JP2020046474A - Projection control device and method, projection device - Google Patents

Abstract

To provide a projection device having a function for performing resolution enhancement by pixel shift while avoiding an increase in cost, and a function for suppressing a degradation in image quality caused by disclination.SOLUTION: A projection control device for the projection device using a liquid crystal element having a plurality of pixels comprises: a generation unit for generating a plurality of sub-frames from one frame of an input image; and a conversion unit for converting a gradation value of the plurality of sub-frames to obtain the gradation value used for controlling driving of the liquid crystal element. The conversion unit is capable of applying a different conversion characteristic to each of the plurality of sub-frames, and a difference among the conversion characteristics applied to each sub-frame during pixel shift processing, which executes projection so as to shift a projection position of the plurality of sub-frames, is smaller than the difference among the conversion characteristics applied to each sub-frame when the pixel shift processing is not performed.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a projection control device and method, and a projection device.

  In general, in a digital driving method of a liquid crystal element, a pixel having brightness corresponding to a gradation value is obtained by changing the length of an on period and an off period of each pixel of the liquid crystal element according to the gradation value. Further, as one of such digital driving methods, there is a subfield driving method in which a frame display period is time-divided and an arbitrary gradation is expressed by a combination of a plurality of subfields having different light emitting periods. In the subfield driving method, in one adjacent pixel (two pixels adjacent to each other by a liquid crystal element), one pixel is in an ON period and the other pixel is in an OFF period in one frame period. As described above, when the ON period and the OFF period overlap with each other in time, that is, when a predetermined voltage is applied to one of the adjacent pixels and the other voltage is not applied to the other pixel in the same period, so-called disclination occurs. Occurs, and the brightness of the pixel during the ON period decreases.

  Patent Document 1 proposes a configuration for reducing the influence of such disclination. According to Patent Literature 1, a frame is driven at a double speed, and a gradation value of one frame is made lower than a gradation value of the other frame to drive a liquid crystal element. By doing so, the effect of disclination is suppressed.

  On the other hand, in recent years, a pixel shift technique has been known as a technique for improving the spatial resolution of an image display device. Patent Literature 2 discloses an image shift technique for realizing high resolution by shifting an optical path of an image to be displayed and displaying the shifted image. In the image shift technique, based on an input image, a plurality of sub-frames composed of a plurality of thinned-out images having different thinning-out positions are generated, and a projection position of each sub-frame is shifted by 1/2 pixel and displayed, thereby displaying a display element. To achieve higher resolution than that provided by. As described above, in the pixel shift technique, a plurality of subframes are generated from one input image based on the pixel shift position, and the subframes are sequentially displayed according to the pixel position to improve the resolution.

JP 2017-053945 A JP 2011-203460 A

  However, if the disclination reduction technology disclosed in Patent Literature 1 is combined with the pixel shift technology disclosed in Patent Literature 2, it is necessary to drive the liquid crystal element at high speed. For example, in a pixel shift technique in which a projection position is shifted from one input image by using two thinned images, projection is performed at a double speed because two subframes are projected during one frame period. Further, even in the processing for reducing disclination, it is necessary to drive the frame to be projected at double speed. Therefore, if an attempt is made to combine the disclination reduction technique and the pixel shift technique disclosed in Patent Document 2, processing at a quadruple speed is required. That is, when the technology for reducing disclination is applied to a projection device using the pixel shift technology, high bandwidth image processing and high-speed driving of the display element are required, resulting in a high cost of the display device. there were.

  An object of the present invention is to provide a projection apparatus having a function of increasing the resolution by pixel shift and a function of suppressing a decrease in image quality due to disclination while avoiding an increase in cost. I do.

The projection control device according to one aspect of the present invention includes:
A projection control device for a projection device using a liquid crystal element having a plurality of pixels,
Generating means for generating a plurality of subframes from one frame of the input image;
Converting means for converting the gradation values of the plurality of sub-frames to obtain a gradation value used to control the driving of the liquid crystal element,
The conversion means can apply different conversion characteristics to each of the plurality of sub-frames, and apply the conversion characteristics to each of the plurality of sub-frames when performing a pixel shift process of performing projection so as to shift the projection positions of the plurality of sub-frames. The difference between the conversion characteristics to be performed is smaller than the difference between the conversion characteristics applied to each subframe when the pixel shift process is not performed.

  According to the present invention, it is possible to provide a projection apparatus having a function of increasing the resolution by pixel shift and a function of suppressing a decrease in image quality due to disclination while avoiding an increase in cost. Become.

FIG. 2 is a block diagram showing a configuration example of a liquid crystal projector 100. 2A is a cross-sectional view of the liquid crystal element 151, FIG. 2B is a diagram showing a plurality of subfield periods in one frame period, and FIG. FIG. 6 is a diagram illustrating an example of a driving pattern of all gradations by a subfield driving method. FIG. 2 is a diagram illustrating a pixel arrangement according to the first embodiment. (A) A diagram showing the response characteristics of the liquid crystal when switching from full white display to black and white display, and (b) a diagram showing a change in brightness when switching from full white display to black and white display. (A) A diagram showing the response characteristics of the liquid crystal when switching from all black display to black and white display, and (b) a diagram showing a change in brightness when switching from all black display to black and white display. FIG. 2 is a block diagram showing an example of the internal configuration of an image processing unit. (A) A schematic diagram for explaining a sampling position with respect to an input image, and (b) a schematic diagram for explaining a projected position of a pixel shift. 4A and 4B are block diagrams illustrating an example of an internal configuration of a gradation conversion unit. 7A to 7C are diagrams illustrating gain processing performed by a gradation conversion unit. 5 is a flowchart illustrating projection control according to the first embodiment. FIG. 8 is a diagram for explaining the effect of a difference in gain coefficient used in the gradation conversion unit and the effect of pixel shift on higher resolution. FIG. 4 is a diagram illustrating a reduction in visibility of dark lines due to disclination due to pixel shift. 9 is a flowchart illustrating projection control according to the second embodiment. 9 is a flowchart illustrating projection control according to the third embodiment.

  Hereinafter, some embodiments of the present invention will be described with reference to the accompanying drawings.

<First embodiment>
The liquid crystal projector as the projection device according to the first embodiment controls on / off of a pixel shift process and a gain coefficient according to the resolution of an input image, thereby suppressing a decrease in image quality due to disclination, and achieving high resolution by pixel shift. Realization. In the pixel shift processing, a plurality of subframes (for example, two thinned images) having different thinning positions are generated in one frame period of the input image, and the projection positions of these subframes are set to a predetermined amount (for example, 例 え ば in the horizontal and vertical directions). (Pixel) for display. The thinning-out position for generating each sub-frame corresponds to the projection position of each sub-frame. According to such a pixel shift process, it is possible to realize a higher resolution than the resolution of the display element. On the other hand, in order to suppress deterioration in image quality due to disclination, the period of one frame of the input image is divided into a plurality of periods (for example, two periods), and a sub-frame is displayed by switching a gain coefficient for each period. I do. In this case, the same image as the input image is used as the subframe. When these pixel shifts and disclination reduction are combined, for example, it is necessary to project each of two thinned images using two different gain coefficients. As a result, quadruple speed processing is required. On the other hand, since the liquid crystal projector according to the first embodiment always operates at double speed processing, high-band image processing and high-speed driving of the display element are not required, and the cost can be reduced. Hereinafter, a specific configuration and method will be described.

  FIG. 1 is a block diagram illustrating an overall configuration of a liquid crystal projector 100 according to the first embodiment. The liquid crystal projector 100 according to the first embodiment includes a CPU 110, a ROM 111, a RAM 112, an operation unit 113, an image input unit 130, and an image processing unit 140. The liquid crystal projector 100 includes a liquid crystal control unit 150, liquid crystal elements 151R, 151G, 151B, a light source control unit 160, a light source 161, a color separation unit 162, a color synthesis unit 163, a pixel shift element 170, a shift control unit 171, an optical system control unit. 180, and a projection optical system 181.

