KR20080086087A - Portable terminal having power saving image communication function and method of power saving in image communication - Google Patents

Abstract

A portable terminal having a power-saving video telephony function and a method thereof are provided to minimize the power consumed at a second code and an image processing part by transmitting only the first image to the other side in case that the remaining power of a battery is below a preset threshold without combining the first image with the second image. A portable terminal having a power-saving video telephony function comprises a first camera part(101), a second camera part(103), a first codec(105), a second codec(107), and a control part(130). The first camera part photographs the first image. The second camera part photographs the second image. The first codec encodes the first image at the first encoding rate. Based on an encoding control signal, the second codec encodes the second image at the second encoding rate equivalent to the encoding control signal. Based on the remaining power of a battery(190), the control part generates the encoding control signal to adjust the second encoding rate of the second codec.

Description

Portable terminal having power saving image communication function and method of power saving in image communication

1 is a block diagram showing a configuration of a portable terminal having a power saving video call function according to an embodiment of the present invention.

2 is a table illustrating encoding rates according to battery remaining power in a portable terminal having a power saving video call function according to an embodiment of the present invention.

3 is a flowchart illustrating a power saving video call process of a portable terminal according to an embodiment of the present invention.

4 is a flowchart illustrating a power saving video call process of a portable terminal according to another embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

101: first camera unit 103: second camera unit

105: first codec 107: second codec

110: image processing unit 120: video codec

130: control unit 140: display unit

150: wireless transceiver 190: battery

195: analog-to-digital converter

The present invention relates to a portable terminal, and more particularly, to a portable terminal having a power-saving video call function that can be applied to a portable terminal having a video call function, and a power-saving video call method of the portable terminal.

As mobile communication evolved into 3.5 generations, High Speed Downlink Packet Access (HSDPA) service began and video call service became commercially available. You can talk while watching.

The video call service takes a picture of a caller using a camera provided in a portable terminal, processes the recorded video to meet the transmission standard of the video call, and transmits it to the video call receiver, and transmits the video signal transmitted from the video call receiver. Is converted to be displayed on the display device of the portable terminal and displayed on the sender's portable terminal to allow the caller and the receiver to talk while looking at each other.

In order to provide such a video call service, a camera for capturing an image of a user, an image processor for processing an image captured by the camera, and an image codec for encoding the processed image to comply with a video call transmission standard are additionally required. Due to the operation of the above components, the power consumption is drastically increased than during voice calls.

Korean Patent Laid-Open Publication No. 2004-80847 (name of the invention: “Image screen adjusting method for preventing power consumption of a mobile communication terminal”) reduces battery consumption by adjusting the size of a video screen displayed on an LCD display device according to battery power remaining. A method is disclosed.

However, Korean Patent Laid-Open Publication No. 2004-80847 uses a method of reducing the frame size of a video encoded according to the remaining battery power, and when the battery remaining amount of the portable terminal of the video call is reduced, the corresponding reduced image is displayed. Is sent to the portable terminal. Therefore, the reduced image is displayed on the portable terminal of the video call counterpart.

In general, a portable terminal is provided with a display device having a small display area, and in consideration of the fact that a small display area of the display device is divided so that both a sender and a receiver are displayed when a video call is made, Korean Patent Application Publication 2004-80847 As described above, when the size of the video screen is reduced and transmitted according to the remaining battery power, the portable terminal of the video call receiver is displayed with a smaller size of the sender, which makes it difficult to recognize the appearance of the other party.

Recently, a video call method has been introduced in which two cameras are provided in a portable terminal to which various effects are added. If a video call is performed using two cameras, power consumption is greater than that of a video call using one camera. Accordingly, when performing a video call using two cameras, a corresponding power saving method is required.

Accordingly, a first object of the present invention is to provide a portable terminal having a power saving type video call function that can reduce power consumption during a video call using at least one camera.

In addition, a second object of the present invention is to provide a power-saving video call method of a portable terminal that can reduce power consumption during video calls using at least one camera.

