JP2009069661A - Projection device, projection method, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To cope with degradation in image quality due to A/D conversion errors of an image signal, without being conspicuous on a projection. <P>SOLUTION: A projection device includes: an input/output connector part 21 and an input/output I/F 22 for inputting an image signal having an analog value; an A/D conversion part 22a for digitizing the input image signal; projection systems 23 to 37 for forming and emitting an optical image according with the image signal obtained by the A/D conversion part 22a; an image storage part 42 for storing the image signal obtained by the A/D conversion part 22a; and control systems 38 to 40 for judging whether an image obtained by the A/D conversion part 22a is a still image or not and using the image signal stored by the image storage part 42 instead of the image signal obtained by the A/D conversion part 22a, to project an image by the projection systems 23 to 37, in accordance with the determination result. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a projection apparatus, a projection method, and a program for inputting and projecting an analog image signal from the outside.

2. Description of the Related Art Conventionally, a wide range of projector apparatuses that connect an external device such as a personal computer, form an optical image corresponding to an analog image signal sent from the external device, and irradiate the image onto a projection target screen Widely used and various technologies are considered. (For example, Patent Document 1)
JP 2001-228537 A

  In the projector apparatus having an A / D converter that performs projection after digitizing an input analog value image signal including the technique described in Patent Document 1, an A / D conversion error is caused by an image frame. By expressing each, noise due to the variation occurs.

  This is because the projected image acts as an afterimage with the naked eye, and particularly when projecting a still image in which the content of the image does not change, it appears as flickering of the image, and it is recognized that the image quality has deteriorated significantly. was there.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to process degradation of image quality due to a conversion error when digitizing and projecting an analog image signal without conspicuously appearing on the projected image. An object of the present invention is to provide a projection apparatus, a projection method, and a program that can be used.

  The invention described in claim 1 is obtained by an image input means for inputting an analog image signal, an A / D conversion means for digitizing the image signal input by the image input means, and the A / D conversion means. A projection unit that forms and emits an optical image according to an image signal, a storage unit that stores an image signal obtained by the A / D conversion unit, and an image obtained by the A / D conversion unit are still images. A first determination means for determining whether or not the image signal stored in the storage means is used instead of the image signal obtained by the A / D conversion means in accordance with the determination result of the first determination means. Projection control means for projecting by the projection means.

  The invention described in claim 2 is obtained by an image input means for inputting an analog image signal, an A / D conversion means for digitizing the image signal input by the image input means, and the A / D conversion means. Projection means for forming and emitting a light image corresponding to the image signal, storage means for storing the image signal obtained by the A / D conversion means, and image signal input by the image input means are the A / D A second judging means for judging whether or not a digital image signal having a higher precision than the precision in the converting means is an analog signal, and according to the judgment result in the second judging means, the A / Projection control means for projecting by the projection means using the image signal stored in the storage means instead of the image signal obtained by the D conversion means is provided.

  According to a third aspect of the present invention, in the first and second aspects of the present invention, the projection control means prioritizes the determination result of one of the first and second determination means.

  The invention according to claim 4 is a projection method in a projection apparatus that inputs an analog image signal, digitizes the input image signal, forms a light image, and emits the light image. A storing step for storing, a first determining step for determining whether or not the digitized image is a still image, and the digitized image signal instead of the digitized image signal according to the determination result in the first determining step. And a projection control step of projecting using the image signal stored in the storage step.

  The invention according to claim 5 is a projection method in a projection apparatus for inputting an analog image signal, digitizing the input image signal to form an optical image, and emitting the optical image. A storing step for storing; a second determining step for determining whether the input image signal is an analog image signal having a digital value higher than the accuracy of the digitizing process; A projection control step of projecting using the image signal stored in the storage step instead of the digitized image signal in accordance with the determination result in the second determination step.

  The invention described in claim 6 is a program executed by a computer incorporated in a projection apparatus that inputs an analog image signal, digitizes the input image signal to form a light image, and emits the light image. A storage step for storing the digitized image signal, a first determination step for determining whether or not the digitized image is a still image, and the digitization according to a determination result in the first determination step. And a projection control step of projecting using the image signal stored in the storing step instead of the image signal.

