JPH07170428A - Method and device for displaying picture - Google Patents

Abstract

PURPOSE:To provide a method and device for displaying a picture in which a improved contrast picture is displayed on a display device with a low contrast. CONSTITUTION:The display device is provided with a luminance level conversion circuit 1 converting a luminance level of a picture into a luminance level able to be displayed on a display device with a low contrast, a noise elimination filter 17 eliminating a noise of the input picture, a contrast improvement circuit 12 superimposing a waveform used to cause illusion in the luminance level onto an input picture so as to improve the contrast, and a luminance correction circuit 6b correcting the input picture so that a bright point with a high luminance due to the presence in a luminance change gets dark and conversely a dark point with a low luminance due to the presence in a luminance change gets bright, and then the picture whose contrast is improved is displayed on the display device with a low contrast.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device capable of obtaining a higher quality image on a display of a television signal, for example.

[0002]

2. Description of the Related Art In recent years, TV screens have become larger, and
For screens of inches or more, projection-type systems using liquid crystal panels are promising. Also, with the start of broadcasting high-definition television, the need for high-resolution, large-area display devices is increasing. However, high-resolution, large-area display devices do not have sufficient contrast performance, and as a method for improving this, the conventional methods are: 1) Uniformization of luminance frequency 2) Signals to be displayed by methods such as combining images with different lighting amounts. A method of mapping (luminance conversion) the level into a displayable dynamic range has been taken.

[0003]

However, the above method has a problem that the contrast is lowered and the noise component is amplified when a signal having a wider range than the dynamic range of the display device is input and displayed. Was there. That is, in the conventional mapping method for the entire image, the luminance range of the mapping destination is limited to a certain range. Therefore, if the contrast in a specific luminance range is improved, the contrast is lowered in other luminance ranges. Also, in the histogram equalization method that performs luminance conversion so that the luminance frequency after conversion is uniform and the local histogram equalization method that locally performs this, the luminance range with high luminance frequency becomes a wide luminance range during luminance conversion. Since it is mapped, the noise component is amplified in a region having a large area and uniform brightness.

In view of the above points, the present invention provides an image display method and an image display device for displaying an image with improved contrast without amplifying noise components on a display having a narrow dynamic range and low contrast. To aim.

[0005]

The present invention superimposes a waveform that causes an illusion of a brightness level on an image in which the brightness level is converted into a brightness level that can be displayed by a display device having a low contrast, and further, The brightness level and the distribution of brightness changes are detected, and the bright points with large brightness values and large brightness values are corrected to be dark, and conversely, the dark points with small brightness values and small brightness values are corrected to be bright. , Improving the apparent (psychological) contrast of an image displayed on a display device with a narrow dynamic range and low contrast, and correcting the brightness to make the brightness level easier for the display device to display. Image display method,
Also, a 1-frame delay circuit that delays and outputs the input image by 1 frame, a brightness level conversion circuit that converts the brightness level of the input image into a brightness level that can be displayed by a low-contrast display device, and removes noise from the input image Noise removal filter, and a contrast improvement circuit that superimposes a waveform that causes an illusion of brightness level on the input image to improve the apparent (psychological) contrast of the image displayed on a low-contrast display device, and an input Detects the brightness level of the image and the distribution of brightness changes, and corrects the dark points where the brightness changes and the brightness value is large, and conversely corrects the dark points where the brightness value is small and the brightness value is small to become bright. Then, in an image display device equipped with a brightness level correction circuit that makes the brightness level of the image easier for the display device to display. That.

[0006]

With the above-described structure, the present invention improves the apparent (psychological) contrast of an image displayed on a low-contrast display device by superimposing a waveform that causes an illusion of a brightness level on an input image. In addition, the brightness level of the input image and the distribution of brightness changes are detected, and correction is performed so that bright points with large brightness values and large brightness values become dark, and conversely, dark points with small brightness values with small brightness values become bright. Are corrected so that the brightness level of the image becomes a brightness level easier to display by the display device.

