1. Field of the Invention
The present invention relates to an image display apparatus and a control method therefor.
2. Description of the Related Art
A hold-type image display apparatus, such as a liquid crystal display apparatus (liquid crystal display), incurs a phenomenon called “motion blur” by which a moving object is seen to have tailing in displaying a moving image.
There is a technique for improving the motion blur of such a liquid crystal display apparatus which is called “BL scan” which causes a backlight (BL) to perform impulse-type light emission (by black insertion, or inserting a black image between frames). For example, a technique exists such that in driving a backlight having a plurality of LEDs (light sources) arranged in a matrix form, BL lines of LEDs (matrix lines each formed of a plurality of LEDs) are sequentially lit and sequentially extinguished from the upper side toward the lower side of the screen. If the BL scan is performed only once per frame, a flicker disturbance occurs.
Conventional techniques for reducing the flicker disturbance are disclosed in Japanese Patent Application Laid-open Nos. 2000-322029 and 2008-65228 for example. Specifically, the techniques disclosed in Japanese Patent Application Laid-open Nos. 2000-322029 and 2008-65228 perform a control such as to light the backlight plural times per frame. Further, according to the technique disclosed in Japanese Patent Application Laid-open No. 2008-65228, the backlight is lit with different timings on a frame-to-frame basis.
However, when the techniques disclosed in Japanese Patent Application Laid-open Nos. 2000-322029 and 2008-65228 and the like are used, a double-image blur takes place by which the contour of an object is seen to be multiple. The following description is directed to the motion blur and the double-image blur.
Firstly, the motion blur is described with reference to
The next description is directed to the double-image blur with reference to
By performing only the BL scan disclosed in Japanese Patent Application Laid-open Nos. 2000-322029 and 2008-65228, the flicker disturbance and the motion blur can be reduced, but the double-image blur is allowed to occur.
A conventional technique for reducing such a double-image blur is disclosed in Japanese Patent Application Laid-open No. 2006-18200 for example. Specifically, the technique disclosed in Japanese Patent Application Laid-open No. 2006-18200 uses a lighting signal (backlight drive signal) which is the OR of a pulse signal given once per frame and a pulse signal given with a higher frequency than the frame frequency. The technique disclosed in Japanese Patent Application Laid-open No. 2006-18200 reduces the double-image blur by using such a lighting signal.
However, some display images relying upon the above-described techniques disclosed in Japanese Patent Application Laid-open Nos. 2000-322029, 2008-65228 and 2006-18200 allow the flicker disturbance to be visually observed because the number of times of lighting of the backlight within one frame is constant.
The present invention provides an image display apparatus which is capable of reducing the flicker disturbance, motion blur and double-image blur.
An image display apparatus according to the present invention comprises:
a light-emitting unit configured to emit light;
a display panel configured to display an image by transmitting the light from the light-emitting unit at a transmittance based on an input image signal; and
a control unit configured to set a plurality of lighting periods respectively having different lengths on a frame-by-frame basis and control lighting and extinction of the light-emitting unit in such a manner that the light-emitting unit is lit during the lighting periods and extinguished during a period other than the lighting periods,
wherein the control unit makes the number of lighting periods within one frame larger when a brightness of the image is bright than when the brightness of the image is dark.
A method of controlling an image di splay apparatus, according to the present invention, having a light-emitting unit configured to emit light and a display panel configured to display an image by transmitting the light from the light-emitting unit at a transmittance based on an input image signal, the method comprises:
a set step of setting a plurality of lighting periods respectively having different lengths on a frame-by-frame basis; and
a control step of controlling lighting and extinction of the light-emitting unit in such a manner that the light-emitting unit is lit during the lighting periods and extinguished during a period other than the lighting periods,
wherein in the set step, the number of lighting periods within one frame is made larger when a brightness of the image is bright than when the brightness of the image is dark.
According to the present invention, the flicker disturbance, motion blur and double-image blur can be reduced.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, embodiments of the present invention will be described. It should be noted that, though the following description is directed to a liquid crystal display apparatus and a control method therefor, an image display apparatus (and a control method therefor) according to the present invention is not limited to such a liquid crystal display apparatus (and a control method therefor). The image display apparatus according to the present invention may be any image display apparatus that includes a light-emitting unit configured to emit light and a display panel configured to display an image by transmitting the light from the light-emitting unit at a transmittance based on an input image signal.
