JP2011158917A - Screen image persistence preventing device and method for preventing screen image persistence - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screen image persistence device which suppresses sense of incongruity in visual effects. <P>SOLUTION: A screen image based on a video data stored in a frame memory 104 is displayed in a liquid crystal panel 107. Each time video data are stored in the frame memory 104, a CPU 106 detects a difference between the video data stored in the preceding time and the video data newly stored, and determines that the screen image is a moving image, when the difference is equal to or larger than a threshold value and that the screen image is a still image, when the difference is smaller than the threshold. When still images are determined continuously for a prescribed number of times, the CPU 106 controls readout of video data from the frame memory 104 so as to shift the display position of the image on the screen, and controls a shifting means that shifts a projection screen so as to adjusts the shift in the display position on the projection screen. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an apparatus and a method for preventing screen burn-in of a display device such as a liquid crystal display, a liquid crystal projector, or a plasma display.

  In a display device such as a liquid crystal display or a plasma display, when a still image is displayed for a long time, the screen is burned. A similar screen burn-in also occurs in the liquid crystal projector. As an apparatus capable of preventing such screen burn-in, Japanese Patent Application Laid-Open No. 2004-228561 determines a still image and a moving image based on a difference between two consecutive fields of a video signal input in units of fields. In addition, there is described a burn-in prevention device configured to display another image prepared in advance when a still image is displayed for a predetermined time. Patent Document 2 describes a burn-in prevention circuit configured to move the display position of the screen slightly in the vertical direction and the horizontal direction when there is no change in the average luminance level of the video signal.

JP-A-8-292740 Japanese Patent No. 3454292

  However, those described in Patent Documents 1 and 2 described above have the following problems.

  In the case of the one described in Patent Document 1, when a still image is displayed for a predetermined time, an image that has nothing to do with the image that has been displayed so far is displayed. Work cannot be continued.

  In addition, since still images and moving images are determined by comparing all video data between fields, the amount of data to be compared is enormous, and the determination process takes time. For example, when displaying color image data (R, G, B) with a resolution of 1024 × 768 (dots), the number of data on one screen is 2359296 (= 1024 × 768 × 3). In the described one, all these data are compared between fields.

  In addition, video data that has a fixed pattern in a part of the image and a moving image in the other part is determined to be a video, and the fixed pattern may be displayed for a long time, causing screen burn-in. is there.

  In the thing of patent document 2, when a still picture is displayed over predetermined time, the display position of a screen is moved little by little in the up-down direction and the left-right direction. , Will not switch to another video.

  However, the process described in the cited document 2 also takes time to process because all video data is compared between fields.

  Further, as in the case of Patent Document 1, a screen burn may occur for a moving image including a fixed pattern.

  Furthermore, even if the display position is shifted, some fixed patterns (still images) may overlap before and after the shift. In this case, screen burn-in may occur in the overlapped portion.

  Furthermore, although the image burn-in itself is suppressed by shifting the display position of the image on the screen, such a shift in the display position may give the user a visually uncomfortable feeling.

  An object of the present invention is to provide an apparatus and a method that can solve the above-described problems and can perform still image and moving image determination processing in a shorter time.

  Another object of the present invention is to provide an apparatus and method that can prevent screen burn-in even for an image including a fixed pattern.

  Another object of the present invention is to provide an apparatus and method capable of suppressing visual discomfort.

  In order to achieve the above object, according to the present invention, every time video data supplied from the outside is stored in the frame memory, a screen is displayed between the previously stored video data and the video data stored this time. If the difference (specifically, inter-frame difference) of the data corresponding to the monitoring area set as a part of the video is detected and the detected difference is greater than or equal to the threshold value, the difference is less than the threshold value. Judged as a still image. When a still image is continuously determined for a predetermined number of times or for a predetermined time, the display position of the video on the display screen of the display means for displaying the screen based on the video data stored in the frame memory is shifted. Thus, the reading of the video data from the frame memory to the display means is controlled. According to this configuration, since it is not necessary to compare data in portions other than the monitoring area, the amount of data necessary for determining a still image / moving image is reduced accordingly.

