CN108462826A - A kind of method and mobile terminal of auxiliary photo-taking - Google Patents

Abstract

The present invention provides a kind of method of auxiliary photo-taking and mobile terminals.The method of the auxiliary photo-taking includes：Preview image is acquired by camera；The first subject image and the first scene image in addition to the first subject image are identified from preview image；According to the second feature of the fisrt feature of the first subject image and the first scene image, composition information is obtained；According to composition information, prompt message of taking pictures is exported.The present invention is according to the feature of the feature of subject image in preview image and the scene image in addition to subject image, to determine the composition information being adapted to the scene in preview image, to carry out shooting prompt, allow the user to shoot the good photo of effect according to shooting prompt.

Description

Method and mobile terminal for assisting photography

technical field

The invention relates to the field of communication technologies, in particular to a method for assisting in taking pictures and a mobile terminal.

Background technique

With the continuous popularization of smart mobile terminals, more and more people have given up traditional cameras to take pictures, but choose smart mobile terminals (such as mobile phones) as their main daily photo taking tools. At the same time, taking pictures has also become an indispensable part of people's daily life in today's society. People are used to holding mobile phones to take pictures of the content they are interested in anytime and anywhere, and share it with friends through social application software.

However, since ordinary users have not received special photography training, the photos they take often cannot achieve the desired effect. Users may choose to delete photos because the photos they take are not good-looking, or just save the photos in their mobile terminals and are unwilling to share them with friends, which will reduce the frequency of using mobile phones to take pictures.

Contents of the invention

Embodiments of the present invention provide a method for assisting in taking pictures and a mobile terminal to solve the problem in the prior art that it is difficult for a user to take pictures with good effects when taking pictures with a mobile terminal.

In order to solve the problems of the technologies described above, the present invention is achieved in that:

In a first aspect, an embodiment of the present invention provides a method for assisting in photographing, which is applied to a mobile terminal with a camera. Wherein, the method for assisting in taking pictures includes:

collecting a preview image through the camera;

identifying a first subject image and a first scene image other than the first subject image from the preview image;

acquiring composition information according to the first feature of the first subject image and the second feature of the first scene image;

According to the composition information, the photographing prompt information is output.

In a second aspect, an embodiment of the present invention provides a mobile terminal, where a camera is set on the mobile terminal. Wherein, the mobile terminal also includes:

A collection module, configured to collect a preview image through the camera;

An identification module, configured to identify a first subject image and a first scene image other than the first subject image from the preview image;

A first acquiring module, configured to acquire composition information according to the first feature of the first subject image and the second feature of the first scene image;

An output module, configured to output photographing prompt information according to the composition information.

In a third aspect, an embodiment of the present invention provides a mobile terminal, including a processor, a memory, and a computer program stored on the memory and operable on the processor, and the computer program is executed by the processor When realizing the steps of the method for assisting taking pictures as described above.

In a fourth aspect, an embodiment of the present invention provides a computer-readable storage medium, where a computer program is stored on the computer-readable storage medium, and when the computer program is executed by a processor, the steps of the method for assisting photographing as described above are implemented .

In the embodiment of the present invention, according to the characteristics of the subject image in the preview image and the characteristics of the scene images other than the subject image, the composition information adapted to the scene in the preview image is determined, so as to provide shooting prompts, so that the user can Take photos with good effects according to the shooting prompts to improve user satisfaction.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments of the present invention. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention , for those skilled in the art, other drawings can also be obtained according to these drawings without paying creative labor.

FIG. 1 shows a flow chart of a method for assisting in taking pictures provided by an embodiment of the present invention;

Fig. 2 shows the flowchart of discriminator training provided by the embodiment of the present invention;

Fig. 3 represents one of the block diagrams of the mobile terminal provided by the embodiment of the present invention;

FIG. 4 shows the second block diagram of the mobile terminal provided by the embodiment of the present invention;

FIG. 5 shows the third block diagram of the mobile terminal provided by the embodiment of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

According to an aspect of the embodiments of the present invention, a method for assisting in photographing is provided, which is applied to a mobile terminal with a camera.

