JP2012150262A - Difference calculation circuit, projector, and control method of difference calculation circuit - Google Patents

Abstract

A difference calculation circuit capable of detecting a change in an entire image is provided.
A difference calculation circuit includes a plurality of frame memories (a first frame memory 32a and a second frame memory 33a) for storing image information based on an input image signal, and an image stored in the frame memory. A pixel difference calculation unit 33c1 that calculates a difference between a plurality of frame memories as a pixel difference value for pixel information that is information for each pixel based on the information, and a difference average that calculates an average of the pixel difference values as a pixel difference average value The calculation unit 33c2, the all-pixel calculation unit 33c3 that calculates the pixel difference average value for all the pixels based on the image information, and all the pixels that calculate the average of the pixel difference average values of all the pixels as the all-pixel difference average value The comparison result of the average calculation unit 33c4, the comparison unit 33c6 that compares the average value of all pixel differences with a predetermined threshold, and the comparison result of the comparison unit 33c6 Zui by, and a notification unit 33f to output a predetermined notification signal.
[Selection] Figure 2

Description

  The present invention relates to a difference calculation circuit, a projector, and a control method for the difference calculation circuit.

  In a display device such as a liquid crystal display, a liquid crystal projector, or a plasma display, when a still image is displayed for a long time, a screen burn-in occurs. Therefore, a difference between data corresponding to the monitoring area set in a part of the screen is calculated, and a still image / moving image determination processing unit is provided that takes a moving image when the difference is equal to or larger than the threshold and a still image when the difference is smaller than the threshold. A screen burn-in prevention device is disclosed (Patent Document 1).

JP 2006-259287 A

  However, since the screen burn-in prevention device described in Patent Document 1 detects a difference in a specific area (monitoring area), there is a problem in that a change in the screen cannot be detected when the change area is out of the specific area. . In addition, when the difference detection in the screen burn-in prevention process is performed by software, there is a problem that the process takes time.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

  Application Example 1 The difference calculation circuit according to this application example includes a plurality of frame memories that store image information based on an input image signal, and information for each pixel based on the image information stored in the frame memory. For the pixel information, a pixel difference calculation unit that calculates a difference between the plurality of frame memories as a pixel difference value, and an average of the pixel difference values calculated by the pixel difference calculation unit is calculated as a pixel difference average value. A difference average calculation unit, an all-pixel calculation unit that calculates the pixel difference average value calculated by the difference average calculation unit for all pixels based on the image information, and all of the pixels calculated by the all-pixel calculation unit An all-pixel average calculating unit that calculates an average of the pixel difference average values as an all-pixel difference average value, and the all-pixel difference average value calculated by the all-pixel average calculating unit A comparator for comparing the threshold value, based on the comparison result of the comparison unit, characterized in that it and a notification unit for outputting a predetermined notification signal.

  According to such a difference calculation circuit, the pixel difference calculation unit calculates a pixel difference value between a plurality of frame memories. The difference average calculation unit calculates a pixel difference average value. The all pixel calculation unit calculates the pixel difference average value for all the pixels. The all-pixel average calculation unit calculates an average of the pixel difference average values of all the pixels to obtain a difference information value. Thereby, the average of the differences (pixel difference average value) is calculated for all the pixels, and further, the average of the pixel difference average values is calculated to obtain the total pixel difference average value, so that a change in the entire image information can be detected. it can.

  Application Example 2 In the difference calculation circuit according to the application example, the plurality of frame memories sequentially store image information based on sequentially input image signals.

  According to such a difference calculation circuit, the plurality of frame memories sequentially store image information based on sequentially input image signals. Thereby, since the all pixel difference average value is calculated based on all the input image information, the processing accuracy of the all pixel difference average value calculation is improved.

  Application Example 3 In the difference calculation circuit according to the application example, the all-pixel average calculation unit calculates the all-pixel difference average value when the image information based on the input image signal reaches a predetermined number. It is characterized by calculating.

  According to such a difference calculation circuit, the average value of all pixel differences is calculated when the image information reaches a predetermined number. As a result, the number of times of performing the calculation process of all pixel difference average values is reduced, and the processing load of the difference calculation circuit is reduced.

  Application Example 4 In the difference calculation circuit according to the application example described above, the difference calculation circuit further includes an addition value storage unit that adds the pixel difference values calculated by the pixel difference calculation unit and stores them as an addition difference value, and calculates the difference average calculation The unit calculates the pixel difference average value using the addition difference value stored in the addition value storage unit.

