping comparison value as a comparison value; And a subfield mapping value matching the subfield mapping value calculated through the subfield mapping is tracked on the subfield mapping table and the actual gray level of the matched subfield mapping value is determined as the integer part of the corrected inverse gamma value The method comprising the steps of:

The first subfield mapping comparison value among the subfield mapping comparison values is an inverse gamma value of the input gray level, and the subfield mapping comparison value and the adjusted sustain pulse for each subfield The count value is sequentially compared with the highest subfield (the subfield having the largest number of adjusted sustain pulses) from the lowest subfield to the lower subfield, and the corresponding subfield mapping comparison value in the specific subfield is compared with the adjusted sustain pulse Field, the mapping value of the corresponding sub-field is 0, and the same mapping comparison value is also used as a comparison value in the next sub-field, and the comparison value of the sub-field mapping in the specific sub- Field is greater than the number of pulses, the mapping value of the corresponding sub-field becomes 1. When the sub-field mapping comparison value of the corresponding sub- And a value obtained by subtracting the adjusted number of sustain pulses from the adjusted number of sustain pulses in the corresponding subfield may be a subfield mapping comparison value.

If the subfield mapping comparison value in the lowest subfield (first subfield) is greater than the adjusted number of sustain pulses, a value obtained by subtracting the adjusted number of sustain pulses from the subfield mapping comparison value is used as the corrected The decimal part of the inverse gamma value can be constructed.

The inverse gamma correction method of the plasma display panel according to the present invention has the following effects.

The increase / decrease of the total number of sustain pulses according to the increase / decrease of the APL is uniformly distributed in each subfield, so that all gradations can be relatively uniformly brightened or darkened.

Hereinafter, a method of inverse gamma correction of a plasma display panel according to an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 4 is a block diagram of a driving circuit for implementing an inverse gamma correction method of a plasma display panel according to an exemplary embodiment of the present invention, FIG. 5 is a flowchart illustrating a method of inverse gamma correction of a plasma display panel according to an exemplary embodiment of the present invention Fig.

First, a driving circuit for implementing the inverse gamma correction method of the plasma display panel according to an embodiment of the present invention will be described. 4, the driving circuit of the plasma display panel of the present invention includes a signal receiving unit 101, a frame buffer unit 102, an inverse gamma calculating unit 103, an APL calculating unit 104, (105) and a half-toning unit (106).

The signal receiving unit 101 receives digital image data input through a video board of the PDP, that is, R, G, and B data. The inverse gamma calculator 103 receives the digital image data, G, and B data input through the input unit 101, using the following Equation (1).

The frame buffer unit 102 temporarily stores the digital image data input from the signal receiving unit 101. This is to recognize the APL value of the input image in advance, A frame is delayed while being stored in the APL unit 102. At the same time, the APL value of the corresponding input image is calculated by the APL calculation unit 104 described later. Then, the image data input to the frame buffer unit 102 is read in the next frame, and the inverse gamma value can be corrected according to the previously calculated APL value. Also, the APL calculation unit 104 calculates the APL using Equation (2) and Equation (3) below.

&Quot; (1) "

(Where Input is the R, G, B data, SFM Level is the subfield mapping level, and 2.2 is the gamma value)

&Quot; (2) "

(Where Gamma value is 2.2)

&Quot; (3) "

On the other hand, the inverse gamma correction unit 105 as serving to compensate for the inverse gamma values for a given APL, specifically, the number (Ref of the total number of sustain pulses of the total sustain number (T _sus) to the reference APL of the pulse for a specific APL _{-S sus} ), multiplies the ratio by the number of sustain pulses for each subfield of the specific APL, and then outputs the calculated number of sustain pulses for each subfield to the inverse gamma calculator Field mapping value by comparing the calculated inverse gamma value with the inverse gamma value calculated by the inverse gamma correction unit 103, and calculates the corrected inverse gamma value by tracking the calculated sub-field mapping value on the sub-field mapping table. The function of the inverse gamma correction unit 105 corresponds to the inverse gamma correction method of the plasma display panel according to the present invention, and a detailed description thereof will be described later.

Lastly, the half-toning unit 106 performs half-toning of the decimal part of the corrected inverse gamma value calculated by the inverse gamma correction unit 105 by either error diffusion or dithering .