As shown in Figure 1, the method for assisting in taking pictures includes:

Step 101, collect a preview image through the camera on the mobile terminal.

In the embodiment of the present invention, when the user activates the camera on the mobile terminal, the camera on the mobile terminal collects a preview image, and displays the preview image through the display screen of the mobile terminal for the user to view.

Step 102, identifying a first subject image and a first scene image other than the first subject image from the preview image.

In the embodiment of the present invention, the subject (i.e. the target object) that the user wants to shoot is firstly determined, and then the scene around the subject is determined, so that the first subject image corresponding to the subject and the first subject image corresponding to the scene around the subject are identified in the preview image. scene image.

Preferably, when determining the first subject image, the image of the object at the focal point in the preview image is determined as the first subject image. Wherein, the focus position may be determined automatically by the mobile terminal, or manually selected by the user.

Wherein, if there is no identifiable object at the focus position, the entire scene in the preview image may be determined as the subject. For example, when the user is shooting a landscape, it is likely that there is no object recognizable by the mobile terminal in the landscape to be photographed, and at this time, the entire landscape presented in the preview image is taken as the subject.

Step 103: Obtain composition information according to the first feature of the first subject image and the second feature of the first scene image.

After the first subject image and the first scene image are identified, the features of the first subject image (ie, the first feature) and the features of the first scene image (ie, the second feature) are respectively extracted, and then according to the features of the first subject image Based on the features of the first scene image, composition information corresponding to the scene in the preview image is determined. Wherein, the composition information includes but not limited to: composition type information.

Wherein, the extracted features (comprising the first feature and the second feature) include but are not limited to: SIFT (Scale-invariant feature transform, scale-invariant feature transform) feature, corner feature (can be detected by Harris focus detection method) , contour features, etc.

Step 104, outputting prompt information for taking photos according to the acquired composition information.

After determining the composition information corresponding to the scene in the preview image, the mobile terminal outputs prompt information that can guide the user to take a photo with better effect according to the composition information, so that the user can proceed according to the prompt information.

In the embodiment of the present invention, according to the characteristics of the subject image in the preview image and the characteristics of the scene images other than the subject image, the composition type suitable for the scene in the preview image is determined, so as to give shooting prompts, so that the user can Take photos with good effects according to the shooting prompts to improve user satisfaction.

Specifically, when obtaining composition information according to the first feature of the first subject image and the second feature of the first scene image, the first feature and the second feature can be input to a preset composition discriminator to obtain the preview image corresponding composition information.

Wherein, the composition discriminator is a discriminator trained based on sample images of different composition types for outputting composition information. The specific training process for the discriminator will be described below.

After the first feature and the second feature are input to the composition discriminator, the composition discriminator can output composition type information suitable for the scene in the preview image according to previous training results.

Wherein, the composition types mentioned here include but not limited to: thirds composition method, diagonal composition method, S-curve composition method and other composition methods in the prior art.

Specifically, in this embodiment of the present invention, before obtaining composition information according to the first feature of the first subject image and the second feature of the first scene image, the method for assisting in taking photos further includes:

A depth map of the preview image is obtained, the first subject image and the first scene image in the depth map are separated, and the first feature of the first subject image and the second feature of the first scene image are respectively extracted.

Wherein, for the depth map of the preview image, the embodiment of the present invention may use dual cameras on the mobile terminal to obtain it, or may use other feasible ways to obtain it.

Wherein, in the depth map, the darker the pixel point is, the closer it is to the camera of the mobile terminal, and the brighter it is, the farther it is from the camera. Generally, there is a significant difference in the depth of the subject and the surrounding scenery, so the two can be separated relatively quickly. Wherein, when separating the first subject image and the first scene image in the depth map, a sampling segmentation algorithm may be used for separation, and other feasible methods may also be used for separation.

It should be noted that, when the entire scene in the preview image is used as the subject, the step of image separation is not necessary.