  Further, according to the present invention, it is possible to arbitrarily set the monitoring area. Therefore, when the video data supplied from the outside includes a fixed pattern, the monitoring area can be set to a position where the fixed pattern can be detected.

  In addition, according to the present invention, when a still image is determined, the moving direction and movement of the display position so that the display pattern (fixed pattern) does not overlap before and after the video display position is shifted. The amount is determined, and the display position of the video is shifted based on the determined moving direction and moving amount. According to this configuration, since the display pattern (fixed pattern) does not overlap before and after the shift, a part of the fixed pattern overlaps before and after movement as in the conventional case, causing screen burn-in. Such a problem does not occur.

  Further, according to the present invention, the projection screen is shifted in order to adjust the shift of the display position on the projection screen on the screen caused by the shift of the display position of the image on the display screen such as the liquid crystal panel. ing. According to this configuration, the shift due to the shift of the display position of the video on the display screen is canceled by the shift of the projection screen.

  According to the present invention, since it is not necessary to compare data in portions other than the monitoring area in the still image / moving image determination, there is an effect that the time required for the comparison process can be shortened accordingly.

  Moreover, since the display position is detected and the display position is shifted, there is an effect that screen burn-in can be prevented even for an image including a fixed pattern that could not be detected conventionally.

  Furthermore, since display patterns (fixed patterns) do not overlap before and after the shift, screen burn-in can be more reliably suppressed.

  In addition, since the shift of the projection screen can cancel the display shift caused by the shift of the display position of the video on the display screen, there is an effect that it is possible to suppress a visually uncomfortable feeling.

1 is a block diagram illustrating a schematic configuration of a screen burn-in prevention device according to a first embodiment of the present invention. It is a block diagram which shows the specific structure of the process part of the screen image sticking prevention apparatus shown in FIG. 3 is a flowchart illustrating a procedure of still image / moving image determination processing performed in the screen burn-in prevention device illustrated in FIG. 1. 3 is a flowchart showing a procedure of display adjustment processing performed in the screen burn-in prevention device shown in FIG. 1. It is a schematic diagram which shows the content and monitoring area of the video data stored in the frame memory of the screen image sticking prevention apparatus shown in FIG. It is a schematic diagram which shows the image image before the shift in the monitoring area shown in FIG. It is a schematic diagram which shows the image image after the shift in the monitoring area shown in FIG. It is a schematic diagram for demonstrating adjustment of the display position in the projection screen on the screen of the screen image sticking prevention apparatus shown in FIG. It is a block diagram which shows the structure of the principal part of the screen image sticking prevention apparatus which is the 2nd Embodiment of this invention.

  Next, embodiments of the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 is a block diagram showing a schematic configuration of a screen burn-in prevention device according to the first embodiment of the present invention. This screen burn-in prevention device is applied to a liquid crystal projector, and its main components are an A / D converter 103, a frame memory 104, a memory 105, a CPU 106, a liquid crystal panel 107, a horizontal motor 108, and a vertical motor. 109, a projection lens 110 with a lens shift function, and a lamp unit 111.

  The A / D converter 103 converts a video signal (analog) 101 supplied from an external video supply device such as a personal computer into a digital video signal. The output of the A / D converter 103 is supplied to the frame memory 104.

  The frame memory 104 is supplied with a synchronization signal 102 necessary for performing a display operation based on the video signal (analog) 101 from an external video supply device. Based on the synchronization signal 102, the A / D converter 103 is provided. The digital video signal supplied from is stored in units of frames. For example, when the video signal (analog) 101 is a video signal, the synchronization signal 102 is a vertical synchronization signal and a horizontal synchronization signal, and video data for one screen is stored in the frame memory 104 based on these synchronization signals. Can do.

