CORRECTION METHOD AND PROJECTOR

A method for correcting a projection image projected from a projector onto a projection surface, the method including: acquiring depth information indicating multiple distances from a distance sensor to multiple positions on the projection surface based on an output from the distance sensor, the distance sensor configured to irradiate the projection surface with radiated light and receive reflected light reflected off the projection surface; acquiring intensity information indicating an intensity of the reflected light at each of the multiple positions; generating a parameter that defines the projection surface based on the depth information and the intensity information; and correcting the projection image based on the parameter.

The present application is based on, and claims priority from JP Application Serial Number 2024-087948, filed May 30, 2024, the disclosure of which is hereby incorporated by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a correction method and a projector.

2. Related Art

There has been a related-art technology for determining the normal vector for a projection surface by using a value measured by a distance sensor provided in a projector, and correcting a projection image by using the determined normal vector.

For example, according to WO 2022/193560 acquires multiple pieces of depth information at multiple light spots on a projection surface by using a time-of-flight (ToF) sensor, and determines the normal vector for the projection surface based on the multiple depth information. Furthermore, the projector acquires offset information on the amount of offset of the projector based on the normal vector, and corrects a projection image based on the offset information.

WO 2022/193560 is an example of the related art.

In the technology according to WO 2022/193560, however, the accuracy of the multiple pieces of depth information at the multiple light spots decreases in some cases depending on the inclination and shape of the projection surface. When the scale of the original image is corrected based on the depth information with reduced accuracy, the result of the correction also deteriorates.

SUMMARY

A correction method according to an aspect of the present disclosure is a method for correcting a projection image projected from a projector onto a projection surface, the method including: acquiring depth information indicating multiple distances from a distance sensor to multiple positions on the projection surface based on an output from the distance sensor, the distance sensor configured to irradiate the projection surface with radiated light and receive reflected light reflected off the projection surface; acquiring intensity information indicating an intensity of the reflected light at each of the multiple positions; generating a parameter that defines the projection surface based on the depth information and the intensity information; and correcting the projection image based on the parameter.

A projector according to another aspect of the present disclosure includes one or more processors configured to acquire depth information indicating multiple distances from a distance sensor to multiple positions on a projection surface based on an output from the distance sensor, the distance sensor configured to irradiate the projection surface with radiated light and receive reflected light reflected off the projection surface; acquire intensity information indicating an intensity of the reflected light at each of the multiple positions; generate a parameter that defines the projection surface based on the depth information and the intensity information; and correct a projection image based on the parameter.

DESCRIPTION OF EMBODIMENTS

An embodiment for implementing the present disclosure will be described below with reference to the drawings. Note, however, that dimensions and scales of portions in the drawings are made different from actual ones as appropriate. Furthermore, the embodiment described below is a preferable specific example of the present disclosure, and various technically preferable restrictions are therefore imposed on the embodiment, but the scope of the present disclosure is not limited to the embodiment unless there is a description that the present disclosure is particularly limited to the embodiment in the following description.

1: First Embodiment

A projector 1 and a correction method according to a first embodiment will be described below with reference to FIGS. 1 to 7.

1-1: Configuration of First Embodiment

FIG. 1 is a block diagram showing an example of the configuration of the projector 1 according to the first embodiment. The projector 1 includes a projection apparatus 11, a processing device 12, a storage device 13, a communication device 14, and a distance sensor 15. The elements of the projector 1 are connected to each other via a single bus or multiple buses for information communication. The elements of the projector 1 each include a single or multiple instruments. Some of the elements of the projector 1 may be omitted.

The projection apparatus 11 is an apparatus that projects a projection image PI generated by a projection image generator 121, which will be described later, on a screen SC, a wall, or any other surface. The projection apparatus 11 projects various images under the control of the processing device 12. The projection apparatus 11 includes, for example, a light source, a liquid crystal panel, and a projection lens, modulates light from the light source through the liquid crystal panel, and projects the modulated light onto the screen SC, the wall, or any other surface via the projection lens. The aspect in which the projection apparatus 11 includes a liquid crystal panel is merely an example, and aspects according to the present embodiment are not limited thereto. For example, the present embodiment is also applicable to a digital light processing (DLP: registered trademark) configuration including a digital mirror device (DMD) in place of a liquid crystal panel.

