KR20060029476A - Mobile communication terminal with digital photographying facility and method for picking up a digital image - Google Patents

Abstract

The present invention relates to a mobile communication terminal capable of digital photographing and a digital image acquisition method.

The mobile communication terminal according to the present invention calculates the brightness of the image by averaging the remaining values except when the variation value is abnormally large in the frame average brightness value for a predetermined time, and photographing every fixed time according to the calculated brightness value. It is characterized by controlling the negative exposure time.

According to this aspect of the present invention, the mobile communication terminal according to the present invention can avoid the hysteresis problem in which the exposure time is frequently repeated so that the captured image becomes unstable.

Camera, mobile communication, mobile phone, exposure, frame, color, image quality

Description

Mobile communication terminal with digital photographying facility and method for picking up a digital image}

1 is a block diagram schematically showing the configuration of a mobile communication terminal according to an embodiment of the present invention.

2 is a flowchart schematically illustrating an image acquisition control method of a mobile communication terminal according to an exemplary embodiment of the present invention.

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

100 control unit 110 communication processing unit

130: brightness calculator 150: exposure controller

170: color conversion controller 210: voice input / output circuit

230: wireless communication unit 250: keypad

270 display unit 300 signal processing unit

321: image processing unit 323: image output unit

325: color conversion unit 500: camera unit

510: imaging unit 530: conversion unit

550: imaging controller 590: lens system

The present invention relates to a mobile communication terminal capable of digital photographing and a digital image acquisition method.

The digital camera converts the image signal obtained from the image pickup device into digital data, stores it, and displays it. Since the image pickup device outputs a signal proportional to light, the brightness of the subject is directly reflected in the acquired image. Therefore, when the subject is too bright or dark, the acquired image data is mainly composed of data of too large or small values, and thus the image quality is poor.

In order to solve this problem, the digital camera is equipped with a separate illuminance sensor to detect the brightness of the surroundings and automatically adjust the aperture accordingly to improve the image quality. However, the separate sensor not only interferes with the compactness of the device, but also causes additional costs. This problem is more serious in a mobile communication terminal having a digital photographing function.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and an object of the present invention is to provide a digital photographing apparatus for automatically adjusting a photographing mode according to the brightness of a subject without additional components, and a mobile communication terminal having a digital photographing function.

Furthermore, an object of the present invention is to provide a digital photographing method having a stable luminance characteristic and a mobile communication terminal having a digital photographing function.

According to an aspect of the present invention, a mobile communication terminal detects a brightness of a subject from a brightness value of a photographed image itself, and automatically adjusts an exposure time of an imaging device according to the detected brightness. It is done.

According to this aspect of the present invention, the digital photographing apparatus and the mobile communication terminal according to the present invention can maintain good image quality regardless of the amount of light of the subject without a separate illuminance sensor.

The mobile communication terminal according to an additional aspect of the present invention is characterized by correcting the color value of the image output from the image pickup device according to the detected brightness value.

According to this aspect of the present invention, the mobile communication terminal according to the present invention can maintain a balance between brightness and color of a captured image.

Further, the mobile communication terminal according to an additional aspect of the present invention calculates the brightness of the image by averaging the remaining values except when the variation value is abnormally large in the frame average brightness value for a predetermined time, and according to the calculated brightness value It is characterized by controlling the exposure time every predetermined time.

According to this aspect of the present invention, the mobile communication terminal according to the present invention can avoid the hysteresis problem in which the exposure time correction is frequently repeated.

The foregoing and further aspects of the present invention will become more apparent through the preferred embodiments described with reference to the accompanying drawings. Hereinafter, the present invention will be described in detail so that those skilled in the art can easily understand and reproduce the present invention.