  The invention described in claim 7 is a program executed by a computer incorporated in a projection apparatus that inputs an analog image signal, digitizes the input image signal to form a light image, and emits the light image. A storage step for storing the converted image signal, and a second determination for determining whether the input image signal is an analog image signal having a digital value higher than the accuracy of the digitization process. And causing the computer to execute a step and a projection control step of projecting using the image signal stored in the storage step instead of the digitized image signal in accordance with the determination result in the second determination step. And

  According to the present invention, it is possible to process image quality deterioration due to a conversion error when digitizing and projecting an analog image signal without conspicuously appearing on the projected image.

(First embodiment)
A first embodiment in which the present invention is applied to a DLP (Digital Light Processing) (registered trademark) data projector apparatus will be described below with reference to the drawings.

  FIG. 1 shows an external configuration of a data projector apparatus 10 according to the embodiment. In the figure, the data projector device 10 is provided with a projection lens unit 12 and an Ir receiving unit 13 on the front surface of a rectangular parallelepiped main body casing 11.

  Further, a speaker unit 14, an indicator unit 15, and a key operation unit 16 are disposed on the upper surface of the main body casing 11.

  The projection lens unit 12 enlarges an optical image created inside and projects it onto a screen or the like, and can change the in-focus position and the zoom position (projection angle of view) arbitrarily.

  The Ir receiving unit 13 is a part that receives an infrared modulation signal from a remote controller (not shown) of the data projector device 10, and a similar receiving unit is also provided on the back side of the data projector device 10. .

  The speaker unit 14 emits a voice signal input together with the image signal, a voice message stored in the data projector device 10 in advance, a beep sound, and the like.

  The indicator unit 15 displays the power on / off state, the case where the temperature of the light source lamp described later becomes abnormal, and the like by lighting / flashing of an LED (light emitting diode) provided therein.

  The key operation unit 16 directly accepts user key operations and controls various projection operations. For example, a power key, an input switching key, a zoom up / down key, an AFK (Auto Focus / automatic Keystone correction) Focus / automatic keystone correction) key, menu key, cursor keys (“↑”, “↓”, “←”, “→”), enter key, cancel key, etc.

  In addition, a pair of adjustment legs 17A and 17B are provided at the left and right ends of the lower front end of the data projector device 10. Although not shown, another fixed leg portion is provided at the center of the rear end of the lower surface of the data projector device 10, and the data projector device 10 is supported by a total of three leg portions and located on the front side. By adjusting the respective leg lengths of the adjusting leg portions 17A and 17B, the elevation angle of the projection optical axis of the projection lens unit 12 and the left / right inclination of the projected image can be adjusted.

  Although not shown here, the back surface of the main body casing 11 is provided with a connector portion for inputting / outputting various image signals, an anti-theft fitting mounting portion, an Ir receiving portion similar to the Ir receiving portion 13 and the like.

FIG. 2 is a block diagram showing a functional configuration of an electronic circuit provided in the data projector device 10.
In the figure, reference numeral 21 denotes an input / output connector portion provided on the back side of the main body casing 11 and includes, for example, a pin jack (RCA) type video input terminal, RGB input terminal, and USB terminal.

  Image signals of various standards input from the input / output connector unit 21 are A / D converted by the A / D conversion unit 22a in the input / output interface (I / F) 22, if necessary, and then via the system bus SB. After the image conversion unit 23 unifies the image signal in a predetermined format including the number of gradations, the image conversion unit 23 sends the image signal to the projection drive unit 24.

  At this time, the OSD (On Screen Display) mode image and symbols such as a pointer are also sent to the projection drive unit 24 in a state of being superimposed on the image signal as necessary.

  The projection drive unit 24 develops and stores the transmitted image signal in the video RAM 25 and then generates a video signal from the stored contents of the video RAM 25.

  The projection driving unit 24 multiplies the frame rate of the video signal, for example, 60 [frames / second], the number of color component divisions, and the number of display gradations, to perform a spatial light modulation element ( For example, the micromirror element 26 which is SOM) is driven to display.

  On the other hand, a light source lamp 28 using, for example, an ultra-high pressure mercury lamp disposed in the reflector 27 emits white light with high luminance. The white light emitted from the light source lamp 28 is colored into a primary color in a time-sharing manner through the color wheel 29, converted into a luminous flux having a uniform luminance distribution by the integrator 30, and then totally reflected by the mirror 31 to the micromirror element 26. Irradiated.