  The liquid crystal panel 107 is illuminated with light from the lamp unit 111 and displays a screen based on video data for one screen read from the frame memory 104. The projection lens 110 with a lens shift function projects image light (transmitted light or reflected light) from the display screen of the liquid crystal panel 107 onto the screen 112. Specifically, the lens shift function is a function in which a specific lens among the lens groups constituting the projection lens moves in a direction perpendicular to the optical axis of the lens group. The panel surface of the liquid crystal panel 107 is substantially perpendicular to the optical axis of the projection lens 110 with a lens shift function. The entire projection screen on the screen 112 is shifted according to the shift amount of the specific lens.

  The horizontal motor 108 and the vertical motor 109 are for moving the liquid crystal panel 107 in the vertical and horizontal directions in the in-plane direction of the liquid crystal panel 107. Here, the vertical direction and the horizontal direction correspond to the up-down direction and the left-right direction on the projection screen on the screen, respectively. By moving the liquid crystal panel 107 by the horizontal motor 108 and the vertical motor 109, the projection screen on the screen 112 is shifted.

  The CPU 106 controls the operations of the projection lens 110 with a lens shift function, the horizontal motor 108 and the vertical motor 109 in addition to controlling the overall operation as a projector according to a program stored in a storage device (not shown). Further, the CPU 106 controls reading of the video data stored in the frame memory 104 to the liquid crystal panel 107, or stores a part of the video data stored in the frame memory 104 in the memory 105. Further, the CPU 106 has a screen burn-in prevention processing unit as shown in FIG.

  Referring to FIG. 2, the screen burn-in prevention processing unit includes a still image / moving image determination process 300, a counter unit 301, an image data analysis unit 302, and a movement control unit 303. Any of these configurations can be realized by software.

  The still image / moving image determination processing 300 performs still image / moving image determination based on comparison of image data between frames, and determines that the image data stored in the frame memory 104 is an image data analysis unit when it is determined as a still image. 302 is supplied. In the still image / moving image determination processing, video data for one screen stored in the frame memory 104 is compared with data in a predetermined area on the screen. Here, monitoring areas are set as the predetermined areas in the vicinity of the four corners of the screen, and the still image / moving image determination processing 300 is performed in each monitoring area in the video data for one screen stored in the frame memory 104. Data is stored in the memory 104. Each time video data for one screen is stored in the frame memory 104, the data of each monitoring area of the previous video data stored in the memory 105 and the video data stored in the current frame memory 104 are stored. The data of the monitoring area is compared, and a still image / moving image determination is performed based on whether or not the difference between the two data (difference between frames) exceeds a threshold value A. If any one of the differences in each monitoring area is less than the threshold value A, the still image / moving image determination processing 300 determines that the difference is a still image and increases the count value of the counter unit 301 by one. When all the differences in each monitoring area are equal to or greater than the threshold value A, the still image / moving image determination process 300 determines that the difference is a moving image and clears the count value of the counter unit 301. Here, the threshold value A is a value that allows determination of a still image and a moving image, and is desirably set as appropriate according to the resolution of the video signal 101.

  The image data analysis unit 302 performs image analysis of the video data supplied from the still image / moving image determination process 300 to determine the direction and amount of shifting the video display position on the display screen of the liquid crystal panel 107. Specifically, the video data supplied from the still image / moving image determination processing 300 detects the fixed pattern of the still image portion by taking an intra-frame difference, and the detected fixed pattern is overlapped before and after the shift. The moving direction and the moving amount are determined so as not to become. The determination of the moving direction and the moving amount by the image data analysis unit 302 may be performed once during a still image display period in which still images are continuously displayed. Here, in the still image display period, the moving direction and the moving amount are determined by the image data analysis unit 302 at the timing when the still image / moving image determination processing 300 first determines that the image is a still image. . The movement direction and the movement amount determined by the image data analysis unit 302 are supplied to the movement control unit 303.