  CPU 110 controls each operation block of liquid crystal projector 100 by executing a program stored in ROM 111 or RAM 112. The ROM 111 stores a control program describing the processing procedure of the CPU 110. The RAM 112 functions as a work memory for the CPU 110, and temporarily stores control programs and data.

  The operation unit 113 receives a user instruction and transmits an instruction signal to the CPU 110. The operation unit 113 includes, for example, switches, buttons, dials, and the like. The operation unit 113 may include, for example, a signal receiving unit (such as an infrared receiving unit) that receives a signal from a remote controller, and may be configured to transmit a predetermined instruction signal to the CPU 110 based on the received signal. . The CPU 110 receives control signals input from the operation unit 113 and the communication unit 193, and controls each operation block of the liquid crystal projector 100.

  The image processing unit 140 has, for example, a microprocessor for image processing, performs processing for changing the number of frames, the number of pixels, the image shape, and the like on the image signal received from the image input unit 130 and transmits the processed signal to the liquid crystal control unit 150. . Note that the image processing unit 140 does not necessarily need to have a configuration including a dedicated microprocessor. For example, the CPU 110 may execute the same processing as the image processing unit 140 using a program stored in the ROM 111. . Further, the image processing unit 140 can execute functions such as frame thinning processing, frame interpolation processing, resolution conversion (scaling) processing, and distortion correction processing (keystone correction processing). Further, the image processing unit 140 can also perform the above-described change processing on an image reproduced by the CPU 110, in addition to the image signal received from the image input unit 130. Details of the image processing performed by the image processing unit 140 will be described later.

  The liquid crystal control unit 150 controls the voltage applied to the liquid crystal of each pixel of the liquid crystal elements 151R, 151G, and 151B based on the image signals processed by the image processing unit 140, and controls the liquid crystal elements 151R, 151G, and 151B. To adjust the reflectance or transmittance. That is, the liquid crystal control unit 150 controls the application time of the ON voltage / OFF voltage to each of the plurality of pixels of the liquid crystal element 151 based on the gradation value of the input image. In the present embodiment, sub-field driving is performed. Details of the subfield driving will be described later. The liquid crystal element 151 </ b> R is a liquid crystal element corresponding to red, and is a liquid crystal element output from the light source 161 and separated into red (R), green (G), and blue (B) by the color separation unit 162. Adjust the light transmittance. The liquid crystal element 151G is a liquid crystal element corresponding to green, and adjusts the transmittance of green light among the R, G, and B lights separated by the color separation unit 162. The liquid crystal element 151B is a liquid crystal element corresponding to blue, and adjusts the transmittance of blue light among the R, G, and B lights separated by the color separation unit 162.

  The light source control unit 160 has a microprocessor dedicated to light source control, and controls on / off and brightness of the light source 161. However, the light source control unit 160 does not necessarily have to have a dedicated microprocessor. For example, the CPU 110 may execute the same processing as the light source control unit 160 by a program stored in the ROM 111. . The light source 161 outputs light for projecting an image on a screen (not shown). For example, a laser, an LED, a halogen lamp, a xenon lamp, a high-pressure mercury lamp, or the like can be used as the light source.

  The color separation unit 162 includes, for example, a dichroic mirror and / or a prism, and separates light output from the light source 161 into red (R), green (G), and blue (B). When a laser corresponding to each color, an LED, or the like is used as the light source 161, the color separation unit 162 can be omitted. The color combining unit 163 includes, for example, a dichroic mirror and / or a prism, and combines red (R), green (G), and blue (B) light transmitted through the liquid crystal elements 151R, 151G, and 151B. The light combined by the color combining unit 163 is sent to the pixel shift element 170. At this time, the liquid crystal elements 151 </ b> R, 151 </ b> G, and 151 </ b> B are controlled by the liquid crystal control unit 150 so as to have a light transmittance corresponding to the image input from the image processing unit 140. Therefore, when the light combined by the color combining unit 163 is projected on the screen by the projection optical system 181, an image corresponding to the image input by the image processing unit 140 is displayed on the screen.

  The shift control unit 171 controls the pixel shift element 170 by changing the voltage or current applied to the pixel shift element 170 in synchronization with the timing at which the liquid crystal control unit 150 drives the liquid crystal element 151, and controls the color synthesis unit. The optical path of the combined light from the 163 is shifted. The pixel shift element 170 is not limited as long as it can shift the optical path of the combined light from the color combining section 163. For example, a parallel flat plate made of a transparent optical member may be used. Alternatively, an element in which a liquid crystal and a birefringent material are bonded may be used. In the present embodiment, the pixel shift element 170 operates so that the display period of one frame of the input image is divided into the first frame period and the second frame period, and the optical paths are different in the display in each period. A method for generating the first and second sub-frames displayed on the liquid crystal element 151 in the first and second frame periods will be described later.

  The optical system control unit 180 has a dedicated microprocessor and controls the projection optical system 181. However, the optical system control unit 180 does not necessarily need to have a dedicated microprocessor. For example, the CPU 110 may execute the same processing as the optical system control unit 180 by a program stored in the ROM 111. The projection optical system 181 includes a plurality of lenses and a lens driving actuator, and projects the combined light output from the pixel shift element 170 onto a screen. The projection optical system 181 can perform enlargement, reduction, and focus adjustment of a projected image by driving a lens with an actuator.

  The communication unit 193 is connected for communication with an external device, and receives a control signal, still image data, moving image data, and the like from the external device. Examples of the communication system of the communication unit 193 include a wireless LAN, a wired LAN, a USB, and Bluetooth (registered trademark), but are not particularly limited. If the terminal of the image input unit 130 is, for example, an HDMI (registered trademark) terminal, the terminal may perform CEC (Consumer Electronics Control) communication via the terminal. Here, the external device may be any device such as a personal computer, a camera, a mobile phone, a smartphone, a hard disk recorder, a game machine, and a remote controller as long as it can communicate with the liquid crystal projector 100. .

  Note that the image processing unit 140, the liquid crystal control unit 150, the light source control unit 160, the shift control unit 171, and the optical system control unit 180 of the present embodiment are singular or plural which can perform the same processing as these blocks. There may be a microprocessor. Alternatively, for example, the program stored in the ROM 111 may cause the CPU 110 to execute the same processing as the above blocks.

  FIG. 2A is a diagram illustrating a cross-sectional structure of the liquid crystal elements 151R, 151G, and 151B (hereinafter, liquid crystal element 151). The liquid crystal element 151 has a reflective structure and includes an AR coat film 101, a glass substrate 102, a common electrode 103, an alignment film 104, a liquid crystal layer 105, an alignment film 106, a pixel electrode 107, and a Si substrate 108. Note that the liquid crystal element 151 may have a transmissive structure.

  The liquid crystal control unit 150 drives each pixel of the liquid crystal element 151 by a subfield driving method. That is, one frame period is divided into a plurality of subfield periods on a time axis, and ON (application) and OFF (non-application) of a predetermined voltage to a pixel are controlled for each subfield period according to grayscale data. A gradation is formed (displayed) on the pixel. One frame period is a period in which one frame image is displayed on the liquid crystal element. The liquid crystal projector 100 of the present embodiment divides a display period of one frame of an input image into two periods, and projects and displays a sub-frame using each period as one frame period. For example, if the frame frequency of the input image is 60 Hz, the liquid crystal projector 100 drives the liquid crystal element at 120 Hz, and one frame period is 8.33 ms. Turning on and off the predetermined voltage can be referred to as application of the first voltage (predetermined voltage) and application of the second voltage lower than the first voltage.

  Hereinafter, the subfield driving according to the present embodiment will be described. The liquid crystal control unit 150 may be constituted by a computer, and the following subfield driving may be controlled according to a liquid crystal driving program as a computer program.