  According to such a difference calculation circuit, it further has an addition value storage unit, and the difference average calculation unit calculates the pixel difference average value using the addition difference value. Thereby, the pixel difference average value can be calculated over a plurality of frames without increasing the size of the frame memory.

  Application Example 5 A projector according to this application example includes a light source, a light modulation device that modulates light emitted from the light source into image light according to an image signal, and the image light modulated by the light modulation device. A projection optical system that projects a plurality of frame memories that store image information based on the input image signal, and for each pixel based on the image information stored in the frame memory. For pixel information that is information, a pixel difference calculation unit that calculates a difference between the plurality of frame memories as a pixel difference value, and an average of the pixel difference values calculated by the pixel difference calculation unit is calculated as a pixel difference average value A difference average calculation unit, and an all pixel calculation unit that calculates the pixel difference average value calculated by the difference average calculation unit for all pixels based on the image information; An all-pixel average calculating unit that calculates an average of all the pixel difference average values of all the pixels calculated by the all-pixel calculating unit as an all-pixel difference average value, and the all-pixel difference average calculated by the all-pixel average calculating unit A difference calculation circuit comprising: a comparison unit that compares a value with a predetermined threshold; and a notification unit that outputs a predetermined notification signal based on a comparison result of the comparison unit; and the difference calculation circuit that outputs the difference calculation circuit. And a control unit that performs a burn-in prevention process of the light modulation device based on a predetermined notification signal.

  According to such a projector, the burn-in prevention process of the light modulation device is performed based on the predetermined notification signal output from the difference calculation circuit. That is, it is possible to determine whether the input image signal is a still image by comparing the average value of all pixel differences with a predetermined threshold value. Can be prevented. Thereby, the burn-in of the light modulation device can be prevented.

  Application Example 6 A control method for a difference calculation circuit according to this application example is a control method for a difference calculation circuit having a plurality of frame memories for storing image information based on an input image signal. The pixel information, which is information for each pixel based on the image information stored in the pixel information, is calculated by a pixel difference calculation step for calculating a difference between the plurality of frame memories as a pixel difference value, and the pixel difference calculation step. A difference average calculation step for calculating an average of the pixel difference values as a pixel difference average value, and an all pixel calculation for calculating the pixel difference average value calculated by the difference average calculation step for all pixels based on the image information An average of the pixel difference average values of all pixels calculated by the step and the all pixel calculation step An all-pixel average calculating step that is calculated as an all-pixel difference average value, a comparison step that compares the all-pixel difference average value calculated by the all-pixel average calculation step with a predetermined threshold, and a comparison result by the comparison step And a notification step for outputting a predetermined notification signal.

  According to the control method of such a difference calculation circuit, in order to calculate an average difference (pixel difference average value) for all pixels, and further calculate an average of pixel difference average values to obtain an all pixel difference average value, Changes in the entire image information can be detected.

  Further, when the above-described difference calculation circuit and the control method thereof are constructed using a computer provided in the difference calculation circuit, the form and the application example described above are a program for realizing the function, or It is also possible to configure the recording medium in such a manner that the program is recorded so as to be readable by the computer. As a recording medium, a flexible disk, a hard disk, a CD-ROM (Compact Disk Read Only Memory), a DVD (Digital Versatile Disk), a Blu-ray Disc (registered trademark), a magneto-optical disk, a nonvolatile memory card, a difference calculation circuit, etc. Uses various computer-readable media such as internal storage (semiconductor memory such as RAM (Random Access Memory) and ROM (Read Only Memory)), and external storage (USB (Universal Serial Bus) memory, etc.) can do.

1 is a block diagram showing a circuit configuration of a projector according to an embodiment. The block diagram which shows the circuit structure of a difference information calculation part. Explanatory drawing of the outline | summary of a difference calculation process. The flowchart explaining the difference calculation process which a difference calculation circuit performs.

  Hereinafter, embodiments will be described.

  In the present embodiment, a projector that includes a difference calculation circuit and performs a screen burn-in prevention process based on an average calculation result of all pixel differences of the difference calculation circuit will be described. Hereinafter, the process for calculating the average difference of all pixels is also referred to as a difference calculation process.