The processing device 12 is a processor that controls the entire projector 1, and is configured, for example, with a single chip or multiple chips. The processing device 12 is configured, for example, with a central processing unit (CPU) including an interface with a peripheral apparatus, an arithmetic device, a register, and so on. Note that some or all of the functions of the processing device 12 may be realized by hardware such as a digital signal processor (DSP), an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA). The processing device 12 performs various types of processing in parallel or in sequence.

The storage device 13 is a recording medium readable by the processing device 12, and stores multiple programs including a control program PRI to be executed by the processing device 12. The storage device 13 may be configured, for example, with at least one of a read-only memory (ROM), an erasable programmable ROM (EPROM), an electrically erasable programmable ROM (EEPROM), and a random access memory (RAM). The storage device 13 may be called a register, a cache, a main memory, a main storage device, or the like.

The communication device 14 is hardware serving as a transmission and reception device for communicating with other apparatuses. Particularly in the present embodiment, the communication device 14 is a communication device that connects the projector 1 to the other apparatuses in a wired or wireless manner. The communication device 14 is also called, for example, a network device, a network controller, a network card, or a communication module.

The distance sensor 15 measures the distance between the distance sensor 15 and an object located around the projector 1. In the present embodiment, the distance sensor 15 irradiates a projection surface PP of the screen SC with radiated light and receives reflected light reflected off the projection surface PP. The distance sensor 15 measures the distance between the distance sensor 15 and multiple points on the projection surface PP based on the result of the detection of the reflected light. The distance sensor 15 is preferably a ToF sensor. The distance sensor 15 may instead, for example, be a light detection and ranging (LIDAR) device. The distance sensor 15 in the present embodiment has pixels the number of which is 6 px in each of an X-axis direction and a Y-axis direction. The number of pixels (resolution) of the distance sensor 15 in the present embodiment is therefore 6 px×6 px.

The processing device 12 functions as a projection image generator 121, an acquisition section 122, a parameter generator 123, a corrector 124, and a projection controller 125 by reading the control program PR1 from the storage device 13 and executing the control program PR1. Note that the control program PR1 may be transmitted via a communication network that is not shown from another apparatus such as a server that manages the projector 1.

The projection image generator 121 generates the projection image PI based on an input image acquired by the projection image generator 121. Note that the projection image generator 121 may acquire an input image from an apparatus external to the projector 1 or may acquire an input image stored in the storage device 13.

The acquisition section 122 acquires depth information DI, which indicates multiple distances from the distance sensor 15 to multiple positions on the projection surface PP, and intensity information SI, which indicates the intensity of the reflected light at each of the multiple positions, based on the output from the distance sensor 15.

FIG. 2 shows an example of the depth information DI acquired by the acquisition section 122. It is assumed that the projector 1 and the projection surface PP are set in an XYZ coordinate system, which is a world coordinate system, as shown in FIG. 2. It is further assumed that the optical axis of the projector 1 is substantially parallel to the Z-axis. The optical axis of the projector 1 is, for example, the optical axis of the projection lens. Note that the term “substantially parallel” means being parallel with an error within an allowable range. As an example, when the distance sensor 15 is a ToF sensor, the distance sensor 15 irradiates multiple positions on the projection surface PP with multiple laser beams L. The multiple laser beams L radiated onto the projection surface PP form multiple light spots LP on the projection surface PP. The distance sensor 15 outputs the depth information DI indicating multiple distances from the distance sensor 15 to the multiple light spots LP based on a period from the time at which the distance sensor 15 radiates the multiple laser beams L to the time at which light receiving sensors provided in the distance sensor 15 detect reflected light from the multiple light spots LP formed by the multiple laser beams L on the projection surface PP. The acquisition section 122 acquires the depth information DI output from the ToF sensor as the distance sensor 15. FIG. 2 shows a case where the light spots LP are formed at eight positions out of 36 positions on the projection surface PP that are the maximum number of positions detectable by the distance sensor 15.