Description will be made of a liquid crystal display apparatus and a control method therefor according to Embodiment 1 of the present invention.
As shown in
The liquid crystal panel 104 is a display panel having a plurality of liquid crystal elements of which the transmittances are controlled based on an input image signal.
The display control unit 105 controls the transmittances of the plural liquid crystal elements of the liquid crystal panel 104 based on the input image signal.
The backlight 103 is a light-emitting unit configured to emit light against the back side of the liquid crystal panel 104. In the present embodiment, the backlight 103 has a configuration capable of controlling lighting and extinction of blocks obtained by dividing the screen region of the liquid crystal panel 104 (i.e. dividing the image) on a block-by-block basis. Specifically, the backlight 103 has a plurality of LEDs arranged in a matrix form opposed to the back side of the liquid crystal panel 104 as light sources. In the present embodiment, the brightness of the backlight is variable.
There is no limitation to such a backlight. For example, an edge light type backlight may be used which includes a light guide plate having a plate surface opposed to the back side of the liquid crystal panel 104, and a light source provided on an edge portion of the light guide plate. The light source is not limited to an LED. For example, the light source may be a cold cathode tube.
The pulse modulating unit 101 sets a lighting period of the backlight. In the present embodiment, the pulse modulating unit 101 sets a plurality of lighting periods respectively having different lengths on a frame-by-frame basis. A method of setting a lighting period will be described later.
The backlight control unit 102 controls lighting and extinction of the backlight 103 in such a manner that the backlight 103 is lit during the lighting period of the backlight set by the pulse modulating unit 101 and extinguished during a period other than the lighting period. In the present embodiment, the period during which the backlight 103 is extinguished is referred to as an “extinction period”.
In the present embodiment, the lighting period of LEDs belonging to each block is set on a block-by-block basis, while lighting and extinction of those LEDs belonging to the block concerned is controlled. Specifically, all the LEDs on one BL line (matrix line formed of a plurality of LEDs) form one block of LEDs. BL lines of LEDs are lit sequentially from the upper side toward the lower side of the screen.
In the present embodiment, the brightness of the backlight at each point in time within the lighting period (instantaneous value, i.e., instantaneous brightness) is a predetermined fixed value. The instantaneous brightness of the backlight may be determined by the display control unit 105 based on the input image signal or the like. For example, when the input image signal is a signal indicative of a dark image, the instantaneous brightness of the backlight may be lowered. By so doing, the total amount of light emission from the backlight during one frame is decreased, thereby lowering the brightness of the backlight in one frame. In such a case, the display control unit 105 may perform image processing of the input image signal based on the instantaneous brightness of the backlight and control the transmittance of each liquid crystal element based on the input image signal having been subjected to the image processing. For example, the display control unit 105 may perform image processing of the input image signal so as to prevent the brightness of the screen from being changed by the change in the brightness of the backlight based on the input image signal. With such an arrangement, it is possible to improve the contrast of an image and reduce the power consumption. The total time length of lighting periods within one frame may be determined based on the input image signal.
The following description is directed to the method of setting (determining) a lighting period of the backlight by the pulse modulating unit 101.
The pulse modulating unit 101 determines number n of times of lighting (frequency n of lighting) of the backlight within one frame (i.e., the number of lighting periods within one frame) and the length BLd(x) and start time BLp(x) of each lighting period by using a BL light control value BLa. x is an integer from 1 to n and represents a lighting period's turn. BLa represents the total time length of lighting periods within one frame. With increasing BLa value, the total time length of lighting periods within one frame becomes longer and, hence, the brightness of the backlight in one frame becomes higher (that is, the total amount of light emission of the backlight during one frame becomes larger). Stated otherwise, with decreasing BLa value, the total time length of lighting periods within one frame becomes shorter and, hence, the brightness of the backlight in one frame becomes lower (that is, the total amount of light emission of the backlight during one frame becomes smaller). BLd(x) represents the length of the xth lighting period of the plural lighting periods in one frame. BLp(x) represents the start time of the xth lighting period of the plural lighting periods in one frame.