FIG. 1 is a block diagram showing a circuit configuration of a projector according to the present embodiment.
As shown in FIG. 1, the projector 1 includes an image projection unit 10, a control unit 20, an operation reception unit 21, a light source control unit 22, an image signal input unit 31, an image processing unit 32, a difference information calculation unit 33, and the like. It is configured.

  The image projection unit 10 includes a light source 11, three liquid crystal light valves 12R, 12G, and 12B as light modulation devices, a projection lens 13 as a projection optical system, a light valve drive unit 14, and the like. The image projection unit 10 modulates the light emitted from the light source 11 with the liquid crystal light valves 12R, 12G, and 12B to form image light, projects the image light from the projection lens 13, and displays it on the screen SC or the like. .

  The light source 11 includes a discharge-type light source lamp 11a made of an ultra-high pressure mercury lamp, a metal halide lamp, or the like, and a reflector 11b that reflects light emitted from the light source lamp 11a toward the liquid crystal light valves 12R, 12G, and 12B. ing. Light emitted from the light source 11 is converted into light having a substantially uniform luminance distribution by an integrator optical system (not shown), and each color light of red R, green G, and blue B, which is the three colors of light, by a color separation optical system (not shown). After being separated into components, they are incident on the liquid crystal light valves 12R, 12G, and 12B, respectively.

  The liquid crystal light valves 12R, 12G, and 12B are configured by a liquid crystal panel in which liquid crystal is sealed between a pair of transparent substrates. In the liquid crystal light valves 12R, 12G, and 12B, a plurality of pixels (not shown) arranged in a matrix are formed, and a driving voltage can be applied to the liquid crystal for each pixel. When the light valve driving unit 14 applies a driving voltage corresponding to the input image information to each pixel, each pixel is set to a light transmittance corresponding to the image information. For this reason, the light emitted from the light source 11 is modulated by transmitting through the liquid crystal light valves 12R, 12G, and 12B, and an image corresponding to the image information is formed for each color light. The formed color images are synthesized for each pixel by a color synthesis optical system (not shown) to form a color image, and then projected from the projection lens 13.

  The control unit 20 includes a CPU (Central Processing Unit), a RAM used for temporary storage of various data, and a non-volatile memory such as a mask ROM, flash memory, FeRAM (Ferroelectric RAM), etc. (Not shown) and functions as a computer. The control unit 20 performs overall control of the operation of the projector 1 by the CPU operating according to a control program stored in a nonvolatile memory.

  Further, when the control unit 20 receives a predetermined notification signal that the image is a still image from the difference information calculation unit 33, the control unit 20 prevents the image processing unit 32 from burning the liquid crystal light valves 12R, 12G, and 12B. To give instructions. For example, the image processing unit 32 can output a screen saver screen. Note that the burn-in prevention process is not limited to the screen saver screen output process, and may be another process.

  The operation receiving unit 21 receives an input operation from the user, and includes a plurality of operation keys for the user to give various instructions to the projector 1. The operation keys included in the operation receiving unit 21 include a power key for switching power on / off, an input switching key for switching an input image signal, and display / non-display of a menu screen for performing various settings. There are a menu key to be switched, a cursor key used for moving a cursor on the menu screen, and a determination key for determining various settings. When the user operates (presses) various operation keys of the operation receiving unit 21, the operation receiving unit 21 receives this input operation and outputs an operation signal corresponding to the operation content of the user to the control unit 20. The operation receiving unit 21 may be configured using a remote control (not shown) capable of remote operation. In this case, the remote controller transmits an operation signal such as an infrared ray corresponding to the operation content of the user, and a remote control signal receiver (not shown) receives the signal and transmits it to the controller 20.

  The light source control unit 22 performs an insulation breakdown between electrodes of an inverter (not shown) that converts a direct current generated by a power supply circuit (not shown) into an alternating current rectangular wave current and an electrode of the light source lamp 11a. An igniter (not shown) for urging the start of 11a is provided, and lighting of the light source 11 is controlled based on an instruction from the control unit 20. Specifically, the light source control unit 22 can turn on the light source 11 by starting the light source 11 and supplying predetermined power, and can stop the supply of power and turn off the light source 11. The light source control unit 22 can adjust the luminance (brightness) of the light source 11 by controlling the power supplied to the light source 11 based on an instruction from the control unit 20.

