JP4981350B2 - Image projection apparatus, image display system, control method for image projection apparatus, and control program - Google Patents

Description

  The present invention relates to an image projection apparatus having a function of detecting reflected light from a projection surface and performing a color tone correction process.

  Projection surfaces on which images are projected by the projector include not only a dedicated white screen but also projection surfaces that are not necessarily white, such as walls and partitions. In addition, projectors are often used not only in dark rooms but also in illuminated rooms.

  Japanese Patent Application Laid-Open No. 2004-228867 discloses a projector that automatically corrects white balance by detecting the influence of the color of the projection surface and the color tone (color balance) of the projected image using a light sensor or a CCD camera. This projector detects red (R), green (G), and blue (B) components during white projection, and adjusts the gains of the R, G, and B components so as to obtain a predetermined white balance.

Patent Document 2 discloses a projector that sequentially projects three primary color lights of R, G, and B onto a projection surface and detects reflected light on each projection surface with a color sensor. In this projector, a color correction matrix is generated from the detected color information, and color correction is performed by performing mapping on the RGB input signal of an image to be projected using the generated matrix.
Japanese Patent Laying-Open No. 2003-333611 (paragraphs 0002 to 0005, FIG. 4 etc.) JP 2003-323610 A (paragraphs 0078 to 0084, etc.)

  However, in the color correction method disclosed in Patent Document 2, the R, G, and B images are sequentially projected as the reference image for correction, so that the time required for color correction becomes long. Further, since the reference image of only R, G, or B, which is far from the normal projection image, must be displayed for a certain period of time, the user feels uncomfortable.

  On the other hand, in the color tone correction method disclosed in Patent Document 1, a white image is projected as a reference image for correction, and thus there is no drawback like the color tone correction method in Patent Document 2. However, even when the detected levels of the respective colors (R, G, and B) are perfectly balanced, the same color as the white color of the reference image cannot be obtained for the following reason.

FIG. 8 shows an example of the projection light spectrum of the projector. In FIG. 8, when the R light is PJ_R (λ), the G light is PJ_G (λ), and the B light is PJ_B (λ), the white light PJ_W (λ) is
PJ_W (λ) = PJ_R (λ) + PJ_G (λ) + PJ_B (λ)
It is represented by

On the other hand, FIG. 9 shows spectral sensitivities of color sensors that detect reflected light. In this figure, R sensor: S_R (λ), G sensor: S_G (λ), and B sensor: S_B (λ). Here, when the reflectance distribution of the screen is REFx (λ), the R component: Rx obtained by detecting the screen reflected light of the white light projection by the color sensor is
Rx = ∫ {PJ_W (λ) * REFx (λ) * S_R (λ)} dλ (1)
It is.

Similarly, the G component and the B component are
Gx = ∫ {PJ_W (λ) * REFx (λ) * S_G (λ)} dλ (2)
Bx = ∫ {PJ_W (λ) * REFx (λ) * S_B (λ)} dλ (3)
It is represented by

  From equations (1) to (3), it can be seen that the sensor detection values may be equal even if the spectrum shapes (PJ_W (λ) * REFx (λ)) are not the same. FIG. 10A and FIG. 10B show an example in that case.

  10A and 10B, the spectrum shapes of the blue component (near 380 nm to 500 nm) are different. However, both B sensor values are equal. That is, the difference between the case of FIG. 10A and the case of FIG. 10B cannot be distinguished by the sensor.

  Such a phenomenon is particularly prominent when there is a peak of the projected light spectrum of the projector at a low spectral sensitivity of each color sensor.

  For the reasons described above, an error occurs only by performing correction so that the balance of the level of each color (R, G, and B) detected by the sensor matches the balance of the color level of the reference white, High-precision correction is not possible.

  Accordingly, an object of the present invention is to provide an image projection apparatus that can perform highly accurate automatic color tone (color balance) correction while reducing the burden on the user and a sense of discomfort.

