Projector and method for controlling the same

A projector calculates an input-output characteristic for converting a tone value of an input image so as to perform display in a given projectable luminance range in a display absolute luminance range of an input signal, in accordance with the brightness of the projection surface. An output signal is generated from the input signal and projected, based on the calculated input-output characteristic. With the disclosed projector, image data having an input luminance range that is different from the output luminance range can be appropriately displayed.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to projectors and methods for controlling the same.

Description of the Related Art

Conventionally, image data is compressed into a narrow dynamic range that is defined in standards (e.g. BT.709 (Rec.709)) based on the assumption that the image data is to be displayed on a CRT (Cathode Ray Tube) display. However, display devices having a wider dynamic range than that of CRT displays, such as liquid-crystal display devices, are commonly used at present, and there are situations where, on the contrary, the capability of display devices cannot be fully utilized with image data that conforms to conventional standards.

For this reason, standards that define image data having a wider dynamic range than in conventional standards (hereinafter referred to as “HDR (High Dynamic Range) image data”) have been proposed. Examples of the HDR image data standards include ST.2084, which is proposed by SMPTE (Society of Motion Picture and Television Engineers). Signal characteristics in the ST.2084 standard are defined by an EOTF (Electro-Optical Transfer Function). The EOTF in ST.2084 is expressed by the following equation, and a scene luminance value (video signal level) is assigned within an absolute display luminance range with a maximum value of 10000 nit (or cd/m2) (Japanese Patent Laid-Open No. 2015-159543).

Here, L denotes a display luminance (0≤L≤1, L=1 corresponds to 10000 nit), and E′ denotes a video signal level (digital value). m1, m2, and c1to c3are constants, and specific values are defined for those constants in ST.2084. The EOTF in ST.2084 has a non-linear quantization step that corresponds to human visual characteristics, and is therefore also called a PQ (Perceptual Quantization) curve.

For example, in the case of displaying such HDR image data on a common device having a dynamic range that is larger than that in BT.709 but small than in ST.2084, the display luminance range (input luminance range) of the image data may be larger than the display luminance range (output luminance range) of the device. In this case, if the input luminance range is compressed in accordance with the output luminance range to display the image data, the displayed image data appears dark overall. If a decrease in luminance due to compression of the dynamic range is corrected, the tone continuity may decrease or the original tone is impaired due to the influence of the tone that was lost as a result of compression. When the input luminance range is smaller than the output luminance range, a problem arises in that, even if display is performed while expanding the input luminance range in accordance with the output luminance range, naturally the image data is not displayed with the correct tone either.

In particular, regarding devices in which the output luminance range (projection surface luminance range) varies depending on settings or the environment as in the case of projectors, a configuration for appropriately displaying image data having an input range that is different from the output luminance range has been hitherto unknown.

SUMMARY OF THE INVENTION

The present invention provides a projector capable of appropriately displaying image data having an input luminance range that is different from an output luminance range, and a method for controlling this projector.

According to an aspect of the present invention, there is provided a projector comprising: a first obtaining unit configured to obtain information that defines a relationship between a tone value and an absolute luminance value of image data to be projected; a second obtaining unit configured to obtain a maximum luminance on a projection surface that is achieved by the projector; a generation unit configured to generate a tone-conversion characteristic based on the information and the maximum luminance; and an application unit configured to apply the tone-conversion characteristic to the image data and supply the image data to projection unit, wherein the generation unit generates the tone-conversion characteristic such that a relationship between the tone value of the image data after the tone-conversion characteristic has been applied thereto and a luminance on the projection surface satisfies the relationship between the tone value and the absolute luminance value obtained by the first obtaining unit in at least part of a tone value range.

According to another aspect of the present invention, there is provided a method for controlling a projector, the method comprising: obtaining information that defines a relationship between a tone value and an absolute luminance value of image data to be projected; obtaining a maximum luminance on a projection surface that is achieved by the projector; generating a tone-conversion characteristic based on the information and the maximum luminance; and applying the tone-conversion characteristic to the image data and supplying the image data to projection unit, wherein, during the generating, the tone-conversion characteristic is generated such that a relationship between the tone value of the image data after the tone-conversion characteristic has been applied thereto and a luminance on the projection surface satisfies the relationship between the tone value and the absolute luminance value obtained during the obtaining in at least part of a tone value range.

According to a further aspect of the present invention, there is provided a non-transitory computer-readable medium that stores a program for causing a computer provided in a projector to function as: a first obtaining unit configured to obtain information that defines a relationship between a tone value and an absolute luminance value of image data to be projected; a second obtaining unit configured to obtain a maximum luminance on a projection surface that is achieved by the projector; a generation unit configured to generate a tone-conversion characteristic based on the information and the maximum luminance; and a application unit configured to apply the tone-conversion characteristic to the image data and supply the image data to a projection unit, wherein the generation unit generates the tone-conversion characteristic such that a relationship between the tone value of the image data after the tone-conversion characteristic has been applied thereto and a luminance on the projection surface satisfies the relationship between the tone value and the absolute luminance value obtained by the first obtaining unit in at least part of a tone value range.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will now be described in detail in accordance with the accompanying drawings.FIG. 1is a block diagram showing an exemplary functional configuration of a projector using LCD devices (LCD projector), which serves as an example of a projector according to the embodiments of the present invention.

First Embodiment

Overall Configuration

An LCD projector100has a CPU110, a ROM111, a RAM112, an operation unit113, an image input unit130, and an image processing unit140. The LCD projector100also has a LCD control unit150, LCD devices151R,151G, and151B, a light source control unit160, a light source161, a color separation unit162, a color composition unit163, an optical system control unit170, and a projection optical system171. The LCD projector100may also have a recording and reproducing unit191, a recording medium192, a communication unit193, an image capturing unit194, a display control unit195, and a display unit196.