  The image signal input unit 31 includes various input terminals (for example, a personal computer, a video playback device, a memory card, a USB storage, a digital camera, etc.) for connecting to an external image supply device (not shown) via a cable. (Not shown), and an image signal is input from the image supply device. The image signal input unit 31 converts the input image signal into image information in a format that can be processed by the image processing unit 32, and outputs the image information to the image processing unit 32.

  The image processing unit 32 includes a first frame memory 32a configured by a RAM or the like. Then, the image information input from the image signal input unit 31 is converted into image information representing the gradation of each pixel of the liquid crystal light valves 12R, 12G, and 12B, and is stored in the first frame memory 32a in units of frames (screens). Remember. The image information for one screen stored in the frame memory is called a frame image.

  Here, the converted image information is for each color light of R, G, and B, and is composed of a plurality of pixel values corresponding to all the pixels of the liquid crystal light valves 12R, 12G, and 12B. The pixel value determines the light transmittance of the corresponding pixel, and the intensity (gradation) of light emitted from each pixel is defined by the pixel value. Further, the image processing unit 32 performs image quality adjustment processing for adjusting brightness, contrast, sharpness, hue, and the like on the converted image information based on an instruction from the control unit 20, and the first frame memory. The image information in 32a is updated. Then, the processed image information is output to the light valve drive unit 14 and the difference information calculation unit 33.

  The difference information calculation unit 33 is a circuit that performs a difference calculation process for calculating an average value of all pixel differences. The difference information calculation unit 33 includes a second frame memory 33a and an addition value storage unit 33b. In the present embodiment, the first frame memory 32a and the difference information calculation unit 33 included in the image processing unit 32 correspond to a difference calculation circuit.

Here, the difference information calculation unit 33 will be described.
FIG. 2 is a block diagram illustrating a circuit configuration of the difference information calculation unit 33 according to the present embodiment.
As shown in FIG. 2, the difference information calculation unit 33 includes a second frame memory 33a, an addition value storage unit 33b, a difference calculation processing unit 33c, a pixel number counter 33d, a frame number counter 33e, a notification unit 33f, and the like. It is configured.

  The second frame memory 33a is a frame memory constituted by a RAM or the like. In the second frame memory 33a, the image information of the previous frame stored in the first frame memory 32a is copied and stored. The difference calculation processing unit 33c performs writing and reading to the second frame memory 33a.

  The added value storage unit 33b is a storage unit configured by a RAM or the like. In the addition value storage unit 33b, pixel image information stored in the first frame memory 32a (pixel image information is also referred to as “pixel information”) and pixel image stored in the second frame memory 33a. The absolute value of the difference from the information can be added to the past n-2 times for each pixel and stored as an added difference value. The difference calculation processing unit 33c performs writing to and reading from the addition value storage unit 33b.

  The pixel number counter 33d receives a pixel number clock output from the image processing unit 32 and included in the image information, and measures the number of pixels. In the present embodiment, the number N of pixels on one screen is measured as the number of pixels. For example, when the image information is XGA, 1024 × 768 pixels are measured as the number of pixels N per screen. Note that the setting value of the number of pixels measured by the pixel number counter 33d may be changeable. In this case, the difference information calculation unit 33 includes a pixel number measurement setting register (not shown), and changes the setting value of the pixel number measurement setting register according to an instruction from the control unit 20 based on a user operation. Then, the number of pixels to be measured is changed based on the setting value of the pixel number measurement setting register. In this way, it is possible to cope with image information (image signal) having a different number of pixels on one screen.

  The frame number counter 33e receives a vertical synchronization signal output from the image processing unit 32 as included in the image information, and measures the number of frames (that is, the number of screens). In this embodiment, n frames are measured as the number of frames. Here, n corresponds to a predetermined number. For example, if n is 3600 frames, 60 seconds can be measured with a projector that displays an image of 60 frames per second. Note that the setting value of the number of measurement frames measured by the frame number counter 33e may be changeable. In this case, the difference information calculation unit 33 includes a frame number measurement setting register (not shown), and changes the setting value of the frame number measurement setting register according to an instruction from the control unit 20 based on a user operation. Then, the number of frames to be measured is changed based on the setting value of the frame number measurement setting register. By doing this, it is possible to change the measurement time of the difference calculation process (that is, the process of determining whether an image is a still image) by changing the number of frames to be measured.