An image projection apparatus according to an aspect of the present invention is an image projection apparatus that projects a color image onto a projection surface based on a video signal, and includes first, second, and third of reflected light from the projection surface. First, second, and third light receiving sensors for detecting light in the wavelength region, processing means for performing processing related to color tone adjustment on the video signal, and the first, second, and third wavelength regions, respectively. Based on the output from one of the first to third light receiving sensors and the output from the other light receiving sensor when the reference light including light is projected onto the projection surface, the one light receiving sensor Control means for setting parameters for processing the video signal corresponding to the wavelength region detected by the processing means, and the first, second and third when the reference light is projected onto a reference projection surface Output from the light receiving sensor Reference output storage means for storing a quasi-output is stored, and the control means is a ratio of outputs from the one light receiving sensor and the other light receiving sensors when the reference light is projected onto the projection surface, and these light receiving sensors. The parameter is set on the basis of a value calculated using the ratio of the reference output and the correction coefficient determined based on the output from the light receiving sensor when the reference light is projected onto a plurality of different projection surfaces. It is characterized by that.

  Note that an image display system including the image projection apparatus and an image supply apparatus that supplies image information to the image projection apparatus also constitutes another aspect of the present invention.

According to another aspect of the present invention, there is provided a control method for an image projection apparatus, which projects a color image on a projection surface based on a video signal, and includes a reflected light from the projection surface. A detection step of detecting light in the first, second, and third wavelength regions by the first, second, and third light receiving sensors, a processing step of performing processing related to color tone adjustment on the video signal, Output from one light receiving sensor and other light receiving sensors among the first to third light receiving sensors when the reference light including light in the first, second and third wavelength regions is projected onto the projection surface. And setting a parameter for processing the video signal corresponding to the wavelength region detected by the one light receiving sensor in the processing step based on the output of the one light receiving sensor, wherein the parameter projects the reference light to the projection A ratio of outputs from the one light receiving sensor and the other light receiving sensors when projected onto the reference projection surface, a ratio of outputs from the light receiving sensors when the reference light is projected onto a reference projection surface, and a plurality of different projection surfaces It is calculated using a correction coefficient determined based on an output from the light receiving sensor when the reference light is projected .
According to another aspect of the present invention, the control program includes: an image projection device that projects a color image on a projection surface based on a video signal; and first, second, and third wavelengths of reflected light from the projection surface. A detection step of detecting light in the region by the first, second, and third light receiving sensors, a processing step of performing processing related to color tone adjustment on the video signal, and the first, second, and third wavelengths Based on the output from one light receiving sensor and the output from the other light receiving sensor among the first to third light receiving sensors when the reference light including the light of the region is projected onto the projection surface, The step of setting a parameter for processing the video signal corresponding to the wavelength region detected by the light receiving sensor in the processing step is executed, and the parameter is projected when the reference light is projected onto the projection surface. The ratio of outputs from one light receiving sensor and other light receiving sensors, the ratio of outputs from these light receiving sensors when the reference light is projected onto a reference projection surface, and the reference light projected onto a plurality of different projection surfaces And a correction coefficient determined based on the output from the light receiving sensor.

  According to the present invention, since the reference light including light in the first to third wavelength regions such as R, G, B, etc. is projected onto the projection surface to obtain the light receiving sensor output, the burden on the user and the uncomfortable feeling are reduced. Can do. In addition, since the parameters for the color tone adjustment processing of the video signal are set using not only the light receiving sensor in the wavelength region corresponding to the video signal but also the output from other light receiving sensors, the shape of the spectrum of the reflected light ( High-accuracy color tone correction reflecting the distribution).

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows a configuration of a liquid crystal projector as an image projection apparatus that is Embodiment 1 of the present invention.

  In FIG. 1, reference numeral 1 denotes a video input circuit which AD-converts an analog video signal 21 output from an image supply apparatus such as a personal computer PC or video equipment to generate a digital video signal in a predetermined format. The generated digital video signal is output to the digital signal processing circuit 2. The digital signal processing circuit 2 performs, for the digital video signal, resolution conversion processing and frame rate conversion processing suitable for driving the liquid crystal panel 4 as an image forming element. The digital signal processing circuit 2 generates a video signal for displaying a test pattern as a reference image.

  The R, G, and B video signals output from the digital signal processing circuit 2 are input to the display driving circuit 3. The display drive circuit 3 is provided with a gain / offset processing unit 5 and a γ correction unit 6, which enables independent gain / offset processing and γ correction processing for R, G, and B video signals. Performs signal processing related to brightness and color. The display drive circuit 3 generates drive signals for the three liquid crystal panels 4 (R panel 4R, G panel 4G, and B panel 4B) based on the processed R, G, and B video signals. The display driving circuit 3 generates a timing pulse for causing the liquid crystal panel 4 to form an image corresponding to the driving signal.