In order to achieve the first object of the present invention, a portable terminal having a power saving video call function according to an aspect of the present invention includes a first camera unit for photographing a first image, a second camera unit for photographing a second image, A first codec for encoding the photographed first image at a first encoding rate, a second codec for encoding the photographed second image at a second encoding rate corresponding to the encoding control signal based on an encoding control signal, and a battery And a controller configured to generate the encoding control signal for adjusting the second encoding rate of the second codec based on the remaining power of. The controller may generate the encoding control signal for reducing the second encoding rate of the second codec when the battery residual power decreases. The controller may stop the encoding operation of the second codec when the battery residual power is less than or equal to a preset threshold. The portable terminal may include an image processor for synthesizing the encoded first image and the encoded second image to generate a synthesized image, a video codec for encoding the synthesized image to a video call standard, and a voltage provided from a battery in a digital format. The apparatus may further include an analog-digital converter configured to convert voltage data. The controller controls the image processor to synthesize the last encoded frame of the encoded first image and the encoded second image when the battery residual power is equal to or less than a preset threshold. To generate an image. The controller may control the image processor to directly transfer the encoded first image to the video codec without generating the composite image when the battery residual power is less than or equal to a preset threshold.

In addition, according to an aspect of the present invention to achieve a second object of the present invention, a power-saving video call method of a portable terminal, encoding a first image photographed by a first camera unit at a first encoding rate, remaining battery power; Confirming an image, generating an encoding control signal for adjusting a second encoding rate of a second image photographed by a second camera unit based on the identified battery remaining power, and generating the encoding control signal based on the encoding control signal. Encoding a second image at the second encoding rate. The generating of the encoding control signal may generate an encoding control signal for reducing the second encoding rate of the second image when the battery residual power decreases. The generating of the encoding control signal may generate an encoding control signal for stopping the encoding operation of the second codec when the battery residual power is less than or equal to a preset threshold. The method may further include generating a composite image by synthesizing the encoded first image and the encoded second image, and encoding the synthesized image into a video call standard. The generating of the synthesized image by synthesizing the encoded first image and the encoded second image may be performed when the battery remaining power is less than or equal to a preset threshold value, which is the most of the encoded first image and the encoded second image. Finally, the synthesized image may be generated by synthesizing the encoded frames. The generating of the synthesized image by synthesizing the encoded first image and the encoded second image may directly generate the encoded first image without generating the synthesized image when the battery remaining power is less than or equal to a preset threshold. It can be encoded in a video call standard.

As the present invention allows for various changes and numerous embodiments, particular embodiments will be illustrated in the drawings and described in detail in the written description.

However, this is not intended to be limited to the specific embodiment of the present invention, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Hereinafter, with reference to the accompanying drawings, it will be described in detail a preferred embodiment of the present invention. Hereinafter, the same reference numerals are used for the same components in the drawings, and duplicate descriptions of the same components are omitted.

Terms such as first and second may be used to describe various components, but the components should not be limited by the terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the first component may be referred to as the second component, and similarly, the second component may also be referred to as the first component. The term and / or includes a combination of a plurality of related items or any item of a plurality of related items.

1 is a block diagram showing a configuration of a portable terminal having a power saving video call function according to an embodiment of the present invention.

Referring to FIG. 1, a portable terminal having a power saving video call function according to an embodiment of the present invention may include a first camera unit 101, a second camera unit 103, a first codec 105, and a second codec ( 107, the image processor 110, the video codec 120, the controller 130, the display 140, the wireless transceiver 150, the key input unit 161, the microphone 163, the speaker 165, and voice. A codec 170, a storage unit 180, a battery 190, and an analog-to-digital converter 195 are included.

Each of the first camera unit 101 and the second camera unit 103 converts an optical signal of an object incident through an optical device (not shown) into an electrical signal through an image sensor (not shown), and A provided therein. The converted electrical signal is converted into a digital image signal using a / D (Analog to Digital) converter (not shown) and output.