1 is a block diagram schematically showing the configuration of a mobile communication terminal according to an embodiment of the present invention. As shown, the mobile communication terminal according to the present embodiment includes a camera unit 500 for acquiring digital image data, a storage unit 290 for storing the acquired digital image data, and a display unit for displaying the acquired digital image data. And a controller 100 that calculates a brightness value of the subject from the obtained digital image data and outputs a control command for controlling the exposure time of the camera unit 500 from the calculated brightness value. The display unit 270 displays a menu and an operation state in addition to the captured image, and may be, for example, a display device such as a liquid crystal display device.

The accessory circuits include a keypad 250, a wireless communication unit 230 for extracting voice and data signals from a wireless signal transmitted and received through an antenna, and a voice input / output circuit for inputting and outputting a voice call signal from the wireless communication unit through a microphone and a speaker. 210, which are typical configurations of a mobile communication terminal.

The wireless communication unit 230 includes an antenna and an RF circuit for communication with the base station. In the present specification, the wireless communication unit is interpreted to cover not only various versions of CDMA but also existing methods such as cellular, GSM, and W-CDMA, as well as mobile communication. The voice input and output circuit 210 processes the conversion of digital voice data into an analog voice signal or vice versa, and is a well-known configuration including an additional circuit such as an audio amplification circuit or a filter.

The baseband circuit of the wireless communication unit 230 and most of the circuits of the control unit 100 are commercially provided as a single integrated circuit. This integrated circuit, commonly referred to as an MSM chip, includes internally dedicated hardware for processing communications, a digital signal processor and a general purpose microprocessor.

The camera unit 500 converts an optical signal input from the lens system into an electrical signal and outputs the electrical signal. The signal processor 300 may process an image signal output from the camera unit 500 and output the image signal to the display unit 270 or may be a storage device such as an internal or removable external flash memory or a hard disk. ).

According to a characteristic aspect of the present invention, the control signal exchange between the control unit 100, the signal processing unit 300, and the camera unit 500 is performed through a serial bus. In one embodiment, the serial bus is an I ² C bus. Also called Inter-IC, I ² C is a two-wire, bidirectional serial bus that provides a communication link between integrated circuits. Philips introduced the I ² C bus 20 years ago for mass production products such as TVs, VCRs and audio equipment.

In an exemplary embodiment, the camera unit 500 may convert the lens unit 590, the imaging unit 510, and the analog image signal captured by the imaging unit 510 into digital image data and output the digital image data. ) And an imaging control unit 550 for outputting a control signal to the imaging unit 510 according to a control command of the control unit 100. The lens unit 590 is composed of one or more small lenses, and collects and supplies light to the imaging unit 510.

The imaging unit 510 is generally a CMOS imaging device or CCD imaging device, and is a known device that sequentially outputs an electrical signal in synchronization with a clock in proportion to the light stored for each pixel. The charging time of the photocharges corresponds to the exposure time of the film to the light in the conventional film type camera. The charging time of the photocharges is controlled by the frequency and duty of the clock supplied from the imaging controller 550. Most of the digital cameras are processed in the image pickup unit 510 as a moving image, and the formats of the signal processing unit 300 to store them in the storage unit 290 are different from those of still cameras and video camcorders.

According to a characteristic aspect of the present invention, the exposure time of the imaging unit 510 is controlled by a frame rate. For example, the exposure time available for printing at 30 frame rates per second is shorter than the exposure time available for printing screens at 20 frame rates per second.

 The converter 530 converts a current or voltage signal string proportional to the image brightness output from the imaging unit 510 into a digital data string, and converts the data value into a YUV format for output.

The imaging controller 550 controls the overall operation of the camera unit 500 according to command data received from the outside through the I ² C bus. Furthermore, according to a characteristic aspect of the present invention, the imaging controller 550 outputs a control signal to the imaging unit 510 according to the exposure time control command received from the exposure controller 150 of the controller 100 to expose the exposure time of the imaging device. To control. In the camera unit 500, the imaging controller 550 may be implemented as a microprocessor or may be configured by simple digital logic. The imaging controller 550 supplies a driving clock for imaging to the imaging device of the imaging unit 510. The control command outputted by the imaging unit to control the exposure time may be this driving clock. For example, the collection clock, i.e., the exposure amount of the optical charges for each pixel of the imaging device may be controlled by the driving clock. The converter 530 also performs data conversion in synchronization with this clock.