  The difference calculation processing unit 33c includes a pixel difference calculation unit 33c1, a difference average calculation unit 33c2, an all pixel calculation unit 33c3, an all pixel average calculation unit 33c4, a threshold storage unit 33c5, a comparison unit 33c6, and the like.

  The pixel difference calculation unit 33c1 calculates a difference between pixel information input from the first frame memory 32a of the image processing unit 32 and pixel information input from the second frame memory 33a as a pixel difference value, and calculates a difference average It outputs to the calculation part 33c2.

  The difference average calculation unit 33c2 adds the absolute value of the input pixel difference value and the addition difference value stored in the addition value storage unit 33b. When the number of measurement frames is less than n frames, the added value is stored in the added value storage unit 33b. When the number of measurement frames becomes n frames, the added value is divided by n−1 and calculated as a pixel difference average value.

  The all-pixel calculating unit 33c3 causes the difference average calculating unit 33c2 to calculate the pixel difference average value for all the pixels of the frame image.

  The all-pixel average calculation unit 33c4 calculates the all-pixel difference average value by adding the pixel difference average values of all the pixels and dividing by the number of pixels N.

  The threshold value storage unit 33c5 is a non-volatile memory that stores a predetermined threshold value (hereinafter also simply referred to as “threshold value”) for comparison with the average value of all pixel differences. The predetermined threshold is a comparison value for determining whether or not the image is a still image, and a suitable value is determined in advance by an experiment or the like. Further, the threshold value stored in the threshold value storage unit 33c5 may be changeable. In this case, the difference information calculation unit 33 includes a threshold setting register (not shown), and changes the setting value of the threshold setting register according to an instruction from the control unit 20 based on a user operation. Then, the threshold value is changed based on the set value of the threshold value setting register.

  The comparison unit 33c6 compares the all pixel difference average value calculated by the all pixel average calculation unit 33c4 with the threshold value set in the threshold value storage unit 33c5, and determines whether or not the all pixel difference average value is smaller than the threshold value. To do. Then, the comparison unit 33c6 notifies the notification unit 33f of the comparison result.

  The notification unit 33f includes a predetermined communication unit and notifies the control unit 20 of the notification. The predetermined communication means may be RS-232C, for example, but is not limited thereto. Based on the comparison result input from the comparison unit 33c6, the notification unit 33f provides a predetermined notification indicating that the image is a still image to the control unit 20 when the average value of all pixel differences is smaller than the threshold value. Send a signal.

  Returning to FIG. 1, when the light valve driving unit 14 drives the liquid crystal light valves 12R, 12G, and 12B according to the image information input from the image processing unit 32, the liquid crystal light valves 12R, 12G, and 12B correspond to the image information. An image is formed, and this image is projected from the projection lens 13.

Next, an outline of the difference calculation process of the projector 1 will be described.
FIG. 3 is an explanatory diagram of an outline of the difference calculation process.

  In FIG. 3, a first frame F1, a second frame F2, a third frame F3, an (n-1) th frame Fn-1, and an nth frame Fn are displayed. In the difference calculation process, a pixel difference value between frames, that is, a difference in pixel information is calculated for a predetermined pixel p1 of the frame. In the present embodiment, the difference between the pixel information is the sum of the differences between the R, G, and B color light values. Note that the difference in pixel information is not limited to this calculation method. For example, the luminance value is calculated based on the values of R, G, and B color light, and the difference between the luminance values may be used as the difference in pixel information. Good.

  As shown in FIG. 3, the difference (pixel difference value) in the pixel p1 between the frames F1 and F2 is Δ1, the difference (pixel difference value) in the pixel p1 between the frames F2 and F3 is Δ2, and the frame Fn−1 The difference (pixel difference value) in the pixel p1 of the frame Fn-2 (not shown) is Δn−2, and the difference (pixel difference value) in the pixel p1 of the frame Fn and the frame Fn−1 is Δn−1.

  Here, the addition difference value S stored in the addition value storage unit 33b is a value obtained by adding absolute values from Δ1 to Δn−2, as shown in Expression (1) of FIG. Further, the pixel difference average value P1 of the pixel p1 is a value obtained by adding the addition difference value S to the absolute value of Δn−1 and dividing by n−1 as shown in the equation (2) of FIG. Such a pixel difference average value P1 is applied to all the pixels of the frame, and P1 to PN are calculated. Then, as shown in Expression (3) in FIG. 3, the total pixel difference average value C is calculated by adding the pixel difference average values P1 to PN and dividing by the pixel number N.