The CPU110controls each functional block and realizes the functions of the LCD projector100by loading a program in, for example, the RAM112, the program being stored in a nonvolatile memory (e.g. the ROM111), and executing the loaded program. Programs to be executed by the CPU110, various set values, GUI data, product information, and the like are stored in the ROM111, which may be at least partially rewritable. The RAM112serves as a work memory for the CPU110, and programs and data are temporarily stored in the RAM112.

Still image data and moving image data that are reproduced from the recording medium192by the recording and reproducing unit191can be temporarily stored in the CPU110, and the CPU110can also reproduce images and videos from the stored data using a program stored in the ROM111. Still image data and moving image data that are received from the communication unit193can be temporarily stored in the CPU110, and the CPU110can also reproduce images and videos from the stored data using a program stored in the ROM111. Images and videos obtained by the image capturing unit194can be temporarily stored in the RAM112, and converted into still image data and moving image data and recorded in the recording medium192by using a program stored in the ROM111.

The operation unit113is constituted by, for example, a switch, a dial, a touch panel provided on the display unit196, or the like, and accepts instructions from the user. The operation unit113may have a signal reception unit for receiving signals from an external device that functions as a remote controller, for example. The CPU110executes operations corresponding to an operation made to the operation unit113and the input from the communication unit193. Here, the external device may be any electronic device capable of transmitting a signal that can be received by the signal reception unit and recognized by the CPU110. Examples of such an electronic device include a personal computer, a camera, a mobile phone, a smartphone, a hard disk recorder, a game console, and the like, but are not limited thereto.

The image processing unit140is constituted by, for example, a microprocessor for image processing, performs processing to change the number of frames, the number of pixels, the image shape, or the like on video signals received from the image input unit130, and transmits the processed video signals to the LCD control unit150. The image processing unit140does not need to be a dedicated microprocessor, and for example, the CPU110may realize at least some of the functions of the image processing unit140by executing a program stored in the ROM111. The image processing unit140can execute frame-thinning processing, frame interpolation processing, resolution conversion (scaling) processing, distortion correction processing (keystone correction processing), or the like on video signals input in the form of moving images, for example. The image processing unit140can also perform the aforementioned processing to change images and videos that are reproduced by the CPU110.

The LCD control unit150controls the voltage to be applied to the liquid crystal of pixels of the liquid-crystal elements151R,151G, and151B, based on the video signals that have been processed by the image processing unit140, and adjusts the transmission factors of the LCD devices151R,151G, and151B. Note that the LCD devices151R,151G, and151B will be referred to collectively as a LCD device151.

The LCD device151R is a LCD device that corresponds to red, and is used to adjust the transmission factor of red light in light that is output from the light source161and separated into red (R), green (G), and blue (B) by the color separation unit162. Similarly, the LCD device151G and the LCD device151B are used to adjust the transmission factors of green light and blue light, respectively.

The light source control unit160is constituted by a control microprocessor, and controls the light amount and the switching on and off of the light source161. Note that the light source control unit160does not need to be a dedicated microprocessor, and for example, the CPU110may realize at least some of the functions of the light source control unit160by executing a program stored in the ROM111.

The light source161may be a halogen lamp, a xenon lamp, a high-pressure mercury lamp, or the like, for example, and outputs light for projecting an image. The color separation unit162is constituted by a dichroic mirror, a prism, or the like, for example, and separates the light that is output from the light source161into red (R), green (G), and blue (B) light. Note that if the light source161can output red (R), green (G), and blue (B) light, the color separation unit162is not required.

The color composition unit163is constituted by a dichroic mirror, a prism, or the like, for example, and composites the red (R), green (G), and blue (B) light that has passed through the LCD devices151R,151G, and151B. The light composited by the color composition unit163enters the projection optical system171. The transmission factors of the LCD devices151R,151G, and151B are controlled by the LCD control unit150so as to be values that correspond to an image that is input from the image processing unit140. Accordingly, upon the light composited by the color composition unit163being projected by the projection optical system171, the same image as the image input by the image processing unit140is displayed on a projection surface.

The optical system control unit170is constituted by a control microprocessor, and controls the projection optical system171. Note that the optical system control unit170does not need to be a dedicated microprocessor, and for example, the CPU110may realize at least some of the functions of the optical system control unit170by executing a program stored in the ROM111.

The projection optical system171is constituted by a plurality of lenses and an actuator for driving the lenses, and projects the composited light that has entered from the color composition unit163. The projected image can be subjected to zooming in and out, as well as focus adjustment or the like by using the actuator to drive the lenses in the projection optical system171, and the lenses are thus driven by the optical system control unit170.

A luminance range obtaining unit181(first obtaining unit) obtains information, such as an absolute luminance range, that defines a relationship between a tone value of an input image and an absolute luminance value, from meta data (e.g. EXIF data) or header information that accompanies input image data. The absolute luminance range may be values that are manually input by the user using the operation unit113, instead of values obtained from the input image data. When the absolute luminance range is expressed using values, either luminance values (nit or cd/m2) or reflectance (%) may be used. In this embodiment, luminance values (nit) are used. The absolute luminance range obtained by the luminance range obtaining unit181indicates a lower limit value and an upper limit value, such as “0 to 2000 [nit]” or “0 to 10000 [nit]”. However, if the lower limit value is a fixed value such as 0 [nit] or 0.005 [nit], it is sufficient that at least the upper limit value (maximum luminance) is obtainable.