  The movement control unit 303 monitors the count value of the counter unit 301, and when this count value reaches the threshold value B, the movement control unit 303 determines whether the liquid crystal panel 107 is based on the movement direction and movement amount supplied from the image data analysis unit 302. Shift the display position of the video on the display screen. The shift of the display position is performed by controlling reading of video data from the frame memory 104. Simultaneously with this control, the movement control unit 303 cancels the image data display position shift on the projection screen on the screen 112 caused by the shift of the video display position on the display screen of the liquid crystal panel 107. Based on the movement direction and movement amount supplied from the analysis unit 302, the horizontal motor 108 and the vertical motor 109 are controlled, or the projection lens 110 with a lens shift function is controlled. The shift of the image display position on the display screen of the liquid crystal panel 107 and the shift of the projection screen on the screen 112 by the movement control unit 303 are maintained until the count value of the counter unit 301 is cleared.

  It is possible to perform adjustment by the projection lens 110 with a lens shift function and adjustment by the horizontal motor 108 and the vertical motor 109 at the same time, but in that case, it is expected that the control becomes complicated. Since the adjustment amount by the projection lens 110 with the lens shift function is smaller than the adjustment amounts by the horizontal motor 108 and the vertical motor 109, the movement amount supplied from the image data analysis unit 302 is the adjustment amount by the projection lens 110 with the lens shift function. In the range, the adjustment by the projection lens 110 with the lens shift function is prioritized, and the movement amount supplied from the image data analysis unit 302 exceeds the range of the adjustment amount by the projection lens 110 with the lens shift function. In this case, it is desirable to perform adjustment by the horizontal motor 108 and the vertical motor 109.

  In addition, the lens shift amount in the projection lens 110 with a lens shift function can be switched in a stepwise manner, and the shift amount of one stage corresponds to one dot of the liquid crystal display panel. It is possible to easily associate the shift of the image display position with the shift of the projection screen on the screen, and the movement control can be simplified.

  Further, the image analysis by the image data analysis unit 302 can be performed on the entire video data for one screen, but in this case, the amount of data to be processed becomes enormous. Therefore, it is desirable that the still image / moving image determination processing 300 supplies the video data in the monitoring area to the image data analysis unit 302, and the image data analysis unit 302 performs image analysis of the supplied video data. In this case, data to be processed by image analysis can be greatly reduced.

  Next, the operation of the screen burn-in prevention device of this embodiment will be described. Since the display operation as a projector is the same as the existing one, the description thereof will be omitted below, and the description will focus on the operation for preventing screen burn-in, which is a feature.

  The video signal 101 and the synchronization signal 102 are supplied from the external video supply device to the screen burn-in prevention device. The video signal 101 is converted into a digital signal by the A / D converter 103 and then supplied to the frame memory 104. In the frame memory 104, video data is stored in units of frames based on the synchronization signal 102. When video data for one screen is stored in the frame memory 104, a screen burn-in prevention process (a process by the screen burn-in prevention processing unit in FIG. 2) by the CPU 106 is performed.

  The screen burn-in prevention process includes a determination process by the still image / moving image determination process 300 and a display adjustment process by the movement control unit 303.

(1) Judgment processing:
FIG. 3 is a flowchart showing a procedure of determination processing performed by the still image / moving image determination processing 300.

  First, it is determined whether or not video data for one screen has been stored in the frame memory 104 (step 10). When this determination is “Yes”, the data in the monitoring area of the video data stored in the frame memory 104 is stored in the memory 105 (step 11). Next, it is determined whether or not video data for the next one screen has been stored in the frame memory 104 (step 12). If this determination is “Yes”, then the difference between the data in the monitoring area of the video data stored in the frame memory 104 and the data stored in the memory 105 in step 11 is detected (step 13). Subsequently, it is determined whether or not the detected difference is equal to or greater than a threshold value A (step 14). If the difference is greater than or equal to the threshold value A, it is determined that a moving image is displayed, the count value of the counter unit 301 is cleared, and the process returns to step 11. If the difference is less than the threshold value A, it is determined that a still image is displayed, the count value of the counter unit 301 is incremented by 1, and the process returns to step 11.