Initially, the pulse modulating unit 101 determines number n of times of lighting such that the number of lighting periods within one frame becomes larger when the screen (a brightness of the image) is bright than when the screen is dark (step S1021). This is because the flicker disturbance can be visually observed more easily when the screen is bright than when the screen is dark. In the present embodiment, it is possible to suppress the motion blur and control the flicker disturbance precisely by making the number of lighting periods (number n of times of lighting) within one frame larger when the screen is bright than when the screen is dark. On the other hand, increasing number n of times of lighting causes the double-image blur to be visually observed more easily. In the present embodiment, it is possible to suppress the double-image blur while suppressing the motion blur and the flicker disturbance by decreasing number n of times of lighting when the screen is dark.
In cases where the input image signal is indicative of a homochromatic image, the screen becomes brighter as the backlight becomes brighter (as the BL light control value BLa becomes larger). For this reason, the present embodiment determines number n of times of lighting with the brightness of the backlight being taken as the brightness of the screen. Since the instantaneous brightness of the backlight is a fixed value according to the present embodiment as described above, the brightness of the backlight in one frame is determined in accordance with the total time length of lighting periods within the frame concerned, namely, a set value of the BL light control value BLa. For this reason, number n of times of lighting is determined in accordance with the set value of the BL light control value BLa. This can realize the processing in step S1021 with a decreased processing amount. The BL light control value BLa is determined (or set) by a user's operation or based on an image display mode or the input image signal. For example, the BL light control value BLa is determined in accordance with a gradation value (e.g., mean gradation value) of the input image signal. Specifically, number n of times of lighting is determined using a function shown in
Subsequently to step S1021, the pulse modulating unit 101 determines the length BLd(x) of each lighting period (step S1022). In the present embodiment, the length BLd(x) of each lighting period is calculated using Expression 1. In Expression 1, h(x) represents the emission brightness ratio of the backlight (the ratio of the total amount of light emission of the backlight during the xth lighting period in one frame to the total amount of light emission of the backlight in the frame concerned). The emission brightness ratio h(x) is determined using a predetermined table as shown in
BLd(x)=h(x)×BLa (Expression 1)
Subsequently, the pulse modulating unit 101 determines the start time BLp(x) of each lighting period (step S1023). In the present embodiment, the start time BLp(x) of each lighting period is calculated using Expression 2. In Expression 2, Fa represents the length of one frame period.
BLp(x)=BLd(x−1)+BLp(x−1)+(Fa−BLa)/Gt (Expression 2)
In the present embodiment, the start time of one frame period is set to 0 and the start time BLp(1) of the first (x=1) lighting period is set equal to 0.
In the present embodiment, Gt is set equal to n. By so setting, the lighting periods are determined such that extinction periods are uniform in length. By thus making the extinction periods uniform in length, the flicker disturbance can be reduced further than in cases where the extinction periods are not uniform in length.
By steps S1021 to S1023, the lighting periods within one frame are determined.
Subsequently, the pulse modulating unit 101 outputs to the backlight control unit 102n number of lighting period lengths BLd(x) calculated in step S1022 and n number of start times BLp(x) calculated in step S1023 (step S1024). The backlight control unit 102 applies a drive current (BL drive current) to LEDs of the backlight 103 based on BLp(x) and BLd(x) inputted from the pulse modulating unit 101, thereby to light the LEDs.
The LEDs on BL line 1 (the uppermost BL line) are lit for a time period BLd(1) from the frame period start time (in the example illustrated in
dy=one frame period/number of BL lines (Expression 3)
Description will be made of effects of the present embodiment with reference to
By providing the plurality of lighting periods (by dividing one lighting period into the plural lighting periods), the change in the brightness of an edge portion 1061 of the object O shown in
By making the plural lighting periods respectively have different lengths, the brightness of a flat portion 1062 (i.e., a region of the edge portion in which the brightness is constant) shown in
As described above, the present embodiment makes the number of lighting periods within one frame larger when the screen is bright than when the screen is dark. This makes it possible to reduce the flicker disturbance precisely.
According to the present embodiment, the plural lighting periods within one frame are made different in length from one another. This arrangement can bring the brightness of a flat portion closer to the brightness of the background or object, thereby reducing the double-image blur.
According to the present embodiment, the lighting periods are set such that the extinction periods are made uniform in length. This makes the respective time periods for black image display uniform, thereby enabling the flicker disturbance to be reduced further.