A projection surface luminance obtaining unit182(second obtaining unit) obtains the projection surface luminance range. A method for obtaining the projection surface luminance range will be described later.

The recording and reproducing unit191reads out still image data and moving image data from the recording medium192to reproduce the read image data, and receives, from the CPU110, still image data and moving image data obtained by the image capturing unit194and records the received image data in the recording medium192. The recording and reproducing unit191can also record, in the recording medium192, still image data and moving image data received via the communication unit193. The recording and reproducing unit191has an interface for accessing the recording medium192and a microprocessor for communicating with the recording medium192, for example. If the recording medium192is a removable medium, the recording and reproducing unit191also has a mechanism such as a slot for removably holding the recording medium192. Note that the recording and reproducing unit191does not need to have a dedicated microprocessor, and for example, the CPU110may realize at least some of the functions of the recording and reproducing unit191by executing a program stored in the ROM111. Data other than still image data and moving image data, such as control data for the LCD projector100according to this embodiment, can also be recorded in the recording medium192. The recording medium192may be a recording medium in any format, such as a magnetic disc, an optical disk, or a semiconductor memory, and may be either removable or fixed with respect to the LCD projector100.

The communication unit193communicates control signals, still image data, moving image data, or the like with an external device in accordance with the control performed by the CPU110. There is no limitation on communication methods or standards, and for example, communication conforming to one or more of wireless LAN, wired LAN, USB, Bluetooth (registered trademark), and the like can be performed. Note that if the image input unit130conforms to HDMI (registered trademark), the communication unit193may perform CEC communication with an external device that is connected to the image input unit130. If, for example, a terminal of the image input unit130is an HDMI (registered trademark) terminal, CEC (Consumer Electronic Control) communication may be performed via that terminal. Here, the external device may be any electronic device capable of communicating with the LCD projector100, and may be a personal computer, a camera, a mobile phone, a smartphone, a hard disk recorder, a game console, a remote controller, or the like, for example.

The image input unit130includes an interface for mainly receiving image signals from the external device. Accordingly, the image input unit130may have one or more of known video input interfaces such as D-Sub, DVI-D, DVI-I, HDMI, DisplayPort, USB, Composite, S-Video, Component, and D1 to D5.

The image capturing unit194is configured and arranged so as to be able to capture the projection surface of the LCD projector100, and transmits the captured image to the CPU110. The CPU110temporarily stores, in the RAM112, the image obtained by the image capturing unit194, and converts the stored image into still image data or moving image data based on a program stored in the ROM111. The image capturing unit194has imaging lenses for forming an optical image of an object, an actuator for driving a focusing lens and a zoom lens included in the imaging lenses, a microprocessor for controlling the actuator, and an image sensor for converting the optical image formed by the imaging lenses into an image signal. The image capturing unit194may also have an AD conversion unit for converting an analog image signal output by the image sensor into a digital image signal. Note that the image capturing unit194is not limited to one for capturing the projection surface, and may also be one for capturing the side opposite to the side on which the projection surface is, for example.

The display control unit195has a microprocessor, for example, and causes the display unit196to display an operation screen for operating the LCD projector100and GUI images such as a switch icon. Note that the display control unit195does not need to have a dedicated microprocessor, and for example, the CPU110may realize at least some of the functions of the display control unit195by executing a program stored in the ROM111.

The display unit196may be a display device in any form, such as an LCD, a CRT display, an organic EL display, or an LED display. The display unit196is not limited to a matrix display, and may include, for example, light-emitting elements incorporated in a button, a switch, or the like.

Note that the image processing unit140, the LCD control unit150, the light source control unit160, the optical system control unit170, the recording and reproducing unit191, and the display control unit195according to this embodiment may be a single or multiple microprocessors capable of performing the same processing as the processing of those blocks. Alternatively, for example, the CPU110may realize at least some of the functions of one or more functional blocks that do not have a processor by executing a program stored in the ROM111.

Basic Operation

A basic operation of the LCD projector100according to this embodiment will be described using a flowchart shown inFIG. 2. Essentially, the operation in each step in the flowchart inFIG. 2is realized as a result of the CPU110executing a program stored in the ROM111and controlling the functional blocks shown inFIG. 1.

FIG. 2shows processing that is started when an instruction to turn on the power of the LCD projector100is input through the operation unit113or an external device.

Upon the instruction to turn on power being input, the CPU110causes a power supply unit (not shown) to supply power to each unit of the LCD projector100.

Next, the CPU110determines the display mode of the LCD projector100(S210). The display mode is designated via the operation unit113or an external device, for example, and the display mode of the LCD projector100according to this embodiment is one of an “input image display mode”, a “reproduced file display mode”, and a “received file display mode”, but is not limited thereto. In the “input image display mode”, the LCD projector100displays an image that is based on a video signal that is input from the image input unit130. In the “reproduced file display mode”, the LCD projector100displays an image that is based on data that is read out from the recording medium192by the recording and reproducing unit191. In the “received file display mode”, the LCD projector100displays an image that is based on data received from the communication unit193. Note that the display mode when the power is turned on may be the display mode that was last used when the projector was turned off, or a predetermined display mode. In this case, the display mode does not necessarily need to be designated by the user.

A description will be given here of the case where the display mode is the “input image display mode” according to the determination result in step S210.

In the case of the “input image display mode”, the CPU110determines whether a video signal has been input from the image input unit130(S220), and waits if it is not determined that a video signal has been input, or advances the processing to step S230if it is determined that a video signal has been input.