  The three color sensors 9 (R sensor 9R, G sensor 9G, and B sensor 9B) are sensitive to the respective wavelength regions of R, G, and B, and are screens (projection surfaces) S of light projected from the projector. It arrange | positions so that only the reflected light of can be detected.

  Reference numeral 7 denotes a projection lens that projects onto the screen S image light in which R, G, and B lights from the R panel 4R, G panel 4G, and B panel 4B illuminated by the light source lamp 15 are combined.

  The controller 8 is composed of a microcomputer or the like. The controller 8 controls test pattern display for the digital signal processing circuit 2 and controls various processing such as gain / offset processing and gamma processing for the display driving circuit 3. The control includes setting of a gain value that is a parameter for performing gain processing, for example.

  Furthermore, the controller 8 controls the entire system in an integrated manner, such as decoding commands from an operation panel (not shown) and communicating with the nonvolatile memory 10.

  The projector of this embodiment has an automatic color tone adjustment (color tone correction) function, which is also called an automatic wall color correction function. Regarding the color tone correction, the controller 8 includes a sensor driving unit 11 that drives the color sensor 9. The sensor driving unit 11 drives the R sensor 9R, the G sensor 9G, and the B sensor 9B, and is generated by the photoelectric conversion operation of the R component, the G component, and the B component included in the reflected light from the screen S and the photoelectric conversion. The signal is output.

  The controller 8 includes a sensor value correction processing unit 12. The sensor value correction processing unit 12 outputs an output value (hereinafter simply referred to as a sensor value) 22 from the R sensor 9R, the G sensor 9G, and the B sensor 9B, and a sensor reference value 23 stored and stored in the nonvolatile memory 10. To obtain a post-correction sensor value 24 to be described later. Here, the sensor reference value 23 is an output value obtained by the R sensor 9R, the G sensor 9G, and the B sensor 9B when a predetermined reference white light is projected onto the reference (standard) screen, and is adjusted in a factory or the like. The value is measured by and stored in the nonvolatile memory 10.

  Further, the image correction amount calculation unit 13 calculates a gain value for each of the R, G, and B image signals so as to obtain a predetermined color balance from the corrected sensor value 24 and the sensor reference value 23, and performs display driving. Tell to circuit 3.

  Next, the role of the sensor value correction processing unit 12 in this embodiment will be described. FIG. 2A shows an example of a spectrum of projection light (relationship between wavelength and radiance) when a high-pressure mercury lamp is used as the light source lamp 15. FIG. 2B shows spectral sensitivity distributions of the R sensor 9R, G sensor 9G, and B sensor 9B. Note that the wavelength regions in which the R sensor 9R, the G sensor 9G, and the B sensor 9B have sensitivity partially overlap with the adjacent wavelength regions.

  From comparison of these figures, most of the R light, G light, and B light included in the projection light are respectively surrounded by the sensitivity regions of the R sensor 9R, G sensor 9G, and B sensor 9B (the curves in FIG. 2B). It can be seen that it is included in the (region).

  However, as shown in FIG. 2A, the high-pressure mercury lamp is characterized in that a spectrum peak appears at several places. Like P1, one or a plurality of peaks have R sensor 9R, G sensor 9G and B sensor. 9B may not be included in any sensitivity region. Spectral peaks that do not exist in any sensitivity region are not reflected in the sensor value. In addition, as in P2, a plurality of peaks may exist within the sensitivity region of one sensor. Since peaks such as P1 and P2 have a large luminance level, the detection error of the peak greatly affects the chromaticity of the projection light.

  The sensor value correction processing unit 12 corrects the sensor value in consideration of a peak component that easily causes a detection error in the R sensor 9R, the G sensor 9G, and the B sensor 9B.

  FIG. 3 shows the calculation contents of the sensor value correction processing unit 12. This arithmetic processing is executed according to a computer program stored in a memory (not shown) provided in the controller 8.

  First, using the sensor values 22r, 22g, and 22b from the R sensor 9R, G sensor 9G, and B sensor 9B and the R, G, and B sensor reference values 23r, 23g, and 23b from the memory 10, the R sensor attenuation rate is obtained. 54 and the B sensor attenuation rate 55 are obtained. Specifically, the R sensor attenuation ratio 54 is calculated using the ratios of the R and B sensor values and the ratio of the R and B sensor reference values using the equations (4-a) and (4-b) shown below. B sensor attenuation rate 55 is calculated.