  According to the determination process described above, the count value of the counter unit 301 reaches the threshold value B when a still image is displayed for a predetermined time.

(2) Display adjustment processing:
FIG. 4 is a flowchart showing a procedure of display adjustment processing performed by the image data analysis unit 302 and the movement control unit 303.

  First, the image data analysis unit 302 determines whether or not video data has been supplied from the still image / moving image determination process 300 (step 20). When this determination is “Yes”, the image data analysis unit 302 checks whether or not the counter value of the counter unit 301 is “1”. When the counter value is “1”, the image data analysis unit 302 performs image analysis on the video data supplied from the still image / moving image determination process 300 in step 20 (step 22), and the movement method and movement. The amount is calculated (step 23).

  Next, the movement control unit 303 determines whether the count value of the counter unit 301 is greater than or equal to the threshold value B (step 24). When this determination is “Yes”, the movement control unit 303 displays the video display position on the display screen of the liquid crystal panel 107 based on the movement direction and movement amount calculated by the image data analysis unit 302 in step 23. Are shifted (step 25). At the same time, the movement control unit 303 controls the horizontal motor 108 and the vertical motor 109 based on the movement direction and the movement amount calculated by the image data analysis unit 302 in step 23, or controls the projection lens 110 with a lens shift function. The display position of the screen is adjusted so as to cancel the shift of the display position on the projection screen on the screen 112 that is caused by the shift of the display position of the image on the display screen of the liquid crystal panel 107 (step 26).

  The display adjustment process described above is repeatedly executed until the count value of the counter unit 301 is cleared.

  According to the above determination processing and display adjustment processing, when a still image is displayed for a predetermined time, the display position of the video on the display screen of the liquid crystal panel 107 is shifted in step 25. Thereby, it is possible to suppress screen printing.

  Further, due to the shift of the projection screen in step 26, the display position on the projection screen is shifted in the direction opposite to the shift of the display position on the display screen of the liquid crystal panel 107. This shift of the display position on the projection screen just cancels the shift of the display position on the display screen of the liquid crystal panel 107. Thereby, it is possible to provide the user with a video display that does not feel strange.

  Next, the monitoring area and the display adjustment process will be described with specific examples.

  FIG. 5 schematically shows the contents of video data stored in the frame memory 104 and the monitoring area. The video data shown in FIG. 5 is video data stored in the frame memory 104 when the presentation material is displayed on the display, and has contents in which characters are described in an area surrounded by a frame 200. . Monitoring areas 201 to 204 of 20 × 20 dots are set at the four corners of the screen. A part of the frame 200 is applied to each of the monitoring areas 201 to 204.

  As the presentation material, a plurality of video data in which characters are described in a frame 200 as shown in FIG. 5 is used. When these video data are sequentially displayed on the screen in a slide format, the frame 200 is always displayed at the same position, and only the characters in the frame 200 are replaced. In this case, the frame 200 becomes a fixed pattern, and the screen burn-in of the liquid crystal panel 107 occurs due to the fixed pattern.

  In order to prevent the screen burn-in described above, in the screen burn-in prevention device of the present embodiment, the still image / moving image determination processing 300 determines a still image / moving image by taking a difference between frames in the monitoring areas 201-204. Here, in each monitoring area, a case where the number of dots that cause a difference between the previous video data and the current video data is, for example, 40 dots or more is determined as a moving image. In this case, 40 dots is the threshold value A.

  Assume that the difference is less than threshold A. The still image / moving image determination process 300 determines that the image is a still image and increments the count value of the counter unit 301 by one. At the same time, the image data analysis unit 302 detects the fixed pattern of the frame 200 by image analysis, and calculates the moving direction and moving amount so that the fixed pattern does not overlap before and after the slide screen. When the count value of the counter unit 301 reaches the threshold value B, the movement control unit 303 displays the video display position on the display screen of the liquid crystal panel based on the movement direction and movement amount calculated by the image data analysis unit 302. Shift.