  Thus, an optical image is formed by the reflected light from the micromirror element 26, and the formed optical image is projected and displayed on the screen (not shown) to be projected through the projection lens unit 12.

  As described above, the projection lens unit 12 enlarges and projects the light image formed by the micromirror element 26 onto a target such as a screen, and the focus position and the zoom position (projection angle of view) can be arbitrarily changed. Shall.

  That is, among a plurality of optical lenses constituting the projection lens unit 12, both a focus lens and a zoom lens (not shown) are controlled by moving back and forth along the optical axis direction, and these lenses are stepping motors (M). It moves by 32 rotational drive.

  A cooling fan 33 for cooling the light source lamp 28 is rotationally driven by a motor (M) 34. Further, a motor (M) 35 for rotating the color wheel 29 is provided.

  However, the light source lamp 28 is turned on, the color wheel 29 motor 35 is rotated, the cooling fan 33 motor 34 is rotated, and the stepping motor 32 is rotated. Will run.

  In addition, the projection light processing unit 36 receives temperature data from a temperature sensor 37 that is attached to the reflector 27 and detects the temperature of the light source lamp 28.

  The CPU 38 controls all the operations of the above circuits. The CPU 38 uses a main memory 39 composed of SDRAM (synchronous DRAM) and a program memory 40 composed of an electrically rewritable nonvolatile memory storing operation programs, various fixed data, and the like in the data projector apparatus 10. The control operation is executed.

  The CPU 38 executes various projection operations in accordance with operation signals from the operation unit 41. The operation unit 41 includes the key operation unit 16, the Ir reception unit 13, and the Ir reception unit provided on the back surface of the main body casing 11 in the same manner as the Ir reception unit 13. The user can directly or via a remote controller. A key code signal based on the operated key is directly output to the CPU 38.

  The CPU 38 is further connected to the image storage unit 42, the indicator unit 15, the sound processing unit 43, and the power supply controller 44 via the system bus SB.

  The image storage unit 42 has a storage capacity for storing image signals for at least two frames, and the stored content is appropriately rewritten by the CPU 38.

  The sound processing unit 43 includes a sound source circuit such as a PCM sound source, converts the sound data given at the time of the projection operation into an analog signal, drives the speaker unit 14 to emit a loud sound, or generates a beep sound or the like as necessary.

  The power supply controller 44 connects the AC input unit 45. The AC input unit 45 rectifies and transforms an AC voltage applied from the outside of the apparatus into a predetermined voltage, for example, a DC voltage of 6 [V], and outputs the converted voltage to the power supply controller 44.

The power controller 44 transforms and supplies the DC voltage from the AC input unit 45 to a plurality of DC voltages suitable for the operation of each circuit. Next, the operation of the above embodiment will be described.
In FIG. 3, an external device such as a personal computer is connected to a pin jack (RCA) type video input terminal or RGB input terminal of the input / output connector section 21, and an analog image signal is input through these terminals. The projection operation in this case is shown, and all the operation control is executed by the CPU 38 while reading the operation program stored in the program memory 40 and developing it in the main memory 39.

  At the beginning of processing, image signals input via the input / output connector unit 21 are sequentially A / D converted (step S101), and the digitized image signal obtained by the A / D conversion is stored in the image storage unit. 42 (step S102).

  Each time storage in the image storage unit 42 is performed, whether or not an image signal for one frame has been stored is stored in the image storage unit 42, for example, from the vertical synchronization pulse in the image signal to the next vertical synchronization pulse. The determination is made based on whether or not the image data is stored (step S103). If image data for one frame is not stored, the process returns to step S101 again to repeat the same processing, and the image storage unit 42 It waits for an image signal for one frame to be stored.

  Then, when an image signal for one frame is stored in the image storage unit 42, this is determined in step S 103, and then input for one frame and stored in the image storage unit 42 before that. By comparing with the image data (step S104), it is determined whether or not the image signal is a moving image, that is, whether or not there is a difference of a certain threshold value or more between the frames of the two image signals ( Step S105).

  The above-mentioned fixed threshold is, for example, the number of corresponding pixels that are sufficiently larger than the conversion error in the A / D conversion unit 22a and that can be reliably detected if the image signal is a moving image. It shall be.