In step S230, the CPU110executes projection processing. The CPU110transmits the video signal that has been input from the image input unit130to the image processing unit140, and causes the image processing unit140to generate an image for one screen. The image processing unit140applies the necessary transformation processing (e.g. regarding the number of pixels, the frame rate, and the shape) to the video signal, generates an image for one screen, and transmits the generated image to the LCD control unit150. The LCD control unit150controls the transmission factors of respective pixels of the LCD devices151R,151G, and151B so as to obtain the transmission factors corresponding to the tone levels of the respective red (R), green (G), and blue (B) color components of the pixels of the received image for one screen.

The light source control unit160controls the output of light from the light source161based on the peripheral brightness that is based on the image obtained by the image capturing unit194, for example. The light output from the light source161is separated into red (R), green (G), and blue (B) light by the color separation unit162, and is supplied as a light source for the LCD devices151R,151G, and151B. The light of the respective colors for which the transmission factors have been controlled for the respective pixels of the LCD devices151R,151G, and151B is composited by the color composition unit163, and is projected via the projection optical system171.

The CPU110controls a series of operations in those units during the projection processing. The projection processing is sequentially executed until video signal input is no longer detected or an instruction to end display is given.

Note that if an instruction to change the angle of view (magnification ratio) or the focus of the projection optical system171is input from the operation unit113during the processing in steps S220to S250, the CPU110drives the actuator provided in the projection optical system171in accordance with the instruction.

In step S240, the CPU110determines whether an instruction to switch the display mode has been input from the operation unit113, and returns the processing to step S210if it is determined that an instruction has been input, or advances the processing to step S250if it is not determined that an instruction has been input. Note that, in the case of returning the processing to step S210, the CPU110transmits a menu screen for display mode selection as an OSD image to the image processing unit140, and controls the image processing unit140to display the menu screen so as to superimpose the menu screen on a currently-projected image. The user can operate the menu screen displayed in a superimposed manner using the operation unit113, and select a desired display mode.

On the other hand, in step S250, the CPU110determines whether an instruction to end the projection has been input from the operation unit113, and returns the processing to step S220if it is not determined that an instruction has been input, or stops power supply from the power supply unit to each block and ends the processing if it is determined that an instruction has been input. With the above operation, the LCD projector100in the input image display mode projects an image based on the video signal input from the image input unit130.

Note that if it is determined in step S210that the display mode is the “reproduced file display mode”, the CPU110causes the recording and reproducing unit191to read out a file list or thumbnail data of each file in the recording medium192, and temporarily stores the read file list or thumbnail data in the RAM112. The CPU110then generates file selection screen data based on a text character image that is based on the file list that is temporarily stored in the RAM112or the thumbnail data of each file, and transmits the generated file selection screen data to the image processing unit140. The file selection screen is projected through the same processing as the projection processing (S230).

If an instruction to select a specific image file is input from the file selection screen via the operation unit113or an external device, the CPU110controls the recording and reproducing unit191to reproduce the selected image file.

The image data reproduced from the image file is transmitted from the recording and reproducing unit191to the image processing unit140, and is projected through the same projection processing as that in step S230by the image processing unit140, the LCD control unit150, and the light source control unit160. If a moving image is to be reproduced, reproduction and projection processing are sequentially executed for each frame. The CPU110executes the operation performed in the case where an operation related to the projection optical system171has been made and the operations indicated in steps S240and S250in the same manner as in the input image display mode.

If it is determined in step S210that the display mode is the “received file display mode”, the CPU110projects still image data or moving image data received from the communication unit193in the same manner as the image data reproduced by the recording and reproducing unit191in the reproduced file display mode. The CPU110executes the operation in the case where an operation related to the projection optical system171has been made and the operations indicated in steps S240and S250in the same manner as in the input image display mode.

Next, a description will be given, usingFIGS. 3 and 4, of an operation of displaying (projecting) an HDR image in the LCD projector100according to this embodiment.FIG. 3shows constituent elements related to the projecting operation among the constituent elements shown inFIG. 1, and the same reference numerals are assigned to the same constituent elements as those inFIG. 1. Note that, for convenience, processing executed in the HDR image projecting operation by the image processing unit140(application means) is shown as functional blocks.FIG. 4is a flowchart showing the details of the projection processing (S230inFIG. 1) for an HDR image. Note that whether image data or a video signal that is to be projected relates to an HDR image can be determined based on information indicating the type of transfer function used in the standard. For example, a video stream conforming to the HEVC standard can be discriminated based on the value of transfer characteristics in VUI (Video Usability Information), and a multiplexed stream conforming to MPEG-2 TS can be discerned based on the value of transfer_characteristics, which is a video decode control descriptor.

Here, a description will be given of the case where the display mode of the LCD projector100is the input image display mode, and a video signal of an HDR image in which the dynamic range is expressed using a transfer function (EOTF) for indicating the absolute luminance, as in the ST.2084 standard, is input to the image input unit130. However, the same display processing can also be performed in the case where similar HDR image data is read out from the recording medium192or received via the communication unit193. In the case where the image input unit130has an interface for transmitting digital signals such as an interface conforming to HDMI, video signals are input in a digital format. For this reason, a video signal of an HDR image that is input to the image input unit130will be hereinafter called HDR image data, as in the case of image data that is read out from the recording medium192.