There is no limitation to the above-described method of setting the lighting periods. The lighting periods may be set in any manner as long as the number of lighting periods within one frame is made larger when the screen is bright than when the screen is dark while the plural lighting periods within one frame are different in length from one another. For example, the length and the start time of each lighting period may be set by the user.
In the present embodiment, lighting and extinction of the backlight are controlled BL line by BL line. That is, all the light sources on each BL line form one block of light sources. However, there is no limitation to this arrangement. For example, all the light sources of the backlight may form one block of light sources. This means that all the light sources of the entire backlight may be lit and extinguished at a time. Alternatively, a single light source may be used as one block of light source.
In the present embodiment, number n of times of lighting remains invariant throughout the blocks. However, number n of times of lighting may differ between blocks. Specifically, number n of times of lighting of the backlight in a block may be determined in accordance with the brightness of the screen in the block concerned on a block-by-block basis. By so doing, the flicker disturbance can be reduced more precisely. Specifically, the flicker disturbance can be reduced on a block-by-block basis in harmonization with the characteristic of an image displayed in the block concerned.
In the present embodiment, number n of times of lighting is determined using the BL control value (brightness of the backlight in one frame) as the brightness of the screen in the frame concerned. However, there is no limitation to this method of determining number n of times of lighting. For example, the brightness of the screen in one frame may be calculated (predicted) specifically by using the BL control value and the input image signal (transmittance of each liquid crystal element).
In the present embodiment, the plurality of lighting periods are provided on a frame-by-frame basis. In cases where the input image signal is indicative of an image with a little motion, a plurality of lighting periods are provided plural frames by plural frames. In such a case, one lighting period may extend over two frames.
The lighting periods may be set such that the intervals between the lighting periods within one frame become shorter than the time length from the ending time of the last lighting period in the frame concerned to the ending time of the frame. That is, the intervals between the lighting periods within one frame may be set shorter than in the case of
Such lighting periods can be set, for example, by making the value of Gt in Expression 2 larger than number n of times of lighting.
Description will be made of effects brought about when the backlight is driven by the BL drive current shown in
By providing the plurality of lighting periods while shortening the interval between the lighting periods within one frame, the change in the brightness of an edge portion 1081 of the object O shown in
By making the plural lighting periods respectively have different lengths, the example shown in
Further, by shortening the interval between the lighting periods within one frame, the dimensions of respective flat portions 1082 and 1083 in
The start time BLp(x) of each lighting period may be calculated using the following Expression 3. By adding a term “−BLd(x)/2” to Expression 2, the interval between the lighting periods within one frame can be shortened further.
BLp(x)=BLd(x−1)+BLp(x−1)+(Fa−BLa)/Gt−BLd(x)/2 (Expression 3)
When providing three or more lighting periods within one frame, the lighting periods may be set such that the intervals between the lighting periods within the frame concerned become shorter gradually.
Such lighting periods can be simply set, for example, by gradually increasing the value of Gt in calculating the start time BLp(x).
By calculating the start time BLp(x) with the value of Gt gradually increasing, the lighting periods are determined such that the intervals between the lighting periods within one frame become shorter gradually. Specifically, the length of the interval BLe4 is shorter than that of the interval BLe3.
Description will be made of effects brought about when the backlight is driven using the BL drive current shown in
By providing the plurality of lighting periods while shortening the intervals between the lighting periods within one frame, the change in the brightness of an edge portion 1101 of the object O shown in
By making the plural lighting periods respectively have different lengths, the example shown in
By providing the three lighting periods (by dividing one lighting period into three), the dimension of an inclined portion (a portion of an edge portion other than a flat portion) shown in
By shortening the intervals between the lighting periods within one frame, the example shown in
Further, by gradually shortening the intervals between the lighting periods within one frame, plural flat portions of edge portions are made different in dimension from one another as shown in
When providing three or more lighting periods within one frame, the lighting periods may be set such that the intervals between the lighting periods within the frame concerned become longer gradually.
Such lighting periods can be simply set, for example, by gradually decreasing the value of Gt in calculating the start time BLp(x).
By calculating the start time BLp(x) with the value of Gt gradually decreasing, the lighting periods are determined such that the intervals between the lighting periods within one frame become longer gradually.
Specifically, the length of the interval BLe4 is longer than that of the interval BLe3.
