JPH09258685A - Picture display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a means which can secure color balance even in a display device in which average brightness is correctly reproduced and the number of pixels are different in display color when display is performed by performing scanning line conversion or two dimensional filter processing using a matrix display device having a non-linear light emitting characteristic. SOLUTION: This device is provided with a display means 5 in which a light emitting brightness characteristic for a small part of an input amplitude is almost linear and a light emitting brightness characteristic for the other part of the input amplitude is non-linear, and linear compensation means 4R, 4G, 4B for compensating a non-linear characteristic of the display means 5. After exponential function operation is performed for an input signal, operation for changing a frequency characteristic such as a two dimensional filter, scanning line conversion is performed, and after that, linear compensation is performed. Also, input/output characteristics of the linear compensation means 4G, 4R, 4B are a linear characteristic in which correspondence relation between the input and the output is 1:1 in a small amplitude part of an input.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for displaying an image signal. In particular, the present invention relates to an image display device such as a plasma display which corrects non-linearity of brightness characteristics and performs scanning line conversion to display a plurality of signal systems.

[0002]

2. Description of the Related Art A plasma display device is known as one of conventional image display devices, and a configuration example of a portion related to signal processing of the plasma display device will be briefly described with reference to the drawings. In FIG. 12, 101R, 1
01G and 101B are a low-pass filter and 102, respectively.
R, 102G, and 102B are inverse gamma correction circuits,
Reference numerals 103R, 103G and 103B are linearity correction circuits, and 5 is a plasma display panel which is a display unit. The plasma display 5 performs display by irradiating a phosphor with ultraviolet rays generated by gas discharge according to a given signal.

In the plasma display panel 5, the red phosphor emits light by the number of pulses proportional to the panel input signal r ₃ , and the red emission L _R is emitted. Similarly, the green light emission L _G and the blue light emission L _B are emitted by the number of pulses proportional to the panel input signals g ₃ and b ₃ . The average emission brightness of each color of red, green, and blue obtained by temporally averaging the pulsed light emission at this time increases almost in proportion to the panel input signals r ₃ , g _3, and b ₃ , but the characteristics of the phosphor are different. It is known that there is a non-linear portion as shown in the example of FIG. In FIG. 7A, the horizontal axis represents the signal input to the plasma display panel 5, and the vertical axis represents the emission brightness. As a means for correcting this non-linear characteristic, the linearity correction circuit 10
3R, 103G, 103B are provided. When the input signals R, G and B are television signals, so-called gamma characteristic processing is usually applied to the signals themselves, assuming that they are displayed on the cathode ray tube. In order to display a natural image using a plasma display having no exponential emission characteristic, an inverse gamma correction circuit 102R which outputs an exponential signal r ₂ with respect to a red signal r ₁ is provided. There is. For this exponential function, for example, when the input is x, this is squared and x ²
An example may be a process in which is output. Inverse gamma correction circuit 1 with the same characteristics for green and blue
02G and 102B are provided.

When the number of pixels forming the plasma display panel 5 is small with respect to the bandwidth of the input signal R, G or B, so-called folding component occurs and the moire phenomenon occurs, as is apparent from the sampling theorem. In some cases, defects such as coloring at the edges may occur. For example, the pixel array shown in FIG. 3 is known as a so-called DC type plasma display, and as can be seen from FIG. 3, the density of green pixels (G in FIG. 3) is red (R in FIG. 3) or Since the structure is different from the density of blue (B in FIG. 3) pixels, the signal band that can be normally displayed is wide in green and narrow in red or blue. Therefore, when a signal containing many high frequency components in a red or blue signal, that is, an image having a fine pattern or a sharp edge is input, a moiré phenomenon occurs or the edge portion is colored yellow or magenta. The phenomenon sometimes occurred. In order to prevent this, two types of low-pass filters, a wide band low-pass filter 101G and a narrow band low-pass filter 101R and 101B, are used to limit the band of the red and blue signals compared to the green signal, and display normally. Only the frequency components within the possible range are passed.