Note that when the distance sensor 15 is a ToF sensor, the distance sensor 15 may irradiate the projection surface PP with light from a surface emitting laser instead of irradiating the projection surface PP with the multiple laser beams L as described above. In this case, the multiple light receiving sensors discretely incorporated in the distance sensor 15 detect the reflected light from the projection surface PP.

FIGS. 3 and 4 illustrate a correspondence between the depth information DI and the intensity information SI acquired by the acquisition section 122.

The distance sensor 15 measures the distances between the distance sensor 15 and the multiple points on the projection surface PP based on the result of the detection of the reflected light, as described above.

It is now assumed that the projection surface PP spreads in an xy plane by way of example, as shown in FIG. 3. It is further assumed that the projection surface PP includes a pixel group IMs, and that the pixel group IMs is configured with multiple pixels IM(1, 1) to IM(6, 6). In FIG. 3, the pixels IM(1, 1) to IM(6, 1) are arranged in this order in an x-axis direction. The pixel IM(1, 1) is shifted toward the −x side from the pixel IM(6, 1). The pixels IM(1, 1) to IM(1, 6) are arranged in this order in a y-axis direction. The pixel IM(1, 1) is shifted toward the −y side from the pixel IM(1, 6).

The acquisition section 122 acquires the depth information DI indicating the distance between the distance sensor 15 and the center point of each of the pixels IM(1, 1) to IM(6, 6) at each of multiple points of time. Assuming that n is a natural number, the acquisition section 122 acquires the depth information DI in an n-th frame at the point of time of t=tn. The depth information DI in the n-th frame is configured with depth information DI(1, 1, n) to depth information DI(6, 6, n) indicating the distances between the distance sensor 15 and the center points of the pixels IM(1, 1) to IM(6, 6).

The acquisition section 122 further acquires the intensity information SI indicating the intensity of the reflected light reflected at each of the pixels IM(1, 1) to IM(6, 6) at each of the multiple points of time. Assuming that n is a natural number, the acquisition section 122 acquires the intensity information SI in the n-th frame at the point of time of t=tn. The intensity information SI in the n-th frame is configured with intensity information SI(1, 1, n) to intensity information SI(6, 6, n) indicating the intensities of the reflected light reflected at the pixels IM(1, 1) to IM(6, 6).

The intensity information SI may be information on the intensity indicated by an output voltage output from the light receiving sensor corresponding to each of the pixels IM(1,1) to IM(6, 6). Instead, when the distance sensor 15 is a ToF sensor and the distance sensor 15 generates an IR image by capturing an image of the projection surface PP with infrared light, the intensity information SI may be information on the intensity indicated by the magnitude of the signal output from the light receiving sensor described above based on the IR image. Still instead, when the light receiving sensor calculates pseudo reflectance substantially indicating the ratio of the amount of the reflected light received by the light receiving sensor to the amount of the projected light, the intensity information SI may, for example, be information on the intensity indicated by the pseudo reflectance.

The acquisition section 122 acquires the depth information DI(1, 1, n) and the intensity information SI(1, 1, n) at the pixel IM(1, 1) in association with each other at the point of time of t=tn. The same applies to the other pixels IM. The same applies also to the points of time other than t=tn. In FIG. 4, the acquisition section 122 acquires, for example, the depth information DI(1, 6, 1) and the intensity information SI(1, 6, 1) in association with each other. The acquisition section 122 further acquires, for example, the depth information DI(4, 2, 1) and the intensity information SI(4, 2, 1) in association with each other. The acquisition section 122 further acquires, for example, the depth information DI(5, 4, 1) and the intensity information SI(5, 4, 1) in association with each other.