The driving circuit for implementing the inverse gamma correction method of the plasma display panel according to an embodiment of the present invention has been described above. Hereinafter, an inverse gamma correction method of a plasma display panel according to an exemplary embodiment of the present invention will be described in detail.

As described above, the inverse gamma correction method of the plasma display panel according to the present invention is characterized in that the inverse gamma value for a specific APL is corrected, and the inverse gamma value for each APL is corrected in detail, And corrects the number of sustain pulses for each subfield to realize an image close to the actual brightness.

Calculating the ratio of the number of sustain pulses of a reference APL to a specific APL

5, a reference APL is set (S501), and a ratio of the total number of sustain pulses between the reference APL and a specific APL to be corrected is calculated (S502). The reference APL may be any one of a plurality of APLs. For example, the reference APL may be set as a reference APL. The total number of sustain pulses according to the APL and the number of sustain pulses for each of the subfields SF1, SF2, SF3, SF4, SF5, SF6, SF7, and SF8 can be expressed as shown in Table 1 below. ≫ is an APL table having an APL of 128 steps (steps 0 to 127). In Table 1 below, the maximum APL is step 127, and the total number of sustain pulses (Ref.-T _sus ) is 255 in this case.

<Table 1> APL table

On the other hand, if the specific APL to be corrected is step 115, then the total number of sustain pulses T _sus is 311, and the ratio of the number of total sustain pulses of the reference APL to the specific APL is 0.82 _sus / T _sus = 255/311) (see Equation 4 below).

&Quot; (4) &quot;

Ratio = Ref.-T _sus / T _sus

(Where Ref.-T _sus is the total number of sustain pulses of the reference APL, T _sus is the total number of sustain pulses of the particular APL)

Adjusting the number of sustain pulses for each subfield

In this manner, in the state that the ratio of the total number of sustain pulses between the reference APL and the specific APL is calculated, the calculated ratio (Ref.-T _sus / T _sus ) is multiplied by the number of sustain pulses for each subfield of the specific APL The adjusted number of sustain pulses for each subfield of a specific APL is calculated (S503). Table 2 below shows the number of sustain pulses for each subfield of a specific APL (step 115) and the value multiplied by the ratio.

<Table 2>

APL SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 T _sus Step 115 One 2 4 9 19 39 79 158 311 (Step 115)
x 0.82 0.82 1.64 3.28 7.38 15.58 31.98 64.77 129.55 255

Subfield mapping and inverse gamma correction

Then, in step S504, the weighting operation for each subfield, that is, the subfield mapping operation, is performed by comparing the adjusted number of sustain pulses for each subfield calculated for the specific APL with the inverse gamma value corresponding to the specific input gradation. For example, when the input gradation is 40, the inverse gamma value is 4.332 (see Table 3). The inverse gamma value at this time is compared with the adjusted number of sustain pulses for each subfield of the calculated specific APL, The weighting operation for the subfields proceeds.

<Table 3> Inverse gamma value

Input gradation Inverse gamma value 0 0 One 0.001 2 0.006 3 0.015 4 0.027 5 0.045 6 0.067 7 0.094 ·
·
· ·
·
· 40 4.332 41 4.574 ·
·
· ·
·
· 250 244.129 251 246.283 252 248.447 253 250.621 254 252.805 255 255

Specifically, if the subfield mapping comparison value is greater than the adjusted number of sustain pulses per subfield, the mapping value is 1, and the mapping value is 0 when the subfield mapping comparison value is 1. At this time, the first subfield mapping comparison value becomes the inverse gamma value of the input gray level, and the value of the subfield mapping comparison value and the adjusted number of sustain pulses per each subfield are stored in the highest-order subfield (the adjusted number of sustain pulses Field subfields) to the lower subfields, and if the corresponding subfield mapping comparison value in a specific subfield is smaller than the adjusted number of sustain pulses, the mapping value of the corresponding subfield is 0, and in the next subfield Field mapping comparison value, and when the corresponding subfield mapping comparison value in a specific subfield is greater than the adjusted number of sustain pulses, the mapping value of the corresponding subfield is 1, and the sustain value The value obtained by subtracting the pulse number value is a subfield mapping comparison value in which the value is compared with the adjusted number of sustain pulses in the next subfield .