Specifically, in the embodiment of the present invention, the step of outputting prompt information for taking pictures according to the composition information includes:

According to the composition information, determine the target position of the subject corresponding to the first subject image in the preview image; determine the position movement information of the mobile terminal according to the current position and size of the subject corresponding to the first subject image in the preview image, and the target position ; According to the position movement information, outputting prompt information for taking pictures to guide the user to move the position of the mobile terminal so that the subject corresponding to the first subject image is at the target position.

After the composition information is obtained, the position where the subject should be in the preview image (ie, the target position) is determined. Then according to the current position and size of the subject, analyze how to make the subject at the target position by changing the position of the mobile terminal. After the analysis is completed, output the position movement information of the mobile terminal, and output prompt information guiding the user to take pictures according to the position movement information, so that the user can move the position of the mobile terminal according to the prompt information, so that the subject is in the target position, thereby Take good photos.

Wherein, when the main body is at the target position, the mobile terminal will output prompt information for prompting the user that the main body is at the target position.

Wherein, the location movement information of the mobile terminal includes but is not limited to: moving up, moving down, moving to the left, moving to the right and/or flipping and so on.

Specifically, in the embodiment of the present invention, the composition discriminator is pre-trained through a machine learning algorithm, and the composition discriminator may be a neural network model or other machine learning algorithms, which is not limited in this embodiment of the present invention. Wherein, as shown in Figure 2, the composition discriminator can be obtained by training through the following steps:

Step 201. Identify a label for each frame of sample image.

Wherein, different tags correspond to different composition types.

In the embodiment of the present invention, a certain number of sample images are used to train composition judgment. The composition types of these sample images are known, and the composition type of each frame of sample images is identified in the form of labels, and different composition types correspond to different labels. The label can be understood as a number, for example, the number "1" indicates the thirds composition method, and the number "0" indicates the diagonal composition method, etc. The specific situation can be determined according to actual needs.

Step 202, identifying a second subject image and a second scene image other than the second subject image from each frame of sample images.

Before inputting the sample data into the composition discriminator for training, it is necessary to identify the image of the subject (ie, the second subject image) and the images of the scene around the subject (ie, the second scene image) from each frame of sample images.

Step 203, respectively extracting the third feature of the second subject image and the fourth feature of the second scene image.

After identifying the image of the subject and the image of the scene around the subject, the image of the subject and the image of the scene around the subject are separated, and then the features of the image of the subject (ie, the third feature) and the images of the scene around the subject are respectively extracted feature (ie, the fourth feature).

Wherein, if the subject is the entire scene presented in the sample image, only the image features of the subject can be extracted.

Step 204, input the third feature and the fourth feature to the composition discriminator, and train the composition discriminator.

During the training of the composition discriminator, the image features of the sample images frame by frame are input to the composition discriminator, so that the composition discriminator can learn the composition type of each frame of the sample image respectively.

Among them, the output of the composition discriminator is the label of the composition type. If the output label is always consistent with the label of the sample image learned, it means that the calculation accuracy of the composition discriminator is good; If it is inconsistent, it means that the calculation accuracy of the composition discriminator is poor, and the composition discriminator needs to be adjusted. Wherein, each time when the output label is inconsistent with the labeled label of the sample image, the composition discriminator can adjust the weights and thresholds in the composition discriminator according to the error, so as to improve the calculation accuracy of the composition discriminator.

To sum up, the method for assisting photographing provided by the embodiment of the present invention determines the type of composition adapted to the scene in the preview image according to the features of the subject image in the preview image and the features of the scene images other than the subject image, Thus, a shooting prompt is provided, so that the user can take a photo with a good effect according to the shooting prompt, and improve the satisfaction of the user. In addition, this method does not require users to have knowledge about photography, which expands the scope of applicable people, and the method has strong applicability, not only for portraits, but also for various objects, landscapes and close-up close-ups.

According to another aspect of the embodiments of the present invention, a mobile terminal is provided, and the mobile terminal is provided with a camera.

As shown in Figure 3, the mobile terminal also includes:

The acquisition module 301 is configured to acquire a preview image through a camera.

