JP2002318577A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device which can save the electric power furthermore while keeping high display quality. SOLUTION: The image display device is equipped with a 1st storage means 4 which stores image data, an image processing means 8 which performs image processing for decreasing the number of bits of the image data, a 2nd storage means 10 which stores the image data after the image processing, a display means 12 which displays the image data after the image processing, a display driving means 14 which drives the display means 12, and a control means 16 which control the driving of the display driving means 14. The control means 16 decides which of moving picture data and still picture data the image data stored in the 1st storage means 4 are and places only the display driving means 14 and display means 12 in operation after image data of one picture are stored in the 2nd storage means 10 when the image data are the still picture data.

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, and more particularly to an image display device capable of switching and displaying a moving image and a still image.

[0002]

2. Description of the Related Art An image display device used for a personal computer, a portable information terminal, or the like is capable of switching between a moving image and a still image based on a received signal in accordance with the recent development of communication technology and the like. It has been proposed that various information can be provided according to the needs and preferences of the user. In such an image display device,
Since on / off driving is repeated when displaying a moving image, power consumption is increased. In particular, in the case of a portable information terminal, a battery is used as a driving power source, and an increase in power consumption leads to a reduction in a usable time per charge. Therefore, power saving is an important issue.

[0005] For the purpose of power saving of an image display device, a method of reducing the number of bits of image data has been proposed.
FIG. 4 shows a configuration disclosed in Japanese Patent Application Laid-Open No. 9-101771 as an example of an image display device provided with an image processing device for performing such processing.

[0004] As shown in FIG.
Video controller 51 for controlling image display device 50
A VRAM 52 for storing RGB image data;
A liquid crystal display 53 for displaying the B image data and a liquid crystal controller 54 for controlling the liquid crystal display 53 are provided, and are connected to a personal computer 56 and an image processing device 58. When RGB image data is input from a hard disk device (not shown) of the personal computer 56, the image processing device 58 masks the lower three bits that hardly affect display quality, reduces the image data, and then performs scaling processing. And color reduction processing, and outputs the image to the image display device 50. As a method of the color reduction processing, a dither method, an error diffusion method, and the like are conventionally known as described in the publication. The RGB image data input to the image display device 50 is
And displayed on the liquid crystal display 53 by the liquid crystal controller 54.

The above image display device saves power by reducing the number of bits of RGB image data in the image processing device 58. However, while the image is displayed on the liquid crystal display 53, moving images and still images are displayed. Since the image processing device 58 is always operated without distinguishing between the two, there is room for further improvement in power saving.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide an image display device capable of further reducing power consumption while maintaining high display quality.

[0007]

In order to achieve this object, an image display apparatus according to the present invention comprises a first storage means for storing image data, and an image processing apparatus for performing image processing for reducing the number of bits of the image data. Processing means, second storage means for storing the image data after the image processing, display means for displaying the image data after the image processing, display drive means for driving the display means, and display drive means Control means for controlling the driving of the image data. The control means determines whether the image data stored in the first storage means is moving image data or still image data, and determines whether the image data is still image data. In this case, after the image data for one screen is stored in the second storage unit, only the second storage unit, the display drive unit, and the display unit are operated.

In this image display device, it is preferable that the storage capacity of the second storage means is smaller than the storage capacity of the first storage means. Thus, the second storage unit and the display driving unit can be provided on the same chip and integrated, and further power saving can be achieved.

Preferably, the image processing means performs image processing by a dither method or an error diffusion method. Further, the image processing means includes an RG included in the image data.
It is more preferable to perform a process of reducing the total number of bits of the three elements B so that the number of bits of G is the largest and the number of bits of B is the smallest after image processing. Thereby, higher display quality can be obtained.