In FIG. 1, the parameter generator 123 generates parameters that define the projection surface PP based on the depth information DI and the intensity information SI acquired by the acquisition section 122.

More specifically, the parameter generator 123 may generate the parameters described above by using the intensities indicated by the intensity information SI as weights to calculate a weighted average of the distances indicated by the depth information DI. The parameter generator 123 may instead remove outliers from the distances indicated by the depth information DI based on the result of comparison between the intensities indicated by the intensity information SI and a threshold, and generate the parameters described above based on the distances indicated by the depth information DI from which the outliers have been removed. The parameter generator 123 may still instead generate the parameters described above by using a weighted least squares method for producing coordinates calculated by using the distances indicated by the depth information DI, and the intensities indicated by the intensity information SI as the weights.

Note that the “parameters that define the projection surface PP” may, for example, be a normal vector for the projection surface PP or coefficients of the equation of a plane that defines the position of the projection surface PP in the XYZ coordinates.

A: A Case Where the Weighted Average is Calculated

The parameter generator 123 may generate the parameters that define the projection surface PP based on a weighted average of the distances indicated by multiple pieces of depth information DI at the multiple points of time, the weighted average produced by using as the weights the intensities indicated by multiple pieces of intensity information SI corresponding to the multiple pieces of depth information DI.

FIG. 5 shows the depth information DI at the pixel IM(1, 6) in multiple frames. As an example, let a distance di be the distance indicated by the depth information DI(1, 6, i) at the pixel IM(1, 6), and a weight wi be the intensity indicated by the intensity information SI(1, 6, i) corresponding to the depth information DI(1, 6, i), and the parameter generator 123 uses Expression 1 below to calculate a distance dff, which is a weighted average of the distances from the distance sensor 15 to the pixel IM(1, 6) over frames. Note that i is an integer greater than or equal to one but smaller than or equal to seven.

In FIG. 5, the same applies to the pixels IM(1, 1) to IM(6, 6) other than the pixel IM(1, 6). In the example shown in FIG. 5, seven frames from a first frame to a seventh frame are shown. However, even when the number of frames differs from that in FIG. 5, the same applies except that the number corresponding to the number of frames in Expression 1 is a different number.

The parameter generator 123 may generate the parameters that define the projection surface PP based on a weighted average of the distances indicated by multiple pieces of depth information DI at at least some of the multiple positions adjacent to each other out of the multiple positions on the projection surface PP. Note that the weights in this case are the intensities indicated by the multiple pieces of intensity information SI corresponding to the multiple pieces of the depth information DI.

FIG. 6 shows the depth information DI at the pixel IM(1, 6) and the pixels IM(1, 5), IM(2, 5), and IM(2, 6) adjacent to the pixel IM(1, 6) in the first frame. Let a distance di be the distance indicated by the depth information DI(1, 6, 1) at the pixel IM(1, 6), and a weight w1 be the intensity indicated by the intensity information SI(1, 6, 1) corresponding to the depth information DI(1, 6, 1). Let a distance d2 be the distance indicated by the depth information DI(1, 5, 1) at the pixel IM(1, 5), and a weight w2 be the intensity indicated by the intensity information SI(1, 5, 1) corresponding to the depth information DI(1, 5, 1). Let a distance d3 be the distance indicated by the depth information DI(2, 5, 1) at the pixel IM(2, 5), and a weight w3 be the intensity indicated by the intensity information SI(2, 5, 1) corresponding to the depth information DI(2, 5, 1). Let a distance d4 be the distance indicated by the depth information DI(2, 6, 1) at the pixel IM(2, 6), and a weight w4 be the intensity indicated by the intensity information SI(2, 6, 1) corresponding to the depth information DI(2, 6, 1). In this case, the parameter generator 123 may use the Expression 2 below to calculate a distance dmf, which is a weighted average of the distances to the pixel IM(1, 6) that are averaged over the pixels adjacent thereto. Note that i is an integer greater than or equal to one but smaller than or equal to four.