  FIG. 2B shows the division of one frame period into a plurality of subfield periods (bit lengths) in the subfield driving of the present embodiment. The numerical value described on each subfield indicates the time weight of the subfield within one frame period. In the present embodiment, 96 gradations can be expressed. In the description here, the period of the time weight “1 + 2 + 4 + 8” is referred to as the A subfield period (first period), and the bit indicating the gray scale expressed in binary in the A subfield period is referred to as the lower bit. Further, the ten subfield periods with the time weight of 8 are collectively referred to as a B subfield period (second period), and a bit indicating a gray scale expressed in binary in the B subfield period is referred to as an upper bit. The time weight 1 corresponds to 0.087 ms (8.33 ms / 96), and the time weight 8 corresponds to 0.69 ms (8.33 ms × 8/96).

  Further, the above-described subfield period in which the predetermined voltage is turned on (the first voltage is applied) is referred to as an on period, and the predetermined voltage is turned off (the second voltage lower than the first voltage is applied). Is called an off period. FIG. 2C shows the gradation values and the driving of the pixels in the A subfield period shown in FIG. 2B. The vertical axis indicates the gradation, and the horizontal axis indicates one frame period. In the A subfield period, 16 tones of 1 to 16 are expressed. In the figure, a white subfield period indicates an ON period in which a predetermined voltage is applied so that a pixel is in a white display state, and a black subfield period is an OFF period in which a predetermined voltage is turned off so that a pixel is in a black display state. Is shown.

  FIG. 3 shows a subfield driving pattern (hereinafter, referred to as a driving pattern) in the A subfield period and the B subfield period (lower and upper bits) in the present embodiment. The drive pattern shown in FIG. 3 expresses gradation values of 1 to 96. In this driving pattern, an A subfield period (lower bit) is arranged at the time center of one frame period, and before and after that, a B subfield period (upper bit) is divided into 1SF to 5SF and 6SF to 10SF. Have been. That is, the B subfield period is divided into two, and each of the divided periods includes two or more subfield periods.

  In the driving pattern shown in FIG. 3, attention is paid to a case where two adjacent pixels (adjacent pixels) in the liquid crystal element are displayed with two adjacent gray levels (adjacent gray levels), for example, 48 gray levels and 49 gray levels. In this case, the entire A subfield period is an on period at 48 gray scales and an off period at 49 gray scales. In the 48 gray scale, 1SF, 4SF, 5SF, 6SF, 7SF, and 10SF in the B subfield period are off periods, and 2SF, 3SF, 8SF, and 9SF are on periods. On the other hand, in the 49th gradation, 1SF, 5SF, 6SF, and 10SF in the B subfield period are off periods, and 2SF, 3SF, 4SF, 7SF, 8SF, and 9SF are on periods. When such an adjacent gray scale is displayed on an adjacent pixel, a period in which the ON period and the OFF period overlap (hereinafter, an ON / OFF adjacent period) occurs in the adjacent pixel. Specifically, when displaying 48 gray scales and 49 gray scales on adjacent pixels, 4SF and 7SF in the B subfield period are the on / off adjacent periods.

  In the drive pattern shown in FIG. 3, focusing on the 48th gray scale and the 49th gray scale, the on / off adjacent period continues in the B subfield period as one time subfield period of 8 (= 0. 69 ms). A plurality (two) of the ON / OFF adjacent periods, which are one subfield period, are separated from each other with the A subframe period therebetween. This is the same for the other adjacent gradations of 16 and 17 gradations, 32 and 33 gradations, 64 and 65 gradations, 80 and 81 gradations, and the like.

  Next, the mechanism of occurrence of disclination in the subfield driving method according to the present embodiment will be described.

  First, when the pixels arranged in a matrix as shown in FIG. 4 are switched from the all white display state to the black and white display state in which white and black are alternately displayed for each pixel line, The response characteristics of the liquid crystal when switching to the display state will be described. The 4 × 4 pixels shown in FIG. 4 are arranged in a matrix at a pixel pitch of 8 μm. In the all-white display state, both the pixels on the A pixel line and the pixels on the B pixel line in FIG. 4 display white. In the monochrome display state, the pixels on the A pixel line are switched from the white display state to the black display state, and the pixels on the B pixel line are maintained in the white display state.

  FIG. 5A shows a response characteristic of the liquid crystal. The horizontal axis indicates the position of the pixel, and the vertical axis indicates the brightness (however, the ratio when white is 1) of each pixel. 0 to 8 μm on the horizontal axis indicates the pixels on the A pixel line shown in FIG. 4, and 8 to 16 μm indicate the pixels on the B pixel line. A plurality of curves indicate brightness for each elapsed time (0.3 ms, 0.6 ms, 1.0 ms, 1.3 ms) when the switching point from the all white display state to the black and white display state is 0 ms.

  As described above, the pixels on the A pixel line are switched from the white display state to the black display state, but the pixels on the A pixel line are relatively uniformly bright without being affected by disclination due to the relationship of the direction of the pretilt angle in the liquid crystal. Changes (darkens). On the other hand, in the pixels on the B pixel line, no disclination has occurred in the all white display state. However, the pixels on the B pixel line are affected by the disclination as the monochrome display state is reached (as the pixels on the A pixel line are displayed black). That is, the brightness curve of the pixels on the B pixel line gradually becomes distorted with the passage of time, and particularly, the brightness curve becomes dark around 12 μm to 16 μm (dark lines appear).

  In general, a gamma curve (gamma characteristic) that determines a driving gradation of a liquid crystal element with respect to an input gradation is created on the assumption that a response characteristic when the gradation is changed while displaying the same gradation on the entire surface of the liquid crystal element. . When the same gradation is displayed on the entire screen of the liquid crystal element, no disclination occurs. When the liquid crystal element is driven using the gamma curve created in this way, disclination occurs in a black-and-white display state, and only a brightness lower than the original brightness according to the gamma curve can be obtained.

  FIG. 5B shows a change in brightness depending on the presence or absence of disclination when the liquid crystal element is switched from the all white display state to the black and white display state. The horizontal axis indicates the elapsed time from the switching time, and the vertical axis indicates the integrated value of the total brightness of the pixels of the A and B pixel lines (hereinafter simply referred to as brightness, and the ratio when the all white display state is 1). ). The brightness is shown as a ratio when the all white display state is set to 1. The brightness of the pixels in the A pixel line changes with characteristics close to the response characteristics shown in the vicinity of 1 to 6 μm in FIG. 5A, and when disclination does not occur (“no disclination”), the brightness of the B pixel line changes. The brightness of the pixels is such that white is displayed with 100% brightness over the entire area. In this case, since the A pixel line maintains “1” from “0” and the B pixel line maintains “1”, the brightness changes from “1” to “0.5”, and the amount of decrease in brightness is 0.5. On the other hand, as shown in FIG. 5A, when disclination occurs (“disclination is present”), the amount of decrease in brightness is when disclination does not occur (“no disclination”). It becomes larger than the amount of decrease in brightness.

  On the other hand, when switching from the all-black display state to the black-and-white display state, for example, both the pixels of the A pixel line and the pixels of the B pixel line shown in FIG. The pixels on the B pixel line are set to a white display state. FIG. 6A shows the response characteristics of the liquid crystal at this time. The horizontal axis indicates the position of the pixel, and the vertical axis indicates the brightness (however, the ratio when white is 1) of each pixel. 0 to 8 μm on the horizontal axis indicates the pixels on the A pixel line shown in FIG. 4, and 8 to 16 μm indicate the pixels on the B pixel line. A plurality of curves indicate brightness for each elapsed time (0.3 ms, 0.6 ms, 1.0 ms, 1.3 ms) when the switching point from the all black display state to the black and white display state is 0 ms.

  As described above, the pixels on the B pixel line are switched from the black display state to the white display state. However, the pixels on the B pixel line gradually change over time due to the disclination after the white display state. The brightness curve becomes irregular. And it becomes dark especially in the vicinity of 12 μm to 16 μm (dark lines appear). In addition, the irregular shape of the brightness curve becomes remarkable with the passage of time.

  As described above, in general, the gamma curve (gamma characteristic) that determines the driving gradation of the liquid crystal element with respect to the input gradation changes while displaying the same gradation on the entire surface of the liquid crystal element where disclination does not occur. It is created on the premise of the response characteristics in the case where it is performed. Therefore, when a liquid crystal element is driven using such a gamma curve, disclination occurs in a black-and-white display state, and only a brightness lower than the original brightness according to the gamma curve can be obtained.