When the portable terminal is a slide type consisting of a slide unit and a main body unit, the first camera unit 101 may be installed to face the user so as to photograph the user, and the second camera unit ( 103 may be installed to photograph the opposite direction to the first camera unit 101 in the main body portion of the portable terminal may be configured to photograph the foreground. Here, the foreground represents a direction viewed by the user.

In addition, in another embodiment of the present invention, the first camera unit 101 and the second camera unit 103 are installed to be rotatable so that the first camera unit 101 and the second camera unit 103 do not overlap each other. It may be configured to shoot a subject that does not.

The first codec 105 is connected to the first camera unit 101 to receive the first image data photographed from the first camera unit 101 and converts the color format of the first image data received to the first image data. Reduce the size of. For example, the first codec 105 may receive raw data in the form of red green blue (RGB) from the first camera unit 101, encode the raw data, and convert the raw data into the YCbCr 420 format.

The second codec 107 is connected to the second camera unit 103 to receive the second image data photographed from the second camera unit 103 and at a predetermined frame per second based on an encoding control signal provided from the controller 130. The size of the second image data is reduced by converting the color format of the second image data. For example, the second codec 107 receives raw data in the RGB form from the second camera unit 103 and converts the raw data in the RGB form at a predetermined frame per second based on the encoding control signal of the controller 130. Can be encoded and converted to the YcbCr 420 format.

The image processor 110 is connected to the first codec 105 and the second codec 107 to receive first image data photographed by the user from the first codec 105 and from the second codec 107. Second image data photographing a subject in a foreground, ie, a direction viewed by a user is provided. The image processor 110 processes the first image data and the second image data, and then outputs an image obtained by combining the first image data and the second image data. The synthesized image output from the image processor 110 becomes an image obtained by synthesizing the user's view in the foreground, which is the direction in which the user looks.

To this end, the image processor 110 receives the first image data received from the first codec 105 based on the synthesis environment information set by the user and the first image data photographing the user's appearance and the background of the user. Extracts a predetermined area corresponding to the synthesis environment information set by the user, such as the location, size, and shape of the extraction object.

For example, if the user has set an ellipse having a predetermined size and position corresponding to the face as extraction information in order to extract only the face from the image where the user is photographed, the image processor 110 may determine the first codec 105. The face part, which is a region corresponding to the set ellipse, is extracted from the first image data provided from the. The image processor 110 performs a sharpening operation on the extracted object using the sharpening filter.

In addition, the image processor 110 receives second image data photographing the foreground, which is the direction viewed by the user, from the second codec 107 and processes the second image data provided according to preset synthesis environment information. For example, the image processor 110 may remove noise present in the second image data by using a filter such as an average filter, a median filter, a Gaussian filter, and convert the second image data into a smooth image. Can be.

The image processor 110 extracts a predetermined region from the first image data, and when the processing of the second image data is finished, the predetermined region and / or the second region extracted from the first image data according to the transparency effect information set by the user. The composite image is output by synthesizing the predetermined region and the second image data extracted by applying a transparent effect to each of the image data.

For example, the image processor 110 assigns an alpha value to each of the extracted predetermined region and the second image data, and semi-transparently processes the predetermined region and / or the second image data extracted from the first image data. A predetermined region and second image data can be synthesized.

The image processor 110 directly processes the first image data provided from the first codec 105 without performing a synthesis process of the first image data and the second image data under the control of the controller 130. You can also pass it on.

The video codec 120 receives the synthesized image from the image processor 110 and encodes the synthesized image into a predetermined video call transmission format to provide it to the controller 130. In addition, the video codec 120 receives an image of a video call counterpart from the controller 130 and decodes the image of the video call counterpart to provide it to the display 140.

The video codec 120 may be applied with a codec such as H.261, H.263, H.264, and MPEG-4, and the video codec 120 satisfies H.263 and MPEG-4 simple profile level 0. Codec can be applied.