  It is possible to determine whether or not the image information is a still image by comparing the average value C of all pixel differences calculated in this way with a threshold value stored in the threshold value storage unit 33c5.

Next, an operation in which the difference calculation circuit (the first frame memory 32a and the difference information calculation unit 33) of the projector 1 performs the difference calculation process will be described.
FIG. 4 is a flowchart illustrating a difference calculation process performed by the difference calculation circuit.

  When new image information is input to the first frame memory 32a, the difference information calculation unit 33 adds 1 to the number of measurement frames measured by the frame number counter 33e (step S101). The difference information calculation unit 33 determines whether the number of measurement frames has reached n (step S102).

  When the number of measurement frames is not n (step S102: NO), the difference calculation processing unit 33c of the difference information calculation unit 33 performs the processing from step S103 to step S106 for all the pixels (N) of the frame image. Is repeated (loop 1) (step S103). First, the pixel difference calculation unit 33c1 of the difference calculation processing unit 33c calculates a pixel difference value for the same pixel in the first frame memory 32a and the second frame memory 33a (step S104). Next, the difference calculation processing unit 33c adds the absolute value of the pixel difference value to the addition difference value S stored in the addition value storage unit 33b, and stores it in the addition value storage unit 33b (step S105). Then, the process returns to step S103 (step S106).

  When the loop 1 is completed, the difference calculation processing unit 33c copies the image information of the frame in the first frame memory 32a to the second frame memory 33a (step S107). Then, the difference calculation process ends.

  When the number of measurement frames is n (step S102: YES), the difference calculation processing unit 33c of the difference information calculation unit 33 performs the processing from step S108 to step S112 for all the pixels (N) of the frame image. Repeat (loop 2) (step S108). First, the pixel difference calculation unit 33c1 of the difference calculation processing unit 33c calculates a pixel difference value for the same pixel in the first frame memory 32a and the second frame memory 33a (step S109). Next, the difference average calculation unit 33c2 of the difference calculation processing unit 33c adds the absolute value of the pixel difference value and the addition difference value S stored in the addition value storage unit 33b (step S110). And the difference average calculation part 33c2 calculates the pixel difference average value (P1-PN) by dividing the added result by n-1 (step S111). Then, the process returns to step S108 (step S112).

  When the loop 2 ends, the all-pixel average calculation unit 33c4 of the difference calculation processing unit 33c sums up the calculated pixel difference average values for all the calculated pixels (N) (step S113). Then, the all-pixel average calculating unit 33c4 calculates the all-pixel difference average value C by dividing the total of all the pixel difference average values by the number of pixels N (step S114).

  The comparison unit 33c6 of the difference calculation processing unit 33c determines whether or not the calculated all-pixel difference average value C is smaller than the threshold value stored in the threshold value storage unit 33c5 (step S115). When the all-pixel difference average value C is smaller than the threshold value (step S115: YES), the difference calculation processing unit 33c issues an instruction to the notification unit 33f and notifies the control unit 20 that the image based on the image information is a still image. Is transmitted (step S116). Then, the difference calculation processing unit 33c clears the addition difference value S stored in the addition value storage unit 33b (step S117). Further, the difference information calculation unit 33 clears the number of measurement frames measured by the frame number counter 33e (step S118). Then, the process proceeds to step S107.

  When the all-pixel difference average value C is equal to or larger than the threshold (step S115: NO), the process proceeds to step S117.

  As described above, the difference calculation circuit calculates the pixel difference value and stores it as the addition difference value S until the number of measurement frames reaches n. When the number of measurement frames reaches n, the difference between all pixels is calculated. When the average value C is calculated and the all-pixel difference average value C is smaller than the threshold value, a predetermined notification signal indicating that the image between the frame number n is a still image is transmitted to the control unit 20. To do.

According to the embodiment described above, the following effects can be obtained.
(1) The projector 1 calculates an average difference (pixel difference average values P1 to PN) for all pixels, and further calculates an average of the pixel difference average values P1 to PN to obtain an all pixel difference average value C. It is possible to detect a change in the entire image information, not a change in the image information in a specific area of the frame image. Then, the average value C of all pixel differences is compared with the threshold value, and when the image is determined to be a still image, the burn-in prevention process for the liquid crystal light valves 12R, 12G, and 12B can be performed.