[0007]

FIG. 2 is a block diagram of an image display device according to a first embodiment of the present invention. In FIG. 2, reference numeral 21 is a 1-frame delay circuit that delays the input image by 1 frame and outputs, and 1 is a brightness level conversion circuit that converts the brightness level of the input image into a brightness level that can be displayed by a low-contrast display device. Reference numeral 17 denotes a noise removal filter (median filter) that removes noise from the input image. Reference numeral 2 indicates a contrast of an image displayed on a low-contrast display device by superimposing a waveform that causes an illusion of a brightness level on the input image. 3a is a low frequency component attenuation filter that attenuates the low frequency component of the input image, 4a is a characteristic conversion circuit that converts the characteristics of the output of the low frequency component attenuation filter 3a, Is an adder circuit that superimposes the output of the characteristic conversion circuit 4a on the output of the brightness level conversion circuit 1.

The operation of the above configuration will be described below. The 1-frame delay circuit 21 delays the input image by 1 frame and outputs it. The brightness level conversion circuit 1 converts the brightness level of the input image into a brightness level that can be displayed by a low-contrast display device. FIG. 4 shows an example of the input / output characteristics of the brightness level conversion circuit 1.

The noise removing filter 17 removes noise from the input image and prevents the contrast improving circuit 2 from adding noise components in the image to the input image. Figure 3
An example of the configuration of the noise removal filter is shown in FIG. In FIG. 3, reference numeral 18 is a write change switch to a frame memory, 19a, 19b and 19c are frame memories for storing images of three temporally consecutive frames, and 20 is each pixel of an image of three temporally consecutive frames. Is a median value calculation circuit for calculating the median value for. The operation of the noise removal filter 17 will be described below. The write changeover switch 18 is sequentially changed over for each frame, and writes three consecutive frames of images in the frame memories 19a, 19b and 19c. The median value calculation circuit 20 reads out image data (pixel value) from the frame memories 19a, 19b, 19c in the scanning order, calculates the median value (median value) of the read three pixels, and outputs it as a pixel value after noise removal. . In the static part of the image,
Since the noise generated in the image has little correlation in the time direction, the noise can be removed by calculating the median value. Further, in the moving image portion of the image, the pixel value at the position of interest continuously changes, and therefore the calculation of the median value does not cause unnatural movement.

The contrast improving circuit 2 superimposes a waveform that causes an illusion of a brightness level on an input image to improve the contrast of an image displayed on a low-contrast display device. The contrast improving circuit 2 is composed of a low frequency component attenuation filter 3a, a characteristic converting circuit 4a and an adding circuit 5. The low frequency component attenuation filter 3a attenuates the low frequency component of the input image after noise removal. FIG. 5 shows a block diagram of the low frequency component attenuation filter 3a. In FIG. 5, 10b is a low-pass filter, and 11b is a subtraction circuit for calculating the difference between the input image and the output of the low-pass filter 10b.

For the sake of simplicity, the improvement of the contrast when the input image is stepwise step input will be described below.

FIGS. 6, 7 and 8 show the step input and the step response of the low pass filter 10b and the low frequency component attenuation filter 3a, respectively. 6, 7 and 8 show the luminance distribution one-dimensionally for simplicity, and the step response of the low-pass filter 10b of FIG. 5 is a Gaussian integral function and is shown in FIG. With the circuit shown in FIG.
By calculating the difference between the input image and the output of the low-pass filter 10b, the output (FIG. 8) in which the low frequency components of the input image shown in FIG. 6 are attenuated can be obtained.

The characteristic conversion circuit 4a converts the characteristic of the output of the low frequency component attenuation filter 3a shown in FIG.
Superimposes the output of the characteristic conversion circuit 4a on the output of the brightness level conversion circuit 1. The input / output characteristics of the characteristic conversion circuit 4a are determined so that the illusion amount due to the output of the contrast improvement circuit 2 becomes large within a range where the observer does not feel uncomfortable when observing the image in which the contrast is enhanced by the contrast improvement circuit 2. To do. FIG. 9 shows an example of input / output characteristics of the characteristic conversion circuit 4a. In this embodiment, the output level of the characteristic conversion circuit 4a is converted to ± 10% or less of the input image.

FIG. 10 shows the step response of the contrast improving circuit 2 and the luminance distribution perceived during observation. Figure 1
At 0, the solid line is the step response of the contrast improving circuit 2, and the broken line is the luminance distribution perceived during observation.
The wavy line in FIG. 10 indicates that the contrast improving circuit 2 improves the psychological contrast. Further, in the case of the luminance distribution as shown by the solid line in FIG. 11, the luminance difference of i1-i0 is perceived at the position x1, the luminance difference of i2-i1 is perceived at the position x2, and the position x1
And x2 do not perceive the brightness difference between i1 and i2,
In the brightness range of I3-I0, the brightness differences I1-I0 and I3-I2 having a larger sum total than the brightness range of I3-I0 can be displayed, and the contrast can be improved.