  FIG. 6B shows a change in brightness depending on the presence or absence of disclination when the liquid crystal element is switched from the all black display state to the black and white display state. The horizontal axis indicates the elapsed time from the switching point, and the vertical axis indicates the integrated value of the total brightness of the pixels of the A and B pixel lines (hereinafter, simply referred to as brightness, and the ratio when the all white display state is 1). ). When the disclination does not occur (“no disclination”), the brightness is such that the pixels on the A pixel line are always in the black display state, and the pixels on the B pixel line are switched from the black display state to the white display state. It shows the change in brightness when going. On the other hand, when disclination occurs ("discontinuation is present"), the change in the integrated value of the sum of the brightness of the pixels of the A pixel line and the B pixel line shown in FIG. Is shown.

  In FIG. 6B, when disclination occurs, the amount of increase in brightness over time is smaller than when disclination does not occur. In other words, the longer the time during which disclination occurs after switching from the all-black display state to the black-and-white display state, the darker is the case where no disclination occurs.

  A case will be described in which pixels on the A pixel line display 48 tones and pixels on the B pixel line display 49 tones using the drive pattern shown in FIG. When this drive pattern is used, during the period in which disclination occurs, 4SF in the B subfield period in which the pixels in the A pixel line are in a black display state and the pixels in the B pixel line are in a white display state in a disclination occurrence display state. And 7SF. The 3SF before the 4SF is a period in which the pixels on the A pixel line and the pixels on the B pixel line are both in a white display state and no disclination occurs. The response characteristic of the liquid crystal in the 4SF is a characteristic corresponding to “with disclination” in FIG. 5B. Since 3SF is in the all-white display state, 100% of the brightness is output, and disclination occurs during 0.69 ms of 4SF. Therefore, the start time of 4SF corresponds to 0 ms in FIG. 5B, and the end time of 4SF corresponds to 0.69 ms. At this time, the brightness decreases to 0.62 from 0.67 when no disclination occurs.

  In addition, the response characteristic of the liquid crystal in 7SF, which is a subfield period in which another disclination occurs, is a characteristic corresponding to “discontinuation is present” in FIG. 6B. In 6SF, the brightness is 0% because of the all-black display state, and disclination occurs within 0.69 ms of 7SF. Therefore, the start time of 7SF corresponds to 0 ms in FIG. 6B, and the end time of 7SF corresponds to 0.69 ms. At this time, the brightness decreases to 0.18 from 0.25 when no disclination occurs. The sum of brightness when disclination does not occur in 4SF and 7SF is 0.92 (= 0.67 + 0.25), whereas the sum of brightness when disclination occurs is 0.80 (= 0.62 + 0.18). As described above, on the basis of the gamma characteristic created on the assumption that the entire surface has the same gradation, the ratio becomes dark to 87% (= 0.80 / 0.92) in the disclination occurrence display state.

  Next, a case where another adjacent gray scale is displayed will be described. In the present embodiment, a case will be described in which the pixels on the A pixel line display 16 tones and the pixels on the B pixel line display 17 tones using the drive pattern shown in FIG. When the gradation data is used, the period in which the disclination occurs is in the B subfield period in which the pixels in the A pixel line are in a black display state and the pixels in the B pixel line are in a white display state in a disclination occurrence display state. 3SF and 8SF. In 2SF before 3SF, both the pixels on the A pixel line and the pixels on the B pixel line are in the black display state, and this is a period in which disclination does not occur. The response characteristic of the liquid crystal in the 3SF is a characteristic corresponding to “with disclination” in FIG. 6B. In 2SF, the brightness is 0% because of the all-black display state, and disclination occurs during 0.69 ms of 3SF. Therefore, the start of 3SF corresponds to 0 ms in FIG. Is equivalent to 0.69 ms. At this time, the brightness decreases to 0.18 from 0.25 when no disclination occurs.

  The response characteristic of the liquid crystal in 8SF, which is a subfield period in which another disclination occurs, is also a property corresponding to “discrimination is present” in FIG. 6B. In 7SF, the brightness is 0% because of the all-black display state, and disclination occurs during 0.69 ms of 8SF. Therefore, the start of 8SF corresponds to 0 ms in FIG. Is equivalent to 0.69 ms. At this time, the brightness decreases to 0.18 from 0.25 when no disclination occurs. The sum of brightness when no disclination occurs in 3SF and 8SF is 0.50 (= 0.25 + 0.25), whereas the sum of brightness when disclination occurs is 0.36 (= 0.18 + 0.18). On the basis of the gamma characteristic created on the assumption that the entire surface has the same gradation, the ratio becomes dark to 72% (= 0.36 / 0.50) in the disclination occurrence display state.

  As described above, disclination occurs due to the mechanism described above, and pixels in which disclination has occurred are displayed darker than pixels in which disclination does not occur. In the present embodiment, the principle of the occurrence of disclination has been described using the drive pattern shown in FIG. 3. However, disclination occurs according to the same principle in other subfield drive patterns. The method of making the decrease in brightness due to disclination less visible will be described later. However, the effect of making the decrease in brightness less due to disclination less visible due to the method described below does not depend on the drive pattern of the subfield drive system. .

  Next, the internal configuration and operation of the image processing unit 140 and the operation of the liquid crystal control unit 150 will be described with reference to FIG. As shown in FIG. 7, the image processing unit 140 includes a pre-processing unit 141, a reduced image generation unit 142, an image memory 143, a gradation conversion unit 145, and an output synchronization signal generation unit 149, and each unit includes a register bus 199. It is connected to the CPU 110 through the CPU.

  The pre-processing unit 141 converts an image input from the image input unit 130 into a color space and resolution suitable for the liquid crystal elements 151R, 151G, and 151B. Specifically, color space conversion, geometric deformation correction (warping, trapezoidal correction), display layout conversion processing including enlargement / reduction processing, and the like are performed. The processed image IMG is supplied to the reduced image generation unit 142.

  The reduced image generation unit 142 writes the image IMG output from the preprocessing unit 141 into the image memory 143, and generates a first subframe DIV_A and a second subframe DIV_B for pixel shift display. The reduced image generation unit 142 outputs the first subframe DIV_A and the second subframe DIV_B at double speed. That is, when the frame frequency of the input image is 60 Hz, the first subframe DIV_A and the second subframe DIV_B are output at 120 Hz. Further, the reduced image generation unit 142 outputs a synchronization signal that can identify whether the image output at the timing is the first subframe DIV_A or the second subframe DIV_B.

  Next, a method of generating the first subframe DIV_A and the second subframe DIB_B for pixel shift processing from the image IMG output from the preprocessing unit 141 will be specifically described. When the pixel shift process is performed, the reduced image generation unit 142 generates a plurality of subframes by sampling the gradation values of the pixels of one frame at different sampling phases. More specifically, first, the reduced image generation unit 142 converts the pixel data (tone values of the pixels) of the image IMG stored in the image memory 143 whose horizontal and vertical coordinates are both even numbers in FIG. As shown in (a), sampling is performed and output as the first subframe DIV_A. Next, as shown in FIG. 8A, the reduced image generation unit 142 samples pixel data in which the horizontal and vertical coordinates of the image IMG are both odd from the image memory 143 and outputs the sampled data as the second sub-frame DIV_B. I do. Note that the reduced image generation unit 142 can also output the input image input to the reduced image generation unit 142 as it is to the gradation conversion unit 145 as a first subframe and a second subframe without generating a reduced image.