R sensor attenuation factor = (R sensor value / G sensor value) / (R sensor reference value / G sensor reference value)
... (4-a)
B sensor attenuation rate = (B sensor value / G sensor value) / (B sensor reference value / G sensor reference value)
(4-b).

  The sensor correction amount calculation unit 56 uses the following expressions (5-a), (5-b), and (5-c) from the R sensor attenuation rate 54 and the B sensor attenuation rate 56 obtained by the above calculation. A correction amount for each sensor value is calculated.

R sensor value after correction = α * (1-R sensor attenuation rate) * R sensor value (5-a)
G sensor value after correction = G sensor value (5-b)
B sensor value after correction = β * (1−B sensor attenuation rate) * B sensor value (5-c).

  Here, α and β are correction gains, respectively, and indicate the intensity of correction for each sensor value. The correction gains α and β are determined based on the data collected by performing projection on as many screens or wall surfaces as possible.

  In Formula (5-a), since the point A exists at the boundary of the sensitivity distribution between the G sensor and the R sensor, the attenuation rate (increase rate) at the point A is estimated from the change in the output of the G sensor and the R sensor. This means that correction processing is performed on the R sensor.

  Further, the expression (5-c) is obtained by estimating the shape of the B light spectrum (for example, presence or absence of P2), in other words, the distribution from the degree of change in the sensor values of the G sensor 4G and the B sensor 4B. This means that correction processing is performed on the value.

  Here, although the case where correction is performed on the R sensor value and the B sensor value has been described, correction may be performed on the other two sensor values or one sensor value.

  Next, the calculation in the video correction amount calculation unit 13 that determines the correction amount for the video signal using the corrected sensor value will be described. This arithmetic processing is also executed according to a computer program stored in a memory (not shown) provided in the controller 8.

  FIG. 4 shows an example of a processing flow in the video correction amount calculation unit 13.

(PAHSE1)
First, a “target sensor value” is calculated such that the RGB balance of the “corrected sensor value” matches the RGB balance of the “sensor reference value”. That is,
Target R sensor value: Target G sensor value: Target B sensor value =
The “target sensor value” is calculated so as to satisfy the relationship of R sensor reference value: G sensor reference value: B sensor reference value.

(PAHSE2)
Next, a “sensor correction gain”, which is a gain correction amount necessary to make the “corrected sensor value” coincide with the calculated “target sensor value”, is obtained. The “sensor correction gain” is calculated by the following equation (6).

R sensor correction gain = target R sensor value / corrected R sensor value G sensor correction gain = target G sensor value / corrected G sensor value B sensor correction gain = target B sensor value / corrected B sensor value (6).

(PAHSE3)
Next, the “video signal correction gain” that realizes the “sensor correction gain” is obtained using the “luminance-signal characteristics”. The “luminance-signal characteristic” is a characteristic that represents a change in the color sensor 9 with respect to a signal level change, and is generally known as a γ characteristic. The “video signal correction gain” is calculated by the following equation (7).

R video signal correction gain = [luminance−signal characteristic (R component)] ⁻¹ (R sensor correction gain)
G video signal correction gain = [luminance−signal characteristic (G component)] ⁻¹ (G sensor correction gain)
B video signal correction gain = [luminance−signal characteristic (B component)] ⁻¹ (B sensor correction gain)
... (7).

  The controller 8 transmits the “video signal correction gain” calculated in this way to the display drive circuit 3. The display drive circuit 3 performs gain processing on the R, G, and B video signals input from the digital signal processing circuit 2 using the R, G, and B “video signal correction gains”. Then, a driving signal for each liquid crystal panel is generated based on the video signal subjected to the gain processing and the like.

  As described above, according to the present embodiment, the gain processing parameter (video signal correction gain) for each color video signal is obtained from other light receiving sensors in addition to the light receiving sensor in the wavelength region corresponding to the color video signal. The output is also set. For this reason, highly accurate color tone correction reflecting even the spectral distribution of reflected light can be performed.

  In addition, since the reference white light including R, G, B light is projected onto the projection surface to obtain the sensor value, the burden on the user and the uncomfortable feeling are reduced as compared with the case of sequentially projecting the R, G, B light. Can do.