As described above, in the related art, the plasma display panel 5 having the pixel structure as shown in FIG.
In order to display G and B correctly, as shown in FIG. 12, the low-pass filters 101R, 101G, and 101B are used to match the signal bandwidth of the input signal with the number of pixels of the plasma display panel 5, and vice versa. The gamma correction circuits 102R, 102G, and 102B make the emission characteristics of the plasma display panel 5 have the same emission characteristics as a cathode ray tube, and further, the linearity correction circuit 103R that corrects the non-linear characteristics of the plasma display panel 5 itself, Processing for displaying an image on the plasma display panel 5 has been performed as a configuration in which 103G and 103B are provided.

[0006]

However, in this conventional plasma display device, since the low-pass filter process is performed before the inverse gamma correction process, the average level of the displayed image is different from what is expected. There was a case. A first example will be described with reference to FIGS. 12, 13 and 14.

Here, a signal having exactly the same high frequency components for red, green and blue inputs, eg red,
A case will be described in which sine waveforms having the same amplitude are input to and displayed on a conventional plasma display device for green and blue inputs. The signal value of each portion and the light emission amount of each color in the plasma display panel 5 are normalized and expressed with the maximum value being 1.

As described above, the low-pass filter for green has a wide band, and the signal for green is supplied to the inverse gamma correction circuit 102G of the next stage without being subjected to band limitation by the low-pass filter 101G and subjected to exponential conversion. To be done. Further, it is supplied to the green signal input terminal G _IN of the plasma display panel 5 via the linearity correction circuit 103G, and the green light emission L _G is emitted. Linearity correction circuit 1
Since the non-linearity of the plasma display panel 5 is corrected by 02G, the green light emission L _G is proportional to g ₂ . Therefore, with respect to the sine wave input (G in FIG. 12) shown in FIG. 13A, the green emission (L _{G in} FIG. 12) is as shown in FIG. 13B due to the non-linear characteristic of the inverse gamma correction circuit 102G. become. Therefore, the average luminance of green light emission in the horizontal direction of the screen is about 0.375, as shown by the alternate long and short dash line (c) in FIG. FIG.
Further, the vertical axis in FIG. 15 is normalized by the maximum value of light emission amount or signal level, and the horizontal axis is time or horizontal screen position.

On the other hand, the signals for red and blue are band-limited by the low-pass filters 101R and 101B, unlike the case of green, so that the inputs to the inverse gamma correction circuits 102R and 102B are both shown in FIG.
As shown in (b), the amplitude is reduced unlike the case of green. The inverse gamma correction circuits 102R and 102R
The signals squared by B both have the waveforms shown by the dotted line (c) in FIG. 14, and the red and blue emission amounts of the plasma display panel 5 are also proportional to L _R or L _{B in} FIG. 15 (c). The average light emission amounts of red and blue are about 0.275, as shown in FIG. As described above, the average light emission amount is about 0.375 in the case of green, which is different from the case of red or blue (about 0.275). This means that in the high-frequency component of the image, that is, in the portion of the fine pattern, the average level of the light emission amount differs between green and other colors even if the average level of the input signal is the same, and the color balance is It means to collapse.

Although not shown, when DC signals of the same level are input to the red, green and blue inputs instead of the sine waveform as an input signal, there is a difference in the frequency characteristics of the low pass filters. However, it is clear that the outputs of the respective low-pass filters are signals of exactly the same level, and the average light emission amount of each color is naturally the same. This means that the flat portion of the image is displayed with color balance secured.

As described above, in the conventional plasma display device, since the low-pass filter process is performed before the inverse gamma correction process, even if the color balance is secured in the flat portion of the image, the high frequency component of the image, that is, This indicates that the color balance is lost in the portion of the fine pattern, and there is a problem that an appropriate image cannot be displayed.

Further, when absorbing a difference in the number of effective scanning lines of an input signal source or enlarging and displaying a screen, a matrix display such as a plasma display panel performs signal processing such as scanning line conversion. There is a need.
In such a process involving calculation between scanning lines, the calculation coefficient varies depending on the position of the scanning line, and as a result, the frequency characteristic may vary depending on the scanning line position, that is, the display screen position. Even if the plasma display panel has a structure in which the pixel densities of red, green, and blue are the same, the frequency characteristics differ depending on the scanning line position, that is, the display screen position, by performing scanning line conversion. Is generated, the average brightness level is displayed differently depending on the scanning line position, that is, the screen position when a fine horizontal stripe pattern is converted into a scanning line and displayed, and the occurrence of a so-called moire phenomenon is emphasized. Had a problem.