  Next, how the first sub-frame DIV_A and the second sub-frame DIV_B are output on the projection plane in the pixel shift processing will be described. FIG. 8B shows the relationship between the projection positions of the first sub-frame DIV_A and the second sub-frame DIV_B on the projection plane. In FIG. 8B, a rectangle with coordinates described therein represents one pixel at the projection position in the first frame period, and a set of the rectangles becomes a projection image (1st sub-frame DIV_A) in the first frame period. On the other hand, the hatched rectangle represents one pixel at the projection position in the 2nd frame period, and an aggregate of the rectangles becomes a projection image (2nd subframe DIV_B) in the 2nd frame period. The 1st sub-frame DIV_A and the 2nd sub-frame DIV_B are projected at positions shifted by 1/2 pixel in the horizontal and vertical directions, respectively, as a result as shown in FIG. You.

  Returning to FIG. 7, the tone conversion unit 145 can apply different tone conversion processes to image data input thereto for each frame. In the present embodiment, an example in which an input image is multiplied by a predetermined gain coefficient as a conversion characteristic from an input gradation to an output gradation used by the gradation conversion unit 145 will be described. FIG. 9A shows an example of the configuration of the tone conversion unit 145. The tone conversion unit 145 in the present example includes a gain coefficient determination unit 200 and a gain processing unit 201.

  The gain coefficient determination unit 200 determines a different gain coefficient for each divided period obtained by dividing one frame period in synchronization with the output synchronization signal input thereto, and notifies the gain processing unit 201 of the determined gain coefficient. Here, it is assumed that the gain coefficient for a certain divided period is 100% and the gain coefficient for the next divided period is 90%. The gain processing unit 201 performs a gain process of multiplying the input image signal by the gain coefficient determined by the gain coefficient determination unit 200. Thus, the first subframe and the second subframe output from the reduced image generation unit 142 are multiplied by different gain coefficients.

  As described above, the gradation conversion unit 145 performs different gain processing for each divided period, that is, for each subframe, so that it is possible to make it difficult to visually recognize a decrease in pixel brightness due to disclination. This mechanism will be described with reference to FIG. In FIG. 10, dark lines due to discrimination are schematically shown for understanding, and do not accurately represent the density of the dark lines actually generated.

  FIG. 10A shows the relationship between the input tone value and the output tone value (input / output tone characteristic) when the gain coefficient is 100%, and the image of the projected image visually recognized by the observer. Here, a case is shown in which a liquid crystal element 151 having 96 pixels in the horizontal direction displays a gradation image that simply increases by one gradation in the right direction. In the display of this gradation image, pixels in which disclination does not occur have a smooth gradation. On the other hand, in an adjacent gray scale in which the on-period and the off-period overlap each other for a long time in the driving state of the adjacent pixel, the brightness decreases due to the effect of disclination and a dark line is perceived. In FIG. 10A, a description will be given assuming that five dark lines due to disclination are perceived.

  Hereinafter, in order to simplify the description that makes it difficult to visually recognize the decrease in the brightness of the pixel due to the disclination, the projection in the case where the pixel shift element 170 is not driven, that is, the case where the optical path is not shifted for each subframe is described. This will be described with reference to an image.

  Attention is paid to disclination occurring at a position where the gradation value 64 and the gradation value 65 are adjacent to each other. Here, a change in the position of disclination when a gain of 90% is applied to a gradation image similar to the above will be described with reference to FIG. By the gain processing with the gain coefficient of 90%, the adjacent relationship between the gradation value 64 and the gradation value 65 moves to the pixels whose input gradation values are 71 and 72. Therefore, a dark line due to disclination is generated in a pixel having an input gradation value of 71 and displaying a gradation value of 64.

  Since the gradation conversion unit 145 alternately switches the gain coefficient of 100% and the gain coefficient of 90% for each subframe (for each divided period), the projected images are also shown in FIGS. 10A and 10B. The image switches alternately for each sub-frame. If the switching cycle is longer than a certain period, the observer integrates and perceives the image of the two frames, so that the dark line due to the disclination becomes about 1/2 dark as shown in FIG. Perceived. The above is the principle that the operation of the gradation conversion unit 145 makes it difficult for a dark line due to disclination to be visually recognized. This principle applies to disclinations occurring at other positions.

  Returning to FIG. 7, the output synchronization signal generation unit 149 is a block for generating an output synchronization signal, and generates an output synchronization signal by counting a reference clock serving as a base of a dot clock (not shown) input thereto. . The output synchronization signal synchronizes the read timing of the image memory 143 by the reduced image generation unit 142, the drive timing of the liquid crystal elements 151R, G, B by the liquid crystal control unit 150, and the drive timing of the pixel shift element 170 by the shift control unit 171. The reference signal is

  Next, the projection processing according to the first embodiment will be described. The CPU 110 controls on / off of the pixel shift processing and the gain coefficient applied by the gradation conversion unit 145 according to the resolution of the input image, thereby suppressing cost reduction and suppressing image quality deterioration due to disclination. Achieve higher resolution by shifting. That is, the gradation conversion unit 145 can apply different conversion characteristics (gain coefficients in this example) to each of a plurality of subframes obtained from one frame of the input image. Then, the gradation conversion unit 145 calculates the difference between the conversion characteristics applied to each sub-frame at the time of performing the pixel shift process of performing projection so as to shift the projection positions of the plurality of sub-frames, and performs the conversion at the time of non-execution of the pixel shift process. The difference is smaller than the difference between the conversion characteristics applied to the frame. In the following, a configuration will be described in which a gain coefficient is used as an example of the conversion characteristic, and the difference between the gain coefficients applied to each subframe is zero when the pixel shift process is performed. FIG. 11 shows a flowchart of the projection control performed by the CPU 110 in the first embodiment. Note that the processing from step S110 to S115 is executed by the CPU 110 every time the image format input to the image input unit 130 changes.

  In step S110, CPU 110 acquires resolution information of an input image input to image input unit 130. The resolution information can be obtained, for example, from header information of an input image (image data). In step S111, the CPU 110 compares the resolution of the input image acquired in step S110 with a predetermined displayable resolution of the liquid crystal element 151. For example, in this example, the maximum resolution that the liquid crystal element 151 can display is used as the predetermined resolution. If the CPU 110 determines that the resolution of the input image is larger than the maximum resolution of the liquid crystal element 151, the process proceeds to step S114. If the CPU 110 determines that the resolution of the input image is equal to or less than the maximum resolution of the liquid crystal device 151, the process proceeds to step S112.

  In step S112, the CPU 110 turns off the pixel shift processing. Specifically, it instructs the shift control section 171 not to drive the pixel shift element 170. Further, it instructs the reduced image generation section 142 to output the input image of the reduced image generation section 142 to the gradation conversion section 145 without generating the reduced image. In step S113, the CPU 110 instructs the gradation conversion unit 145 to perform a gain process for applying different gain coefficients between the first subframe and the second subframe.

  On the other hand, when it is determined in step S111 that the resolution of the input image is larger than the resolution of the liquid crystal element 151, in step S114, the CPU 110 turns on the pixel shift process. Specifically, it instructs the shift control unit 171 to drive the pixel shift element 170. Further, it instructs the reduced image generation unit 142 to generate thinned images (1st subframe DIV_A and 2nd subframe DIV_B) for pixel shift and output them to the gradation conversion unit 145. In step S115, the CPU 110 issues an instruction to the gradation conversion unit 145 so that the gradation conversion unit 145 applies the same gain coefficient to the first subframe and the second subframe.

  In the above processing, when the pixel shift processing is valid (ON), the same gain coefficient is applied in the first frame period and the second frame period (step S115). This is because, when the pixel shift processing is valid (ON), performing gain processing using different gain coefficients may reduce the effect of high resolution by pixel shift. An example in which the effect of high resolution is reduced by performing gain processing using different gain coefficients on each of the first subframe DIV_A and the second subframe DIV_B in the pixel shift processing will be described with reference to FIG. I do.