The HDR image data that is input from the image input unit130is first converted by a linear conversion unit141in the image processing unit140so as to obtain a liner input-output characteristic. For example, if the maximum tone value of the image is 1023 (10-bit image) and is associated with an absolute luminance of 2000 nit, the linear conversion unit141converts the tone value to obtain a linear relationship in which the absolute luminance is 1000 nit when the tone value is 512, and the absolute luminance is 0 nit when the tone value is 0. In the case where the tone value and the luminance value are thus in a linear relationship, it is called a linear luminance characteristic.

The HDR image data that has been converted by the linear conversion unit141to have a linear luminance characteristic is input to a range conversion unit142. The range conversion unit142corrects the HDR image data using, for example, a one-dimensional look-up table (1D-LUT), and supplies the corrected HDR image data to a gamma conversion unit143. The gamma conversion unit143corrects, in accordance with a gamma characteristic of the LCD device151, the corrected HDR image data into gamma space data so as to be displayed with the linear luminance characteristic (gamma correction), and supplies the gamma-corrected HDR image data to the LCD control unit150.

The details of the operation will be described with reference toFIG. 4.

In step S401, the luminance range obtaining unit181reads EXIF data or header information of the image data that has been input to the image input unit130, determines whether absolute luminance range data regarding the input image exists, and notifies the CPU110of the determination result. This determination also serves as a determination as to whether the input image is an HDR image, and may be a determination as to whether the designated transfer function type indicates a transfer function using the absolute luminance range. The CPU110advances the processing to step S402if the luminance range obtaining unit181determines that the absolute luminance range data regarding the input image exists, or advances the processing to step S408if not.

In step S408, the CPU110, the image processing unit140, the LCD control unit150, and the light source control unit160execute an operation for projecting the image data (SDR image data) that has a normal dynamic range, such as sRGB. In this case, the same processing as that in steps S220to S250inFIG. 2need only be executed, and accordingly, the description of subsequent processing will be omitted. A series of projecting operations for SDR image data will be called an SDR mode operation.

Note that if it is determined in step S401by the luminance range obtaining unit181that EXIF data or header information itself does not exist, the CPU110may cause an input setting screen such as one shown inFIG. 5Ato be displayed as an OSD to have the user designate characteristics of an input image, for example. Note that the OSD shown inFIGS. 5A and 5Bcan also be displayed in the case where a menu display instruction is input from the operation unit113or an external device.

On the input setting screen shown in FIG.5A, an operation mode for HDR images (HDR mode) or an operation mode for SDR images (SDR mode) can be selected in an “operation mode” section. If the HDR mode is selected in the “operation mode” section, the luminance range of an input image can be set in a “dynamic range” section. In addition, the size of an image to be projected by the LCD projector100(at a predetermined distance) can be designated in a “projection size” section, and the screen gain (reflectance) can be designated in a “screen gain” section. Each item can be set by selecting prepared options that are displayed in accordance with an operation of selecting the corresponding item name. For example,FIG. 5Ashows a state where the item “projection size” is selected, and 100 inches is selected from among four settable options. Upon a decision instruction being input in this state, the CPU110ends display of the options, and performs display at the set projection size of 100 inches. If an instruction to end the display of the OSD is given, the CPU110causes an end check screen to be displayed and has the user select whether to save the set content or end without saving the set content. If the HDR mode is set via the input setting screen, the CPU110advances the processing to step S402rather than to step S408. Note that the input setting screen can be switched to a video setting screen (FIG. 5B) or an information display screen by selecting a tab.

In step S402, the CPU110transmits the set projection size and screen gain to the projection surface luminance obtaining unit182. The projection surface luminance obtaining unit182calculates the projection surface luminance range using the received projection size and screen gain, and transmits the calculated projection surface luminance range to the CPU110. The details thereof will be described later using a flowchart inFIG. 6A.

In step S403, the CPU110generates an input-output characteristic (tone-conversion characteristic) of the tone value to be applied by the range conversion unit142, based on the input luminance range obtained from the luminance range obtaining unit181(or the input setting screen) and the projection surface luminance range obtained from the projection surface luminance obtaining unit182. The CPU110then sets the generated input-output characteristic to a 1D-LUT that the range conversion unit142has. The details thereof will be described later using a flowchart inFIG. 6B.

In step S404, image processing performed by the linear conversion unit141, the range conversion unit142, and the gamma conversion unit143is applied to the input image data, and this image data is output to the LCD control unit150.

In step S405, the LCD control unit150controls the transmission factors of the LCD devices151R,151G, and151B in accordance with the image data that is input from the image processing unit140(gamma conversion unit143).

In step S406, the CPU110checks the value of a readjustment flag, and returns the processing to step S402if the value is 1 (i.e. the flag is ON), or ends the processing (i.e. advances the processing to step S240) if the value is 0 (i.e. if the flag is OFF). In this embodiment, the readjustment flag is set to 1 if the projection size or the screen gain has been changed on the input setting screen inFIG. 5A, or if a setting on the video setting screen inFIG. 5Bhas been changed, or if the in-focus position or the zoom magnification ratio in the projection optical system171has been changed.

Thus, projection processing for one frame is performed. Note that the processing in steps S402and S403may not be executed in every projection process for one frame.

Next, the operation of obtaining the projection surface luminance range executed in step S402will be described using the flowchart shown inFIG. 6A.

In step S501, the projection surface luminance obtaining unit182receives the set projection size and screen gain from the CPU110.