As described above, in the conventional image display device, the inverse gamma correction process is provided after the process of changing the equivalent frequency characteristic depending on the display color or the display position, such as the low-pass filter and the scanning line conversion. In addition, there are problems that the color balance is lost in the high frequency component of the image, that is, the portion of the fine pattern, and the moire phenomenon is emphasized when performing the scan line conversion.

[0014]

In order to solve the above-mentioned problems, in the image display device of the present invention, the emission luminance characteristic for a portion where the input level is small is substantially linear, and the emission luminance for other levels of the input. The display device having a portion having a non-linear characteristic, means for performing a non-linear operation on an input signal, means for changing a frequency characteristic, and linearity correction means for correcting the non-linear characteristic of the display device are provided. The means for applying is provided before the means for changing the frequency characteristic, and the linearity correcting means is provided after the means for changing the frequency characteristic.

According to the present invention, there is provided an image display device capable of ensuring a good color balance in both a flat portion and a fine pattern portion of an image when the pixel density of the display device varies depending on the display color. be able to.

Further, according to the present invention, there is provided an image display device capable of accurately reproducing the average luminance of the screen regardless of the picture pattern of the image when the display is performed by scanning line conversion to support a plurality of signal systems. can do.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the image display device according to the first aspect of the present invention, the light emission luminance characteristic with respect to a portion having a small input level is substantially linear, and the light emission luminance characteristic with respect to another level of the input is non-linear. A display device having a certain portion, comprising a linearity correction means for correcting the non-linear characteristic of the emission luminance characteristic of the display device, and performing a non-linear operation on an input signal and then performing a calculation for changing the frequency characteristic. To
The linearity correction means is input. That is, the input signal is first subjected to a non-linear process such as inverse gamma correction, and then a scan line conversion process or an operation for changing the frequency characteristic of a two-dimensional frequency filter is performed, and then the non-linearity of the display device is changed. Since the correction process is performed, it is possible to make the relationship between the signal level and the emission luminance characteristic linear after the portion where the frequency characteristic changes.When a small pattern is input, the average luminance level is It is possible to prevent different levels from being displayed. Further, even when a display device having different pixel densities depending on the display color is used, it is possible to prevent the color balance in a fine portion from being broken and coloring to occur.

Next, in the image display device according to the second aspect of the present invention, the means for performing the non-linear operation on the input signal is an operation approximated by an exponential function or a polygonal line function, so that the display on the cathode ray tube is assumed. Then, a normal television signal or the like that has been gamma-corrected and transmitted can be inverse-gamma-corrected and appropriately displayed on the plasma display.

Next, the image display device according to claim 3 of the present invention is characterized in that the operation for changing the frequency characteristic is a one-dimensional filter operation or a two-dimensional filter operation corresponding to the pixel structure of the display device. Therefore, even when a display device having a different number of pixels depending on the display color is used, it is possible to display an image without causing an unnatural coloring phenomenon on the edge portion, and the display color can be changed depending on the display color like a so-called DC type plasma display. Good image display can be realized even in a display device having a pixel structure in which the number of pixels is different.

Next, in the image display device according to a fourth aspect of the present invention, since the calculation for changing the frequency characteristic is the scanning line interpolation calculation, the number of effective lines of the input signal is different from the number of lines of the display device. In this case as well, even when a fine image is displayed, the average brightness is not displayed differently from the original level, and good image display can be performed.

Next, in the image display device according to a fifth aspect of the present invention, the input / output characteristic of the linearity correction means is a linear characteristic in which there is a one-to-one correspondence between the input and the output in the small amplitude portion of the input. Therefore, the small amplitude characteristic of the signal up to the preceding stage of the linearity correction means can be favorably preserved, and subtle gradation reproduction can be ensured in the low luminance portion of the image.

(Embodiment 1) Embodiments of the invention described in claim 1 of the present invention will be described below with reference to the drawings.

