Projection apparatus and image calibration method thereof

A projection apparatus and an image calibration method thereof are provided. The image calibration method of the projection apparatus includes: transmitting N optical pulse signals to N calibration reference points on a projection plane respectively, wherein N is greater than or equal to 2; receiving N reflected optical pulse signals that are generated by reflecting the optical pulse signals; and respectively calculating time intervals between pulse waves of the optical pulse signals and the corresponding reflected optical pulse signals to obtain N time differences, thereby performing an image calibration.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application serial no. 201410049824.8, filed on Feb. 13, 2014. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a projection apparatus and an image calibration method thereof, and particularly relates to a keystone correction method for an image projected by the projection apparatus.

2. Description of Related Art

With the progress of the electronic technology, electronic devices have become indispensable in our daily lives. One important function of the electronic devices, which is being developed now, is to achieve information exchange and communication through image projection provided by the electronic devices.

In order to meet the needs of portability, a pico-projector that can be configured in a handheld electronic apparatus has been proposed. Unlike the conventional stationary projection apparatus, the pico-projector is easy to carry with and can perform image projection in any location at any time. However, compared to the stationary projection apparatus, problems such as image shaking or deformation may easily occur on the pico-projector disposed in the handheld electronic device due to the shaking of the hand that holds the electronic device. Therefore, how to effectively solve the problem of image shaking or deformation resulting from the shaking of the hand is an issue that needs to be overcome.

SUMMARY OF THE INVENTION

The invention provides a projection apparatus and an image calibration method thereof for dynamically and instantly performing a keystone correction of an image on the projected image.

The projection apparatus of the invention is adapted to generate an image on a projection plane. The image calibration method of the projection apparatus includes steps of: respectively transmitting N optical pulse signals to N calibration reference points of the projection plane, wherein N is greater than or equal to 2; receiving N reflected optical pulse signals that are generated by reflecting the optical pulse signals; and respectively calculating time intervals between pulse waves of the optical pulse signals and the corresponding reflected optical pulse signals to obtain N time differences, thereby performing an image calibration.

In an embodiment of the invention, at least two of the calibration reference points are disposed along a horizontal axis of the projection plane.

In an embodiment of the invention, at least two of the calibration reference points are disposed along a vertical axis of the projection plane.

In an embodiment of the invention, the step of respectively calculating the time intervals between the pulse waves of the optical pulse signals and the corresponding reflected optical pulse signals to obtain the time differences includes: respectively calculating time intervals between rising edges of the pulse waves of the optical pulse signals and rising edges of the pulse waves of the corresponding reflected optical pulse signals to obtain the time differences.

In an embodiment of the invention, the step of respectively calculating the time intervals between the pulse waves of the optical pulse signals and the corresponding reflected optical pulse signals to obtain the time differences includes: respectively calculating time intervals between falling edges of the pulse waves of the optical pulse signals and falling edges of the pulse waves of the corresponding reflected optical pulse signals to obtain the time differences.

In an embodiment of the invention, the N calibration reference points include a first calibration reference point, a second calibration reference point, a third calibration reference point, and a fourth calibration reference point that are located at four corners of the projection plane corresponding to the image.

In an embodiment of the invention, the step of respectively transmitting the optical pulse signals to the calibration reference points of the projection plane includes: respectively transmitting a first optical pulse signal, a second optical pulse signal, a third optical pulse signal, and a fourth optical pulse signal to the first calibration reference point, the second calibration reference point, the third calibration reference point, and the fourth calibration reference point, wherein a first reflected optical pulse signal, a second reflected optical pulse signal, a third reflected optical pulse signal, and a fourth reflected optical pulse signal are respectively generated by reflecting the first optical pulse signal, the second optical pulse signal, the third optical pulse signal, and the fourth optical pulse signal.

In an embodiment of the invention, the steps of respectively calculating the time intervals between the pulse waves of the optical pulse signals and the corresponding reflected optical pulse signals to obtain the time differences and performing the image calibration based on the time differences include: respectively calculating the time intervals between the first to the fourth optical pulse signals and the first to the fourth reflected optical pulse signals to obtain the time differences, and performing a keystone calibration of the image on the projection apparatus based on the time differences.

The projection apparatus of the invention includes an optical pulse signal transceiver and a controller. When the projection apparatus generates an image on a projection plane, the optical pulse signal transceiver transmits N optical pulse signals to N calibration reference points of the projection plane respectively, wherein N is greater than or equal to 2. The optical pulse signal transceiver further receives N reflected optical pulse signals generated by reflecting the optical pulse signals. The controller is coupled to the optical pulse signal transceiver. The controller respectively calculates time intervals between pulse waves of the optical pulse signals and the corresponding reflected optical pulse signals to obtain N time differences and performs an image calibration based on the time differences.