As described above, according to this embodiment, the brightness level of the input image is converted into a brightness level that can be displayed by a low-contrast display device, and a waveform that causes an illusion of the brightness level is superimposed on the input image. By doing so, the contrast of the image displayed on the low-contrast display device can be improved. Further, the waveform that causes the illusion of the brightness level is generated from the image obtained by passing the input image through the noise removal filter, so that the contrast of the image can be improved without emphasizing the noise component of the image.

It should be noted that when there are no extremely bright or dark points of the brightness level in the input image, and an image in which a waveform that causes an illusion of the brightness level is superimposed on the input image can be displayed on a low-contrast display device. However, it is not necessary to perform the conversion by the brightness level conversion circuit. Also, in the noise removal filter 17, the same effect as that of the present embodiment can be obtained by using either a weighted averaging circuit such as a Gaussian filter or an average value calculation circuit instead of the median value calculation circuit used in the present embodiment. You can Further, even if the noise removing filter 17 is arranged between the low frequency component attenuating circuit 3a and the characteristic converting circuit 4a, the same effect as that of the present embodiment can be obtained. The frame memories 19a to 19c are
If an image can be output at the same timing when a signal is input, the number of frame memories can be two, and the third signal can be processed by directly inputting the input signal to the median value calculation circuit 20. Even if a low-pass filter whose step response is a quadratic equation or a cubic equation is used, substantially the same effect as that obtained by using the low-pass filter whose step response is a Gaussian integral function in the present embodiment can be obtained. You can Further, the input / output characteristics of the characteristic conversion circuit 4a may be changed according to the brightness of the superimposed image. Such an embodiment will be described below.

FIG. 12 is a block diagram of an image display device according to the second embodiment of the present invention. In FIG. 12, 1 is a brightness level conversion circuit that converts the brightness level of the input image into a brightness level that can be displayed by a low-contrast display device, 17 is a noise removal filter that removes noise from the input image, and 12 is the brightness. A contrast improving circuit that superimposes a waveform that causes an optical illusion on the input image to improve the contrast of an image displayed on a low-contrast display device, and 10 is a low-pass smoothing output of the brightness level converting circuit 1. Filter, 3a
Is a low frequency component attenuation filter that attenuates the low frequency component of the input image, and 4c is a characteristic conversion circuit that converts the characteristics of the output of the low frequency component attenuation filter 3a according to the low-pass output of the brightness level conversion circuit 1. 5 is a characteristic conversion circuit 4c
Is an addition circuit that superimposes the output of the above on the output of the brightness level conversion circuit 1.

The operations other than the low-pass filter 10a and the characteristic conversion circuit 4c in the above-mentioned configuration are the same as those of the first embodiment of the present invention, and therefore the description thereof is omitted, and the operation of the low-pass filter 10 and the characteristic conversion circuit 4c will be described below. Will be described.

The low-pass filter 10 smoothes the output of the brightness level converting circuit 1. The characteristic conversion circuit 4c converts the characteristic of the output of the low frequency component attenuation filter 3a shown in FIG. 8, and the addition circuit 5 superimposes the output of the characteristic conversion circuit 4c on the output of the brightness level conversion circuit 1. The characteristic conversion by the characteristic conversion circuit 4c is performed in consideration of the average brightness of the step input.
A method of characteristic conversion in consideration of the average brightness of step input will be described below.

FIG. 13 shows the offset waveform of the step response of the low frequency component attenuation filter 3a and the luminance distribution perceived during observation. In FIG. 13, the solid line graph shows a waveform in which the step response of the low frequency component attenuation filter 3a is offset by the average luminance (i0 + i1) / 2 of the step input. The illusion caused by this waveform will be described below.