  (2) The projector 1 compares the average value C of all pixel differences with a threshold value, and determines whether the image is a still image. Therefore, by setting a suitable threshold value through an experiment or the like in advance, even if there is a local change in the image, it can be determined as a still image, and the burn-in prevention process can be performed.

  (3) In the projector 1, since the difference information calculation unit 33 is configured as a dedicated circuit (hardware), the difference calculation process can be speeded up. That is, the load on the CPU provided in the control unit 20 can be reduced. Therefore, the time during which the software can be executed on the CPU increases. For this reason, even if the same CPU is used, it is possible to provide a product having more functions than in the past.

  (4) In the projector 1, the first frame memory 32a and the second frame memory 33a sequentially store image information based on sequentially input image signals. Thereby, since the all-pixel difference average value C is calculated based on all input image information, the still image detection accuracy by the difference calculation processing is improved.

  (5) The projector 1 calculates the all-pixel difference average value C when the number of measurement frames reaches n frames. Thereby, since the number of times of performing the calculation process of the all-pixel difference average value C is reduced, the processing load of the difference information calculation unit 33 (difference calculation circuit) is reduced.

  (6) The projector 1 includes the addition value storage unit 33b, and the difference information calculation unit 33 calculates the all-pixel difference average value C using the addition difference value S. Thereby, the number of frame memories for calculating the all-pixel difference average value C can be reduced.

  In addition, it is not limited to embodiment mentioned above, It is possible to implement by adding various change, improvement, etc. A modification will be described below.

  (Modification 1) In the above embodiment, pixel difference values are added until the number of measurement frames reaches n frames, and the average value C of all pixel differences is calculated when the number of measurement frames reaches n frames. The calculation process for every n frames is repeated. However, when the difference information calculation unit 33 is provided with n frame memories (or frame memories capable of storing n frame images), the pixel difference average is obtained by sequentially inputting the image information to the n frame memories. The values P1 to PN may be calculated for each input of image information, and the all pixel difference average value C may be calculated each time and compared with a threshold value. In this way, it is always possible to determine whether or not the image is a still image, and the determination accuracy is improved.

  (Modification 2) In the above embodiment, the difference calculation process is performed by a difference calculation circuit, that is, hardware. However, the difference calculation process performed by the difference calculation processing unit 33c may be performed by software. Further, the difference calculation circuit may be configured by hardware (circuit) in which a software program is incorporated.

  (Modification 3) In the above embodiment, the comparison unit 33c6 determines whether or not the all-pixel difference average value C is smaller than the threshold value. Good.

  (Modification 4) In the above embodiment, if the comparison unit 33c6 determines that the all-pixel difference average value C is equal to or greater than the threshold, the notification unit 33f does not transmit a predetermined notification signal to the control unit 20. However, a notification signal indicating that the image is a moving image may be transmitted to the control unit 20.

  (Modification 5) In the above-described embodiment, the calculated all-pixel difference average value C cannot be monitored (monitored), but the difference calculation circuit may include an all-pixel difference average value monitoring register (not shown). Good. This makes it possible to monitor the average value C of all pixel differences.

  (Modification 6) In the above embodiment, the image information input to the first frame memory 32a is sequentially copied to the second frame memory 33a and the difference calculation process is performed. The image information input to 32a may be copied to the second frame memory 33a once every predetermined number of times (frames), and the difference calculation process may be performed once every predetermined number of times (frames). In this way, the processing load on the projector 1 can be reduced.

  (Modification 7) In the above embodiment, the projector 1 including the difference calculation circuit is described as an example, but the present invention is not limited to the projector. For example, the present invention can be applied to a rear projector, a plasma display, an organic EL (Electro Luminescence) display, and the like that are integrally provided with a transmission screen.

  (Modification 8) In the above embodiment, the light source 11 is constituted by the discharge-type light source lamp 11a, but a solid light source such as an LED (Light Emitting Diode) light source or a laser, or other light sources can also be used. .

  (Modification 9) In the above embodiment, the transmissive liquid crystal light valves 12R, 12G, and 12B are used as the light modulator, but a reflective light modulator such as a reflective liquid crystal light valve may be used. Is possible.