  FIG. 12A illustrates an input image (image IMG) input to the reduced image generation unit 142. Note that one square represents one pixel of each image data, and the number in the square represents the gradation value of each pixel. The reduced image generation unit 142 generates a first subframe DIV_A by sampling pixels surrounded by a solid line in FIG. 12A and generates a second subframe DIV_B by sampling pixels surrounded by a broken line. In this case, the first subframe DIV_A and the second subframe DIV_B are shown in FIGS. 12B and 12C, respectively. FIG. 12D shows an image of a projected image when the first subframe DIV_A and the second subframe DIV_B are output without going through the processing of the gradation conversion unit 145. The second sub-frame DIV_B is projected with a shift of 1/2 pixel to the lower right with respect to the first sub-frame DIV_A. As a result, each pixel in FIG. 12D has a grayscale value obtained by time-integrating (averaging) the grayscale values of the first subframe DIV_A and the second subframe DIV_B shifted by 画素 pixel.

  Next, a case is considered where the first subframe DIV_A and the second subframe DIV_B are output through the processing of the gradation conversion unit 145 (processing using different gain coefficients). Since the first sub-frame DIV_A and the second sub-frame DIV_B are output to the gradation converter 145 in a time-division manner, the gradation converter 145 applies different gain coefficients to the first sub-frame DIV_A and the second sub-frame DIV_B. FIGS. 12E and 12F show images when a 100% gain coefficient is applied to the first subframe DIV_A and a 90% gain coefficient is applied to the second subframe DIV_B. FIG. 12 (g) shows an image when FIGS. 12 (e) and 12 (f) are projected by pixel shift. Ideally, as shown in FIG. 12 (d), a line having an obliquely high gradation value from the upper left to the lower right should be uniformly projected. However, in FIG. 12 (g), pixels having a gradation value of 47 and pixels having a gradation value of 52 are displayed alternately on both sides (upper right side and lower left side) of an oblique line having a high gradation value 91. . The pixel having the tone value 47 and the pixel having the tone value 52 are visually recognized as jaggies that did not exist in the input image. Therefore, in the case where the pixel shift processing is ON, if the gradation conversion unit 145 performs gain processing with different gain coefficients for each of the first subframe DIV_A and the second subframe DIV_B, the effect of high resolution by pixel shift is achieved. Will decrease.

  As described above, it is desirable to reduce the difference between the gain coefficients applied to each of the first sub-frame DIV_A and the second sub-frame DIV_B in order not to reduce the effect of the high resolution due to the pixel shift. In step S115, the CPU 110 in the first embodiment multiplies the same gain coefficient in the first subframe DIV_A and the second subframe DIV_B (makes the difference between the gain coefficients zero). Therefore, the projected image is as shown in FIG. 12D, and the jaggy as shown in FIG. 12G is not visually recognized, and the effect of increasing the resolution can be made ideal.

  Next, it will be described that, even if the same gain coefficient is multiplied in the first sub-frame DIV_A and the second sub-frame DIV_B in the gradation conversion unit 145 in step S115, the effect of making the dark line hard to be visually recognized due to disclination does not decrease.

  FIG. 13A is an image of a projection surface for four pixels of the liquid crystal element 151 when the pixel shift process is off, that is, when the optical path is not shifted for each subframe by the pixel shift element 170. As described with reference to FIG. 5A, since disclination occurs in only a part of one pixel, it is visually recognized as a dark line having a width of less than one pixel on the projection surface, for example, as shown in FIG. You. On the other hand, when the pixel shift is on, as shown in FIG. 13B, one sub-frame is shifted and projected to the lower right by 画素 pixel with respect to the other sub-frame. Therefore, the display position of the disclination is also shifted and projected by 画素 pixel. As a result, even if disclination occurs at the same pixel position on the panel, no dark line due to disclination is projected on the projection plane at the same position for two consecutive frames. Further, since the images of the two frames are integrated and visually recognized by the observer, the dark line due to the disclination is visually recognized as having a density of about 1/2 as shown in FIG. As described above, by performing the pixel shift driving, it is possible to make it difficult to visually recognize a dark line due to disclination. Therefore, in the case of performing pixel shift driving, even if the difference in gain applied by the gradation conversion unit 145 is reduced, the effect of making dark lines hard to be visually recognized by disclination does not decrease.

  As described above, if a large gain is applied to the first sub-frame DIV_A and the second sub-frame DIV_B generated by the reduced image generating unit 142 with a large difference in gain coefficient, the effect of increasing the resolution by the pixel shift is reduced. Therefore, when the pixel shift processing is on, the gradation conversion unit 145 reduces the difference between the gain coefficients used in each field. On the other hand, with respect to disclination, by performing pixel shift driving, there is an effect that dark lines due to disclination are hardly visually recognized. Therefore, in the case of performing pixel shift driving, even if the difference in gain applied by the gradation conversion unit 145 is reduced, the effect of making dark lines hard to be visually recognized by disclination does not decrease.

  As described above, according to the projection control according to the first embodiment, ON / OFF of the pixel shift process and the gain coefficient applied by the gradation conversion unit 145 are controlled according to the resolution of the input image. When the shift processing is off, disclination is reduced by applying a different gain coefficient to each subframe. Further, when the shift processing is on, by applying the same gain coefficient to each subframe, the effect of high resolution can be maintained and the influence of disclination can be suppressed. Further, in the above-described projection control, when the shift process is on, the double speed process for generating the first sub-frame DV_A and the second sub-frame DV_B is required, but time division for making the gain coefficient different is performed. It becomes unnecessary. Therefore, high-band image processing and high-speed driving of the liquid crystal element 151 are unnecessary. Therefore, according to the liquid crystal projector 100 of the first embodiment, it is possible to suppress a decrease in image quality due to disclination and to realize a high resolution by pixel shift, while suppressing costs.

<Modification 1>
In step S111 of FIG. 11, the CPU 110 of the first embodiment controls on / off of the pixel shift process and the gain used by the gradation conversion unit 145 according to the resolution of the input image. However, the present invention is not limited to this. Absent. In step S111, the process may branch based on image format information other than the resolution.

  For example, on / off of the pixel shift processing and the gain used by the gradation conversion unit 145 may be controlled according to the frequency of the synchronization signal of the input image. In that case, if the frequency of the vertical synchronization signal of the input image is equal to or lower than the predetermined value, the CPU 110 proceeds to step S112 and turns off the pixel shift processing. On the other hand, when the CPU 110 determines that the frequency of the vertical synchronization signal of the input image is higher than the predetermined value, the process proceeds to step S114, and the pixel shift process is turned on. This is because when the frequency of the vertical synchronizing signal of the input signal is low, the driving frequency of the pixel shift element is also lowered accordingly, and the state of the optical path shift may be visually recognized. When it is determined that the frequency of the vertical synchronization signal of the input image is equal to or lower than the predetermined value, the optical path shift can be prevented from being visually recognized by turning off the pixel shift processing. The predetermined value in this case is desirably set so that the state of the optical path shift is not visually recognized, and in practice, it is more desirably 30 Hz or less.

<Modification 2>
Further, as another configuration example of the gradation conversion unit 145 according to the first embodiment, as shown in FIG. 9B, a look-up table (LUT) group in which different input / output gradation characteristic data are stored is used. A configuration for switching the conversion characteristic of the tone conversion may be used. For example, the LUT 220 records the input / output gradation characteristic data shown in FIG. 10A, and the LUT 221 records the input / output gradation characteristic data shown in FIG. Then, the selector 222 switches the LUT for each subframe in synchronization with the output synchronization signal, so that different input / output gradation characteristics are applied to each subframe.

  Although the LUTs 220 and 221 may hold gradation conversion data for all gradations, there is a problem that the RAM capacity increases. In order to solve this problem, the LUTs 220 and 221 hold only the grayscale conversion data of the representative grayscale, and the grayscale conversion data of the grayscales not held are the grayscale conversion data of the representative grayscale data before and after the grayscale conversion data. May be calculated by interpolation.

  As described above, by operating each unit of the liquid crystal projector 100, it is possible to suppress a decrease in image quality due to disclination and realize a high resolution by pixel shift, while suppressing costs.

