Patent Application
20060221046
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2005-098263, filed Mar. 30, 2005, the entire contents of which are incorporated herein by reference.
1. Field
The present invention relates to a display device, and in particular, to a display device and a method of driving a display device, the display device being capable of making the best of a dynamic range of the display device to express gradation by lowering the brightness of back light and in contrast, improving a given picture signal when the picture signal is lower than a predetermined value.
2. Description of the Related Art
Recently, in place of a conventional cathode ray tube (CRT), a liquid crystal display (LCD) unit is popularly used as TV sets and computer displays. In this kind of LCD unit, the liquid crystal itself does not emit light but in the backlight, the liquid crystal is irradiated from behind.
In this kind of patent document 1 (Jpn. Pat. Appln. KOKAI Publication No. 2000-321571), there is indicated a display which can display images on an LCD screen in accordance with a picture signal given, and irradiate the LCD screen from behind by the backlight. In this case, display for each region is achieved in accordance with mean brightness of picture signals by adjusting the backlight brightness for each region in accordance with the mean brightness of the picture signals given.
However, in the prior art of patent document 1, it can be understood that the backlight brightness corresponds to the mean brightness of the picture signals, but there is not definitely indicated how picture signals should be adjusted. Consequently, there has been a problem that it is unclear how the gradation capability of the low region of an image (dark screen) could be improved.
A general architecture that implements the various feature of the invention will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate embodiments of the invention and not to limit the scope of the invention.
Various embodiments according to the invention will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment of the invention, a display device according to one embodiment of the present invention comprises: a display drive unit which generates a display drive signal that corresponds to a picture signal to be supplied; a light-emitting drive unit which generates a light-emitting drive signal that corresponds to the picture signal to be supplied; a display unit which displays images in accordance with the display drive signal from the display drive unit; an irradiation unit which emits light in accordance with the light-emitting drive signal from the light-emitting drive unit and irradiates the display unit from behind; a detection unit which converts a brightness distribution of the picture signal to be supplied into histograms; and a control unit which compares a displayable bandwidth of the display unit with a bandwidth from the minimum brightness of the brightness distribution posted to the histogram, and when the bandwidth from the minimum brightness of the brightness distribution posted to the histogram is equal to or less than a predetermined ratio of the displayable bandwidth of the display unit, controls the light-emitting drive signal so as to lower the degree of irradiation of the irradiation unit in accordance with the picture signal and controls the display drive signal so as to improve brightness of image display of the display unit in accordance with the picture signal.
Embodiments of the present invention will be described in detail with reference to the accompanying drawings.
<Liquid Crystal Display Device According to One Embodiment of the Present Invention>
(Configuration)
A liquid crystal display device according to one embodiment of the invention has a picture signal level detection circuit 11, a control circuit 12, a backlight driver 13, a scan line drive unit 14, a picture signal line drive unit 15, an LCD panel 16, and a backlight unit 17. The picture signal level detection circuit 11 generates a histogram according to picture signals as shown in
(Basic Operation)
When a histogram distribution of picture signals is equal to or less than a dynamic range of a display screen, the liquid crystal display device 1 according to one embodiment of the present invention lowers backlight brightness and improves display brightness in accordance with the picture signals, thereby improving the display gradation property.
The backlight control of drive signals of the liquid crystal display device 1, one embodiment of the invention, is carried out as follows as shown in the flow chart of
In the distribution of picture signal data of one scan line shown in
In the case where the histogram distribution T is determined to be equal to or less than ½ the maximum value in the dynamic range, the light quantity of a lighting light source for backlight is set to ½ that at the normal display (same as above). At the same time, at the normal time, the lower 4-bit data of the picture signal is discarded, whereas the lower 3-bit data only is discarded to input into the picture signal line drive unit 15. By doing so, the number of gradations which can be expressed in a narrow brightness region in which the picture signal exists becomes practically double, and fine gradation can be reproduced, which has never been expressed when it is displayed without control of the backlight.
The similar correspondence should be achieved when the histogram distribution T is equal to or less than ¼ the maximum value in the dynamic range of the picture signal and is equal to or less than ⅛, and quadruplicate and octuplex improvements, respectively, are expected in gradation property.
That is, as shown in the flow chart of
In the above embodiment, processing is explained for each screen. However, it is not always necessary to take this form but it is preferable that the screen may be divided into 2 regions or 4 regions, and same processing is carried out for each divided screen. In addition, it is preferable to carry out processing with the screen divided into four regions or more.