The identification module 302 is configured to identify the first subject image and the first scene image other than the first subject image from the preview image.

The first acquiring module 303 is configured to acquire composition information according to the first feature of the first subject image and the second feature of the first scene image.

The output module 304 is configured to output photographing prompt information according to the composition information.

Further, as shown in FIG. 4, the first acquisition module 303 includes:

The first obtaining unit 3031 is configured to input the first feature and the second feature to a preset composition discriminator, and obtain composition information corresponding to the preview image.

Wherein, the composition discriminator is a discriminator trained to output composition information based on sample images of different composition types.

Further, as shown in Figure 4, the mobile terminal also includes:

The determining module 305 is configured to determine the image of the object at the focal point in the preview image as the first subject image.

Further, as shown in Figure 4, the mobile terminal also includes:

The second acquiring module 306 is configured to acquire the depth map of the preview image.

An image separation module 307, configured to separate the first subject image and the first scene image in the depth map.

The feature extraction module 308 is configured to extract the first feature of the first subject image and the second feature of the first scene image respectively.

Further, the cameras on the mobile terminal are dual cameras.

As shown in Figure 4, the second acquisition module 306 includes:

The second acquiring unit 3061 is configured to acquire the depth map of the preview image through the dual cameras.

Further, as shown in FIG. 4, the output module 304 includes:

The first determining unit 3041 is configured to determine the target position of the subject corresponding to the first subject image in the preview image according to the composition information.

The second determining unit 3042 is configured to determine the position movement information of the mobile terminal according to the current position and size of the subject corresponding to the first subject image in the preview image and the target position.

The output unit 3043 is configured to output photographing prompt information for guiding the user to place the subject corresponding to the first subject image at the target position by moving the position of the mobile terminal according to the position movement information.

Further, the composition discriminator is trained based on sample images of different composition types through the following steps:

A label is identified for each frame of the sample image, where different labels correspond to different composition types.

A second subject image and a second scene image other than the second subject image are identified from each frame of sample images.

The third feature of the second subject image and the fourth feature of the second scene image are respectively extracted.

The third feature and the fourth feature are input to the composition discriminator, and the composition discriminator is trained.

To sum up, the mobile terminal provided by the embodiment of the present invention determines the composition type adapted to the scene in the preview image according to the features of the subject image in the preview image and the features of the scene images other than the subject image, so as to perform Shooting prompts, so that users can take photos with good effects according to the shooting prompts, and improve user satisfaction. In addition, this method does not require users to have knowledge about photography, which expands the scope of applicable people, and the method has strong applicability, not only for portraits, but also for various objects, landscapes and close-up close-ups.

FIG. 5 is a schematic diagram of a hardware structure of a mobile terminal implementing various embodiments of the present invention.

The mobile terminal 500 includes, but is not limited to: a radio frequency unit 501, a network module 502, an audio output unit 503, an input unit 504, a sensor 505, a display unit 506, a user input unit 507, an interface unit 508, a memory 509, a processor 510, and Power supply 511 and other components. Those skilled in the art can understand that the structure of the mobile terminal shown in Figure 5 does not constitute a limitation on the mobile terminal, and the mobile terminal may include more or less components than shown in the figure, or combine some components, or different components layout. In the embodiment of the present invention, the mobile terminal includes, but is not limited to, a mobile phone, a tablet computer, a notebook computer, a palmtop computer, a vehicle-mounted terminal, a wearable device, and a pedometer.

The processor 510 is configured to collect a preview image through a camera; identify a first subject image and a first scene image other than the first subject image from the preview image; The second feature of the method is to obtain composition information; according to the composition information, output photo-taking prompt information.

In the embodiment of the present invention, according to the characteristics of the subject image in the preview image and the characteristics of the scene images other than the subject image, the composition type suitable for the scene in the preview image is determined, so as to give shooting prompts, so that the user can according to Shooting Tips Take good photos and improve user satisfaction. In addition, this method does not require users to have knowledge about photography, which expands the scope of applicable people, and the method has strong applicability, not only for portraits, but also for various objects, landscapes and close-up close-ups.