The average brightness (i0 + i) of the step input in FIG.
Peak value Amp of the step response of FIG. 8 for 1) / 2
The contrast of

[0022]

[Equation 1]

When defined as, when the contrast is low (25 to 30% or less), there is little discomfort during observation, and an illusion of 10% to 20% with respect to the actual brightness occurs.
It is perceived as a luminance distribution indicated by a broken line in FIG.
However, if the contrast is high (30% or more),
The brightness gradient near the edge is perceived, which gives a feeling of strangeness during observation. Therefore, the input / output characteristics of the characteristic conversion circuit 4c are set so that the illusion amount due to the output of the contrast improving circuit 12 becomes large within a range where the observer does not feel uncomfortable when observing an image in which the contrast is enhanced by the contrast improving circuit 12. To decide. The output of the low-pass filter 10 corresponds to the denominator (i0 + i1) / 2 of (Equation 1), and the characteristic conversion circuit 4c converts the output characteristic of the low-frequency component attenuation filter 3c according to the low-pass output of the brightness level conversion circuit 1. To do. FIG. 14 shows a block diagram of the characteristic conversion circuit 4c.

In FIG. 14, the characteristic conversion circuit 4c is composed of a division circuit 13, a contrast conversion rate calculation circuit 14, and a multiplication circuit 9. The division circuit 13 divides the output of the low frequency component attenuation filter 3c by the output of the low pass filter 10 to calculate the contrast represented by (Equation 1).
The contrast conversion rate calculation circuit 14 has a contrast of 30.
The output of the division circuit 13 is converted so that it becomes less than or equal to%. FIG. 15 shows an example of input / output characteristics of the characteristic conversion rate calculation circuit 14. The multiplication circuit 9 multiplies the contrast converted by the contrast conversion rate calculation circuit 14 by the output of the low frequency component attenuation filter 3a, and outputs a waveform to be superimposed to improve the contrast.

As described above, according to this embodiment, the brightness level of the input image is converted into a brightness level that can be displayed by a low-contrast display device, and a waveform that causes an illusion of the brightness level is converted into the brightness of the image. By superimposing accordingly, the contrast of an image displayed on a low-contrast display device can be improved. At that time, by determining the output of the contrast improving circuit according to the brightness level of the input image, it is possible to further improve the contrast as compared with the first embodiment without causing a sense of discomfort during observation.

In this embodiment, the input of the low pass filter 10 is the output of the brightness level converting circuit 1, but
Even if the input image is directly input to the low pass filter 10,
It is possible to obtain the same effect as that obtained in this embodiment. Even if a low-pass filter whose step response is a quadratic equation or a cubic equation is used, substantially the same effect as that obtained by using the low-pass filter whose step response is a Gaussian integral function in the present embodiment can be obtained. You can Further, the same effect can be obtained even if the characteristic conversion by the characteristic conversion circuit 4c is performed by a method different from that of the present embodiment.

FIG. 1 is a block diagram showing the arrangement of an image display device according to the third embodiment of the present invention. In FIG. 1, 1
Is a brightness level conversion circuit that converts the brightness level of the input image into a brightness level that can be displayed by a low-contrast display device, 17 is a noise removal filter that removes noise from the input image, and 12 is an illusion of the brightness level. A contrast improving circuit that superimposes a generated waveform on an input image to improve the contrast of an image displayed on a low-contrast display device, and 6 is a brightness that corrects the brightness level according to the distribution of the brightness change of the input image. It is a level correction circuit.

The operation of the above-mentioned structure other than the brightness level correction circuit 6 is similar to that of the first or second embodiment of the present invention, and therefore its explanation is omitted, and the operation of the brightness level correction circuit 6 will be described below. .

FIG. 18 shows an example of a block diagram of the brightness level correction circuit 6. The brightness level correction circuit 6 includes a low frequency component attenuation filter 3b, an absolute value calculation circuit 7, an offset circuit 8, a multiplication circuit 9, a characteristic conversion circuit 4b, a low pass filter 10a and a subtraction circuit 11a.

The low frequency component attenuation filter 3b attenuates the low frequency component of the input image. Low frequency component attenuation filter 3b
Is a block diagram of the low frequency component attenuation filter 3 shown in FIG.
The same as a. The absolute value calculation circuit 7 calculates the absolute value of the output of the low frequency component attenuation filter 3b. The offset circuit 8 offsets the brightness level of each pixel of the input image in the minus direction of about ½ of the number of gradations. The multiplication circuit 9 multiplies each pixel of the output of the absolute value calculation circuit 7 and the output of the offset circuit 8. As a result, the output level of the multiplication circuit 9 becomes large at the point where there is a change in brightness in the input image and the brightness value has a brightness difference compared to half the number of gradations, that is, in bright or dark areas.