The controller 130 transmits the composite image provided from the video codec 120 to the portable terminal of the video call counterpart through the wireless transceiver 150, and receives and provides an image of the video call counterpart via the wireless transceiver 150. The received image is provided to the video codec 120.

The controller 130 displays a user interface screen for selecting a power saving video call function through the display unit 140, and when the user selects the power saving video call function through the key input unit 161, the analog-digital converter ( The remaining power of the battery is checked based on the battery voltage data provided at 195, and an encoding control signal for adjusting the encoding rate of the second codec 107 according to the remaining power of the battery is provided to the second codec 107. It reduces power consumption by reducing the encoding rate per second.

For example, when a power saving video call is performed, the controller 130 checks the remaining power of the battery at predetermined time intervals based on the battery voltage data provided through the analog-to-digital converter 195, and gradually performs the operation according to the remaining battery power. When the encoding rate per second of the second codec 107 is reduced, and the battery remaining power is lower than or equal to a preset limit value, the encoding operation of the second codec 107 is stopped and the last encoded value of the second codec 107 is stopped. A video call is performed by synthesizing the frame and the image data encoded by the first codec 105.

In addition, in another embodiment of the present invention, when the remaining battery power is less than or equal to a predetermined threshold value, the controller 130 stops the operations of the second camera unit 103 and the second codec 107, and the image processing unit 110. The power consumption may be further reduced by directly transmitting the first image data provided from the first codec 105 to the video codec without performing image synthesis.

In addition, the controller 130 displays the user interface screen for setting the environment of the image synthesis through the display unit 140 and stores the environment setting information set by the user through the key input unit 161 in the storage unit 180. The image processor 110 is provided. The configuration information of the image composition may be, for example, a camera selection, a foreground update period, a location of an extracted object, a size, a shape, and a translucent effect setting value.

The display unit 140 is, for example, a display device such as a liquid crystal display (LCD) and displays a user interface for displaying a function and selecting a function of the portable terminal, or executing various applications provided in the portable terminal. Display the screen.

In particular, when the video call is executed, the display 140 displays a composite image of the user, that is, the caller and the video of the video call counterpart.

The wireless transceiver 150 converts a radio frequency (RF) signal received through the antenna ANT into a base band signal and provides it to the controller 130, and a base band signal provided from the controller 130. Is converted into a wireless signal and output through the antenna (ANT). The baseband signal provided to the controller 130 when the video call is executed may include a video signal and an audio signal of a video call counterpart, and the baseband signal provided from the controller 130 may be an image of a caller, that is, a portable terminal user. Signal and voice signal.

The key input unit 161 includes a plurality of text, numeric input keys, and function keys for executing a special function, and provides the control unit 130 with a key input event signal corresponding to a key operation input from a user. In particular, the key input unit 161 provides the control unit 130 with a key event signal corresponding to selection and execution of a power saving video call function and a key event signal corresponding to a key operation for setting an environment for image synthesis.

The microphone 163 receives the caller's voice during the video call and converts the caller's voice into an electrical signal to provide the voice codec 170. The speaker 165 receives the voice signal of the video call counterpart from the voice codec 170 and outputs the voice signal in the audio frequency band.

The voice codec 170 encodes the caller's voice provided from the microphone 163 into a predetermined format and provides the control unit 130. In addition, the voice codec 170 receives the voice of the video call counterpart from the controller 130, decodes the voice of the video call counterpart, and provides the decoded voice to the speaker 165.

The speech codec 170 may perform encoding and decoding of speech using, for example, codec standards such as G.711, G.723, G.723.1, G.728, and the like.

The storage unit 180 stores system programs such as an operating system for basic operations of the portable terminal, various application programs, and temporary data generated while the portable terminal processes application programs. In particular, the storage unit 180 may store a synthesized image according to a user's selection and store environment setting information of the image synthesis.

The battery 190 supplies power required for the operation of the portable terminal. In particular, the battery 190 is connected to the analog-to-digital converter 195 to convert the voltage to the analog-to-digital converter 195.