Referring to Table 4, the mapping operation is performed from the highest sub-field SF8. The adjusted number of sustain pulses (129.55) of SF8 is the inverse gamma value (4.33) of the input gradation which is the first sub- The mapping value of SF8 is zero. In the next surge field SF7, the subfield mapping comparison value 4.33 of the previous subfield SF8 is again a comparison value, and the adjusted sustain pulse number value 64.77 of SF7 is larger than the comparison value, so that the mapping value becomes 0 . If the mapping operation is sequentially performed in this manner, the adjusted number of sustain pulses (129.55 = SF8, 64.77 = SF7, 31.98 = SF6, 15.58 = SF5, 7.38 = SF4) of each subfield from SF8 to SF4 is sub- Is larger than the inverse gamma value (4.33) of the input gradation which is a comparative value, the mapping value of SF8 to SF4 becomes zero. Since the sub field mapping comparison value, which is the inverse gamma value (4.33) of the input gray level in SF3, is larger than the adjusted sustain pulse number value (3.28), the mapping value of SF3 becomes 1, and the sub field mapping comparison value (1.05 = 4.33-3.28) obtained by subtracting the adjusted sustain pulse number value (3.28) from the adjusted sustain pulse number value (1.05 = 4.33-3.28) becomes the subfield mapping comparison value in the next subfield SF2. In SF2, since the subfield mapping comparison value (1.05) is smaller than the adjusted number of sustain pulses (1.64), the mapping value becomes 0, and the comparison value 1.05 serves as a subfield mapping comparison value in the following SF1.

Finally, in SF1, since the subfield mapping comparison value (1.05) is larger than the adjusted sustain pulse number value (0.82), the mapping value of SF1 becomes 1, and the sustain value adjusted by the subfield mapping comparison value The value obtained by subtracting the pulse number value (0.82) (0.23 = 1.05-0.82) means the prime number of the corrected inverse gamma value, which will be described later.

<Table 4> Sub-field mapping operation

SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 The adjusted number of sustain pulses 0.82 1.64 3.28 7.38 15.58 31.98 64.77 129.55 Subfield mapping comparison value 1.05 1.05 4.33 4.33 4.33 4.33 4.33 4.33 Subfield mapping value One 0 One 0 0 0 0 0

On the other hand, a mapping value (1 0 1 0 0 0 0 0) of all the subfields to the adjusted number of sustain pulses of the specific APL through the mapping value extraction operation for each subfield, that is, the subfield mapping operation, Field mapping value is derived from the subfield mapping table (see Table 5 below) (S505), and the derived derived subfield mapping value is obtained as shown in the actual gradation step 5 is weighted by each subfield (1 0 1 0 0 0 0 0) (S506).

Table 5 Subfield mapping table

SF1 SF2 SF3 SF4 SF5 SF6 SF7 SF8 Actual Gradation \ Weight One 2 4 8 16 32 64 128 0 0 0 0 0 0 0 0 0 One One 0 0 0 0 0 0 0 2 0 One 0 0 0 0 0 0 3 One One 0 0 0 0 0 0 4 0 0 One 0 0 0 0 0 5 One 0 One 0 0 0 0 0 6 0 One One 0 0 0 0 0 7 One One One 0 0 0 0 0 8 0 0 0 One 0 0 0 0 9 One 0 0 One 0 0 0 0 10 0 One 0 One 0 0 0 0 ·
·
· ·
·
· 40 0 0 0 One 0 One 0 0 41 One 0 0 One 0 One 0 0 ·
·
· ·
·
· 252 0 0 One One One One One One 253 One 0 One One One One One One 254 0 One One One One One One One 255 One One One One One One One One

The actual gradation level step 5 having the same weight as the derived subfield mapping value becomes the inverse gamma value of the input gradation 40 in the specific APL (step 115), that is, the integer part 5 of the corrected inverse gamma value, The fractional part 0.23 obtained through the correction is added as a prime number of the corrected inverse gamma value (S507). That is, in the APL step 115, the inverse gamma value of the input gradation 40 is corrected from 4.33 to 5.23. Here, the fractional part obtained through the subfield mapping operation is half-toned by either error diffusion or dithering through the half-toning unit 105.