Description will be made of effects brought about when the backlight is driven using the BL drive current shown in
By providing the plurality of lighting periods while shortening the intervals between the lighting periods within one frame, the change in the brightness of an edge portion 1171 of the object O shown in
By making the plural lighting periods respectively have different lengths, the example shown in
By providing the three lighting periods, the example shown in
By shortening the intervals between the lighting periods within one frame, the example shown in
By gradually lengthening the intervals between the lighting periods within one frame, plural flat portions of edge portions are made different in dimension from one another as shown in
By making a lighting period situated closer to the time coinciding with the center of the frame have a larger length, the plural flat portions of the edge portions are separated into a flat portion having a brightness closer to the brightness of the background B and a flat portion having a brightness closer to the brightness of the object O. This makes it possible to bring the brightness of a flat portion closer to the brightness of the background B or object O, thereby to further reduce the double-image blur. For example, the brightness of a flat portion can be brought closer to the brightness of the background B or object O than in cases where the lighting period having the largest length is used as the first or last lighting period (see
By contrast to
Even when number n of times of lighting is more than 2, the arrangement in which the lighting periods within one frame become longer gradually and the arrangement in which the lighting periods within one frame become shorter gradually are similar in effect to one another.
Description will be made of a liquid crystal display apparatus and a control method therefor according to Embodiment 2 of the present invention. Description of components and features common to Embodiments 1 and 2 will be omitted.
As shown in
The motion detecting unit 201 calculates the amount of motion of image between frames.
The motion adaptive pulse modulating unit 202 sets lighting periods of the backlight by using the amount of motion calculated by the motion detecting unit 201.
The following detailed description is directed to the process carried out by the motion detecting unit 201. Based on an input image signal, the motion detecting unit 201 calculates a motion determining value Sh indicative of the amount of motion of image between frames.
Initially, the motion detecting unit 201 calculates and stores the mean gradation value of the input image signal in a current frame (step S2001).
Subsequently, the motion determining unit 201 calculates the absolute value of a difference between the stored mean gradation value of the frame immediately preceding the current frame and the mean gradation value of the current frame (absolute difference value A) (step S2002).
Subsequently, the motion detecting unit 201 calculates the motion determining value Sh from the absolute difference value A calculated in step S2002 and a predetermined value Uth by using Expression 4 (step S2003).
Sh=A/Uth (Expression 4)
The value A decreases with decreasing amount of motion and, hence, the value Sh decreases with decreasing amount of mot ion. Stated otherwise, the value A increases with increasing amount of motion and, hence, the value Sh increases with increasing amount of motion.
Subsequently, the motion detecting unit 201 outputs the motion determining value Sh calculated in step S1023 to the motion adaptive pulse modulating unit 202 (step S2004).
There is no limitation to the above-described method of calculating the amount of motion (motion determining value Sh). Any method can be used as long as the amount of mot ion can be determined. For example, a method is possible such that the mean gradation value of each of frames inputted at predetermined intervals is sampled and stored and then the amount of motion is calculated based on the amount of a change in the mean gradation value thus stored. Instead of the mean gradation value, use may be made of a most frequent gradation value, a gradation value histogram, a brightness histogram, or the like to calculate the amount of mot ion. Alternatively, it is possible to detect a motion vector of input image signal between frames and then calculate the amount of motion from the magnitude of the motion vector. However, calculation of the amount of motion based on the amount of a change in mean gradation value, most frequent gradation value, gradation value histogram or brightness histogram does not require detailed analysis of the input image signal and hence can reduce the processing load.
The following detailed description is directed to the process carried out by the motion adaptive pulse modulating unit 202. The motion adaptive pulse modulating unit 202 determines number n of times of lighting, the length BLd(x) of each lighting period, and the start time BLp(x) of each lighting period. Specifically, number n is determined as in Embodiment 1, while BLd(x) and BLp(x) are determined using the motion determining value Sh calculated by the motion detecting unit 201.
Initially, the motion adaptive pulse modulating unit 202 determines number n of times of lighting in accordance with a set value of the BL light control value BLa (step S2101). Since the method of determining number n of times of lighting is the same as in Embodiment 1, description thereof is omitted.