The analog-to-digital converter 195 receives a voltage from the battery 190, converts the provided battery voltage into battery voltage data in a digital format, and is provided to the controller 130.

In the portable terminal having a power saving video call function according to an embodiment of the present invention illustrated in FIG. 1, the encoding rate of the second image data is adjusted according to the remaining battery power. In some embodiments, the encoding rate of the first image data and the second image data may be adjusted according to the remaining battery power.

2 is a table showing an encoding rate according to battery remaining power in a portable terminal according to an embodiment of the present invention.

Referring to FIG. 2, when a power saving type video call function is performed by a user, the controller 130 receives the digital battery voltage data from the analog-digital converter 195 and checks the remaining battery power at predetermined time intervals. .

When the determined battery residual power is 80% or more, the controller 130 controls the second codec 107 so that the second image data is encoded at a basic encoding rate (for example, 15 frames per second), and the battery When the remaining power is 60 to 80%, the second codec 107 is controlled to reduce the encoding rate of the second image data to 10 frames per second. When the battery remaining power is 40 to 60%, the second codec 107 Reduce the encoding rate to 5 frames per second.

When the battery residual power is 40% or less, the controller 130 controls the second codec 107 to stop the encoding operation of the second codec 107. In addition, when the battery residual power is 40% or less, the controller 130 controls the image processor 110 to control the last encoded frame and the first codec 105 of the second image data encoded by the second codec 107. ) Synthesizes first image data encoded at a predetermined frame (for example, 15 frames) per second.

3 is a flowchart illustrating a power saving type video call process of a portable terminal according to an embodiment of the present invention. It is assumed that a user selects a power saving type video calling function after the portable terminal is initialized.

Referring to FIG. 3, when a video call starts, the first codec 105 encodes the first image data according to a preset encoding rate (for example, 15 frames per second) and provides the first image data to the image processor 110 (step). 301).

The controller 130 receives the battery voltage data from the analog-to-digital converter 195 (step 303), and checks the remaining power of the battery based on the provided battery voltage data (step 305).

Thereafter, the controller 130 determines whether the remaining power of the battery 190 is 80% or more (step 307), and when the remaining power of the battery 190 is 80% or more, the controller 130 determines the second codec 107. ), So that the second image data is encoded at 15 frames per second (step 309).

If it is determined in step 307 that the remaining power of the battery 190 is not 80% or more, the controller 130 determines that the remaining power of the battery 190 is 60% or more, that is, the remaining power of the battery 190 is 60-80%. In operation 311, if it is determined that the remaining power of the battery 190 corresponds to 60 to 80%, the second codec 107 is controlled to encode the second image data at 10 frames per second (step 311). 313).

If it is determined in step 311 that the remaining power of the battery 190 is not 60% or more, the controller 130 determines that the remaining power of the battery 190 is 40% or more, that is, the remaining power of the battery 190 is 40 to 60%. In operation 315, if the remaining power of the battery 190 is determined to correspond to 40 to 60%, the second codec 107 is controlled to encode the second image data at 5 frames per second (step 315). 317).

As described above, the second image data is encoded at a predetermined encoding rate corresponding to the remaining power of the battery 190 through steps 303 to 317.

Thereafter, the image processor 110 synthesizes the first image data and the second image data encoded by the first codec 105 and the second codec 107, respectively, to generate a synthesized image (step 319).

If it is determined in step 315 that the remaining power of the battery 190 is not 40% or more, the controller 130 controls the second codec 107 to stop encoding of the second image data (step 321). The processor 110 controls the processor 110 to synthesize the last encoded frame of the first image data and the second image data provided from the first codec 105 (step 323).

When the remaining power of the battery 190 is 40% or less, the controller 130 stops the encoding operation of the second codec 107 and controls the image processor 110 to encode the most recently encoded second image data. The first image data encoded in real time according to a predetermined frame (that is, a still image) and a preset encoding rate (for example, 15 frames per second) to output a synthesized image.