The image processing means includes a moving image processing means for performing image processing for reducing the number of bits of moving image data, a still image processing means for performing image processing for reducing the number of bits of still image data, A configuration may also be provided that includes a switching unit that switches processing in the moving image processing unit or the still image processing unit. In this case, the control unit determines whether the image data stored in the first storage unit is moving image data or still image data, and activates the switching unit based on a result of the determination. Accordingly, it is possible to cause the moving image processing unit to perform image processing on moving image data, and to perform image processing on the still image processing unit for still image data. The moving image processing unit preferably performs image processing by an FRC method, and the still image processing unit preferably performs image processing by a dither method or an error diffusion method.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic block diagram of an image display device according to one embodiment of the present invention. This image display device can be mounted on, for example, a portable information terminal.

As shown in FIG. 1, the image display device includes a signal processing unit 2 for outputting digital image data based on an input signal, a VRAM 4 serving as first storage means for storing the image data, A gamma processing unit (γ processing unit) 6 for correcting the gamma characteristic of the image data, an image processing unit 8 for reducing the number of bits of the image data to reduce the data, and a second storage for storing the reduced image data It includes a panel-compatible RAM 10 as a means, a display panel 12 composed of a liquid crystal panel for displaying image data, and a driver unit 14 for driving the display panel 12. These signal processing unit 2, VRAM 4, gamma processing unit 6, image processing unit 8, panel-compatible RAM 10, display panel 12, and driver unit 14
Is controlled by the control unit 16. The signal processing unit 2 includes a DSP (Digital Signal Processor),
For example, it has a function of decompressing data compressed according to the MPEG (Moving Picture Experts Group) standard.

Next, the operation of the image display device will be described. For example, a signal demodulated after being input via an antenna (not shown) is input to the signal processing unit 2 and subjected to digital signal processing, and then stored in the VRAM 4. The control unit 16 determines whether the data is moving image data or still image data based on a signal input to the signal processing unit 2, and controls the image display device based on the determination result.
Here, it is assumed that moving image data of R (red), G (green), and B (blue), each having 6 bits, is stored in the VRAM 4. When determining that the data is moving image data, the control unit 16 activates all of the signal processing unit 2, the VRAM 4, the gamma processing unit 6, the image processing unit 8, the panel corresponding RAM 10, the display panel 12, and the driver unit 14.

The image data stored in the VRAM 4 is input to the image processing unit 8 after gamma correction is performed in the gamma processing unit 6 based on predetermined gamma correction data.
The image processing unit 8 reduces the number of bits of image data by a predetermined image processing method. The image processing method can be performed by various known methods for reducing the number of gradations of image data. For example, although it is possible to simply cut off lower bits, there is a possibility that a contour line is generated due to gradation drop. Therefore, it is preferable to perform a color reduction process such as a dither method or an error diffusion method. The dither method is a processing method of comparing the gradation value of image data with a threshold value of a predetermined dither matrix to reduce the gradation. Further, the error diffusion method is a processing method for dispersing an error generated when reducing the gradation to adjacent pixels. With such a method, it is possible to prevent the generation of an outline due to gradation drop. In the present embodiment, the RGB image data is stored in the panel corresponding RAM 10 after being reduced from 6 bits to 4 bits by the image processing unit 8.

The image data stored in the panel-compatible RAM 10 is displayed on the display panel 12 by driving the driver unit 14. When the control unit 16 determines that the data is moving image data based on a signal input to the signal processing unit 2, the control unit 16 controls the above-described operation to be repeated.

On the other hand, when the control unit 16 determines that the image data is still image data based on the signal input to the signal processing unit 2, the display of the first one screen (one frame) is performed using the above-described moving image data. The same control as in the above case is performed, but after that, the operations of the signal processing unit 2, the VRAM 4, the gamma processing unit 6, and the image processing unit 8 are stopped, and the panel-compatible RAM 1
0, only the display panel 12 and the driver section 14 are operated. As a result, the initially displayed still image is maintained on the screen of the display panel 12. Such control is performed until the control unit 16 determines the moving image data based on the input signal.