The control unit 100 includes a communication processing unit 110 for controlling voice and data communication, and according to a characteristic aspect of the present invention, the control unit 100 includes a brightness calculating unit 130 and an exposure control unit 150. .

The brightness calculator 130 calculates a brightness value from the image data converted by the converter 530. In one embodiment, the brightness value of the subject is obtained as an average of luminance values of image data of one frame. In another embodiment, the brightness value is calculated by averaging the remaining frame average brightness values except when the variation value is abnormally large in the frame average brightness values for a predetermined time. This brightness calculation method is described in more detail later.

The exposure controller 150 determines the exposure time of the imaging unit 510 from the brightness value calculated by the brightness calculator and outputs an exposure time control command to the imaging controller 550.

The brightness values of the subjects are grouped appropriately for simplicity of control. In the first embodiment, when the brightness value of the subject obtained from the average of the luminance values is Y;

Y: 0 ~ 34 (0 ~ 5 Lux) ---> Dark-Night Mode

Y: 35 ~ 88 (6 ~ 120 Lux) ---> Night Mode

Y: 89 ~ 255 (120 Lux or more) ---> Day Mode

Grouped into three groups of differently controlled according to each group.

According to an additional aspect of the present invention, the control signal output from the exposure controller 150 may be data related to the number of frames per second. That is, if the Y value detected by the exposure controller 150 is a dark-night mode, the control signal is output to increase the exposure time in the imaging unit 510 to reduce the number of frames photographed per second. As a result, the exposure time per frame is extended to absorb a sufficient amount of light.

For example, in dark-night mode, the frame rate drops to 10 frames per second, for example to increase exposure time. In night mode, the frame rate is limited to around 20 frames for proper exposure time. In the day mode, the frame rate is restored to the normal 30 frames. Thereby, it is possible to obtain a detailed and clear image by ensuring sufficient exposure time even in a very low illuminance.

By detecting the brightness of the captured image and adjusting the brightness of the next captured image, a light sensor for detecting the brightness of the captured image is not required as in the prior art, and the exposure time is automatically controlled so that the user requires manual operation. none.

The signal processor 300 receives YUV-format digital image data photographed and converted from the camera unit 500, processes the signal, and stores the signal in the storage unit 290. The signal processor 300 processes the image data or the storage unit 290. The read image data is output to the display unit 270. In one embodiment, the signal processor 300 includes an image processor 321 and an image output unit 323.

The image processor 321 may perform image enhancement processing on the image data input from the converter 530, and may compress and store the compressed image data stored in the storage 290 or stored in the storage 290. Decompress In this case, the stored image data may be moving image data or may be a still image capturing a part of an input frame.

The image output unit 323 converts image data that is improved in image quality by the image processing unit 321 or image data that is read and decompressed and output from the storage unit 290 into a form suitable for display on the display unit 270. Buffered output.

According to an additional aspect of the present invention, the signal processor 300 further includes a color converter 325, and the controller 310 further includes a color converter controller 170. The color conversion unit 325 controls the color conversion control unit 170 to describe U and V values, which are color components, among the YUV format data inputted by the conversion unit 530 of the camera unit 500 to digital image data. Convert according to

The color conversion controller 170 controls the U and V mapping of the color converter 325 according to the brightness value calculated by the brightness calculator 130. If the brightness of the captured image is increased by artificially increasing the exposure time in a dark environment, the color may be distorted. According to a characteristic aspect of the present invention, the color conversion unit 325 includes an optimal U and V conversion table for each mode, and selects and inputs one conversion table under the control of the color conversion control unit 170. Handles mapping of U and V data. In one embodiment, the color conversion controller 170 operates with the same algorithm as the exposure controller 150, in which case the two components may be integrated into one. In another embodiment, the color conversion controller 170 may provide a more granular mode than the exposure controller 150.