The image data synthesized by the image processing unit 110 in step 319 or step 323 is encoded into a transmission format suitable for a video call by the video codec 120, and then is transmitted to the video call counterpart through the wireless transceiver 150. Is sent to the portable terminal (step 325).

Thereafter, the controller 130 determines whether an event signal (for example, a key event signal) indicating the end of the video call has been generated (step 327), and if it is determined that no event signal indicating the end of the video call has been generated, Returning to 301, the subsequent steps are sequentially performed to continue the power saving video call, and when it is determined that an event signal indicating the end of the video call is generated, the power saving video call process is terminated.

As shown in FIG. 3, the power saving video call method of the portable terminal according to an embodiment of the present invention may gradually reduce the encoding rate of the second image data according to the remaining power of the battery 190, and maintain the remaining battery 190. When the power is lower than or equal to a preset threshold (for example, 40%), the second codec 107 is stopped and the second codec 107 is consumed by synthesizing the first encoded data with the last encoded frame. The power is reduced, and the image processing unit 110 synthesizes the last encoded frame and the first image data to reduce the processing load of the image processing unit 110.

4 is a flowchart illustrating a power saving type video call process of a portable terminal according to another embodiment of the present invention. It is assumed that a user selects a power saving type video calling function after the portable terminal is initialized.

Referring to FIG. 4, when the video call starts, the first codec 105 encodes the first image data according to a preset encoding rate (for example, 15 frames per second) and provides the first image data to the image processing unit 110 ( Step 401).

The controller 130 receives the battery voltage data from the analog-digital converter 195 (step 403), and checks the remaining power of the battery 190 based on the provided battery voltage data (step 405).

Thereafter, the controller 130 determines whether the remaining power of the battery 190 is 80% or more (step 407), and when the remaining power of the battery 190 is 80% or more, the controller 130 determines the second codec 107. ) So that the second image data is encoded at 15 frames per second (step 409).

If it is determined in step 407 that the remaining power of the battery 190 is not 80% or more, the controller 130 determines that the remaining power of the battery 190 is 60% or more, that is, the remaining power of the battery 190 is 60-80%. In operation 411, if it is determined that the remaining power of the battery 190 corresponds to 60 to 80%, the second codec 107 is controlled to encode the second image data at 10 frames per second (step 411). 413).

If it is determined in step 411 that the remaining power of the battery 190 is not 60% or more, the controller 130 determines that the remaining power of the battery 190 is 40% or more, that is, the remaining power of the battery 190 is 40 to 60%. In operation 415, if the remaining power of the battery 190 corresponds to 40 to 60%, the second codec 107 is controlled to encode the second image data at 5 frames per second (step 415). 417).

As described above, the second image data is encoded at a predetermined encoding rate corresponding to the remaining power of the battery 190 through steps 403 to 417.

Thereafter, the image processor 110 synthesizes the first image data and the second image data encoded by the first codec 105 and the second codec 107, respectively, and provides the synthesized image data to the video codec 120 (step 419). The video codec 120 encodes the synthesized video into a video call format (step 421).

If it is determined in step 415 that the remaining power of the battery 190 is not more than 40%, the controller 130 controls the second codec 107 to stop the encoding operation of the second image data (step 423). The image processor 110 is controlled to transfer the first image data provided from the first codec 105 directly to the video codec 120. The video codec 120 encodes the first video data into a transmission format suitable for a video call (step 425).

The video encoded in the video call transmission format by the video codec 120 in step 421 or step 425 is transmitted to the portable terminal of the video call counterpart via the wireless transceiver 150 (step 427).

Thereafter, the controller 130 determines whether an event signal (for example, a key event signal) indicating the end of the video call has been generated (step 429), and if it is determined that no event signal indicating the end of the video call has been generated, Returning to 401, the subsequent steps are sequentially performed to continue the power saving video call, and when it is determined that an event signal indicating the end of the video call is generated, the power saving video call process is terminated.