  As shown in FIG. 1, a general projector signal processing configuration includes a gamma correction unit 6 on the panel 4 side rather than a gain / offset processing unit 5. In the projector, in order to change the display characteristics of the projected image in accordance with the switching of the projection mode, the γ characteristic data stored in the γ correction unit (display characteristic storage means) 6 is rewritten. For this reason, the “luminance-signal characteristic” (γ characteristic) described in the PAHSE 3 of the first embodiment changes according to the image display characteristic.

  The inconvenience caused by this will be described with reference to FIG. In a certain projection mode, as described in PHASE 3 above, referring to the “luminance-signal characteristic” (γ characteristic 1) drawn by a solid line in FIG. Gain 1 "is calculated.

  However, when the projection mode is changed and the image display characteristic changes to a dotted line characteristic (γ characteristic 2), the sensor correction gain corresponding to “video signal correction gain 1” becomes “sensor correction gain 2”. . For this reason, a gain difference ΔGain occurs between the “sensor correction gain 1” actually obtained. As can be seen from FIG. 5, the ideal video signal correction gain for the γ characteristic 2 is “video signal correction gain 2” which is the intersection of “sensor correction gain 1” and “γ characteristic 2”.

  Therefore, in order to solve this problem, actually, the “video signal correction gain” calculated in PHASE 3 is further corrected.

  First, with respect to the “luminance-signal characteristic” (γ characteristic 1) used as a reference in PHASE 3, the “luminance-signal characteristic” (γ characteristic k, k = 1 to N: in each image display characteristic (projection mode). A difference value of N is the number of image display characteristics). Hereinafter, this difference value is referred to as a γ characteristic correction function k (k = 1 to N).

  Next, a new “video signal correction gain_IMG” is calculated using the “video signal correction gain” calculated in PHASE 3 and the γ characteristic correction function k corresponding to the current image display characteristics.

(PAHSE4)
Next, a more specific process and calculation method will be described with reference to the characteristic diagram of FIG. 6 and the process flowchart of FIG. FIG. 6 shows an example of the “γ characteristic correction function k” used for the calculation. For example, if the “luminance-signal characteristic” used in PHASE 3 is γ characteristic 1 in FIG. 5, the γ characteristic correction function 1 is a linear characteristic, and the γ characteristic correction function 2 is a difference characteristic between the γ characteristic 2 and the γ characteristic 1. Show.

  First, information on the current image display characteristic (projection mode) k is acquired. Next, the γ characteristic correction function k corresponding to the image display characteristic k is read. Then, the following calculation is performed on the “video signal correction gain”.

R video signal correction gain_IMG = [γ characteristic correction function k_R component (R video signal correction gain)]
G video signal correction gain_IMG = [γ characteristic correction function k_G component (G video signal correction gain)]
B video signal correction gain_IMG = [γ characteristic correction function k_B component (B video signal correction gain)]
As described above, the video signal correction gain_IMG is calculated by switching the γ characteristic correction function according to the image display characteristics. The controller 8 transmits the “video signal correction gain_IMG” calculated in this way to the display drive circuit 3. The display drive circuit 3 uses the R, G, and B video signals input from the digital signal processing circuit 2 and the “R, G, and B video signal correction gain_IMG” to use the R panel 4R, the G panels 4G, and B. A drive parameter for the panel 4B is set, and a drive signal for each panel is generated.

  The “γ characteristic correction function” may be stored in the internal memory as a table value, or may be stored in the internal memory as a coefficient of an approximate function.

1 is a diagram illustrating a configuration of a projector that is Embodiment 1 of the present invention. FIG. FIG. 3 is a diagram illustrating a spectrum of light projected from the projector according to the first embodiment. FIG. 3 is a diagram illustrating spectral sensitivity of a color sensor in the projector according to the first embodiment. 3 is a flowchart showing a flow of sensor value correction processing in the first embodiment. 3 is a flowchart illustrating a flow of video correction amount calculation processing in the first embodiment. FIG. 10 is a diagram illustrating a difference in correction values depending on γ characteristics in the projector according to the second embodiment of the present invention. FIG. 6 is a diagram illustrating a γ characteristic correction function in the second embodiment. 3 is a flowchart illustrating a flow of video correction amount calculation processing in the first embodiment. The figure which showed the projection light spectrum of the conventional common projector. The figure which showed the spectral sensitivity distribution of the conventional common color sensor. The figure which shows the projection light spectrum in the conventional common projector. The figure which showed the spectral sensitivity of the color sensor in the conventional common projector.