In FIG. 1, 1R, 1G and 1B are inverse gamma correction circuits, 3R and 3B are narrow band low-pass filters, and their frequency characteristics are those shown in FIG. 2 (a). 3G is a wide band low-pass filter having frequency characteristics shown in FIG. 2 (b). 4R, 4
G and 4B are linearity correction circuits, and 5 is a plasma display panel which is a display unit, and has a pixel structure as shown in FIG. A sine wave having the same waveform as shown in FIG. 4A is input to each of the R, G and B input terminals in FIG. The operation of the embodiment of the present invention thus configured will be described below.

The input signal R corresponding to red is shown in FIG. The inverse gamma correction circuit 1R performs inverse gamma correction on the input signal R corresponding to red and outputs the output signal R ₁ (see FIG. 4).
(B)) is output. Operations to be performed by the inverse gamma correction circuit 1R is, for example, R ₁ = R ^{2 .2} becomes exponential calculation, which is what conventional corresponds to the light-emitting luminance characteristics of a cathode ray tube itself has been widely used as a display device Is.

Next, the red pixel is subjected to a narrow band low-pass filter process having the characteristic shown in FIG. 2A by using the low-pass filter 3R. As a result, the high frequency component is attenuated, and R ₃ has a waveform as shown in FIG. Since the red light emission level emitted from the plasma display panel 5 via the linearity correction circuit 4R is proportional to R ₃ , the average value of this red light emission level is about 0.375. The description for blue is omitted because it is similar to that for red.

On the other hand, for green, the pass band of the low-pass filter is wide, and G ₂ ≉G ₃ , so that G ₃ has a waveform substantially as shown in FIG. 4 (b), and passes through the linearity correction circuit 4G. The green emission level emitted from the plasma display panel 5 is proportional to G ₃ . The average value of the emission level of green is calculated to be about 0.375, which is the same as the average value of red and blue. In addition,
When the DC signal is input to each color of red, green, and blue, that is, when the signal corresponding to a flat pattern is input, the light emission amount of each color is the expression in which each light emission amount is normalized by each maximum value, and is 1: 1: 1. It is clear that it will be a normalized value.

Therefore, the inverse gamma correction circuits 1R, 1G
By arranging 1B and 1B in front of the low-pass filters 3R, 3G, and 3B, respectively, even when the frequency characteristics of the low-pass filters are different, the average light emission amounts of the respective colors are equal to each other, and high frequencies such as a sine waveform are obtained. Even when a signal having components is input, the average luminescence amount is displayed without being disturbed, and good color balance is maintained. This is also clear from the comparison with the above-mentioned conventional example (FIGS. 13 and 14).

As described above, even when a display device having different pixel densities depending on the display color is used, the calculation for changing the frequency characteristic is performed after the non-linear calculation is performed on the input signal. It is possible to secure the color balance of such a portion and prevent the occurrence of coloring due to the color balance being lost in the fine pattern portion of the image.

(Embodiment 2) An embodiment of the invention described in claim 4 of the present invention will be described below with reference to FIGS. The inverse gamma correction circuits 1R, 1
The processing by G and 1B and the linearity correction circuits 4R, 4G, and 4B is the same as that in the case of FIG.

In FIG. 5, reference numerals 2R, 2G, and 2B denote scanning line conversion circuits, and the processing for each color of red, green, and blue is the same, so the signal for red will be described below.

In the scanning line conversion circuit 2R, in order to match the number of effective lines of the input signal with the number of display lines of the plasma display panel 5, scanning line conversion is performed by using a method known as so-called linear interpolation. In a matrix display device such as a plasma display device, unlike the conventional cathode ray tube, it is not possible to control the voltage waveform of the deflection circuit to adjust the screen size, so that an image of a signal system in which the number of effective scanning lines is different is predetermined. In order to display in accordance with the screen size of, such scanning line conversion is required. FIG. 6 is a diagram showing the concept of scan line conversion known as linear interpolation, which is used in 2R, and 5 before conversion.
6 shows the relationship between the scanning lines (FIG. 6A, S0 to S4) and the seven scanning lines after conversion (FIG. 6C, T0 to T6). In FIG. 6 (b), the arrows show the correspondence relationship of how one scan line after conversion is created from two or one scan line before conversion, and 1 /
Numerical values such as 3, 2/3 and the like indicate mixing ratios when one scan line is newly created from two scan lines. For example, a signal of two scanning lines S0 and S1 before conversion is used to newly create a scanning line of T1.
Means that a new scanning line T1 is created by mixing S1 at a ratio of 1/3 and S1 at a ratio of 2/3. In this way, in scanning line conversion, one scanning line is newly created from two scanning lines. It is self-evident that, assuming that the signals of the scanning lines before conversion have the same brightness in all lines, for example, assuming that the image before conversion is a flat image such as gray in all screens, the image after conversion also It goes without saying that the gray level images are at the same level and the brightness of each scanning line is the same. That is, it means that the signal level of the scanning line does not change before and after the conversion in the flat portion of the image even if the scanning line conversion is performed.