  Here, when there is a difference between the frames of the two image signals and it is determined that the image signal is a moving image, the image signal for one frame that has been A / D converted immediately before is used for the next comparison in the image storage unit 42. The image signal is stored again as the image signal for the previous frame to be used, and the image signal is read from the image storage unit 42 and transferred to the image conversion unit 23 (step S106), and a corresponding optical image is formed by the micromirror element 26. After executing the projection process emitted from the projection lens unit 12 (step S107), the process returns to the process from step S101 again to deal with the next input image signal.

  On the other hand, if it is determined in step S105 that there is no difference between the two image signals and the image signal is not a moving image but a still image, the image signal for one frame that has been A / D converted immediately before is obtained. Discard and read out the image signal for the previous frame already stored in the image storage unit 42 from the image storage unit 42 and transfer it to the image conversion unit 23 (step S108), and the micromirror element 26 forms a corresponding optical image. Then, after executing the projection process emitted from the projection lens unit 12 (step S107), the process returns to the process from step S101 again to deal with the next input image signal.

Thus, according to the present embodiment, when it is determined that the input image signal is a still image, not the image signal of the frame input this time, but the previous frame already stored in the image storage unit 42. The image signal is continuously read out and used for projection processing.
Therefore, even if minute noise is generated between frames due to the conversion error in the A / D conversion unit 22a of the input / output interface 22, the projection image emitted from the projection lens unit 12 is caused by such a conversion error. Flickering of the image can be eliminated.

  The conversion error by the A / D conversion unit 22a naturally occurs even when the image signal is a moving image. However, in the case of moving images, the same image is not output continuously like a still image, the image itself is moving, and the noise due to flickering as an afterimage effect is a level that does not matter to the human naked eye. In particular, no deterioration of the image is felt, and there is no particular problem in this embodiment.

(Second Embodiment)
A second embodiment when the present invention is applied to a DLP (registered trademark) data projector apparatus will be described below with reference to the drawings.

  The external configuration of the data projector apparatus according to the embodiment is basically the same as that in FIG. 1 and the schematic functional configuration of the electronic circuit included in the data projector apparatus is basically the same as in FIG. Are denoted by the same reference numerals, and illustration and description thereof will be omitted.

Next, the operation of the above embodiment will be described.
In FIG. 4, an external device such as a personal computer is connected to a pin jack (RCA) type video input terminal or RGB input terminal of the input / output connector section 21, and an analog image signal is input through these terminals. The projection operation in this case is shown, and all the operation control is executed by the CPU 38 while reading the operation program stored in the program memory 40 and developing it in the main memory 39.

  The analog image signal supplied to the input / output connector unit 21 needs to be subjected to a so-called down-sampling method in which sampling intervals are appropriately thinned depending on the resolution of the external device on the output side.

  For example, the input band of the A / D conversion unit 22a of the input / output interface 22 is 110 [MHz] corresponding to SXGA (Super extended Trends Graphics Array) (display resolution: 1280 dots wide × 1024 dots high). When the band of the analog image signal input externally is 121 [MHz] corresponding to SXGA + (display resolution: horizontal 1400 dots × vertical 1050 dots), the A / D converter 22a performs the original sampling timing 10 Sampling processing is performed at 110 [MHz] or less by sampling only nine times out of the times and intentionally thinning out the image signal without performing the remaining one sampling. This downsampling operation is automatically switched by measuring the period of one field of the image signal input at the input / output interface 22, for example.

  At the beginning of processing, image signals input via the input / output connector unit 21 are sequentially A / D converted (step S201), and the sampling conditions for the A / D conversion are checked (step S202). It is determined whether sampling has been performed (step S203).

  If it is determined that downsampling is not performed, there is no variation in data between frames due to thinning of sampling timing, and the projected image does not flicker as an afterimage with the human eye. As a result, the digitized image signal obtained by A / D conversion is transferred to the image conversion unit 23 as it is (step S208), and a corresponding optical image is formed by the micromirror element 26 and emitted from the projection lens unit 12. After executing the projection process (step S209), the process returns to the process from step S201 to cope with the next input image signal.

  If it is determined in step S203 that downsampling is being performed, data variation between frames due to thinning of sampling timing occurs, and the projected image flickers as an afterimage with the human naked eye. As a matter of fact, the digitized image signal obtained by the A / D conversion is stored in the image storage unit 42 (step S204).