In FIG. 6, the same applies to the pixels IM(1, 1) to IM(6, 6) other than the pixel IM(1, 6).

The parameter generator 123 may combine the method described with reference to FIG. 5 for calculating the distance dff, which is the weighted average over the frames, with the method described with reference to FIG. 6 for calculating the distance dmf, which is the weighted average over the adjacent pixels IM.

Specifically, the parameter generator 123 may calculate the distance dff, which is the weighted average over the frames corresponding to the pixels IM(1, 1) to IM(6, 6), and then use the distance dff to calculate the distance dmf, which is the weighted average over the adjacent pixels IM.

Instead, the parameter generator 123 may calculate the distance dmf, which is the weighted average over the pixels IM adjacent to each of the pixels IM(1, 1) to IM(6, 6), and then use the distance dmf to calculate the distance dff, which is the weighted average over the frames corresponding to the pixels IM(1,1) to IM(6, 6).

B: A Case Where Outliers Are Removed

The parameter generator 123 may compare the intensities indicated by multiple pieces of intensity information S with a threshold, extract intensity information St indicating intensities exceeding the threshold value, and generate the parameters that define the projection surface PP based on the average of the distances indicated by multiple pieces of depth information DI corresponding to the multiple pieces of intensity information SI.

For example, when the intensities indicated by the intensity information SI(1, 6,2), the intensity information SI(1, 6, 3), and the intensity information SI(1, 6, 5) out of the intensities indicated by the multiple pieces of intensity information SI(1, 6, i) (i is an integer greater than or equal to one but smaller than or equal to seven) at the pixel IM(1, 6) in multiple frames exceed the threshold, the parameter generator 123 sets the average of a distance d2 indicated by the depth information DI(1, 6, 2), a distance d3 indicated by the depth information DI(1, 6, 3), and a distance d5 indicated by the depth information DI(1, 6, 5) in FIG. 5 as a distance dfs from the projection apparatus 11 to the pixel IM(1, 6).

In FIG. 5, the same applies to the pixels IM(1, 1) to IM(6, 6) other than the pixel IM(1, 6). In the example shown in FIG. 5, seven frames from a first frame to a seventh frame are shown. Note, however, that the same applies to a case where the number of frames differs from that in FIG. 5.

Instead, when the intensities indicated by the intensity information SI(1, 6, 1), the intensity information SI(1, 5, 1), and the intensity information SI(2, 6, 1) out of the multiple pieces of intensity information SI at the pixel IM(1, 6) and the pixel IM(1, 5), the pixel IM(2, 5), and the pixel IM(2, 6) adjacent to the pixel IM(1, 6) in the first frame exceed the threshold, the parameter generator 123 sets the average of the distance d1 indicated by the depth information DI(1, 6, 1), the distance d2 indicated by the depth information DI(1, 5, 1), and the distance d4 indicated by the depth information DI(2, 6, 1) in FIG. 6 as a distance dms from the projection apparatus 11 to the pixel IM(1, 6).

The parameter generator 123 may combine the method described with reference to FIG. 5 for calculating the distance dfs, which is the average over the frames, with the method described with reference to FIG. 6 for calculating the distance dms, which is the average over the adjacent pixels IM.

Specifically, the parameter generator 123 may calculate the distance dfs, which is the average over the frames corresponding to the pixels IM(1, 1) to IM(6, 6), and then use the distance dfs to calculate the distance dms, which is the average over the adjacent pixels IM.

Instead, the parameter generator 123 may calculate the distance dms, which is the average over the pixels IM adjacent to each of the pixels IM(1, 1) to IM(6, 6), and then use the distance dms to calculate the distance dfs, which is the average over the frames corresponding to the pixels IM(1, 1) to IM(6, 6).