The calibrated inverse gamma value calculated through the above method is found to be close to the actual brightness through the following. Specifically, in the APL step 115, the inverse gamma value (4.33) of the input gradation 40 should be increased by 1.22 (311/255) (5.28 = 4.33 * 1.22), which is the total sustain pulse ratio of the reference APL and the specific APL (step 115) , And the corrected inverse gamma value calculated through the above method is 5.23, it can be confirmed that it approaches the theoretical actual brightness.

Also, according to the inverse gamma correction method of the plasma display panel according to the present invention, as the increase / decrease of the total number of sustain pulses due to the increase / decrease of the APL is uniformly distributed over all the gradations, the brightness varies at a constant rate The reliability of image quality can be improved. 6 and 7 show brightness curves according to the conventional technique and the inverse gamma correction method of the plasma display panel according to the present invention, respectively. In the conventional technique, when the APL changes to steps 127, 103, and 102 It can be seen that the luminance value is abruptly changed at a specific gradation. In the present invention, as shown in FIG. 7, it can be seen that the luminance value is evenly increased or decreased over all the gradations even if the APL varies.

In addition, even if the APL changes, the brightness gamma curve displayed on the actual panel changes slightly (see FIG. 8). However, as shown in FIG. 9, . Here, the luminance gamma curve is a curve obtained by dividing the luminance value of each gradation in the APL step by the luminance value of the maximum gradation in the APL step and multiplying by 255, that is, the gamma curve expressed by the actual brightness in the specific APL step .

1 is a configuration diagram of a general plasma display panel.

2 is a reference view showing a principle of realizing an image of a plasma display panel.

3 shows an APL curve;

4 is a block diagram of a driving circuit for implementing an inverse gamma correction method of a plasma display panel according to an embodiment of the present invention.

FIG. 5 is a flowchart illustrating an inverse gamma correction method of a plasma display panel according to an exemplary embodiment of the present invention. Referring to FIG.

6 is a reference diagram showing a luminance curve according to the prior art.

7 is a reference view showing a luminance curve to which the inverse gamma correction method of the plasma display panel according to the present invention is applied.

8 is a reference diagram showing a luminance gamma curve according to the prior art;

9 is a reference view showing a luminance gamma curve to which the inverse gamma correction method of the plasma display panel according to the present invention is applied.

Claims (6)

The APL table in which the number of sustain pulses per subfield is allocated to each of the plurality of APLs is used and one of the plurality of APLs is set as the reference APL and the number of the sustain pulses of the specific APL to be corrected & The total number of sustain pulses of the APL > Calculating the adjusted number of sustain pulses for each subfield by multiplying the calculated ratio by the number of sustain pulses for each subfield of the specific APL; Performing a subfield mapping on the adjusted number of sustain pulses for each of the subfields using a comparison value of a subfield mapping as a comparison value; And A step of tracking the subfield mapping value matching the subfield mapping value calculated through the subfield mapping on the subfield mapping table and determining the actual gray level of the matched subfield mapping value as the integral part of the corrected inverse gamma value Wherein the inverse gamma correction of the plasma display panel comprises: 2. The method of claim 1, wherein the sub- The first subfield mapping comparison value among the subfield mapping comparison values is an inverse gamma value of the input gray level. The comparison value of the subfield mapping value and the adjusted number of sustain pulses of each subfield are stored in the highest level subfield Field of the corresponding subfield to the lower subfields, and if the corresponding subfield mapping comparison value in a specific subfield is smaller than the adjusted number of sustain pulses of the corresponding subfield, If the comparison value of the corresponding subfields in the specific subfield is greater than the adjusted number of sustain pulses in the corresponding subfield, Is 1, and the value obtained by subtracting the adjusted number of sustain pulses of the corresponding subfield from the corresponding subfield mapping comparison value Field comparison value to be compared with the adjusted number of sustain pulses of the corresponding sub-field in the next sub-field. 3. The method of claim 2, wherein when the subfield mapping comparison value in the lowest subfield (first subfield) is greater than the adjusted number of sustain pulses, a value obtained by subtracting the adjusted number of sustain pulses from the subfield mapping comparison value Gamma value of the corrected gamma value is a fractional part of the corrected inverse gamma value. The method of claim 3, further comprising halftoning the decimal part. The method of claim 1, wherein the reference APL is one of a plurality of APL steps. 6. The method of claim 5, wherein the reference APL is APL of a highest level among a plurality of APL stages.

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