Here, let us consider a case in which an image before scanning line conversion is displayed by performing scanning line conversion on a line every other line, that is, a pattern in which white or black lines are repeated every line. As shown in FIG. 6D, the input line is 1
(White) or 0 (black) is repeated. An output obtained by performing inverse gamma correction on this, FIG. 6 (e) also shows 1 (white) or 0.
(Black) is repeated. When scanning line conversion is further performed, as is clear from FIGS. 6A to 6C, T0 becomes 1 which is the same value as S0, and T1 is S0 × 1/3 + S1 × 2/3 =
It becomes 1/3. Similarly, the value of T2 is also 1/3. This is repeated below. It should be noted that even if the same white or black line is repeated, two cases in which the phases are different are considered, and the case is A or the case is B.

As in the above example, two cases, that is, a pattern in which white or black lines are repeated for each line as they are, and a case in which scanning lines are converted and displayed, are particularly averaged on the screen. Pay attention to the luminance of and compare. As is clear from p or q in FIG. 6D, the average luminance of the screen when the image is displayed as it is without being converted into scanning lines is a level (0 ..) which is between the white level (1.0) and the black level (0). 5). On the other hand, when the display is performed by scanning line conversion, the relative value of the average brightness level of the screen is r in FIG.
(1 + 1/3 + 1/3) /3≈0.555 (in the case of A), or (1 + 2/3 + 2/3) /3≈0.444 (as shown by s in FIG. 6F). In the case of B), the average of A and B becomes 0.5, which is exactly the same as the average brightness of the screen when the image is displayed as it is without being converted into a scanning line. This means that even if a fine image is scan-line converted, the average luminance is correctly reproduced. Note that FIG. 6G shows, for comparison, a case where the scanning line conversion process is performed before the inverse gamma correction process, and a pattern in which white or black lines are repeated for each line 6 is displayed by scanning line conversion by the conventional method, the average brightness of the screen is as shown in FIG.
As can be seen from t in (g) and u in FIG. 6 (g), (1 + 1/9 + 1/9) /3≈0.4074 (for A) or (0 + 4/9 + 4/9) /3≈0.2962 (for B) ), The average luminance of A and B becomes about 0.35, and the average luminance is greatly reduced as compared with the case where scanning line conversion is not performed. This means that in the conventional method, when the image is displayed by scanning line conversion, the average luminance is displayed differently in the flat image portion and the image portion of the fine pattern, This means that natural image display cannot be performed.

As described above, the calculation for interpolating the scanning lines is provided at the subsequent stage of the inverse gamma correction means, so that the average brightness of the screen can be accurately reproduced when the scanning lines are converted into a fine image and displayed. Will be possible.

In the description of the embodiment of the present invention, as the non-linear operation, the inverse gamma correction having the characteristic of the exponential function has been described as an example, but it is also possible to make a modification such as the polygonal line approximation instead of the exponential function. . The scanning line conversion method is not limited to the linear interpolation method used in the description, and it goes without saying that various methods may be used.

(Embodiment 3) An embodiment of the invention described in claim 5 of the present invention will be described below with reference to FIGS.
This will be described with reference to FIG. In the present embodiment, the image display device shown in FIG. 1 is characterized in particular by the method of configuring the linearity correction circuit 4R, so this part will be described in detail.