Subsequently, the motion adaptive pulse modulating unit 202 determines the length BLd(x) of each lighting period (step S2102). In the present embodiment, the lighting periods are set such that the difference in length among the lighting periods within one frame becomes larger when the amount of motion is large than when the amount of motion is small. Specifically, the motion adaptive pulse modulating unit 202 calculates the emission brightness ratio h(x) of each lighting period by using the following Expression
The length BLd(x) of each lighting period is then calculated using the emission brightness ratio h(x) thus calculated and Expression 1.
In Expression 5, β(x) and α(x) are constants for determining h(x). The values β(x) and α(x) are predetermined such that the difference in length among the lighting periods within one frame becomes larger when the amount of motion is large than when the amount of motion is small. For example, when number n of times of lighting is 2, β(1) and α(1) are set equal to 3.5 and 0.2, respectively. With such values, h(2) and h(1) are 0.49 and 0.51, respectively, when Sh=0 (that is, when the input image signal is a signal indicative of a still image) and, hence, the emission brightness ratios of the respective lighting periods are substantially uniform. When Sh=1 (that is, when the input image signal is a signal indicative of a moving image), h(2) and h(1) are 0.2 and 0.8 respectively. Therefore, the emission brightness ratios of the respective lighting periods are values largely different from each other. As a result, the difference in length among the lighting periods within one frame becomes larger when the amount of motion is large than when the amount of motion is small.
While the present embodiment is directed to the arrangement in which the difference in length among the lighting periods within one frame becomes larger with increasing amount of motion (i.e., the arrangement in which the lengths of the lighting periods change continuously in accordance with the amount of motion), there is no limitation to this arrangement. For example, the lengths of the lighting periods may change stepwise in accordance with the amount of motion.
Subsequently, the motion adaptive pulse modulating unit 202 determines the start time BLp(x) of each lighting period by using Expression 2, as in Embodiment 1 (step S2103). In the present embodiment, the start time BLp(x) is determined such that the intervals between the lighting periods within one frame become shorter when the amount of motion is large than when the amount of motion is small. Further, the start time BLp(x) is determined such that the extinction periods become more uniform in length when the amount of motion is small than when the amount of motion is large. Specifically, the value of Gt is determined using Expression 7 in step S2103.
Gt=n+γ×Sh (Expression 7),
where γ is a constant which determines the amount of a change in Gt value relative to the amount of a change in Sh value. According to Expression 7, Gt increases with increasing amount of motion (Sh). Therefore, Gt is brought closer to n with decreasing amount of motion (Sh). As a result, the intervals between the lighting periods within one frame become shorter with increasing amount of motion. The extinction periods become more uniform in length with decreasing amount of motion.
While the present embodiment is directed to the arrangement in which the intervals between the lighting periods change continuously in accordance with the amount of motion, there is no limitation to this arrangement. For example, the intervals between the lighting periods may change stepwise in accordance with the amount of motion.
When BLd(x) and BLp(x) are determined according to the above-described method in response to input of an input image signal indicative of a largely moving image, the resulting BL drive waveform is similar to that shown in
On the other hand, when BLd(x) and BLp(x) are determined according to the above-described method in response to input of an input image signal indicative of an image in small motion, the resulting BL drive waveform is similar to that shown in
Subsequently to step S2103, the motion adaptive pulse modulating unit 202 outputs n number of lighting period lengths BLd(x) which have been calculated in step S2102 and n number of lighting period start times BLp(x) which have been calculated in step S2103 to the backlight control unit 102 (step S2104).
According to the present embodiment, the lighting periods are set using the amount of motion of image between frames, as described above. By so doing, the flicker disturbance, motion blur and double-image blur can be reduced more appropriately in accordance with input image signals.
Specifically, when the amount of motion of an image is large, the motion blur and the double-image blur make the viewer feel more disturbed than the flicker disturbance. When the amount of motion of an image is small, the flicker disturbance makes the viewer feel more disturbed than the motion blur and the double-image blur. As described above, when the amount of motion of an image is large, the present embodiment increases the difference in length among the lighting periods within one frame while shortening the intervals between the lighting periods within one frame. Therefore, the motion blur and the double-image blur can be reduced intensively. When the amount of motion is small, the present embodiment makes the lighting periods more uniform in length and also makes the extinction periods more uniform in length. Therefore, the flicker disturbance can be reduced intensively.
While the present embodiment is configured to determine the lengths of the lighting periods and the intervals between the lighting periods based on the amount of motion, only one of these factors may be determined based on the amount of motion.