In step S502, the projection surface luminance obtaining unit182determines the value of a video setting parameter. In the case where the light amount does not vary due to the settings, step S502does not need to be executed. The video setting parameter is a coefficient for the light amount, and has a value other than 1 when the projector light amount varies due to the settings. In the LCD projector100according to this embodiment, set values for “projection mode”, “brightness”, “contrast”, “gamma”, and “lamp mode” among settable items on the video setting screen shown inFIG. 5Baffect the amount of emitted light. For this reason, the projection surface luminance obtaining unit182determines the value of the video setting parameter corresponding to the current set values for these items. The projector light amount and the relationship between the set values and the value coefficient of the video setting parameter can be stored in a nonvolatile storage device that can be accessed by the projection surface luminance obtaining unit182, e.g. in the ROM111or within the projection surface luminance obtaining unit182.

Note that, for example, either a “presentation mode” or a “standard mode” can be set as the “projection mode”. Here, it is assumed that the “presentation mode” corresponds to a video setting parameter of 1, and the “standard mode” corresponds to a video setting parameter of a value smaller than in the “presentation mode” (e.g. 0.9). Either “normal” or “energy-saving” can be set as the “lamp mode”, and it is assumed that “normal” and “energy-saving” correspond respectively to a video setting parameter of 1 and a video setting parameter of a value smaller than in the case of “normal” (e.g. 0.9). For the other items as well, the relationship between settable values and a corresponding video setting parameter is determined in advance. Accordingly, the projection surface luminance obtaining unit182can determine the ultimate value of a video setting parameter by multiplying the set value of each item by the corresponding value of the video setting parameter. Note that the types of set items that affect the light amount and the relationship between the set values and the video setting parameter described above merely are examples, and are not limited thereto. The ultimate value of a video setting parameter may alternatively be obtained using other methods, e.g. by referencing correspondence between combinations of the set values and the value of the video setting parameter that is stored in advance.

In step S503, the projection surface luminance obtaining unit182calculates the projection surface luminance according to Equation 1 below, for example, based on the predetermined projector light amount, the projection size and the screen gain received in step S501, and the video setting parameter determined in step S502. Note that, if the projection size is in units of inches, the projection surface luminance obtaining unit182converts the projection size into square meters and applies the converted projection size to Equation 1.
Projection surface luminance=(projector light amount [lm]×video setting parameter×screen gain)/(projection size [m2]×Pi)  (Equation 1)

Here, the projector light amount may be a specification value (e.g. a measured value under JIS X 6911:2015). In the case where the light amount varies due to the settings, a predetermined reference light amount is applied. The maximum luminance on the projection surface that is achieved with the current settings is obtained based on Equation 1.

In this embodiment, the projection surface luminance at the time of an all-white screen (when all pixels project an image having the maximum tone value) (maximum luminance) is calculated using Equation 1, and the projection surface luminance at the time of an all-black screen (when all pixels project an image of a tone value of 0) is 0 [nit]. The projection surface luminance range is determined by the projection surface luminance at the time of an all-white screen (maximum luminance) and the projection surface luminance at the time of an all-black screen (minimum luminance). The projection surface luminance obtaining unit182notifies the CPU110of the projection surface luminance range. Note that if the minimum luminance that defines the projection surface luminance range is always 0 [nit], the projection surface luminance obtaining unit182may notify the CPU110of only the maximum luminance.

Next, the details of the operation to generate the input-output characteristic in step S403will be described using the flowchart inFIG. 6B.

In step S701, the CPU110obtains the input luminance range and the projection surface luminance range from the luminance range obtaining unit181(or the input setting screen) and the projection surface luminance obtaining unit182, respectively.

In step S702, the CPU110generates the input-output characteristic of the tone value that is to be set in the 1D-LUT in the range conversion unit142, based on the input luminance range and the projection surface luminance range obtained in step S701.

For example, it is assumed that the input luminance range is from 0 [nit] to 2000 [nit], and the projection surface luminance range is from 0 [nit] to 1000 [nit], as shown inFIG. 7A.

A relationship between the tone value and the absolute luminance is defined for the HDR image data that is addressed in this embodiment, and it is assumed that an absolute luminance of 2000 [nit] is defined for a maximum tone value of 1023 (10-bit image data; the tone value will be hereinafter denoted by assuming 10-bit image data). Thus, the CPU110generates an input-output characteristic for converting the tone value so as to satisfy the defined relationship between the tone value and the absolute luminance in at least part of the tone value range in which display can be performed as defined in the projection surface luminance range. Accordingly, even if the input luminance range and the projection surface luminance range are different, display (projection) with the defined absolute luminance can be achieved in part of the tone value range.

Since the input image has been converted by the linear conversion unit141so as to have a linear relationship between the tone value and the luminance value, the absolute luminance value is 1000 [nit] when the tone value of the input image is 512. When the output tone value is 1023, which is the maximum tone value, the output luminance value is 1000 [nit], which is the maximum luminance in the projection surface luminance range. Accordingly, the CPU110generates the input-output characteristic so as to satisfy the relationship between the tone value and the absolute luminance value defined for the input image in a range equal to or smaller than the tone value (512 or smaller) at which the input luminance value is 1000 [nit] and less, and such that the output luminance value is saturated at 1000 [nit] when the tone value is greater than 512. This input-output characteristic is indicated by a thick line inFIG. 8A. Note that a thin line inFIG. 8Aindicates a conventional input-output characteristic obtained by compressing the entire input luminance range to adjust the input luminance range to the projection surface luminance range. With such a conventional input-output characteristic, an image for which the relationship between the tone value and the absolute luminance value is defined cannot be displayed with the correct luminance for all tone values.