As described above, according to the image display device of the present embodiment, only the minimum components for maintaining the display screen are operated at the time of displaying a still image. Power saving can be achieved as compared with a case where the moving image and the still image are operated without being distinguished. In particular, in the present embodiment, the image data whose bit number has been reduced by the image processing unit 8 is stored in the panel-compatible RAM.
10 is stored in the panel-compatible RA
The memory capacity of M10 can be made smaller than the memory capacity of VRAM4. Therefore, when a still image is displayed, the VRAM 4 is not operated and the panel-compatible RAM 10 is operated.
Is activated, and the power saving effect when displaying image data can be further enhanced.

Since the memory capacity of the panel-compatible RAM 10 can be reduced in this way, the panel-compatible RAM 10
It becomes easy to integrate the driver 10 and the driver unit 14 into a single chip IC. Therefore, the panel-compatible RAM
The stray capacitance between the driver 10 and the driver unit 14 can be reduced, which can further reduce power consumption. Note that the gamma processing unit 6 and the image processing unit 8 also
Similarly, it can be integrated into a one-chip IC, and by incorporating an interface, versatility can be improved.

As described above, one embodiment of the present invention has been described, but specific aspects of the present invention are not limited to the above embodiment. For example, in the present embodiment, the gamma correction is performed in the gamma processing unit 6 before the image processing is performed in the image processing unit 8. However, the gamma processing unit 6 is not provided, and the image data in the VRAM 4 is subjected to image processing. It is also possible to configure so as to be directly input to the unit 8 and to provide the driver unit 14 with a function of performing gamma correction. In this embodiment, the signal processing unit 2 and the VRAM 4
And the signal processing section 2
A configuration including M4 is also possible.

The processing method in the image processing unit 8 is as follows.
The present invention is not limited to this embodiment as long as the number of bits of image data is reduced, and the number of bits to be reduced may be appropriately determined in consideration of the display capability of the display panel 12 and the like. For example, in the present embodiment, the number of bits after image processing is the same for all three elements of RGB. However, while the number of G bits with high sensitivity due to eye characteristics is maximized, the number of B bits with low sensitivity is high. The number may be minimized. For example, as shown in FIG. 2, the number of bits after image processing in the image processing unit 8 is preferably G: 5 bits, R: 4 bits, and B: 3 bits. Such image processing is particularly effective for a method of spatially dispersing gradations, such as a dither method or an error diffusion method, and the total number of bits of the three RGB elements after image processing is the same as in the present embodiment. However, the roughness of the display screen can be reduced.
Therefore, even if the number of bits is reduced for power saving,
Good image quality can be maintained.

Further, in the present embodiment, the same image processing is performed by the image processing unit 8 for the moving image data and the still image data, but as shown in FIG.
8 is a moving image processing unit 18a, a still image processing unit 18b,
And a switching unit 18c.

In this configuration, when the control unit 16 determines whether the data is moving image data or still image data based on a signal input to the signal processing unit 2, the switching unit 18c To select one of the moving image processing unit 18a and the still image processing unit 18b. Thus, the image data that has passed through the gamma processing unit 6 is subjected to image processing by the moving image processing unit 18a if it is moving image data, and is processed by the still image processing unit 18b if it is still image data. The control means 16
At the time of displaying a still image, the entire image display device is operated until image data for one screen (one frame) is stored in the panel-compatible RAM 10 and displayed on the display panel 12. Display panel 1
2, and only the driver section 14 is operated.

As a result, the image processing method can be changed between a moving image and a still image, so that image processing suitable for each case can be performed, and good image quality can be maintained while saving power. be able to. Further, since the frame rates of the moving image display and the still image display can be made different, the frame rate at the time of displaying a still image is made lower than the frame rate at the time of displaying a moving image, so that image quality can be maintained and power saving can be achieved. Can be planned. To give an example of an image processing method, a spatial color reduction method such as a dither method or an error diffusion method is effective for image processing in the still image processing unit 18b. For the image processing in the moving image processing unit 18a, a temporal color reduction method such as an FRC (Frame Rate Control) method is effective. The FRC method is to express multiple gray scales by adjusting an average applied voltage by inserting an OFF frame at a fixed rate in an ON frame when turning on an arbitrary pixel of the display panel 12. How to

In the present embodiment, the display panel 12 is a liquid crystal panel.
Even if 2 is a light emitting display such as an organic EL, the effect of power saving can be obtained as in the present embodiment.