It is assumed that the plasma display panel 5 has discontinuous characteristics as shown in FIG. 7 (a), for example. Therefore, a linearity correction circuit 4R is provided in the front stage,
The linearity correction circuit R4 converts the red emission luminance L _R with respect to the input R3 of the linearity correction circuit as shown in FIG. 7B. At this time, as shown in FIG.
The input / output characteristics of the linearity correction means have a one-to-one correspondence between the input and the output in the small amplitude portion of the input. FIG.
0 is an enlargement of the vicinity of the origin in FIG. 8. As can be seen from this figure, the input / output characteristics of the linearity correction circuit 4R are 0 for an input of 0 and 1 for an input of 1. It is intended to have an output of 2 for 2 inputs and an output of 3 for 3 inputs, and there is a 1: 1 correspondence between input and output in the small amplitude portion of the input.

In the plasma display according to claim 1 of the present invention, the inverse gamma correction processing is positioned in front of the linearity correction means for the purpose of maintaining good color balance even in the fine pattern portion of the image. Processing after the inverse gamma correction processing system is usually performed by digital processing. Therefore, the output of the inverse gamma correction process is 1 in the low brightness image part.
In the following number, that is, in the expression with a limited number of bits, the output of the inverse gamma correction process is compressed in a dark image portion and tends to be 0, so that a slight gradation difference is secured in the dark portion of the image. In order to achieve this, the low-brightness linearity is particularly emphasized in each part after the inverse gamma correction process. According to the embodiments of the present invention, the characteristics of the linearity correction circuit are such that the linearity of input and output is perfectly ensured especially in the low-luminance portion, and the gradation in the low-luminance portion of the image is improved. The great effect is that it can be maintained.

The characteristics of the plasma display panel 5 are assumed to have non-linear characteristics as shown in FIG. 7 (a). As shown in FIG. 7 (c),
If an attempt is made to correct to a simple linear characteristic such that the maximum value of the emission brightness (L _{max of} FIG. 7) is obtained with respect to the maximum value of the input (d _{max of} FIG. 7), as is apparent from the figure, The input / output characteristics of the linearity correction circuit are as follows:
The slope of the output is 1 or less with respect to the input. This is because the original emission characteristic of the plasma display panel 5 is the inclination of the portion of FIG. 7A in the low luminance portion, whereas the corrected emission characteristic is the inclination of (c) smaller than the inclination of (a). This is so that Therefore, when the characteristic shown in FIG. 7 (a) is simply corrected to the characteristic shown in FIG. 7 (c) instead of the characteristic shown in FIG. 7 (b) according to the embodiment of the present invention, the linearity correction means is turned on. The output characteristic is as shown in, for example, FIG. 9C, and the relationship between the input and the output is not completely 1: 1 in the small amplitude portion of the input. Thus, there is a relationship in which the output is 0, 1, the output is 0, the output is 1, the output is 1, 3 and the output is 2.

This is also apparent from FIG. 11 in which the vicinity of the origin of FIG. 9 is enlarged. As in this example, the output becomes 0 at both the input 0 and the input 1, and the difference in light emission luminance is lost. As a result, the light emission luminance rapidly decreases to 0 in the low luminance portion of the input image. As a result, the gradation characteristics in the dark part of the image become insufficient, and the conventional method has a problem that the image quality deteriorates as compared with the configuration according to the embodiment of the present invention.

As described above, the input / output characteristic of the linearity correction means is such that the input and the output are 1 in the small amplitude portion of the input.
The characteristic of the linearity correction circuit is a linear characteristic having a one-to-one correspondence relationship, and the linearity of the linearity correction circuit is such that the linearity of the input and output is perfectly ensured especially in the low-luminance portion. It is possible to obtain a great effect that good gradation can be maintained.

[0042]

As described above, according to the image display device of the present invention, the following effects can be obtained.

(1) According to the image display device according to the first aspect of the present invention, in a display device which requires calculation for changing frequency characteristics, the non-linearity of the emission luminance characteristic of the display device is corrected and the image is displayed. It is possible to provide an image display device capable of maintaining the color balance in both the fine pattern portion and the flat portion of the image, and reproducing and displaying the average luminance correctly.