<Embodiment 2>
In the first embodiment, ON / OFF of the pixel shift process and control of the gain coefficient applied by the gradation conversion unit 145 are performed according to the format information (for example, the resolution and the frequency of the vertical synchronization signal) of the image. In the second embodiment, on / off control of pixel shift processing and control of a gain coefficient applied by the gradation conversion unit 145 are performed according to the state of image processing applied to an input image. More specifically, in the present embodiment, on / off of the pixel shift processing and control of the gain coefficient applied by the gradation conversion unit 145 are performed in accordance with the amount of geometric deformation correction performed by the preprocessing unit 141. Do. The internal configuration of the liquid crystal projector 100 according to the second embodiment is the same as that of the first embodiment (FIG. 1).

  FIG. 14 is a flowchart illustrating projection control according to the second embodiment. In step S141, the CPU 110 obtains deformation amount information of the geometric deformation correction executed by the pre-processing unit 141. The deformation amount information only needs to include information that can determine how much the geometric deformation correction is performed.For example, the total, average, maximum value, minimum value, and the like of the deformation amounts set for each deformation point may be included. Can be used.

  In step S142, the CPU 110 determines whether or not the deformation amount is equal to or more than a predetermined value based on the deformation amount information of the geometric deformation correction executed by the pre-processing unit 141 acquired in step S141. When the CPU 110 determines that the deformation amount of the geometric deformation correction in the preprocessing unit 141 is equal to or more than the predetermined value, the process proceeds to step S112, and determines that the deformation amount of the geometric deformation correction in the preprocessing unit 141 is less than the predetermined value. In this case, the process proceeds to step S114. Steps S112 to S115 are as described in FIG.

  In general, when the pixel shift processing is turned on, the effect of the high resolution by the pixel shift processing is affected by the influence of the interpolation processing by the geometric deformation correction and the accompanying filter processing as the deformation amount of the geometric deformation correction is large. descend. Therefore, when the deformation amount of the geometric deformation correction is equal to or larger than a predetermined value, it is desirable to turn off the pixel shift processing. Therefore, it is desirable that the predetermined value used in step S142 be determined based on the degree of reduction in the resolution increase according to the amount of deformation. In a simpler configuration, in step S142, the CPU 110 causes the process to proceed to step S112 when the geometric deformation correction is on (when the amount of deformation is not zero), and when the geometric deformation correction is off (when the amount of deformation is zero). ), The process may proceed to step S114.

  As described above, according to the second embodiment, it is possible to appropriately control the pixel shift processing according to the deformation amount of the geometric deformation correction. In addition, when the pixel shift process is on, the same effect as in the case where the pixel shift process is off, which makes it difficult to see dark lines due to disclination, can be maintained without deteriorating the effect of high resolution. Therefore, it is possible to suppress a decrease in image quality due to disclination and to realize a high resolution by pixel shift, while suppressing costs.

<Embodiment 3>
In the first embodiment, the on / off control of the pixel shift processing and the gradation conversion unit 145 are used according to the format information of the image, and in the second embodiment, according to the state of the image processing such as the geometric deformation correction. The example in which the control of the gain coefficient is performed has been described. In the third embodiment, ON / OFF of the pixel shift process and control of the gain coefficient used by the gradation conversion unit 145 are performed according to the feature amount of the input image. In the third embodiment, for example, it is determined whether the input image is a moving image content or a still image content based on the feature amount of the input image, and on / off control of the pixel shift process and gradation are performed according to the determination result. The gain coefficient used by the conversion unit 145 is controlled. Note that the internal configuration of the liquid crystal projector 100 in the third embodiment is the same as in the first and second embodiments (FIG. 1). However, the preprocessing unit 141 calculates the feature amount of the input image and supplies the calculation result to the image processing unit.

  FIG. 15 is a flowchart showing the projection control according to the third embodiment. In step S <b> 151, the CPU 110 acquires an average luminance level (APL) from the preprocessing unit 141 as a feature amount of the input image input to the preprocessing unit 141. In step S152, the CPU 110 determines whether the input image is a moving image content based on the feature amount acquired in step S151. When the CPU 110 determines that the input image is moving image content, the process proceeds to step S112, and when the CPU 110 determines that the input image is not the moving image content, that is, the still image content, the process proceeds to step S114. The processing of steps S112 to S115 is as described in the first embodiment.

  More specifically, the CPU 110 records the APL acquired in the previous frame in the RAM 112, and calculates a difference from the APL of the current frame acquired in step S151. If the difference between the APL of the previous frame and the APL of the current frame is equal to or greater than a predetermined value, CPU 110 determines that the input image is moving image content. When the difference between the APL of the previous frame and the APL of the current frame is smaller than a predetermined value, CPU 110 determines that the input image is not a moving image content, that is, a still image content.

  In the third embodiment, whether or not the input image is moving image content is determined based on a difference value between frames before and after the APL of the input image. However, if it is determined whether the input image is moving image content, the determination is made. It does not limit the method. For example, it is configured to calculate a motion vector or the like, and it is determined whether or not the input image is moving image content based on the size of the motion vector, the number of motion vectors having a size equal to or larger than a predetermined value, and the like. The configuration may be any.

  Next, the reason why the pixel shift process is turned on / off and the gain coefficient used by the gradation conversion unit 145 is controlled depending on whether the input image is moving image content or still image content will be described.

  In general, higher resolution is required when the input image is still content than when it is moving image content. When the input image is a moving image content, it is difficult to visually recognize a change in a small portion of the image because the image has motion. On the other hand, when the input image is still image content, the image has little movement, so that the viewer's attention is more easily directed to a small portion of the image, and a small change is easily recognized. Therefore, when the input image is a still image content, it is desirable to turn on the pixel shift processing to increase the resolution. Therefore, in the third embodiment, ON / OFF of the pixel shift processing is controlled according to whether the input image is a moving image content or a still image content. When the pixel shift process is on, the effect of suppressing the visibility of dark lines due to disclination can be maintained to the same extent as when the pixel shift process is off, without reducing the effect of increasing the resolution. .

  In step S115, as in the first and second embodiments, the same gain coefficient is applied to the first sub-frame DIV_A and the second sub-frame DIV_B. That is, the difference between the gain coefficients is set to zero, but the present invention is not limited to this. As described above. Further, in each of the above embodiments, the magnitude of the difference between the gain coefficients is determined based on the effect of increasing the resolution by the pixel shift, the difficulty of visually recognizing dark lines due to disclination, and the priority of other image quality disturbances. You may.

  For example, in the third embodiment, a gain coefficient to be applied is switched depending on whether a continuously input image is a moving image content or a still image content at each time point. Therefore, when an input image is input in which a scene with large motion and a scene with small motion are frequently switched, the case where the difference between the gain coefficients is large and the case where the difference is zero is frequently switched, which may be visually recognized as flicker. There is. Therefore, in the third embodiment, it is more preferable that the difference between the gain coefficients is larger than zero in step S115 and smaller than the difference between the gain coefficients applied when the pixel is shifted off.

  For example, when the pixel shift process is ON, the gain coefficients applied to the first subframe and the second subframe in step S115 are set to 100% and 98% (2% difference), respectively. If the pixel shift processing is off, the gain coefficients applied to the first and second subframes in step S113 are set to 100% and 90% (difference of 10%), respectively, as in the first and second embodiments. When the gain coefficient is set in this way, the maximum luminance values when the pixel shift is off and on are 95% ((100% + 90%) / 2) and 99% ((100% + 98%) / 2), respectively. It becomes a flicker component with an amplitude of 4%.

  On the other hand, in the first and second embodiments, when the pixel shift processing is ON, the gain coefficients applied to the first subframe and the second subframe are both 100%. Therefore, the maximum luminance values when the pixel shift is off and on in the first and second embodiments are 95% and 100%, respectively. As a result, a flicker component having an amplitude of 5% is obtained. Therefore, it can be understood that the flicker amplitude is improved when the gain coefficient is set to 100% or 98% at the time of pixel shift-on.