The VRAM 4 and the panel-compatible RAM 1
0 can also be another rewritable semiconductor memory.

[0026]

As is apparent from the above description, according to the present invention, it is possible to further reduce power consumption while maintaining high display quality.

[Brief description of the drawings]

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

FIG. 2 is a schematic block diagram of an image display device according to another embodiment of the present invention.

FIG. 3 is a schematic block diagram of an image display device according to still another embodiment of the present invention.

FIG. 4 is a schematic block diagram of a conventional image display device.

[Explanation of symbols]

 Reference Signs List 4 VRAM (first storage means) 8 Image processing unit 10 Panel-compatible RAM (second storage means) 12 Display panel 14 Driver unit 16 Control unit

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G09G 3/20 641 G09G 3/20 641H 5C082 3/36 3/36 5/02 B 5/02 H04N 5 / 14 Z H04N 5/14 5/66 Z 5/66 G09G 5/00 520 J 1006 Ojimon Shin Matsushita Electric Industrial Co., Ltd. (72) Inventor Hitoshi Tsuge 1006 Ojimon Kadoma, Kadoma City, Osaka Pref. DA16 5C006 AA02 AA11 AF53 AF69 AF85 BF01 FA01 FA47 5C021 PA62 PA72 PA79 PA82 RB06 YC09 ZA00 ZA01 5C058 AA06 BA26 BB13 BB25 5C080 AA10 BB05 CC03 DD26 JJ02 KK01 KK43 5C082 AA01 BA12 BA34 BA35 BA39 BB15 BB53 BD02 CA11 CA81 CB06 DA53 DA86 MM02

Claims (8)

[Claims] A first storage unit for storing image data; an image processing unit for performing image processing for reducing the number of bits of the image data; and a second storage unit for storing the image data after the image processing Display means for displaying the image data after the image processing, display drive means for driving the display means, and control means for controlling the drive of the display drive means, the control means comprising: Determine whether the image data stored in the storage means is moving image data or still image data, if it is still image data,
After the image data for one screen is stored in the second storage unit, the second storage unit, the display drive unit,
And an image display device wherein only the display means is operated. 2. The image display device according to claim 1, wherein the storage capacity of said second storage means is smaller than the storage capacity of said first storage means. 3. The image display device according to claim 2, wherein said second storage means and said display drive means are provided on a single chip and integrated. 4. The image processing device according to claim 1, wherein said image processing means performs image processing by a dither method or an error diffusion method.
An image display device according to claim 1. 5. The image processing means according to claim 1, wherein, for the three RGB components of the image data, the number of G bits is the largest and the number of B bits is the least after the image processing.
The image display device according to claim 4, wherein a process of reducing a total bit number of the three elements is performed. 6. The moving image processing means for performing image processing for reducing the bit number of moving image data, the still image processing means for performing image processing for reducing the bit number of still image data, A switching unit for switching processing in a moving image processing unit or a still image processing unit, wherein the control unit determines whether the image data stored in the first storage unit is moving image data or still image data By operating the switching unit based on the result of the determination, the moving image processing unit performs image processing for moving image data, while the still image processing unit performs processing for still image data. The image display device according to claim 1, wherein the image display device performs image processing. 7. The image processing apparatus according to claim 6, wherein the moving image processing unit performs image processing by an FRC method, and the still image processing unit performs image processing by a dither method or an error diffusion method. Image display device. 8. The image display device according to claim 1, wherein said display means is a liquid crystal panel.