As mentioned above, the projection surface luminance range, particularly the maximum luminance value in the projection surface luminance range varies depending on the settings, the projection distance, or the like. For example, if the maximum luminance value in the projection surface luminance range increases up to 1500 [nit] as shown inFIG. 7B, the CPU110generates an input-output characteristic (FIG. 9B) for correctly displaying the input tone value that is associated with an absolute luminance value of 0 to 1500 [nit] in the input image. That is to say, in an input image whose output luminance value is 1500 [nit] when the output tone value is 1023 and that has been converted by the linear conversion unit141, a tone value of 768 is associated with an absolute luminance value of 1500 [nit]. Accordingly, the CPU110generates an input-output characteristic in which the absolute luminance value linearly increases from 0 to 1500 [nit] in the range of the input tone value from 0 to 768, and the output tone value is saturated at 1023 in the range of the input tone value from 768 to 1023. Thus, the input image is displayed (projected) with the correct luminance in the range of the input tone value from 0 to 768.

There are also cases where the projection surface luminance range is larger than the input luminance range.FIG. 7Cshows the case where the input luminance range is 0 to 2000 [nit], while the projection surface luminance range is 0 to 4000 [nit]. In this case, the CPU110generates an input-output characteristic in which only the output luminance in the range from 0 to 2000 [nit] is used, as shown inFIG. 8C. That is to say, the CPU110generates a linear input-output characteristic in which the output luminance value is 2000 [nit] when the output tone value is 1023, and the output luminance value is 0 [nit] when the output tone value is 0. In this case, display (projection) can be correctly performed with the defined absolute luminance for all tone values of the input image. The thin line inFIG. 8Cindicates a conventional input-output characteristic in which the entire input luminance range is expanded in accordance with the projection surface luminance range. With such a conventional input-output characteristic, an image for which the relationship between the tone value and the absolute luminance value is defined cannot be displayed with the correct luminance for all tone values.

Note that the projection surface luminance of the LCD projector100is not 0 [nit] at the time of an all-black projection in some cases. In such cases, the minimum luminance in the projection surface luminance is greater than 0 [nit]. For example,FIG. 8Dshows an example in which the input luminance range is 0 to 2000 [nit], and the projection surface luminance range is 10 to 1000 [nit]. In this case, the LCD projector100cannot perform display with a luminance smaller than 10 [nit]. Accordingly, the CPU110generates an input-output characteristic (FIG. 8D) with which display is correctly performed for the input tone values that correspond to absolute luminances of 10 to 1000 [nit]. This input-output characteristic is equivalent to the characteristic inFIG. 8Athat has been changed such that the output luminance value is 10 [nit] in the range of the input luminance value smaller than 10 [nit].

In this embodiment, when HDR image data is displayed, an input-output characteristic is generated in which the tone characteristic is not compressed or expanded in the range where the tone characteristic can be correctly reproduced. However, depending on the use, e.g. in the case where the presence of a saturated area is not favorable, an input-output characteristic may be generated in which the input luminance value does not coincide with the output luminance value in part of the input tone range where the tone characteristic can be correctly reproduced, in order to suppress saturation. In the example inFIG. 8E, an input-output characteristic is generated in which the input luminance value does not coincide with the output luminance value in part (here, a to 512) of the input tone range (here, 0 to 512) where the tone characteristic can be correctly reproduced. Thus, the input tone range in which the tone characteristic can be correctly reproduced is small, but the tones corresponding to input tones of 512 to 1023 can be expressed.

In step S703, the CPU110sets the input-output characteristic generated in step S702in the form of a 1D-LUT in the range conversion unit142, and ends the input-output characteristic generation processing. The range conversion unit142converts the tone values of the input image using the 1D-LUT. Note that the input-output characteristic generation and range (tone) conversion are executed for each color component of the pixels.

Note that, although a configuration has been described here in which the processing for linearly converting the relationship between the tone of the input image and the luminance and the processing for converting the input tone into the output tone are separately performed in the image processing unit140, a configuration in which an input-output characteristic obtained by combining these two conversions is set in a 1D-LUT may also be employed. In this case, the linear conversion unit141is not required.

According to this embodiment, when an HDR image for which the display luminance relative to the tone values is defined as the absolute luminance values is displayed (projected), the tone-conversion characteristic is determined so as to include a range in which display can be performed with the correct tone, based on the relationship between the input luminance range and the projection surface luminance range. As a result, it is possible to solve the inability to correctly display all tones in the case of using a tone-conversion characteristic in which the entire input luminance range is compressed or expanded in accordance with the projection surface luminance range.

Second Embodiment

Next, the second embodiment of the present invention will be described. This embodiment may be the same as the first embodiment except for the processing to obtain the projection surface luminance range executed in step S402inFIG. 4, and accordingly, the processing to obtain the projection surface luminance range according to this embodiment will be described below using a flowchart shown inFIG. 9A.

In this embodiment, the projection surface luminance range is obtained using the image capturing unit194, which is arranged so as to be able to capture an image in the optical axis direction (projection direction) of the projection optical system171.

In step S1101, the CPU110controls each unit to project a specific image (here, a white image for which the maximum tone value is set for all pixels in order to obtain the maximum value of the projection surface luminance), and thereafter instructs the image capturing unit194to capture an image. The image capturing unit194captures an image in response to the instruction.FIG. 10Aschematically shows an image1200obtained by the image capturing unit194. In the image1200,1201denotes a screen, and1202denotes a projected white image. In the case of also obtaining the minimum value of the projection surface luminance, an image in a state where a black image with the tone value of all pixels being 0 is projected is also captured by the image capturing unit194. The image capturing unit194writes the data of the captured image in the RAM112, for example.