  DESCRIPTION OF SYMBOLS 1 ... Projector, 10 ... Image projection part, 11 ... Light source, 11a ... Light source lamp, 11b ... Reflector, 12R, 12G, 12B ... Liquid crystal light valve, 13 ... Projection lens, 14 ... Light valve drive part, 20 ... Control part, DESCRIPTION OF SYMBOLS 21 ... Operation reception part, 22 ... Light source control part, 31 ... Image signal input part, 32 ... Image processing part, 32a ... 1st frame memory, 33 ... Difference information calculation part, 33a ... 2nd frame memory, 33b ... Addition value storage unit, 33c ... difference calculation processing unit, 33d ... pixel number counter, 33e ... frame number counter, 33f ... notification unit, 33c1 ... pixel difference calculation unit, 33c2 ... difference average calculation unit, 33c3 ... all pixel calculation unit, 33c4... All pixel average calculation unit, 33c5... Threshold storage unit, 33c6.

Claims (6)

A plurality of frame memories for storing image information based on the input image signal;
A pixel difference calculation unit that calculates a difference between the plurality of frame memories as a pixel difference value for pixel information that is information for each pixel based on the image information stored in the frame memory;
A difference average calculation unit that calculates an average of the pixel difference values calculated by the pixel difference calculation unit as a pixel difference average value;
An all-pixel calculation unit that calculates the pixel difference average value calculated by the difference average calculation unit for all pixels based on the image information;
An all-pixel average calculating unit that calculates an average of all the pixel difference average values of all the pixels calculated by the all-pixel calculating unit as an all-pixel difference average value;
A comparison unit that compares the all-pixel difference average value calculated by the all-pixel average calculation unit with a predetermined threshold;
A notification unit that outputs a predetermined notification signal based on a comparison result of the comparison unit;
A difference calculation circuit comprising: The difference calculation circuit according to claim 1,
The plurality of frame memories sequentially store image information based on sequentially input image signals. The difference calculation circuit according to claim 1 or 2,
The all-pixel average calculating unit calculates the all-pixel difference average value when image information based on an input image signal reaches a predetermined number. The difference calculation circuit according to claim 3,
An addition value storage unit that adds the pixel difference values calculated by the pixel difference calculation unit and stores them as an addition difference value;
The difference average calculation unit calculates the pixel difference average value by using the addition difference value stored in the addition value storage unit. A projector comprising: a light source; a light modulation device that modulates light emitted from the light source into image light according to an image signal; and a projection optical system that projects the image light modulated by the light modulation device. And
A plurality of frame memories for storing image information based on the input image signal;
A pixel difference calculation unit that calculates a difference between the plurality of frame memories as a pixel difference value for pixel information that is information for each pixel based on the image information stored in the frame memory;
A difference average calculation unit that calculates an average of the pixel difference values calculated by the pixel difference calculation unit as a pixel difference average value;
An all-pixel calculation unit that calculates the pixel difference average value calculated by the difference average calculation unit for all pixels based on the image information;
An all-pixel average calculating unit that calculates an average of all the pixel difference average values of all the pixels calculated by the all-pixel calculating unit as an all-pixel difference average value;
A comparison unit that compares the all-pixel difference average value calculated by the all-pixel average calculation unit with a predetermined threshold;
A notification unit that outputs a predetermined notification signal based on a comparison result of the comparison unit;
A difference calculation circuit having
Based on the predetermined notification signal output from the difference calculation circuit, a control unit that performs burn-in prevention processing of the light modulation device;
A projector comprising: A method for controlling a difference calculation circuit having a plurality of frame memories for storing image information based on an input image signal,
A pixel difference calculation step of calculating a difference between the plurality of frame memories as a pixel difference value for pixel information that is information for each pixel based on the image information stored in the frame memory;
A difference average calculation step of calculating an average of the pixel difference values calculated by the pixel difference calculation step as a pixel difference average value;
An all pixel calculation step for calculating the pixel difference average value calculated by the difference average calculation step for all pixels based on the image information;
An all-pixel average calculating step of calculating an average of all the pixel difference average values of all the pixels calculated by the all-pixel calculating step as an all-pixel difference average value;
A comparison step of comparing the all-pixel difference average value calculated by the all-pixel average calculation step with a predetermined threshold;
A notification step of outputting a predetermined notification signal based on the comparison result of the comparison step;
A control method for a difference calculation circuit comprising:

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