The characteristic conversion circuit 4b converts the characteristic of the output of the multiplication circuit 9. FIG. 19 shows the input / output characteristics of the characteristic conversion circuit 4b. In FIG. 19, the input / output characteristic of the characteristic conversion circuit 4b determines the range of the output level to about ± 10% of the number of gradations so that the brightness level correction does not cause a feeling of strangeness during observation.

The low-pass filter 10a is a characteristic conversion circuit 4
Smooth the output of b. The subtraction circuit 11a inverts the sign of the output of the low-pass filter 10a, and the contrast improvement circuit 2
Superimposed on the output of.

By the above method and means, the brightness level correction circuit 6 corrects the brightness change in the input image so that the bright point has a large brightness value and becomes dark, and conversely, the brightness level changes in the input image. The brightness value is small and the dark point is corrected to be bright. As a result, it is possible to display the point where the brightness changes in the dark and light parts of the image with the brightness with high expressive ability of the display device,
Moreover, the distribution range of the luminance of the entire image can be narrowed.

As described above, according to the present embodiment, the brightness level of the image is converted into a brightness level that can be displayed by a low-contrast display device, and a waveform that causes an illusion of the brightness level is superimposed on the input image. By doing so, it is possible to improve the contrast of an image displayed on a low-contrast display device, and further correct the input image so that bright points with large brightness values and large brightness values become dark, and vice versa. By correcting the dark point in the input image, which has a brightness change and a small brightness value, to be bright, a point having a brightness change in the bright and dark parts of the image can be displayed with a brightness high in the expressive power of the display device.

FIG. 22 shows a block diagram of the image display device in the fourth embodiment of the present invention. In FIG. 22, reference numeral 21 denotes a 1-frame delay circuit that delays the input image by 1 frame and outputs, and 1 is a brightness level conversion circuit that converts the brightness level of the input image into a brightness level that can be displayed by a low-contrast display device. Yes, 17 is a noise removal filter that removes noise from the input image, and 12 superimposes a waveform that causes an illusion of a brightness level on the input image to improve the contrast of the image displayed on a low-contrast display device. A contrast improving circuit 6b is a brightness level correcting circuit that corrects the brightness level according to the distribution of the brightness change of the input image.

The operation of the above-mentioned structure other than the brightness level correction circuit 6b is similar to that of the first, second or third embodiment of the present invention, and therefore its explanation is omitted and the operation of the brightness level correction circuit 6b will be described below. Will be described.

FIG. 23 shows an example of a block diagram of the brightness level correction circuit 6b. The brightness level correction circuit 6b includes frame memories 23a and 23b, an edge detection circuit 24, a brightness conversion table calculation circuit 25, a table memory 26, and a brightness conversion circuit 27.

The frame memory 23a stores one frame of input image data. The edge extraction circuit 24 detects an edge from the image data in the frame memory 23a and writes the detection result (binary image) in the frame memory 23b.
The brightness conversion table calculation circuit 25 calculates a brightness conversion table based on the brightness frequency of pixels extracted as edges in the vicinity of the pixel of interest, and writes the brightness conversion table in the table memory 26. The read control circuit 27 reads the luminance data from the frame memory 23a in the scanning order, and according to the luminance, the table memory 2
The conversion table data is read from 6 and output as the converted luminance value.