C: A Case Where the Weighted Least Squares Method is Used

The parameter generator 123 calculates the coordinates of the center point of each of the pixel IM(1, 1) to the pixel IM(6, 6) in the XYZ coordinate system based on the distances from the projection apparatus 11 to the center point that are indicated by multiple pieces of depth information DI at multiple points of time. Since the coordinates of the center point of each of the pixels IM(1, 1) to IM(6, 6) are calculated based on the multiple pieces of depth information DI at the multiple points of time, there are as many coordinates as the number of frames. The parameter generator 123 may fit a plane to the point group of the center points of the pixels IM(1, 1) to IM(6, 6), the number of the center points being equal to the number of frames. The parameter generator 123 fits the plane by using the weighted least squares method using as the weights the multiple pieces of intensity information SI at the multiple points of time.

For example, when the equation of the projection surface PP is expressed by pX+qY+rZ=1 as shown in FIG. 2, and the coordinates of the point group of the center points are expressed by (X, Y, Z)=(Xk, Yk, Zk), where k is an integer from 1 to u, the parameter generator 123 generates p, q, and r that minimize mn expressed by Expression 3 below.

The parameter generator 123 uses each of the multiple pieces of intensity information SI corresponding to the multiple pieces of depth information DI at the multiple points of time as σk in Expression 3 described above. The multiple pieces of intensity information SI each correspond to each of the coordinates (X, Y, Z)=(Xk, Yk, Zk) of the point group of the center points.

In FIG. 1, the corrector 124 corrects the projection image PI generated by the projection image generator 121 by using the parameters generated by the parameter generator 123.

As an example, the corrector 124 uses the parameters described above to perform trapezoidal correction on the projection image PI on the projection surface PP so that the projection image PI has a rectangular shape.

The projection controller 125 causes the projection apparatus 11 to project the projection image PI corrected by the corrector 124 onto the projection surface PP.

1-2: Operation in First Embodiment

FIG. 7 is a flowchart showing the operation of the projector 1 according to the present embodiment.

In step S1, the processing device 12 functions as the projection image generator 121. The processing device 12 generates the projection image PI based on an input image.

In step S2, the processing device 12 functions as the acquisition section 122. The processing device 12 acquires the depth information DI indicating multiple distances from the distance sensor 15 to multiple positions on the projection surface PP based on the output from the distance sensor 15.

In step S3, the processing device 12 functions as the acquisition section 122. The processing device 12 acquires the intensity information SI indicating the intensities of the reflected light at the multiple positions on the projection surface PP based on the output from the distance sensor 15.

In step S4, the processing device 12 functions as the parameter generator 123. The processing device 12 generates the parameters that define the projection surface PP based on the depth information DI acquired in step S2 and the intensity information SI acquired in step S3.

In step S5, the processing device 12 functions as the corrector 124. The processing device 12 corrects the projection image PI based on the parameters generated in step S4.

In step S6, the processing device 12 functions as the projection controller 125. The processing device 12 causes the projection apparatus 11 to project the projection image PI corrected in step S5 onto the projection surface PP.

Note in step S4 of the flowchart in FIG. 7 that when the depth information DI and the intensity information SI sufficient for the processing device 12 to generate the parameters have not been successfully acquired, it is preferable that the processing device 12 repeats at least one of steps S2 and S3 until sufficient depth information DI and intensity information SI can be acquired.

The embodiment described above can be changed in various manners. Specific aspects of the variations will be presented below by way of example. The aspects presented below by way of example and the aspects shown in the embodiment described above can be combined with each other as appropriate to the extent that the aspects to be combined with each other do not contradict each other. Note that in the variations presented below by way of example, elements providing effects and having functions that are the same as those in the embodiment have the same reference characters referred to in the above description, and will not be described in detail as appropriate.

In the embodiment described above, for example, when the intensity information SI is information on the intensity indicated by the magnitude of the signal output from each of the light receiving sensors, and when the magnitude of the signal is too strong, the signal is saturated, so that the accuracy of the distance indicated by the depth information DI may decrease. Therefore, when the magnitude of the signal is too strong, it is preferable that the parameter generator 123 reduces the weight by which the distance indicated by the depth information DI corresponding to the light receiving sensor is multiplied. It is instead preferable that the parameter generator 123 widens the range of the distances determined as outliers by increasing the threshold compared with the magnitude of the signal.