(2) According to the image display device of the second aspect of the present invention, the combined characteristic of the input / output characteristic of the linearity correction means and the emission luminance characteristic of the display device is approximated by an exponential function or a logarithmic function. As a result, the total emission luminance characteristic combined with the exponential function calculation in the signal processing up to the preceding stage of the linearity correction means is almost equivalent to the exponential function and can be used as the gamma correction processing of the video signal. it can.

(3) According to the image display device of the third aspect of the present invention, the operation for changing the frequency characteristic is a two-dimensional filter operation or a one-dimensional filter operation corresponding to the pixel structure of the display device. Therefore, even when using a display device with a different number of pixels depending on the display color, it is possible to display an image without causing an unnatural coloring phenomenon at the edge part and without disturbing the color balance due to the design. Therefore, it is possible to provide a means that enables good image display even in a display device in which the number of pixels varies depending on the display color, such as a so-called DC type plasma display.

(4) According to the image display device of the fourth aspect of the present invention, since the calculation for changing the frequency characteristic is the scanning line interpolation calculation, the number of effective lines of the input signal and the number of lines of the display device are equal to each other. Even if it is different, the average brightness of the screen is correctly reproduced regardless of the picture pattern of the image, so it is effective for displaying signals of various methods with different effective scanning lines using a panel with a certain number of pixels. Can provide various means.

(5) According to the image display device of the fifth aspect of the present invention, the input / output characteristics of the linearity correction means have a one-to-one correspondence between the input and the output in the small amplitude portion of the input. Since it is characterized by a linear characteristic,
The small-amplitude characteristic of the signal up to the stage before the linearity correction means can be favorably preserved, and subtle gradation reproduction in the low-luminance portion of the image can be ensured.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an image display device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of frequency characteristics of a low-pass filter according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an example of pixel arrangement of the display device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing a waveform of each part according to the first embodiment of the present invention.

FIG. 5 is a configuration diagram of an image display device according to a second embodiment of the present invention.

FIG. 6 is a conceptual explanatory diagram of scan conversion according to the second embodiment of the present invention.

FIG. 7 is a diagram showing an example of emission luminance characteristics in the third embodiment of the present invention.

FIG. 8 is a diagram showing a characteristic example of a linearity correction circuit according to a third embodiment of the present invention.

FIG. 9 is a diagram showing a characteristic example of a linearity correction circuit in a conventional image display device.

FIG. 10 is a partially enlarged view of FIG.

FIG. 11 is a partially enlarged view of FIG. 9.

FIG. 12 is a diagram showing an example of a configuration diagram of a conventional image display device.

FIG. 13 is a diagram showing an input signal level and a light emission luminance level for green in a conventional image display device.

FIG. 14 is a diagram showing input signal levels and emission luminance levels for red and blue in a conventional image display device.

[Explanation of symbols]

 1R, 1G, 1B Gamma correction circuit 2R, 2G, 2B Scan line conversion circuit 3R, 3G, 3B Low pass filter 4R, 4G, 4B Linearity correction circuit 5 Plasma display panel

Claims (5)

[Claims] 1. A display means having a portion in which a light emission luminance characteristic for a portion having a low input level is substantially linear, and a portion having a non-linear light emission luminance characteristic for another level of the input, and a means for performing a non-linear operation on an input signal. And a means for changing the frequency characteristic and a linearity correcting means for correcting the non-linearity of the emission luminance characteristic of the display means, and the means for performing the non-linear operation is provided in a stage before the means for changing the frequency characteristic, An image display device characterized in that the linearity correction means is provided at a stage subsequent to the means for changing the frequency characteristic and before the display means. 2. The image display device according to claim 1, wherein the means for performing a non-linear operation on the input signal is an operation approximated by an exponential function or a polygonal line function. 3. The image display device according to claim 1, wherein the calculation for changing the frequency characteristic is a two-dimensional or one-dimensional filter calculation corresponding to the pixel structure of the display device. 4. The calculation for changing the frequency characteristic is a calculation for interpolating a scanning line.
The image display device as described in the above. 5. The input / output characteristic of the linearity correction means is a linear characteristic in which the input and the output have a one-to-one correspondence with each other in a portion where the signal level of the input is small. 1. The image display device according to 1.