  Each time storage in the image storage unit 42 is performed, whether or not an image signal for one frame has been stored is stored in the image storage unit 42, for example, from the vertical synchronization pulse in the image signal to the next vertical synchronization pulse. The determination is made based on whether or not the image data is stored (step S205). If the image data for one frame is not stored, the process returns to the process from step S201 again, and the same process is repeated to repeat the image storage unit 42. It waits for an image signal for one frame to be stored.

  Then, when the image signal for one frame is stored in the image storage unit 42, this is determined in step S 205, and then input for one frame and stored in the image storage unit 42 before that. By comparing with the image data (step S206), it is determined whether or not the image signal is a moving image, that is, whether or not there is a difference of a certain threshold value or more between the frames of the two image signals ( Step S207).

  The above-mentioned fixed threshold is, for example, the number of corresponding pixels that are sufficiently larger than the conversion error in the A / D conversion unit 22a and that can be reliably detected if the image signal is a moving image. It shall be.

  Here, when there is a difference between the frames of the two image signals and it is determined that the image signal is a moving image, the image signal for one frame that has been A / D converted immediately before is used for the next comparison in the image storage unit 42. The image signal is stored again as the image signal for the previous frame to be used, and the image signal is read from the image storage unit 42 and transferred to the image conversion unit 23 (step S208), and a corresponding optical image is formed by the micromirror element 26. After executing the projection process emitted from the projection lens unit 12 (step S209), the process returns to the process from step S201 to deal with the next input image signal again.

  On the other hand, if it is determined in step S207 that there is no difference between the frames of the two image signals and the image signal is not a moving image but a still image, an image signal for one frame that has been A / D converted immediately before is obtained. Discard and read out the image signal for the previous frame already stored in the image storage unit 42 from the image storage unit 42 and transfer it to the image conversion unit 23 (step S210), and the micromirror element 26 forms a corresponding optical image. Then, after executing the projection process emitted from the projection lens unit 12 (step S209), the process returns to the process from step S201 to deal with the next input image signal.

As described above, according to the present embodiment, it is assumed that there is a risk of flickering of an image signal that requires downsampling during A / D conversion, and whether the image signal is a still image. If the image is a still image, the image signal of the previous frame already stored in the image storage unit 42 is continuously read instead of the image signal of the frame input this time, and is used for the projection process. .
Therefore, even when noise is generated between frames due to a conversion error due to downsampling in the A / D conversion unit 22a of the input / output interface 22, such conversion is completely performed in the projection image emitted from the projection lens unit 12. It is possible to eliminate flickering of an image due to an error.

  In addition, in the above-described embodiment, it is first determined whether or not downsampling has been performed. If it is determined that downsampling has not been performed, it is determined that the effect of flickering of the immediate image is small, and A / D While the converted image signal is used for the projection process as it is, the image signal determined to have been down-sampled is further affected by flickering of the image if the image signal is a still image. It is determined that the image signal of the previous frame stored in the image storage unit 42 is used in the projection process.

  As described above, the determination as to whether or not the downsampling has been performed is performed prior to the determination as to whether or not the image is a still image. This is based on the input bandwidth of the A / D conversion unit 22a of the input / output interface 22. (Resolution) and the case where priority is given to this depending on the resolution of the image signal that may be supplied to the input / output connector unit 21, the present invention does not limit the priority order. However, flickering can be further suppressed by setting a priority order suitable for the apparatus.

  In other words, in a data projector apparatus using an A / D converter that seems to have a relatively small image flicker due to downsampling, it is determined whether or not the image signal is a still image before the downsampling. It may be determined whether or not sampling has been performed.

  In the first and second embodiments, the case where the present invention is applied to a DLP (registered trademark) data projector apparatus has been described. However, the present invention is affected by a display element that forms a light image. For example, the invention can be similarly applied to a liquid crystal data projector using a transmissive color liquid crystal panel and other various projectors.

  In addition, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the scope of the invention in the implementation stage. In addition, the functions executed in the above-described embodiments may be implemented in appropriate combination as much as possible. The above-described embodiment includes various stages, and various inventions can be extracted by an appropriate combination according to a plurality of disclosed structural requirements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, if the effect is obtained, a configuration from which the constituent requirements are deleted can be extracted as an invention.