However, the parameter generator 123 does not necessarily generate the parameters as described above, and may generate the parameters by using any method using the intensities indicated by the intensity information SI in addition to the distances indicated by the depth information DI.

Depending on the material of the projection surface PP, the parameter generator 123 cannot in some cases calculate the parameters with sufficient accuracy and correct the projection image PI. In such a case, the projector 1 may attach a substance having high reflectance to the surface of the projection surface PP and then perform the correction method shown in the embodiment described above.

3: Summary of Present Disclosure

The present disclosure will be summarized below as additional remarks.

Additional Remark 1 A method for correcting a projection image projected from a projector onto a projection surface, the method including: acquiring depth information indicating multiple distances from a distance sensor to multiple positions on the projection surface based on an output from the distance sensor, the distance sensor configured to irradiate the projection surface with radiated light and receive reflected light reflected off the projection surface; acquiring intensity information indicating an intensity of the reflected light at each of the multiple positions; generating a parameter that defines the projection surface based on the depth information and the intensity information; and correcting the projection image based on the parameter.

The correction method according to the present embodiment, which is configured as described above, improves the accuracy of the correction of the projection image PI. Specifically, the correction method, which calculates the parameter by using the intensity information SI in addition to the depth information DI, improves the accuracy of the calculation of the parameter as compared with a case where the parameter is calculated by using only the depth information DI. The accuracy of the correction of the projection image PI is thus also improved.

In particular, when a ToF sensor is used as the distance sensor 15, and when the distance sensor 15 is separate from the projection surface PP by a long distance, or when the distance sensor 15 inclines with respect to the projection surface PP by a large angle, the accuracy of the measurement of the distance to the projection surface PP decreases. The accuracy may also decrease depending on the material of an object with which the projection surface PP is configured. Under the conditions that the accuracy decreases, variation of the measurement performed by the ToF sensor increases, but the average or the median of the measurement variation does not necessarily coincide with the true value. It is therefore difficult to estimate the distance to the projection surface PP with high accuracy only by using the depth information DI acquired from the ToF sensor.

When the accuracy of the measurement of the distance to the projection surface PP performed by the ToF sensor decreases, appropriate reflected light does not return to the ToF sensor for any of the reasons described above. Therefore, when the measurement accuracy decreases, the magnitude of the signal indicating the light measured by the ToF sensor may decrease. Under the circumstances described above, the correction method according to the present embodiment can be expected to improve the measurement accuracy by using both the depth information DI and the intensity information SI to measure the 3D shape of the projection surface PP with high accuracy.

In the trapezoidal correction performed by the projector, it is therefore necessary to acquire information on the planarity of the projection surface PP with high accuracy. Measuring the projection surface PP in the correction method according to the present embodiment allows the projector 1 to perform trapezoidal correction with high accuracy.

Additional Remark 2 The correction method according to Additional Remark 1, wherein generating the parameter that defines the projection surface based on the depth information and the intensity information includes comparing each intensity indicated by the intensity information with a threshold, and generating the parameter that defines the projection surface based on the depth information corresponding to the intensity information indicating the intensity that exceeds the threshold.

The correction method according to the present embodiment, which is configured as described above, improves the accuracy of the depth information DI, and also consequently improves the accuracy of the correction of the projection image PI.

In the related art, only the depth information DI output from the ToF sensor is used, and an error is reduced, for example, by averaging, but only the depth information DI does not allow identification of a distance that is an outlier, so that the error cannot be completely removed. The correction method according to the present embodiment, which uses the intensity information SI in addition to the depth information DI provided from the ToF sensor, can perform the 3D measurement of the projection surface PP with high accuracy.