FIG. 24 is an example of a block diagram of the luminance conversion table calculation circuit. The coordinate value generator 28 generates pixel coordinate values in the scanning order. Read address controller 29
For a coordinate value of a pixel generated by the coordinate value generation device 28, a reads image data of a region (vertical and horizontal h × w pixels) in the vicinity thereof from the frame memory 23a. The read-out address control device 29b reads the image data of the vicinity (vertical and horizontal h × w pixels) area from the frame memory 23b for the coordinate value of the pixel generated by the coordinate value generation device 28. As shown in FIGS. 25 and 26, the neighborhood area read by the read address control devices 29a and 29b is a coordinate value generating device 28.
Is an area of h × w pixels in the vertical and horizontal directions in the vicinity of the pixel p at the coordinate where the occurrence of. When the data read from the frame memory 23b is a pixel detected as an edge, the frequency calculation circuit 30 increments the data value of the table memory according to the brightness of the brightness data of the same coordinate value read from the frame memory 23b, Calculate the frequency. Counter 31
Counts the number of pixels in the target pixel neighborhood area read from the frame memory 23b. When the value of the counter 31 becomes h × w, the cumulative addition circuit 32 clears the data of the counter 31 to 0, cumulatively adds the luminance frequency data on the table memory in the order of increasing luminance, and calculates the cumulative frequency data of the calculation result. Is written in the table memory, the final cumulative addition value, that is, the total number S of pixels extracted as edges in the area of w × h is output to the normalization circuit 33. Normalization circuit 33
Is 255 / S times (8 bits / pixel) the cumulative frequency data written in the table memory 26 by the cumulative addition circuit 32.
In the case of) and normalize, and write it in the table memory 26 as brightness conversion table data.

By the method and means described above, the brightness level correction circuit 6b extracts a pixel having a brightness change in the input image as an edge, and based on the brightness frequency of the pixel extracted as the edge, the local histogram equalization method. Luminance conversion is performed by. As a result, the brightness conversion table can be calculated only by the brightness change regardless of the size of the area in the image, and the brightness conversion table can be locally calculated for each coordinate in the image, so that the brightness is uniform. The contrast can be improved depending on the place in the image without amplifying the noise component in the large area, and the point where the brightness changes in the light and dark parts of the image is displayed with the brightness that is high in the expressive power of the display device to increase the contrast. Can be improved.

The brightness level correction circuit 6 of the above embodiment
In b, a local histogram is calculated for each pixel, but a method and apparatus for simplifying this will be described below.

FIG. 27 shows an example of the brightness level correction circuit 6b. The frame memory 23c stores the brightness input for one frame. The edge extraction circuit 24b detects an edge from the luminance input. The brightness conversion table calculation circuit 25b is shown in FIG.
The brightness conversion table at 9 points q1 to q9 in 9 areas shown in 8 is calculated and written in the table memory 26b. The luminance conversion table interpolation circuit 34 reads the coordinate value for performing the luminance conversion from the read control circuit 27b, and interpolates the luminance conversion table in q1 to q9 according to the coordinate value (for example, the luminance conversion table at four neighboring points is four points). And linear interpolation for weighted addition according to the distance between the pixels of interest) and writing to the table memory 26c. The read control circuit 27b reads the brightness data from the frame memory 23c in the scanning order,
The read coordinate value is output to the brightness conversion table interpolation circuit, the conversion value corresponding to the brightness is read from the table memory 26c, and output as the converted brightness.

By the method and means described above, the calculation amount and the memory amount can be reduced and the same effect as that of the fourth embodiment of the present invention can be obtained. In FIG. 28, the nine areas for which the brightness conversion table is calculated are in contact with each other and occupy the entire image area. However, the areas of the areas may be reduced so that they are not in contact with each other.

Even when the constituent circuit in the fourth embodiment of the present invention is the brightness level correction circuit 6b alone, the noise component in the area having a uniform brightness and a large area is not amplified and the It is obvious that the contrast can be improved depending on the place, and the point where the brightness changes in the bright and dark portions of the image can be displayed with the brightness having high expressive power of the display device to improve the contrast, and it is included in the present invention.

In the contrast improving circuits of the above embodiments, even if a low-pass filter whose step response is a quadratic equation or a cubic equation is used, the step response is obtained by using a low-pass filter which is a Gaussian integral function. The same effect as the effect can be obtained. Further, the same effect can be obtained by using other methods as the detection means for detecting the bright portion, the dark portion of the image, and the presence / absence of the brightness change.

In each of the above embodiments, the noise removal filter 17 removes noise based on the correlation between frames, but the low frequency component attenuation circuits 3a and 3b are replaced by the coring circuit 22 shown in FIG. By replacing with the added low frequency component attenuation circuit 3c, noise can be removed without using the 1-frame delay circuit 21 and the noise removal filter 17. In FIG. 20, the operations of the LPF 10b and the subtraction circuit 11b other than the coring circuit 22 are the same as those of FIG. 5, and therefore omitted, and the operation of the coring circuit 22 will be described below. The coring circuit 22 converts a low level signal into 0 with respect to the output of the subtraction circuit 11b,
Other signals are output as they are. Since the noise component contained in the image has a smaller level than the actual signal level, the noise can be removed by the coring process. FIG. 21 shows an example of input / output characteristics of the coring circuit 22.
In FIG. 21, the output level is 0 with respect to the level of ± 1% of the input level, but this range may be set according to the level of noise included in the image.