It should be understood that, in the embodiment of the present invention, the radio frequency unit 501 can be used for receiving and sending signals during sending and receiving information or during a call. Specifically, after receiving the downlink data from the base station, the processor 510 processes it; Uplink data is sent to the base station. Generally, the radio frequency unit 501 includes, but is not limited to, an antenna, at least one amplifier, a transceiver, a coupler, a low noise amplifier, a duplexer, and the like. In addition, the radio frequency unit 501 can also communicate with the network and other devices through a wireless communication system.

The mobile terminal provides users with wireless broadband Internet access through the network module 502, such as helping users send and receive emails, browse web pages, and access streaming media.

The audio output unit 503 may convert audio data received by the radio frequency unit 501 or the network module 502 or stored in the memory 509 into an audio signal and output as sound. Also, the audio output unit 503 can also provide audio output related to a specific function performed by the mobile terminal 500 (for example, a call signal reception sound, a message reception sound, etc.). The audio output unit 503 includes a speaker, a buzzer, a receiver and the like.

The input unit 504 is used for receiving audio or video signals. The input unit 504 may include a graphics processing unit (Graphics Processing Unit, GPU) 5041 and a microphone 5042, and the graphics processor 5041 is used for still pictures or video images obtained by an image capture device (such as a camera) in a video capture mode or an image capture mode. The data is processed. The processed image frames may be displayed on the display unit 506 . The image frames processed by the graphics processor 5041 may be stored in the memory 509 (or other storage media) or sent via the radio frequency unit 501 or the network module 502 . The microphone 5042 can receive sound, and can process such sound into audio data. The processed audio data can be converted into a format that can be sent to a mobile communication base station via the radio frequency unit 501 for output in the case of a phone call mode.

The mobile terminal 500 also includes at least one sensor 505, such as a light sensor, a motion sensor, and other sensors. Specifically, the light sensor includes an ambient light sensor and a proximity sensor, wherein the ambient light sensor can adjust the brightness of the display panel 5061 according to the brightness of the ambient light, and the proximity sensor can turn off the display panel 5061 and the display panel 5061 when the mobile terminal 500 moves to the ear / or backlighting. As a kind of motion sensor, the accelerometer sensor can detect the magnitude of acceleration in various directions (generally three axes), and can detect the magnitude and direction of gravity when it is still, and can be used to identify the posture of mobile terminals (such as horizontal and vertical screen switching, related games, etc.) , magnetometer attitude calibration), vibration recognition-related functions (such as pedometer, knocking), etc.; the sensor 505 can also include fingerprint sensors, pressure sensors, iris sensors, molecular sensors, gyroscopes, barometers, hygrometers, thermometers, Infrared sensors, etc., will not be repeated here.

The display unit 506 is used to display information input by the user or information provided to the user. The display unit 506 may include a display panel 5061, and the display panel 5061 may be configured in the form of a liquid crystal display (Liquid Crystal Display, LCD), an organic light-emitting diode (Organic Light-Emitting Diode, OLED), or the like.

The user input unit 507 can be used to receive input numbers or character information, and generate key signal input related to user settings and function control of the mobile terminal. Specifically, the user input unit 507 includes a touch panel 5071 and other input devices 5072 . The touch panel 5071, also referred to as a touch screen, can collect touch operations of the user on or near it (for example, the user uses any suitable object or accessory such as a finger or a stylus on the touch panel 5071 or near the touch panel 5071). operate). The touch panel 5071 may include two parts, a touch detection device and a touch controller. Among them, the touch detection device detects the user's touch orientation, and detects the signal brought by the touch operation, and transmits the signal to the touch controller; the touch controller receives the touch information from the touch detection device, converts it into contact coordinates, and sends it to the For the processor 510, receive the command sent by the processor 510 and execute it. In addition, the touch panel 5071 can be implemented in various types such as resistive, capacitive, infrared, and surface acoustic wave. In addition to the touch panel 5071 , the user input unit 507 may also include other input devices 5072 . Specifically, other input devices 5072 may include, but are not limited to, physical keyboards, function keys (such as volume control keys, switch keys, etc.), trackballs, mice, and joysticks, which will not be repeated here.