  FIG. 6 schematically shows an image image before the shift in the monitoring area 201 displayed on the screen of the liquid crystal panel 107, and FIG. 7 schematically shows an image image after the shift in the monitoring area 201. In contrast to the image image shown in FIG. 6, in the image image shown in FIG. 7, the display position of the video is moved by 2 dots in the right direction and 2 dots in the downward direction toward the screen. As a result, the fixed pattern (frame 200) does not overlap between the slide images, so that occurrence of screen burn-in of the liquid crystal panel 107 can be suppressed.

  When the image display position is shifted on the display screen as described above, the image display position is also shifted in the projection screen on the screen. Such a shift of the display position of the image on the projection screen may cause a visually uncomfortable feeling depending on the user. In order to suppress this uncomfortable feeling on the screen, in the screen burn-in prevention device of the present embodiment, the movement control unit 303 is based on the movement direction and movement amount calculated by the image data analysis unit 302 in the projected screen on the screen. Adjust the display position.

  FIG. 8 schematically shows the adjustment of the display position on the projection screen on the screen. In FIG. 8, the projection screen 502 displays the image image after the video data shift shown in FIG. 7 on the screen. The projection screen 501 is obtained by adjusting the display position by the movement control unit 303. The projected screen 501 is moved in the upper left direction toward the screen with respect to the projected screen 502, and the amount of movement is only 2 dots in the left direction and 2 dots in the upward direction on the display screen of the liquid crystal panel. It corresponds to the amount moved. By this movement, the shift of the video display position on the projection screen on the screen caused by the shift of the video display position on the display screen of the liquid crystal panel is offset. As a result, the display position of the projection screen 501 substantially coincides with the display position of the projection screen before the shift of the image display position on the display screen of the liquid crystal panel.

  The screen burn-in prevention device described above has three characteristics. The first feature is to reduce the amount of comparison data when determining still images / moving images, and to determine still images / moving images by taking the inter-frame difference of video data in the monitoring area. It is in the point which did. According to the first feature, since it is not necessary to compare data in portions other than the monitoring area, the amount of data necessary to determine a still image / moving image can be reduced by that amount, and the comparison process can be performed. Can be shortened. In addition, there are the following advantages.

  An XGA (eXtended Graphics Array) refresh rate (a value representing how many times the screen is updated per second in display display, which is synonymous with the frame rate) is approximately 16.7 ms at 60 Hz. . In this XGA display, it is necessary to detect an inter-frame difference for data of all pixels (1024 × 768 × 3 = 2359296) in each frame in order to perform a strict determination of a still image / moving image. However, it is difficult to perform data comparison of 2359296 times about every 16.7 ms with the current CPU performance. Therefore, conventionally, two frame memories and dedicated hardware (ASIC: Application Specific Integrated Circuit) capable of performing comparison processing at high speed are required, which is disadvantageous in terms of circuit scale, board area, and cost. It was a thing. By reducing the amount of data for comparison processing according to the first feature, such comparison processing in an XGA display can be realized with one frame memory and the current CPU without using dedicated hardware. Is possible.

  The second feature is to reliably suppress screen burn-in. A fixed pattern is extracted by image analysis so that the fixed pattern does not overlap before and after the shift of the display position. The point is that the moving direction and moving amount of the position are determined. If the display position of the image on the display screen of the liquid crystal panel is shifted based on the movement direction and the movement amount thus determined, the fixed patterns do not overlap each other, so that the screen printing can be more reliably suppressed. When shifting the video display position on the display screen in a predetermined direction by a predetermined amount, a part of the fixed pattern may overlap before and after the shift, and the screen burn-in occurs at the overlapping portion. There is a case.