[0047]

As described above, according to the present invention,
The brightness level of the image is converted into a brightness level that can be displayed on a low-contrast display device, and a waveform that causes an illusion of the brightness level is superimposed on the input image. Large bright points are corrected so that they are dark, and conversely, there is a change in luminance in the input image and small dark values are corrected so that dark points are bright, so that the image displayed on a low-contrast display device is displayed. It is possible to improve the contrast, and by performing noise removal on the waveform that causes the illusion of the brightness level, the contrast of the image can be improved without emphasizing the noise component of the image, and its practical effect is great. .

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of an image display device according to a first embodiment of the present invention.

FIG. 3 is a configuration diagram of a noise removal filter according to the present invention.

FIG. 4 is an explanatory diagram of input / output characteristics of a brightness level conversion circuit.

FIG. 5 is a block diagram of a low frequency component attenuation filter.

FIG. 6 is an explanatory diagram of step input.

FIG. 7 is an explanatory diagram of a step response of a low pass filter.

FIG. 8 is an explanatory diagram of a step response of a low frequency component attenuation filter.

FIG. 9 is an explanatory diagram of input / output characteristics of the characteristic conversion circuit 4a.

FIG. 10 is an explanatory diagram of a step response of the contrast improving circuit.

FIG. 11 is an explanatory diagram of a contrast improvement result.

FIG. 12 is a configuration diagram of an image display device according to a second embodiment of the present invention.

FIG. 13 is an explanatory diagram of an offset waveform of a step response of a low frequency component attenuation filter.

FIG. 14 is a block diagram of a characteristic conversion circuit 4c (No. 1).

FIG. 15 is an explanatory diagram of input / output characteristics of the characteristic conversion rate calculation circuit 14.

FIG. 16 is an explanatory diagram of a conversion example by the characteristic conversion circuit 4c (No. 1).

FIG. 17 is a block diagram of a characteristic conversion circuit 4c (part 2).

FIG. 18 is a block diagram of a brightness level correction circuit 6.

FIG. 19 is an explanatory diagram of input / output characteristics of the characteristic conversion circuit 4b.

FIG. 20 is a block diagram of a low frequency attenuator circuit to which a coring circuit is added.

FIG. 21 is a diagram showing an example of input / output characteristics of the coring circuit 22.

FIG. 22 is a configuration diagram of an image display device according to a fourth embodiment of the present invention.

FIG. 23 is a block diagram of a brightness level correction circuit 6b.

FIG. 24 is a block diagram of a luminance conversion table calculation circuit 25.

FIG. 25 is an explanatory diagram of a neighboring area referred to by the local histogram equalization method (when the pixel of interest is far from the edge of the image)

FIG. 26 is an explanatory diagram of a neighboring area referred to by the local histogram equalization method (when the pixel of interest is located at the edge of the image)

FIG. 27 is a block diagram of a brightness level correction circuit 6b.

FIG. 28 is an explanatory diagram of a region for calculating a local histogram.

[Explanation of symbols]

 1 Luminance level conversion circuit 6b Luminance level correction circuit 12 Contrast improvement circuit 17 Noise removal circuit

Claims (22)