In step S1102, the CPU110instructs the projection surface luminance obtaining unit182to obtain the projection surface luminance. In response to the instruction, the projection surface luminance obtaining unit182obtains or calculates pixel values (tone values) in the area of the projected image1202in the image1200stored in the RAM112. Here, it is assumed that the center position of the projected image1202in the image1200is known from the positional relationship between the optical axis of the image capturing unit194and the optical axis of the projection optical system171. Accordingly, the projection surface luminance obtaining unit182calculates the tone value of the projected image1202based on the value of the pixel at the center position in the projected image or the values of the pixels included in a given area from the center in the image1200. Alternatively, the projection surface luminance obtaining unit182may apply binarization or Hough transform to the image1200by using, for example, the image processing unit140to detect the area of the projected image1202, and calculate the tone value based on all pixel values within the area. The projection surface luminance obtaining unit182can average pixel values to calculate the tone value, for example, but may perform the calculation using other methods.

In step S1103, the projection surface luminance obtaining unit182converts the tone value calculated in step S1102into the projection surface luminance. For example, a table or a transformation for indicating the relationship between the tone value and the projection surface luminance such as that shown inFIG. 10Bcan be saved in advance in the ROM111. The projection surface luminance obtaining unit182can then convert the tone value into the projection surface luminance by referencing the table using the tone value or substituting the tone value in the transformation. The conversion table is created through actual measurement before the LCD projector100is shipped, and is saved in the ROM111, for example. Although, in the example inFIG. 10B, a tone value of 255 is converted into a projection surface luminance of 2000 [nit], and the tone value and the projection surface luminance are in a linear relationship, the values of the projection surface luminance relative to the tone values and variation characteristics of the tone value and the projection surface luminance are not limited thereto.

In the case of also obtaining the minimum value of the projection surface luminance, the projection surface luminance obtaining unit182also obtains, in the same manner, the projection surface luminance of an image obtained by projecting a black image and capturing the projected black image.

The projection surface luminance obtaining unit182thus determines the projection surface luminance range, and notifies the CPU110of the determined projection surface luminance range.

This embodiment can also achieve the same effect as that of the first embodiment. In the case where, for example, a light source is provided for each area, the projection surface luminance range can be obtained for each of the areas corresponding to the respective light sources. For example, the projection surface luminance range may be obtained by dividing the projected image area into areas corresponding to the respective light sources, obtaining the tone values for the respective divided areas based on the pixels within those divided areas, and converting the thus-obtained tone values into the projection surface luminances.

Third Embodiment

Next, the third embodiment of the present invention will be described. This embodiment may be the same as the first embodiment except for the processing to obtain the projection surface luminance range executed in step S402inFIG. 4, and accordingly, the processing to obtain the projection surface luminance range according to this embodiment will be described below using a flowchart shown inFIG. 9B.

In this embodiment, the projection surface luminance range is obtained using the in-focus distance in the projection optical system171.

In step S1401, the projection surface luminance obtaining unit182obtains the focusing lens position and the zoom range position in the projection optical system171from the optical system control unit170. The CPU110may obtain these lens positions from the optical system control unit170and notify the projection surface luminance obtaining unit182of the obtained lens positions.

In step S1402, the projection surface luminance obtaining unit182calculates the projection distance. For example, the projection surface luminance obtaining unit182reads out the focal distance of the focusing lens and the shortest distance between the LCD device151and the focusing lens that are stored in advance in the ROM111. As shown inFIG. 11A, the shortest distance between the LCD device151and the focusing lens172, which is included in the projection optical system and moves in the range a, is denoted as A. The focal distance of the focusing lens is denoted as F.

The focusing lens position obtained in step S1401indicates the distance with the position shown inFIG. 11Abeing 0, and therefore, the current distance A′ between the focusing lens and the LCD device151can be found based on the focusing lens position and the shortest distance A between the LCD device151and the focusing lens.FIG. 11Bshows the positional relationship between the LCD device151, the focusing lens172in the projection optical system171, and a screen200. The projection surface luminance obtaining unit182can calculate the distance from the focusing lens172to the screen200, i.e. the projection distance B of the LCD projector100, based on the formula of lens (Equation 2) using the distance A′ and the focal distance F of the focusing lens172.
1/A′+1/B=1/F(Equation 2)
B=FA′/(A′−F)

In step S1403, the projection surface luminance obtaining unit182converts the current zoom lens position into the zoom magnification ratio based on the relationship between the zoom lens position and the zoom magnification ratio that is stored in advance in the ROM111, for example. The projection surface luminance obtaining unit182can then calculate the projection size in accordance with Equation 3 below based on the projection distance B, the zoom magnification ratio, and the size of the LCD device151. Note that the size of the LCD device151may be area [m2], or may be the lengths in the vertical and horizontal directions or the diagonal length, for example.
Projection size=B/A′×zoom magnification ratio×size of LCD device 151  (Equation 3)

Steps S1404and S1405will not be described since these steps are the same as steps S502and S503in the first embodiment.

This embodiment can also achieve the same effect as that of the first embodiment. In addition, the projection size is obtained based on the actual projection distance in this embodiment. Accordingly, when it is possible that the distance between the LCD projector100and the projection surface will change, a more accurate projection surface luminance range can be obtained than in the case of using the set projection size as in the first embodiment.

Note that, in this embodiment, the projection distance is calculated using the focusing lens position and the focal distance, but a configuration in which the LCD projector100directly measures the projection distance may be provided, or the projection distance may be obtained using any other method.

Other Embodiments

This application claims the benefit of Japanese Patent Application No. 2016-066314, filed on Mar. 29, 2016, which is hereby incorporated by reference herein in its entirety.