Based on the above, the invention transmits the optical pulse signals to multiple calibration reference points on the projection plane and receives the corresponding reflected optical pulse signals, and then calculates the optical pulse signals and the corresponding reflected optical pulse signals to obtain the distances that the projection apparatus projects display data to multiple calibration reference points on the projection plane. Based on the differences between the distances, the image projected by the projection apparatus can be calibrated instantly to maintain the display quality.

DESCRIPTION OF THE EMBODIMENTS

With reference toFIG. 1andFIG. 2,FIG. 1is a flowchart illustrating an image calibration method of a projection apparatus according to an embodiment of the invention, andFIG. 2is a schematic diagram illustrating an image calibration performed by the projection apparatus according to an embodiment of the invention. A projection apparatus200includes an optical pulse signal transceiver210, a controller220, and a projection system230. The projection apparatus200generates an image on a projection plane270by the projection system230. According to the image calibration method, in Step S110, when the projection system230generates the image on the projection plane270, the optical pulse signal transceiver210transmits N optical pulse signals to N calibration reference points on the projection plane270respectively, wherein N is greater than or equal to 2. In the embodiment ofFIG. 2, the optical pulse signal transceiver210transmits two optical pulse signals TP1and TP2respectively to two calibration reference points CAL1and CAL2on the projection plane270. The calibration reference point CAL1corresponds to the optical pulse signal TP1and the calibration reference point CAL2corresponds to the optical pulse signal TP2.

Moreover, when the optical pulse signals TP1and TP2reach the projection plane270, the optical pulse signals TP1and TP2are reflected to generate reflected optical pulse signals RP1and RP2respectively. In Step S120, the optical pulse signal transceiver210receives the reflected optical pulse signals RP1and RP2, wherein the number of the reflected optical pulse signals RP1and RP2is equal to the number of the optical pulse signals TP1and TP2that have been transmitted.

In this embodiment, the optical pulse signal transceiver210includes an optical pulse signal transmitter211and an optical pulse signal receiver212. The optical pulse signal transmitter211is configured to send the optical pulse signals TP1and TP2, and the optical pulse signal receiver212is configured to receive the reflected optical pulse signals RP1and RP2. In other embodiments of the invention, the optical pulse signal transceiver210may be constructed with one single duplex device that is capable of receiving or transmitting the optical pulse signals. In addition, the optical pulse signal transceiver210may be an infrared transceiver. In another embodiment, the optical pulse signal transmitter211may be included in the projection system230. More specifically, the projection system230generally includes a light source module for emitting light beams of different colors (e.g. red, green, and blue; three colors RGB) and combining the light beams into an image light beam. In this embodiment, the light source module of the projection system230is further used for sending the optical pulse signals. For example, the light source module of the projection system230may further include an infrared light source that emits infrared light as the optical pulse signal transmitter211.

Further to the above, in Step S130, the controller220respectively calculates time intervals between pulse waves of the optical pulse signals TP1and TP2and the corresponding reflected optical pulse signals RP1and RP2so as to obtain a plurality of time differences and perform image calibration based on the time differences. In the embodiment, the optical pulse signals TP1and TP2may be pulse signals having one pulse wave, and the reflected optical pulse signals RP1and RP2are pulse signals having one pulse wave as well. With reference toFIG. 3A,FIG. 3Ais a diagram illustrating waveforms of the optical pulse signal TP1and the reflected optical pulse signal RP1. The optical pulse signal TP1has a pulse wave P1and the reflected optical pulse signal RP1has a pulse wave P2. When calculating the time interval between the pulse wave P1of the optical pulse signal TP1and the pulse wave P2of the corresponding reflected optical pulse signal RP2, the controller220calculates a time interval TA1between a rising edge REDG1of the pulse wave P1of the optical pulse signal TP1and a rising edge REDG2of the pulse wave P2of the reflected optical pulse signal RP1to complete the calculation. In other embodiment, the controller220may also calculate a time interval TA2between a falling edge FEDG1of the pulse wave P1of the optical pulse signal TP1and a falling edge FEDG2of the pulse wave P2of the reflected optical pulse signal RP1.