  The third feature aims to suppress visual discomfort, and adjusts the display position of the image on the projection screen on the screen based on the moving direction and moving amount of the display position determined by image analysis. It is in the point made. This adjustment of the display position cancels out the shift in the display position of the image on the projection screen on the screen accompanying the shift in the display position of the image on the display screen of the liquid crystal panel, thereby suppressing visual discomfort. When the display position is not adjusted, depending on the user, the visual display position may shift depending on the shift of the image display position on the projection screen on the screen accompanying the shift of the image display position on the liquid crystal panel display screen. You may feel uncomfortable.

  Since the first to third features described above have special effects, an apparatus having these first to third features may be provided.

  In a device having the first or third feature or both features, when a still image is continuously determined a predetermined number of times, the video display position on the display screen of the liquid crystal panel is set to a fixed amount in a fixed direction. The display position may be shifted. In this case, the adjustment of the display position in the third feature is performed based on a fixed amount (corresponding to a certain shift direction and a certain shift amount).

  Further, in the apparatus having the third feature, the still image / moving image determination may be performed by a conventional method. However, in this case, the amount of data to be compared is enormous.

  The device having the first or second feature or both features can be applied to a display device represented by a liquid crystal display or a plasma display in addition to the liquid crystal projector shown in FIG.

(Second Embodiment)
The screen burn-in prevention device of the first embodiment may be configured to arbitrarily set the monitoring area. Here, a screen burn-in prevention device capable of arbitrarily setting a monitoring area will be described.

  The screen burn-in prevention device according to the second embodiment of the present invention includes the screen burn-in prevention processing unit and the operation unit 113 shown in FIG. The screen burn-in prevention processing unit is obtained by adding a monitoring area setting processing unit 304 to the configuration shown in FIG. Basically, the still image / moving image determination processing unit 300 is the same as that shown in FIG. 1 except that still image / moving image determination is performed based on the monitoring area set by the monitoring area setting processing unit 304. Is. Here, the description about the same structure is abbreviate | omitted, and only a different part is demonstrated.

  The operation unit 113 includes operation keys, a touch panel, and the like. The CPU 106 receives an input from the operation unit 113 and executes necessary processing. There are two setting modes, a monitoring area fixed mode and a monitoring area setting mode, and the user can select these modes through the operation unit 113. When the monitoring area fixing mode is selected, the CPU 106 performs the operation described in the first embodiment. When the monitoring area setting mode is selected, the following monitoring area setting process is executed by the monitoring area setting processing unit 304.

  First, the monitoring area setting processing unit 304 reads the monitoring area setting screen data from a storage device (not shown) and supplies it to the frame memory 104. When the monitoring area setting screen data is supplied to the frame memory 104, an image based on the supplied monitoring area setting screen data is displayed on the liquid crystal panel 104, and the display image is projected on the screen 112.

  The user can set the monitoring area on the monitoring area setting screen projected on the screen 112 through the operation unit 113. In the setting of the monitoring area, for example, the position and range of the monitoring area are specified in pixel units. Specifically, coordinates capable of characterizing each pixel on the screen are set in advance, and the area of the monitoring area is designated on the coordinates. For specifying the monitoring area, a coordinate value may be input, or a pointer may be displayed on the screen, and the area may be directly specified with the pointer.

  The monitoring area setting processing unit 304 supplies monitoring area information based on the area set by the user to the still image / moving image determination processing unit 300. The still image / moving image determination processing unit 300 executes the above-described determination processing based on the monitoring area information supplied from the monitoring area setting processing unit 304.

  According to the screen burn-in prevention device of the present embodiment described above, it is possible to arbitrarily set the monitoring area. Therefore, when the video data supplied from the outside includes a fixed pattern, the monitoring area can be set to a position where the fixed pattern can be detected.

  The configuration and operation of the screen burn-in prevention device described in the above embodiments are examples of the present invention, and can be changed as appropriate. For example, although four monitoring areas are set, the number of monitoring areas is not limited to four, and may be one or more. The position of the monitoring area may be a place other than the four corners of the screen. Furthermore, the monitoring area may be 1 dot.

  Although processing is performed in units of frames, when one frame is composed of two fields, processing can be performed in units of fields.