1 is a perspective view showing an external configuration of a data projector apparatus according to a first embodiment of the present invention. FIG. 3 is a block diagram showing a schematic functional configuration of the electronic circuit according to the embodiment. 6 is a flowchart showing the processing contents during a projection operation corresponding to a moving image and a still image according to the embodiment. The flowchart which shows the processing content at the time of the projection operation | movement corresponding to the moving image / still image and sampling rate which concern on the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Data projector apparatus, 11 ... Main body casing, 12 ... Projection lens part, 13 ... Ir receiving part, 14 ... Speaker part, 15 ... Indicator part, 16 ... Key operation part, 21 ... Input / output connector part, 22 ... Input / output Interface (I / F), 22a ... A / D conversion unit, 23 ... Image conversion unit, 24 ... Projection drive unit, 25 ... Video RAM, 26 ... Micromirror element (SOM), 27 ... Reflector, 28 ... Light source lamp, 29 ... Color wheel, 30 ... Integrator, 31 ... Mirror, 32 ... Stepping motor (M), 33 ... Cooling fan, 34 ... Motor (M), 35 ... Motor (M), 36 ... Projection light processing unit, 37 ... Temperature Sensor 38 ... CPU 39 ... Main memory 40 ... Program memory 41 ... Operation unit 42 ... Image storage unit 43 ... Audio processing unit 44 ... Power supply Controller, 45 ... AC input section, SB ... system bus.

Claims (7)

An image input means for inputting an analog image signal;
A / D conversion means for digitizing the image signal input by the image input means;
Projection means for forming and emitting a light image corresponding to the image signal obtained by the A / D conversion means;
Storage means for storing the image signal obtained by the A / D conversion means;
First determination means for determining whether an image obtained by the A / D conversion means is a still image;
Projection control means for projecting by the projection means using the image signal stored in the storage means instead of the image signal obtained by the A / D conversion means according to the judgment result in the first judgment means. A projection apparatus characterized by that. An image input means for inputting an analog image signal;
A / D conversion means for digitizing the image signal input by the image input means;
Projection means for forming and emitting a light image corresponding to the image signal obtained by the A / D conversion means;
Storage means for storing the image signal obtained by the A / D conversion means;
Second determination means for determining whether the image signal input by the image input means is an analog version of an image signal having a digital value higher than that of the A / D conversion means;
Projection control means for projecting by the projection means using the image signal stored in the storage means instead of the image signal obtained by the A / D conversion means in accordance with the judgment result by the second judgment means. A projection apparatus characterized by that.   The projection apparatus according to claim 1, wherein the projection control unit gives priority to a determination result of one of the first and second determination units. A projection method in a projection apparatus that inputs an image signal of an analog value, digitizes the input image signal to form a light image, and emits the light image,
A storage step of storing the digitized image signal;
A first determination step of determining whether the digitized image is a still image;
A projection control step of projecting using the image signal stored in the storage step instead of the digitized image signal in accordance with the determination result in the first determination step. A projection method in a projection apparatus that inputs an image signal of an analog value, digitizes the input image signal to form a light image, and emits the light image,
A storage step of storing the digitized image signal;
A second determination step of determining whether or not the input image signal is an analog image signal having a digital value higher than the accuracy of the digitization process;
And a projection control step of projecting using the image signal stored in the storage step instead of the digitized image signal in accordance with the determination result in the second determination step. A program executed by a computer incorporated in a projection apparatus that inputs an analog image signal and digitizes the input image signal to form and output an optical image,
A storage step for storing the digitized image signal;
A first determination step of determining whether the digitized image is a still image;
A program that causes a computer to execute a projection control step of projecting using the image signal stored in the storage step instead of the digitized image signal in accordance with the determination result in the first determination step. . A program executed by a computer incorporated in a projection apparatus that inputs an analog image signal and digitizes the input image signal to form and output an optical image,
A storage step for storing the digitized image signal;
A second determination step for determining whether or not the input image signal is an analog image signal having a digital value higher than the accuracy of the digitization processing;
A program for causing a computer to execute a projection control step of projecting using the image signal stored in the storage step instead of the digitized image signal in accordance with the determination result in the second determination step. .

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