[Claims] 1. An image display method comprising: superimposing a waveform that causes an illusion of a brightness level on an input image to improve the contrast of an image displayed on a low-contrast display device. 2. A range of brightness levels of an image is converted into a range of brightness levels that can be displayed on a low-contrast display device, and a waveform that causes an illusion of brightness levels is superimposed on the range, and the range is displayed on the low-contrast display device. An image display method, characterized by improving the contrast of a displayed image. 3. A brightness level of an image and a distribution of brightness changes are detected and corrected so that a bright point having a brightness change and a large brightness value becomes dark, and conversely, there is a brightness change in an input image and a brightness value is changed. An image display method characterized in that small dark points are corrected to be bright, and points having a change in brightness in the bright and dark parts of an image are displayed with a brightness that is highly expressive to the display device. 4. A brightness change region of an image is detected as an edge, and brightness correction of a point having a brightness change in a bright and dark portion of the image is performed by locally equalizing the brightness frequency of pixels detected as an edge. The image display method according to claim 3. 5. A waveform which causes an illusion of a luminance level to be superposed on an input image by superimposing the luminance of a point having a luminance change in a bright and dark portion of the image on an image displayed on a low-contrast display device. The image display method according to claim 3, wherein contrast is improved. 6. The image display according to claim 1, 2 or 5, wherein the noise-free image of the input image is combined with a waveform that causes an illusion of a luminance level to reduce amplification of a noise component. Method. 7. A low frequency component attenuation filter for attenuating low frequency components of an input image, a characteristic conversion circuit for converting the characteristics of the output of the low frequency component attenuation filter, and an output of the characteristic conversion circuit for the luminance of the input image. An image display device, comprising: a contrast improving circuit configured by an adding circuit for superimposing on an image, and displaying an image with improved contrast on a low contrast display device. 8. The image display device according to claim 7, further comprising a brightness level conversion circuit for converting a range of brightness levels of an image into a range of brightness levels that can be displayed by a low-contrast display device. 9. A brightness level of an image and a distribution of brightness changes are detected and corrected so that a bright point having a brightness change and a large brightness value becomes dark, and conversely, there is a brightness change in an input image and a brightness value is changed. An image display device, comprising: a brightness correction circuit that corrects a small dark point so that it becomes bright and displays a point having a change in brightness in a bright and dark portion of an image with a brightness that has a high expressive ability of a display device. 10. An image display device comprising a contrast improving circuit and a brightness correcting circuit, and displaying an image with improved contrast on a low contrast display device. 11. The image display device according to claim 10, further comprising a brightness level conversion circuit. 12. A brightness correction circuit, a low frequency component attenuation filter for attenuating a low frequency component of an input image, an absolute value calculation circuit for calculating an absolute value of an output of the low frequency component attenuation filter, and each of the input images. The brightness level of the pixel is almost 2
An offset circuit that offsets in the negative direction by a factor of 1, a multiplication circuit that performs multiplication for each pixel of the output of the absolute value calculation circuit and the output of the offset circuit, and a characteristic conversion circuit that converts the characteristics of the output of the multiplication circuit. 12. The image display device according to claim 9, 10 or 11, comprising a low-pass filter for smoothing the output of the characteristic conversion circuit, and a subtraction circuit for inverting the sign of the output of the low-pass filter and superimposing it on the output of the contrast improving circuit. . 13. A brightness correction circuit, an edge extraction circuit for extracting an edge from a brightness image, and a brightness conversion table calculation circuit for calculating a brightness conversion table for locally uniforming the brightness frequency in pixels extracted as the edge. The image display device according to claim 9, 10 or 11, further comprising: a brightness conversion circuit that converts brightness according to a brightness conversion table. 14. A low-contrast display device comprising a noise removal filter for removing a noise component of an input image and a 1-frame delay circuit for delaying and outputting the input image by 1 frame, without amplifying the noise component of the image. The image display device according to claim 7, 8, 9, 10, 11, 12, 13 or 14, which displays an image with improved contrast. 15. The image display device according to claim 14, wherein a median value calculation circuit is used for the noise removal filter. 16. The image display device according to claim 14, wherein a weighted averaging circuit is used for the noise removal filter. 17. The image display device according to claim 14, wherein an average value calculation circuit is used for the noise removal filter. 18. A low frequency component attenuation filter for attenuating a low frequency component of an input image is composed of a low pass filter for smoothing the input image and a subtraction circuit for calculating a difference between the input image and the output of the low pass filter. Claim 7,
The image display device according to 8, 10, 11, 12, 13, 14, 15, 16 or 17. 19. The image display device according to claim 18, wherein a Gaussian function is used for the low-pass filter. 20. The image display device according to claim 18, wherein a linear function is used for the low-pass filter. 21. The image display device according to claim 18, wherein a quadratic function is used for the low-pass filter. 22. A coring circuit is added to a low frequency component attenuation filter for attenuating a low frequency component of an input image, and noise is removed from the output of the low frequency component attenuation filter. The image display device according to 21.