Explanation of symbols

3 Display drive circuit 4 Liquid crystal panel 7 Projection lens 8 Controller 9 Color sensor 10 Non-volatile memory,
12 Sensor value correction unit 13 Image correction amount calculation unit

Claims (9)

An image projection apparatus that projects a color image on a projection surface based on a video signal,
First, second, and third light receiving sensors that detect light in the first, second, and third wavelength regions, respectively, of the reflected light from the projection surface;
Processing means for performing processing related to color tone adjustment on the video signal;
The output from one of the first to third light receiving sensors when the reference light including the light in the first, second and third wavelength regions is projected onto the projection surface and the other light receiving sensor based on the output and from a control means for said one light-receiving sensor is set parameters for processing by said processing means a video signal corresponding to the wavelength range to be detected,
Reference output storage means for storing a reference output that is an output from the first, second, and third light receiving sensors when the reference light is projected onto a reference projection surface,
The control means includes a ratio of outputs from the one light receiving sensor and the other light receiving sensors when the reference light is projected onto the projection surface, a ratio of the reference outputs of the light receiving sensors, and a plurality of different projection surfaces. An image projection apparatus, wherein the parameter is set based on a value calculated using a correction coefficient determined based on an output from the light receiving sensor when the reference light is projected onto the image sensor . The control means estimates a spectrum distribution in a wavelength region corresponding to the one light receiving sensor based on outputs from the one light receiving sensor and another light receiving sensor, and sets the parameter based on the estimation result. The image projection apparatus according to claim 1 , wherein: The parameter is an image projection apparatus according to claim 1 or 2, characterized in that a gain value for the video signal. Data storage means storing data relating to different display characteristics depending on the projection mode;
The control means includes a ratio of outputs from the one light receiving sensor and the other light receiving sensors when the reference light is projected onto the projection surface, a ratio of the reference outputs of the light receiving sensors, and a plurality of different projection surfaces. 2. The parameter is set based on a correction coefficient determined based on an output from the light receiving sensor when the reference light is projected onto the light and the data corresponding to the projection mode. The image projection device according to any one of 3 . The image projection apparatus according to claim 4 , wherein the data relating to the display characteristics is γ value data. 6. The parameter according to claim 4, wherein the parameter is set using a difference value between data relating to the display characteristic corresponding to the first projection mode and data relating to the display characteristic corresponding to the second projection mode. Image projection device. An image projection apparatus according to any one of claims 1 to 6 ,
An image display system comprising: an image supply device that supplies image information to the image projection device. A control method for an image projection apparatus that projects a color image on a projection surface based on a video signal,
A detection step of detecting light in the first, second, and third wavelength regions in the reflected light from the projection surface by the first, second, and third light receiving sensors, respectively;
Processing steps for performing processing relating to color tone adjustment on the video signal;
The output from one of the first to third light receiving sensors when the reference light including the light in the first, second and third wavelength regions is projected onto the projection surface and the other light receiving sensor based on the output and from, have a steps of a video signal in which the one light-receiving sensor corresponding to the wavelength region for detecting setting the parameters for processing by said processing step,
The parameters are a ratio of outputs from the one light receiving sensor and the other light receiving sensors when the reference light is projected onto the projection surface, and from the light receiving sensors when the reference light is projected onto the reference projection surface. A method for controlling an image projection apparatus , wherein the ratio is calculated using an output ratio and a correction coefficient determined based on an output from the light receiving sensor when the reference light is projected onto a plurality of different projection surfaces. . In an image projection device that projects a color image on a projection surface based on a video signal,
A detection step of detecting light in the first, second, and third wavelength regions in the reflected light from the projection surface by the first, second, and third light receiving sensors, respectively;
Processing steps for performing processing relating to color tone adjustment on the video signal;
The output from one of the first to third light receiving sensors when the reference light including the light in the first, second and third wavelength regions is projected onto the projection surface and the other light receiving sensor And a step of setting a parameter for processing the video signal corresponding to the wavelength region detected by the one light receiving sensor in the processing step based on the output from
The parameter is a ratio of outputs from the one light receiving sensor and the other light receiving sensors when the reference light is projected onto the projection surface, and from the light receiving sensors when the reference light is projected onto the reference projection surface. A control program for calculating using an output ratio and a correction coefficient determined based on an output from the light receiving sensor when the reference light is projected onto a plurality of different projection surfaces.