Furthermore, the touch panel 5071 can be covered on the display panel 5061, and when the touch panel 5071 detects a touch operation on or near it, it will be sent to the processor 510 to determine the type of the touch event, and then the processor 510 can The type of event provides a corresponding visual output on the display panel 5061 . Although in FIG. 5, the touch panel 5071 and the display panel 5061 are used as two independent components to realize the input and output functions of the mobile terminal, in some embodiments, the touch panel 5071 and the display panel 5061 can be integrated. The implementation of the input and output functions of the mobile terminal is not specifically limited here.

The interface unit 508 is an interface for connecting an external device to the mobile terminal 500 . For example, an external device may include a wired or wireless headset port, an external power (or battery charger) port, a wired or wireless data port, a memory card port, a port for connecting a device with an identification module, audio input/output (I/O) ports, video I/O ports, headphone ports, and more. The interface unit 508 can be used to receive input from an external device (for example, data information, power, etc.) transfer data between devices.

The memory 509 can be used to store software programs as well as various data. The memory 509 can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, at least one application program required by a function (such as a sound playback function, an image playback function, etc.); Data created by the use of mobile phones (such as audio data, phonebook, etc.), etc. In addition, the memory 509 may include a high-speed random access memory, and may also include a non-volatile memory, such as at least one magnetic disk storage device, flash memory device, or other volatile solid-state storage devices.

The processor 510 is the control center of the mobile terminal, and uses various interfaces and lines to connect various parts of the entire mobile terminal, by running or executing software programs and/or modules stored in the memory 509, and calling data stored in the memory 509 , execute various functions of the mobile terminal and process data, so as to monitor the mobile terminal as a whole. The processor 510 may include one or more processing units; preferably, the processor 510 may integrate an application processor and a modem processor, wherein the application processor mainly processes the operating system, user interface and application programs, etc., and the modem The processor mainly handles wireless communication. It can be understood that the foregoing modem processor may not be integrated into the processor 510 .

The mobile terminal 500 can also include a power supply 511 (such as a battery) for supplying power to various components. Preferably, the power supply 511 can be logically connected to the processor 510 through a power management system, so as to manage charging, discharging, and power consumption through the power management system. and other functions.

In addition, the mobile terminal 500 includes some functional modules not shown, which will not be repeated here.

Preferably, the embodiment of the present invention also provides a mobile terminal, including a processor 510, a memory 509, and a computer program stored in the memory 509 and operable on the processor 510. When the computer program is executed by the processor 510 The various processes of the above embodiments of the method for assisting photographing are realized, and the same technical effect can be achieved. In order to avoid repetition, details are not repeated here.

The embodiment of the present invention also provides a computer-readable storage medium. A computer program is stored on the computer-readable storage medium. When the computer program is executed by a processor, each process of the above-mentioned method embodiment for assisting photographing is realized, and the same effect can be achieved. Technical effects, in order to avoid repetition, will not be repeated here. Wherein, the computer-readable storage medium is, for example, a read-only memory (Read-Only Memory, ROM for short), a random access memory (Random Access Memory, RAM for short), a magnetic disk or an optical disk, and the like.

It should be noted that, in this document, the term "comprising", "comprising" or any other variation thereof is intended to cover a non-exclusive inclusion such that a process, method, article or apparatus comprising a set of elements includes not only those elements, It also includes other elements not expressly listed, or elements inherent in the process, method, article, or device. Without further limitations, an element defined by the phrase "comprising a ..." does not preclude the presence of additional identical elements in the process, method, article, or apparatus comprising that element.

Through the description of the above embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus a necessary general-purpose hardware platform, and of course also by hardware, but in many cases the former is better implementation. Based on such an understanding, the essence of the technical solution of the present invention or the part that contributes to the prior art can be embodied in the form of software products, and the computer software products are stored in a storage medium (such as ROM/RAM, disk, CD) contains several instructions to make a terminal (which may be a mobile phone, a computer, a server, an air conditioner, or a network device, etc.) execute the methods described in various embodiments of the present invention.