  It should be noted that jaggies may be caused by the presence of a difference between gain coefficients in the pixel shift processing. FIG. 12H shows a state in which the first subframe DIV_A is multiplied by a gain coefficient of 100%, and FIG. 12I shows a state in which the second subframe DIB_B is multiplied by a gain coefficient of 98%. When these are displayed by pixel shift, a projected image as shown in FIG. 12 (j) is displayed. As shown in FIG. 12 (j), the gradation values on both sides (upper right and lower left) of the diagonal line having the high gradation value 95 from the upper left to the lower right are the gradation values 51 and 52, and are almost the same. This is uniform, and the effect of increasing the resolution by the pixel shift is not substantially reduced. That is, by setting a small difference between the gain coefficients, the occurrence of flicker can be suppressed, and the effect of increasing the resolution can be maintained.

  As described above, according to the third embodiment, it is possible to suppress a decrease in image quality due to disclination and realize a high resolution by pixel shift, while suppressing costs.

  As described above, in the first to third embodiments, the ON / OFF of the pixel shift processing and the gain coefficient of the gradation conversion unit 145 used according to the format information of the input image, the state of the image processing, the feature amount of the input image, and the like. Control is shown. However, ON / OFF of the pixel shift processing and control of the gain coefficient used by the gradation conversion unit 145 are not limited to these. For example, the characteristics of the gradation conversion may be controlled according to the on / off setting of the pixel shift processing input by the user via the operation unit or the like. In this case, for example, when the user sets the pixel shift processing to be valid, the gradation conversion unit 145 sets the difference between the gain coefficients used for the plurality of subframes to be smaller than when the user sets the pixel shift processing to be invalid. I do. Further, for example, on / off of the pixel shift process may be controlled in accordance with the on / off setting of the disclination suppression process input by the user via the operation unit or the like. In this case, for example, when the user changes the disclination suppression process from invalid to valid while the pixel shift process is enabled, the pixel shift process is controlled to be turned off.

  The on / off of the pixel shift process and the difference between the gradation conversion characteristics applied to the sub-frames operate in conjunction with each other as in the above-described embodiments, so that cost can be reduced and disclination can be performed. Image quality degradation can be suppressed, and higher resolution can be realized by pixel shift.

<Other embodiments>
The present invention supplies a program for realizing one or more functions of the above-described embodiment to a system or an apparatus via a network or a storage medium, and one or more processors in a computer of the system or the apparatus execute the program. The processing can be implemented by reading and executing. Further, it can also be realized by a circuit (for example, an ASIC) that realizes one or more functions.

  Each embodiment described above is only a typical example, and various modifications and changes can be made to each embodiment when implementing the present invention.

100: liquid crystal projector, 110: CPU, 130: image input unit, 140: image processing unit, 141: pre-processing unit, 142: reduced image generation unit, 143: image memory, 145: gradation conversion unit, 150: liquid crystal control Unit, 151R, 151G, 151B: liquid crystal element, 160: light source control unit, 161: light source, 170: pixel shift element, 171: shift control unit, 199: register bus

Claims (20)

A projection control device for a projection device using a liquid crystal element having a plurality of pixels,
Generating means for generating a plurality of subframes from one frame of the input image;
Converting means for converting the gradation values of the plurality of sub-frames to obtain a gradation value used to control the driving of the liquid crystal element,
The conversion means can apply different conversion characteristics to each of the plurality of sub-frames, and when performing a pixel shift process of performing projection so as to shift the projection position of the plurality of sub-frames, The projection control device according to claim 1, wherein a difference in conversion characteristics to be applied is smaller than a difference in conversion characteristics to be applied to each subframe when the pixel shift process is not performed.   The said generation means, when the said pixel shift process is performed, samples the gradation value of the pixel of the said 1 frame with a different sampling phase, respectively, and produces | generates this several sub-frame. 2. The projection control device according to 1.   2. The liquid crystal device according to claim 1, further comprising: a driving unit configured to control an application time of an on-voltage / off-voltage to each of the plurality of pixels of the liquid crystal element based on the gradation value obtained by the conversion unit. Or the projection control device according to 2.   The conversion means performs tone conversion by multiplying each of the plurality of sub-frames by a different gain coefficient, and the difference between the different gain coefficients when the pixel shift processing is performed is different when the pixel shift processing is not performed. 4. The projection control apparatus according to claim 1, wherein the difference is larger than the difference between the different gain coefficients.   The conversion unit may use the same conversion characteristic for each of the plurality of sub-frames when performing the pixel shift process, and use different conversion characteristics for each of the plurality of sub-frames when not performing the pixel shift process. The projection control device according to claim 1, wherein:   The conversion unit performs tone conversion by multiplying each of the plurality of sub-frames by a common gain coefficient when the pixel shift process is performed, and differs for each of the plurality of sub-frames when the pixel shift process is not performed. 6. The projection control device according to claim 5, wherein gradation conversion is performed by multiplying the gain coefficient.   The pixel shift process is executed when the resolution of the input image is larger than a predetermined displayable resolution of the liquid crystal element, and is not executed when the resolution of the input image is equal to or less than the predetermined resolution of the liquid crystal element. The projection control device according to claim 1, wherein:   7. The method according to claim 1, wherein the pixel shift process is executed when a frame frequency of the input image is higher than a predetermined value, and is not executed when a frame frequency of the input image is lower than the predetermined value. The projection control device according to claim 1.   The pixel shift process is performed when a deformation amount due to geometric deformation correction performed on the input image is smaller than a predetermined value, and is not executed when the deformation amount is equal to or larger than the predetermined value. The projection control device according to any one of claims 1 to 6, wherein   10. The projection control device according to claim 9, wherein the geometric deformation correction includes at least one of processing for reducing, enlarging, and deforming the input image. A determination unit configured to determine whether the input image is a still image content or a moving image content based on a feature amount of the input image;
7. The method according to claim 1, wherein the pixel shift process is executed when the input image is determined to be a still image content, and is not executed when the input image is determined to be a moving image content. The projection control device according to claim 1.   12. The projection control device according to claim 11, wherein the determination unit determines whether the input image is a still image content or a moving image content based on a difference in luminance level between frames before and after the input image.   13. The projection control device according to claim 11, wherein the determination unit determines whether the input image is a still image content or a moving image content based on a motion vector in the input image. A projection control device according to any one of claims 1 to 13,
The liquid crystal element;
Driving means for driving the liquid crystal element using the gradation value obtained by the conversion means,
And a shift unit that changes an optical path from the liquid crystal element so that projection positions of the plurality of sub-frames are different in the pixel shift process. A projection control method for a projection device using a liquid crystal element having a plurality of pixels,
Generating a plurality of sub-frames from one frame of the input image;
Converting a gradation value of the plurality of sub-frames to obtain a gradation value used to control driving of the liquid crystal element,
In the conversion step, different conversion characteristics can be applied to each of the plurality of sub-frames, and each of the plurality of sub-frames is applied to each of the sub-frames at the time of performing a pixel shift process of performing projection so as to shift the projection position. The difference between the conversion characteristics to be performed is smaller than the difference between the conversion characteristics applied to each subframe when the pixel shift process is not performed.   In the generating step, when the pixel shift process is performed, the plurality of sub-frames are generated by sampling grayscale values of pixels of the one frame at different sampling phases. 15. The projection control method according to claim 15.   In the conversion step, tone conversion is performed by multiplying each of the plurality of sub-frames by a different gain coefficient, and the difference between the different gain coefficients when the pixel shift processing is performed is different when the pixel shift processing is not performed. 17. The projection control method according to claim 15, wherein the difference is larger than the difference between the different gain coefficients.   In the conversion step, when the pixel shift processing is performed, the same conversion characteristic is used for each of the plurality of subframes, and when the pixel shift processing is not performed, different conversion characteristics are used for each of the plurality of subframes. The projection control method according to any one of claims 15 to 17, wherein:   In the conversion step, when the pixel shift process is performed, tone conversion is performed by multiplying each of the plurality of sub-frames by a common gain coefficient, and when the pixel shift process is not performed, the gradation is different for each of the plurality of sub-frames. 19. The projection control method according to claim 18, wherein gradation conversion is performed by multiplying the gain coefficient.   A program for causing a computer to execute each step of the projection control method according to any one of claims 15 to 19.