As shown in FIG. 4, the power saving video call method of the portable terminal according to another embodiment of the present invention reduces the encoding rate of the second image data in stages according to the remaining power of the battery 190. When the remaining power is less than or equal to a preset threshold (for example, 40%), the second codec 107 and the image processor by transmitting only the first image to the portable terminal of the video call counterpart without combining the first image and the second image. The power consumed at 110 may be reduced.

According to the power-saving video call method of the portable terminal and the portable terminal having the power-saving video call function as described above, when a full-featured video call starts, the controller checks the remaining power of the battery and encodes the second image data according to the remaining power of the battery. Reduce the rate step by step, and when the remaining battery power is below the preset limit, the second image data is no longer encoded and the frame of the last encoded second image data and the first image data are combined and transmitted. Alternatively, the power consumed by the operation of the second codec and the image processor may be reduced by transmitting only the first image data.

Therefore, power consumption due to video telephony can be reduced within a range that does not significantly impair the quality of the video telephony, thereby further extending the use time of the portable terminal.

Although described with reference to the embodiments above, those skilled in the art will understand that the present invention can be variously modified and changed without departing from the spirit and scope of the invention as set forth in the claims below. I will be able.

Claims (12)

A first camera unit for photographing a first image; A second camera unit for photographing a second image; A first codec for encoding the photographed first image at a first encoding rate; A second codec for encoding the photographed second image at a second encoding rate corresponding to the encoding control signal based on an encoding control signal; And And a control unit for generating the encoding control signal for adjusting the second encoding rate of the second codec based on the remaining power of the battery. The portable communication apparatus of claim 1, wherein the controller generates the encoding control signal for reducing the second encoding rate of the second codec when the battery residual power decreases. terminal. The portable terminal of claim 1, wherein the controller stops the encoding operation of the second codec when the battery residual power is less than or equal to a predetermined threshold value. The method of claim 1, wherein the portable terminal An image processor configured to synthesize the encoded first image and the encoded second image to generate a synthesized image; A video codec for encoding the composite video into a video call standard; And And a digital-to-digital converter for converting a voltage provided from a battery into battery voltage data in a digital format. The method of claim 4, wherein the control unit When the battery residual power is less than or equal to a preset threshold, the image processor controls the image processor to synthesize the last encoded frame of the encoded first image and the encoded second image to generate the synthesized image. Portable terminal having a power-saving video call function, characterized in that. The method of claim 4, wherein the control unit When the battery remaining power is less than or equal to a predetermined threshold value, the image processor controls the image processor to directly transfer the encoded first image to the video codec without generating the composite image. Portable terminal having a call function. In the video call method of a portable terminal, Encoding the first image photographed by the first camera unit at a first encoding rate; Checking battery remaining power; Generating an encoding control signal for adjusting a second encoding rate of the second image photographed by the second camera unit based on the identified battery remaining power; And And encoding the second image at the second encoding rate based on the encoding control signal. The method of claim 7, wherein generating the encoding control signal And when the battery remaining power decreases, generating an encoding control signal correspondingly to reducing a second encoding rate of the second image. The method of claim 7, wherein generating the encoding control signal And generating an encoding control signal for stopping the encoding operation of the second codec when the battery remaining power is less than or equal to a predetermined threshold value. The method of claim 7, wherein the power-saving video call method of the portable terminal Generating a composite image by synthesizing the encoded first image and the encoded second image; And And encoding the synthesized video into a video call standard. The method of claim 10, wherein the generating of the synthesized image by synthesizing the encoded first image and the encoded second image comprises: When the battery remaining power is less than or equal to a preset threshold, the composite image is generated by synthesizing the last encoded frame of the encoded first image and the encoded second image to generate the composite image. Call way. The method of claim 10, wherein the generating of the synthesized image by synthesizing the encoded first image and the encoded second image comprises: And when the battery remaining power is less than or equal to a predetermined threshold value, directly encoding the encoded first image to a video call standard without generating the composite image.

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