Additional Remark 3 The correction method according to Additional Remark 2, wherein the depth information and the intensity information are acquired at multiple points of time, and generating the parameter that defines the projection surface includes generating the parameter that defines the projection surface based on the depth information corresponding to the intensity information indicating the intensity that exceeds the threshold and acquired at one or more points of time.

The correction method according to the present embodiment, which is configured as described above, further improves the accuracy of the depth information DI, and also consequently improves the accuracy of the correction of the projection image PI.

Additional Remark 4 The correction method according to Additional Remark 1, wherein the parameter that defines the projection surface is generated at each of the multiple positions by using a weighted least squares method based on the depth information and the intensity information corresponding to each other and on each intensity indicated by the intensity information as a weight.

The correction method according to the present embodiment, which is configured as described above, improves the accuracy of the depth information DI, and also consequently improves the accuracy of the correction of the projection image Pr.

Additional Remark 5 The correction method according to Additional Remark 1, wherein the depth information and the intensity information are acquired at multiple points of time, and the parameter that defines the projection surface is generated based on a weighted average of distances indicated by the multiple pieces of depth information at the multiple points of time, the weighted average produced by using as a weight each intensity indicated by the intensity information corresponding to each of the multiple pieces of depth information.

The correction method according to the present embodiment, which is configured as described above, further improves the accuracy of the depth information DI, and also consequently improves the accuracy of the correction of the projection image PI.

Additional Remark 6 The correction method according to Additional Remark 1, wherein the parameter that defines the projection surface is generated based on a weighted average of distances indicated by the depth information at at least multiple positions adjacent to each other out of the multiple positions, the weighted average produced by using as a weight each intensity indicated by the intensity information corresponding to the depth information.

The correction method according to the present embodiment, which is configured as described above, further improves the accuracy of the depth information DI, and also consequently improves the accuracy of the correction of the projection image PI.

Additional Remark 7 A projector including one or more processors configured to acquire depth information indicating multiple distances from a distance sensor to multiple positions on a projection surface based on an output from the distance sensor, the distance sensor configured to irradiate the projection surface with radiated light and receive reflected light reflected off the projection surface; acquire intensity information indicating an intensity of the reflected light at each of the multiple positions; generate a parameter that defines the projection surface based on the depth information and the intensity information; and correct a projection image based on the parameter.

The projector 1 according to the present embodiment, which is configured as described above, improves the accuracy of the correction of the projection image PI. Specifically, the projector 1, which calculates the parameter by using the intensity information SI in addition to the depth information DI, improves the accuracy of the calculation of the parameter as compared with a case where the parameter is calculated by using only the depth information DI. The accuracy of the correction of the projection image PI is thus also improved.

In particular, when a ToF sensor is used as the distance sensor 15, and when the distance sensor 15 is separate from the projection surface PP by a long distance, or when the distance sensor 15 inclines with respect to the projection surface PP by a large angle, the accuracy of the measurement of the distance to the projection surface PP decreases. The accuracy may also decrease depending on the material of an object with which the projection surface PP is configured. Under the conditions that the accuracy decreases, variation of the measurement performed by the ToF sensor increases, but the average or the median of the measurement variation does not necessarily coincide with the true value. It is therefore difficult to estimate the distance to the projection surface PP with high accuracy only by using the depth information DI acquired from the ToF sensor.

When the accuracy of the measurement of the distance to the projection surface PP performed by the ToF sensor decreases, appropriate reflected light does not return to the ToF sensor for any of the reasons described above. Therefore, when the measurement accuracy decreases, the magnitude of the signal indicating the light measured by the ToF sensor may decrease. Under the circumstances described above, the projector 1 according to the present embodiment can be expected to improve the measurement accuracy and measure the 3D shape of the projection surface PP with high accuracy by using both the depth information DI and the intensity information SI.

In the trapezoidal correction performed by the projector, it is therefore necessary to acquire information on the planarity of the projection surface PP with high accuracy. Measuring the projection surface PP, onto which the projector 1 according to the present embodiment performs projection, allows the projector 1 to perform trapezoidal correction with high accuracy.