The amount of motion may be calculated on a block-by-block basis. The lighting periods of the light sources may be set on a block-by-block basis by using the amount of motion of the block concerned. Such an arrangement makes it possible to reduce the flicker disturbance, motion blur and double-image blur more appropriately.
Specifically, the flicker disturbance, motion blur and double-image blur can be reduced on a block-by-block basis in harmonization with the characteristic of the image displayed in the block concerned.
In Embodiment 1, number n of times of lighting is determined in accordance with the set value of the BL light control value BLa. In the present embodiment, the number of times of lighting (number n of times of lighting) is determined based on the format (specifically the frame rate) of an input image signal. Description of components and features common to Embodiments 1 and 3 will be omitted.
A liquid crystal display apparatus according to the present embodiment doubles the frame rate of an input image signal to display an image based on the input image signal when the frame rate of the input image signal is low. Specifically, the display control unit 105 of the present embodiment drives the liquid crystal panel with a drive frequency twice as high as the frame rate of the input image signal when the frame rate of the input image signal is low. Therefore, when the frame rate of the input image signal is low, the operation of displaying each frame of the input image signal twice successively is performed with a frequency twice as high as the frame rate of the input image signal. For example, when the frame rate of the input image signal is 24 Hz, the liquid crystal panel is driven with a drive frequency of 48 Hz.
The liquid crystal display apparatus according to the present embodiment fails to change the frame rate in displaying the image based on the input image signal when the frame rate of the input image signal is high. For example, when the frame rate of the input image signal is 60 Hz, the liquid crystal panel is driven with a drive frequency of 60 Hz.
Whether the frame rate of the input image signal is high or low can be determined, for example, by comparing the frame rate of the input image signal to a predetermined frame rate. Specifically, when the frame rate of the input image signal is lower than the predetermined frame rate (e.g., 30 Hz), the frame rate of the input image signal can be determined to be low. When the frame rate of the input image signal is higher than the predetermined frame rate, the frame rate of the input image signal can be determined to be high.
The liquid crystal display apparatus need not necessarily be imparted with such a frame rate changing function.
With such a configuration, when the frame rate of the input image signal is low, the frequency of switching of display image is low and, hence, the poor responsiveness of liquid crystal elements is hard to reflect on the screen (that is, the motion blur and the double-image blur are hard to appear). On the other hand, the flicker disturbance makes the viewer feel more disturbed. For example, when the frame rate of the input image signal is 24 Hz, the drive frequency for the liquid crystal panel is 48 Hz. However, each frame is displayed twice successively and, hence, switching of display image is performed with a frequency as low as 24
Hz.
In such a case, it is more important to reduce the flicker disturbance than the motion blur and double-image blur.
For this purpose, the present embodiment reduces the flicker disturbance more preferentially when the frame rate of the input image signal is low than when the frame rate of the input image signal is high. Specifically, the number of lighting periods within one frame is made larger when the frame rate of the input image signal is low than when the frame rate of the input image signal is high.
The following description is directed to specific examples.
In the present embodiment, the pulse modulating unit 101 determines number n of times of lighting such that “liquid crystal panel drive frequency×n lower limit flicker frequency”. The lower limit flicker frequency is a threshold value for determining whether or not the flicker disturbance makes the viewer feel disturbed. In the present embodiment, the lower limit flicker frequency is a value determined by subjective evaluation. When the above-described frame rate changing is not carried out, the above-noted expression for calculating number n of times of lighting can be rewritten as “input image signal frame rate×n lower limit flicker frequency”.
The pulse modulating unit 101 determines the lighting periods such that the extinction periods are made uniform in length (length of time from the ending time of the lighting period immediately preceding the current lighting period to the start time of the current lighting period) when the frame rate of the input image signal is low. The pulse modulating unit 101 may either acquire the result of determination as to whether or not the frame rate of the input image signal is low from the display control unit 105 or make such determination separately from the determination made by the display control unit 105.
The following is an exemplary relationship among the input image signal, frame rate, number n of times of lighting, Gt, and lower limit flicker frequency.
As can be seen from the relationship noted above, by increasing the number of times of lighting based on determination that the frame rate of 24 Hz is low, the flicker disturbance can be reduced precisely. Further, by making the intervals between the extinction periods uniform based on the determination that the frame rate is low, the flicker disturbance can be reduced intensively.