  Furthermore, in the configuration shown in FIG. 1, screen display by another display device such as a plasma display may be applied instead of screen display by the liquid crystal panel. In addition, instead of the CPU 106, an ASIC that can perform determination of moving images / still images, calculation of moving direction / moving amount, lens shift control, and motor control may be used. However, in this case, since it is necessary to design the ASIC exclusively, the cost becomes higher than that realized by the current CPU.

101 Video signal 102 Synchronization signal 103 A / D converter 104 Frame memory 105 Memory 106 CPU
DESCRIPTION OF SYMBOLS 107 Liquid crystal panel 108 Horizontal motor 109 Vertical motor 110 Projection lens with a lens shift function 111 Lamp unit 112 Screen 113 Operation part 300 Still image / moving image determination process part 301 Counter part 302 Image data analysis part 303 Movement control part 304 Monitoring area setting process part

Claims (7)

Screen burn-in used in a projection-type image display device comprising: a frame memory; a display unit that displays a screen based on video data stored in the frame memory; and a projection lens that projects the display screen of the display unit onto the screen. In the prevention device,
Shift means for shifting the projection screen on the screen;
Every time video data supplied from the outside is stored in the frame memory, a difference is detected between the video data stored last time and the video data stored this time, and the detected difference is equal to or greater than a threshold value. A still image / moving image determination processing unit that determines a case as a moving image and a case that is less than a threshold as a still image;
When the still image / moving image determination processing unit continuously determines a still image for a predetermined number of times or for a predetermined time, the display position of the video on the display screen of the display unit is shifted. A movement control unit that controls reading of video data from a frame memory to the display means,
The movement control unit controls a shift operation of the projection screen by the shift unit to adjust a display position shift on the screen accompanying a shift of a display position of an image on the display screen of the display unit. Screen burn-in prevention device.   2. The screen burn-in prevention device according to claim 1, wherein the movement control unit shifts a display position of an image on the display screen in a certain direction by a certain amount. When the still image / moving image determination processing unit determines a still image, a display pattern on the display screen is extracted based on video data stored in the frame memory, and the extracted display pattern is An image analysis unit for determining a moving direction and a moving amount of the display position so as not to overlap before and after shifting the display position of the image;
The movement control unit controls a video signal read operation from the frame memory and a shift operation of the projection screen by the shift unit based on a movement direction and a movement amount determined by an image analysis unit. The screen burn-in prevention device according to 1. The projection lens includes a plurality of lenses including a specific lens that can be shifted in a direction perpendicular to the optical axis,
The screen burn-in prevention device according to claim 1, wherein the shift unit includes the specific lens.   4. The screen burn-in prevention device according to claim 1, wherein the shift unit includes a moving unit that can move the display unit in two dimensions in an in-plane direction of the display screen. 5. A first step of displaying video data read from the frame memory on a screen;
A second step of projecting the display screen onto a screen;
Every time video data supplied from the outside is stored in the frame memory, a difference between the previously stored video data and the video data stored this time is detected, and the detected difference is equal to or greater than a threshold value. A third step of determining that a moving image is less than a threshold value as a still image;
Fourth step of controlling reading of video data from the frame memory so that the display position of the video on the screen is shifted when a still image is continuously determined for a predetermined number of times or for a predetermined time. When,
And a fifth step of shifting the projection screen on the screen in order to adjust the shift of the display position on the screen accompanying the shift of the display position of the image on the screen. When the still image is determined in the third step, a display pattern on the screen is extracted based on the video data stored in the frame memory, and the extracted display pattern indicates the display position of the video. A step of determining a moving direction and a moving amount of the display position so that they do not overlap before and after shifting,
The fourth step is a step of controlling reading of video data from the frame memory based on the determined moving direction and moving amount;
The screen burn-in prevention method according to claim 6, wherein the fifth step is a step of controlling a shift operation of the projection screen based on the determined moving direction and moving amount.

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