Embodiments of the present invention have been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementations, and the above-mentioned specific implementations are only illustrative, rather than restrictive, and those of ordinary skill in the art will Under the enlightenment of the present invention, without departing from the gist of the present invention and the protection scope of the claims, many forms can also be made, all of which belong to the protection of the present invention.

Claims (12)

1. A method for assisting taking pictures, applied to a mobile terminal with a camera, characterized in that, comprising: collecting a preview image through the camera; identifying a first subject image and a first scene image other than the first subject image from the preview image; acquiring composition information according to the first feature of the first subject image and the second feature of the first scene image; According to the composition information, the photographing prompt information is output. 2. The method for assisting photographing according to claim 1, wherein the step of obtaining composition information according to the first feature of the first subject image and the second feature of the first scene image comprises : Inputting the first feature and the second feature to a preset composition discriminator to obtain composition information corresponding to the preview image; Wherein, the composition discriminator is a discriminator trained based on sample images of different composition types for outputting composition information. 3. The method for assisting photographing according to claim 1, wherein the step of identifying the first subject image and the first scene image other than the first subject image from the preview image is preceded by , the method also includes: The image of the object at the focal point in the preview image is determined as the first subject image. 4. The method for assisting photographing according to claim 1, characterized in that, before the step of acquiring composition information according to the first feature of the first subject image and the second feature of the first scene image, The method also includes: Acquiring a depth map of the preview image; separating the first subject image and the first scene image in the depth map; The first feature of the first subject image and the second feature of the first scene image are respectively extracted. 5. The method for assisting taking pictures according to claim 4, wherein the camera is a dual camera; The step of obtaining the depth map of the preview image includes: A depth map of the preview image is acquired through the dual cameras. 6. The method for assisting photographing according to claim 1, wherein the step of outputting prompt information for photographing according to the composition information comprises: determining a target position of a subject corresponding to the first subject image in the preview image according to the composition information; determining the position movement information of the mobile terminal according to the current position and size of the subject corresponding to the first subject image in the preview image and the target position; According to the position movement information, outputting photographing prompt information for guiding the user to move the position of the mobile terminal so that the subject corresponding to the first subject image is at the target position. 7. The method for assisting taking pictures according to claim 2, wherein the composition discriminator is trained based on sample images of different composition types through the following steps: Marking a label on each frame sample image, wherein different labels correspond to different composition types; identifying a second subject image and a second scene image other than the second subject image from each frame of sample images; respectively extracting a third feature of the second subject image and a fourth feature of the second scene image; Inputting the third feature and the fourth feature to the composition discriminator to train the composition discriminator. 8. A kind of mobile terminal, described mobile terminal is provided with camera, is characterized in that, described mobile terminal also comprises: A collection module, configured to collect a preview image through the camera; An identification module, configured to identify a first subject image and a first scene image other than the first subject image from the preview image; A first acquiring module, configured to acquire composition information according to the first feature of the first subject image and the second feature of the first scene image; An output module, configured to output photographing prompt information according to the composition information. 9. The mobile terminal according to claim 8, wherein the first acquiring module comprises: a first acquiring unit, configured to input the first feature and the second feature to a preset composition discriminator, and acquire composition information corresponding to the preview image; Wherein, the composition discriminator is a discriminator trained based on sample images of different composition types for outputting composition information. 10. The mobile terminal according to claim 8, further comprising: A determining module, configured to determine the image of the object at the focal point in the preview image as the first subject image. 11. A mobile terminal, characterized by comprising a processor, a memory, and a computer program stored on the memory and operable on the processor, when the computer program is executed by the processor, the The steps of the method for assisting photographing described in any one of requirements 1 to 7. 12. A computer-readable storage medium, characterized in that a computer program is stored on the computer-readable storage medium, and when the computer program is executed by a processor, the auxiliary device according to any one of claims 1 to 7 is realized. Steps in the method of taking pictures.