(Backlight Control Using Correction Table)
Next, backlight control is carried out by using a correction table. That is, the relationship between the brightness of the backlight unit and the brightness of the LCD panel 16 is not always linear as described above, and has a predetermined relation which can be measured and specified. Therefore, a plurality of correction tables are provided which store optimum values as to what kind of the backlight brightness and picture signal voltage level should be achieved when the histogram distribution T is equal to or less than ½ the maximum value in the dynamic range of the picture signal. By using the correction tables, backlight control is carried out.
That is, as shown in the flow chart of
In this way, using correction tables prepared in advance enables the intended backlight control to take place even when linearity is not guaranteed, so that the gradation property of image display can be achieved.
(Backlight Control with Indoor Light Quantity Taken into Account)
In addition, it is preferable to provide a light quantity sensor (not shown) around the LCD panel 16, to detect an indoor light quantity, and to decide the value of backlight, etc. in consideration of the detected light quantity as shown in the flow chart of
With respect to the description of steps 31 to S35 of the flow chart of
(Backlight Control with Counter Provided)
Next, as shown in
That is, as shown in the flow chart of
In the case where the histogram distribution T does not fall under in step S42, the counter shall be reset to zero (step S47). This means that when histogram distribution T no longer satisfies the conditions such as being equal to or less than ½, etc., the system immediately returns to the normal mode.
(Backlight Control of Multiple Stages)
Furthermore, it is preferable to carry out not only ½ but also other ratio simultaneously in one processing program as shown in the flow chart of
That is, as shown in the flow chart of
However, even if this does not take place in step S52, it is determined whether or not the histogram distribution T is equal to or less than ½ the dynamic range (step S12). In the case where the histogram has such a value, control data which brings the backlight brightness to ½ is generated in the backlight light quantity control circuit 12, and the generated data is supplied to the backlight driver 13 (step S13). In addition, in the picture signal voltage level control circuit 12, control data is generated such that the picture brightness becomes double and supplied to picture signal line drive unit 15 (step S14). If there is any picture signal of the next screen, processing is repeated from step S11 (step S15).
In this way, by providing a plurality of processing that satisfy a plurality of conditions, ½, ¼, ⅛, and other processing are carried out continuously to achieve the high gradation property by carrying out optimum backlight control in accordance with the screen conditions.
(Combined Use of Error Diffusion Method or Dither Method)
Furthermore, in the embodiment of the present invention, in the case where histogram distribution T does not fall under the desired value, images are processed by using an error diffusion method or a dither method. That is, as shown in
Therefore, in the present invention, for picture signals of the brightness distribution in which backlight control cannot be carried out as shown in
In step S61 of the flow chart of
In each of these above-mentioned embodiments, processing is explained for each screen. However, it is not always necessary to take this form, but it is preferable that the screen may be divided into 2 regions or 4 regions, and same processing is carried out for each divided screen. It is also preferable to carry out processing with the screen divided into four regions or more.
(Field Emission Display (FED) According to One Embodiment of the Present Invention)
Moreover, all the processing of each process described above can be applied not only to a liquid crystal display device but also to the FED shown in
Now, as shown in
However, in the case of a light-emitting type matrix display such as a field emission display (FED), etc., a drive voltage of a scan driver of matrix is varied, whereby control is carried out on light-emitting brightness per unit time, in place of the backlight brightness correction processes (step S13, step S24, step S34, step S45, step S53) of each flow chart of FIGS. 5 to 10. With respect to the portion which corresponds to the signal line driver, the number of expressible gradations in a specific brightness region where picture signals are concentrated can be increased by linking a pulse modulation width and an amplitude value of a drive voltage to this. Consequently, each one of all the embodiments shown in each flow chart of FIGS. 5 to 10 can be applied to display devices using FED.
In the display device described above, a picture concentration histogram is generated in accordance with picture signals given. In the case where the brightness distribution from the minimum brightness of this histogram exists only in the region equal to or less than ½ the displayable dynamic range of the display screen, the gradation property cannot be fully displayed as it is and a merely dark screen as a whole is displayed. Therefore, lowering the brightness of the backlight, which is an irradiation unit, to, for example, ½ enables to double the picture signal voltage, which is a display drive signal in accordance with picture signals, in the case where the relation between the signal size and brightness is substantially linear. In addition, the picture signal voltage results in having double gradation property by fully making the best of the dynamic range of the display screen, and the high-gradation image display can be achieved.
While certain embodiments of the inventions have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-098263 | Mar 2005 | JP | national |