Regarding details of carrying out the calculation of the time interval, please refer toFIG. 3B.FIG. 3Billustrates an embodiment of a calculating method of calculating the time interval between the pulse waves according to the invention. InFIG. 3B, the controller220uses a sampling clock signal CKS to perform sampling between the rising edge REDG1of the pulse wave P1and the rising edge REDG2of the pulse wave P2. More specifically, a counting operation using the sampling clock signal CKS is initiated when the rising edge REDG1of the pulse wave P1occurs, and the counting operation is stopped when the rising edge REDG2of the pulse wave P2occurs. Accordingly, the controller220obtains the time interval between the rising edge REDG1of the pulse wave P1and the rising edge REDG2of the pulse wave P2by means of the counting operation, and thereby obtains the time difference between the pulse wave P1and the pulse wave P2.

Of course, the aforementioned counting operation may also be performed based on the falling edges of the pulse waves P1and P2. Details thereof will not be repeated hereinafter.

With reference toFIG. 4,FIG. 4is a schematic diagram illustrating a relationship between the pulse wave time difference, the projection apparatus, and the projection plane. InFIG. 4, when a projection direction FP of an image generated by a projection apparatus400is not perpendicular to a projection plane410, traveling distances of the optical pulse signal TP1projected to the calibration reference point CAL1and the reflected optical pulse signal RP1are different from traveling distances of the optical pulse signal TP2projected to the calibration reference point CAL2and the reflected optical pulse signal RP2. By respectively calculating the time differences of the pulse waves of the optical pulse signals TP1and TP2and the corresponding reflected optical pulse signals RP1and RP2, a total traveling distance of the optical pulse signal TP1and the reflected optical pulse signal RP1and a total traveling distance of the optical pulse signal TP2and the reflected optical pulse signal RP2are obtained to determine the respective distances between the calibration reference points CAL1and CAL2and the projection apparatus400.

In the example ofFIG. 4, the total traveling distance of the optical pulse signal TP1and the reflected optical pulse signal RP1is smaller than the total traveling distance of the optical pulse signal TP2and the reflected optical pulse signal RP2. That is to say, the distance between the calibration reference point CAL1and the projection apparatus400is smaller than the distance between the calibration reference point CAL2and the projection apparatus400. Thus, an image range displayed by the projection plane410on the top ofFIG. 4is smaller, and an image displayed by the projection plane410on the bottom ofFIG. 4is larger. As a result, the projection apparatus400requires a proper adjustment (e.g. adjusting an angle of image projection) to calibrate the projected image.

In this embodiment of the invention, each calibration reference point may be disposed at a random position on the projection plane. Through comparing the distances between the respective calibration reference points and the projection apparatus, calibration of the projected image can be carried out. Below please refer toFIG. 5AandFIG. 5B.FIG. 5AandFIG. 5Billustrate embodiments of different arrangements of the calibration reference points according to the invention. First, with reference toFIG. 5A, the number of the calibration reference points is at least two. Take the calibration reference points CAL1and CAL2as an example, the calibration reference points CAL1and CAL2are disposed along a vertical axis AXISV of the projection plane510. The calibration reference point CAL1is disposed on the vertical axis AXISV while the calibration reference point CAL2is disposed near the vertical axis AXISV. Simply put, a line connecting the calibration reference point CAL1and the calibration reference point CAL2is almost parallel to the vertical axis AXISV. Here, the calibration reference points CAL1and CAL2are used to perform a keystone correction of the projected image in a vertical direction.

In addition, take the calibration reference points CAL3and CAL4as an example, the calibration reference points CAL3and CAL4are disposed along a horizontal axis AXISH of the projection plane510. The calibration reference point CAL3is disposed above and near the horizontal axis AXISH while the calibration reference point CAL4is disposed below and near the horizontal axis AXISH. Simply put, a line connecting the calibration reference point CAL3and the calibration reference point CAL4is almost parallel to the horizontal axis AXISH. Here, the calibration reference points CAL3and CAL4are used to perform a keystone correction of the projected image in a transverse direction.

Of course, the number of the calibration reference points is not limited to two. The projection apparatus may project optical pulse signals to all the calibration reference points CAL1to CAL4or only three of the calibration reference points for performing calibration of the projected image.

In the embodiment ofFIG. 5B, the calibration reference points CAL1to CAL4are respectively disposed at four corners of the projection plane520corresponding to the projected image. Accordingly, the projection apparatus obtains the distances between the projection apparatus and the four corners of the projection plane510through the four optical pulse signals transmitted to the calibration reference points CAL1to CAL4and the corresponding four reflected optical pulse signals. The keystone correction of the projection apparatus is performed based on the four distances, so as to optimize the projected image.

In conclusion of the above, the invention is to dispose multiple calibration reference points on the projection plane and utilize the projection of optical pulse signals to the calibration reference points. By measuring the time differences between the optical pulse signals and the corresponding reflected optical pulse signals, keystone correction can be carried out on the image projected by the projection apparatus, so as to dynamically and instantly maintain the quality of the projected image.