On the other hand, by setting Gt>n based on determination that the frame rate of 60 Hz is high, the motion blur and the double-image blur can be reduced intensively as in Embodiment 1.
The image signals 1 and 2 are different in lower limit flicker frequency from each other because the image sources of the respective signals are different from each other. For example, a subjectively preferred sensation of flicker differs between the case where the image source is a film source and the case where the image source is a TV source or a like source.
According to the present embodiment described above, the number of lighting periods within one frame is made larger when the frame rate of the input image signal is low than when the frame rate of the input image signal is high. By so doing, the flicker disturbance is reduced more preferentially when the frame rate of the input image signal is low than when the frame rate of the input image signal is high.
The value of the lower limit flicker frequency is not limited to those noted. The value of the lower limit flicker frequency may be set appropriately depending on the purpose and the like.
There is no limitation to the above-described method of determining number n of times of lighting. For example, it is possible to provide in advance a table indicative of number n of times of lighting for each frame rate or for each frame rate range and then determine number n of times of lighting by using the table.
The present embodiment is directed to a case where the number of times of lighting (number n of times of lighting) is determined based on the drive frequency for the liquid crystal panel. Description of components and features common to Embodiments 1 and 4 will be omitted.
When the drive frequency for the liquid crystal panel is low, the frequency of switching of display image is low and, hence, the poor responsiveness of liquid crystal elements is hard to reflect on the screen (that is, the motion blur and the double-image blur are hard to appear). On the other hand, the flicker disturbance makes the viewer feel more disturbed.
In such a case, it is more important to reduce the flicker disturbance than the motion blur and double-image blur.
For this purpose, the present embodiment reduces the flicker disturbance more preferentially when the liquid crystal panel drive frequency is low than when the liquid crystal panel drive frequency is high. Specifically, the number of lighting periods within one frame is made larger when the liquid crystal panel drive frequency is low than when the liquid crystal panel drive frequency is high.
The following description is directed to specific examples.
In the present embodiment, the pulse modulating unit 101 determines number n of times of lighting such that “liquid crystal panel drive frequency×n≧lower limit flicker frequency”.
The pulse modulating unit 101 also determines the lighting periods such that the extinction periods are made uniform in length when the liquid crystal panel drive frequency is low.
Whether or not the liquid crystal panel drive frequency is low can be determined, for example, by comparing the liquid crystal panel drive frequency to a predetermined drive frequency. Specifically, when the liquid crystal panel drive frequency is lower than the predetermined frequency (e.g., 60 Hz), the liquid crystal panel drive frequency can be determined to be low. When the liquid crystal panel drive frequency is equal to or higher than the predetermined frequency, the liquid crystal panel drive frequency can be determined to be high.
The following is an exemplary relationship among the input image signal, liquid crystal panel drive frequency, number n of times of lighting, Gt, and lower limit flicker frequency.
As can be seen from the relationship noted above, by increasing the number of times of lighting based on determination that the drive frequencies of 48 Hz and 50 Hz are low, the flicker disturbance can be reduced precisely. Further, by making the intervals between the extinction periods uniform based on the determination that the drive frequencies are low, the flicker disturbance can be reduced intensively.
On the other hand, by setting Gt>n based on determination that the frame rate is high when the drive frequency is 60 Hz, the motion blur and the double-image blur can be reduced intensively as in Embodiment 1.
According to the present embodiment described above, the number of lighting periods within one frame is made larger when the display panel drive frequency is low than when the display panel drive frequency is high. By so doing, the flicker disturbance can be reduced more preferentially when the display panel drive frequency is low than when the display panel drive frequency is high.
There is no limitation to the above-described method of determining number n of times of lighting. For example, it is possible to provide in advance a table indicative of number n of times of lighting for each display panel drive frequency or for each drive frequency range and then determine number n of times of lighting by using the table.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2012-080930, filed on Mar. 30, 2012, which is hereby incorporated by reference herein in its entirety.
Number | Date | Country | Kind |
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2012-080930 | Mar 2012 | JP | national |
This application is a divisional of application Ser. No. 13/792,631, filed Mar. 11, 2013 the entire disclosure of which is hereby incorporated by reference.
Number | Date | Country | |
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Parent | 13792631 | Mar 2013 | US |
Child | 15132331 | US |