The conversion table can be obtained experimentally. The table is determined by visually observing the color values to be corrected together when the luminance values are corrected for each mode. As described above, the digital imaging apparatus and the mobile terminal according to the present invention control the color together with the brightness control of the captured image to achieve a balance between brightness and color.

2 is a flowchart illustrating a digital photographing method performed in a mobile communication terminal according to an exemplary embodiment of the present invention. As shown, the digital photographing method according to the present embodiment includes the steps of converting the analog image signal captured by the imaging unit 510 into digital image data (S110, S130), and the brightness of the image from the converted digital image data. And calculating (S150, S170, S190, and S210) and controlling the exposure time of the imaging unit 510 according to the obtained luminance value (S230 and S250).

The imaging unit 510 converts and outputs the light collected through the lens system 590 into an electrical analog image signal (step S110). The analog image signal output from the imaging unit 510 is first converted into digital image data by the conversion unit 530 after simple analog signal processing such as amplification and pre-filtering. Step S130). The converted image data is separated into luminance data and chrominance data for signal processing and converted into a standard 4: 2: 2 YUV signal (step S150).

According to an aspect of the present invention, the step of calculating the brightness of the image may include calculating a frame average brightness value for each of the image frames for a predetermined time (S170), and shifting the reference value among the frame average brightness values. And calculating the average value of the remaining frame average brightness values excluding the large values as the brightness of the image (steps S190 and S210).

According to such a characteristic aspect of the present invention, it is substantially prevented that the shooting mode is frequently changed or changed unlike the actual situation. That is, when the exposure time is adjusted according to the brightness of the input image according to the present invention, a mode may be frequently changed in the threshold region of each mode. For example, if the luminance value is read from the threshold value 88 that changes from the day mode to the night mode, and the compensation is made to extend the exposure time after the night mode is determined, the luminance value of the input image is improved to switch back to the day mode. Experimentally, it was confirmed that this boundary value occurred in the range of the luminance value of 82 to 88. Similarly, if the compensation is made to increase the exposure time after determining the dark night mode at the threshold value 34 that changes from the night mode to the dark night mode, the luminance value of the input image is improved and the mode is switched back to the night mode. Experimentally, it was confirmed that this boundary value occurred in the range of the luminance value of 29 to 34. Frequent changes in this mode may occur for other reasons. For example, if the subject is black, this may occur because the average luminance value is low even though it is actually a very bright background, and the mode change may frequently occur depending on the subject's change in the middle when the camera focuses quickly. . Frequent changes in mode degrade the uniformity of the shot quality. This invention can avoid such a problem by the characteristic digital imaging method mentioned later.

In one embodiment, the brightness calculator 130 calculates an average value for a predetermined time period of the frame average brightness values, and the rest of the frame average brightness values except for values having a large deviation from the calculated average value among the frame average brightness values. The average value of these is calculated as the brightness of the image. More specifically, first, an average brightness value is calculated for each of the frames, e.g., 30 frames, during this time interval by a predetermined time T, e.g. 1 second. The T value is obtained empirically, which is the minimum unit time for changing the shooting mode. Changing the shooting mode in increments of 1 to 3 seconds is not a big experience. The frame average brightness value is obtained as an average value of luminance values for all pixels constituting one frame (step S170).

In step S190, brightness values having a large deviation from the reference value are discarded. The reference value is the average of the frame average brightness values for the period T in this embodiment. That is, some values that are highly shifted from the mean values are excluded. For example, in the night mode, frame average brightness values that deviate by more than 6 from the average value are discarded.

In another embodiment, a permutation of frame average brightness values is observed, from which the imaging mode is determined. In the present embodiment, the average value of the remaining frame average brightness values, except for a frame having a frame average brightness value greater than or equal to the frame average brightness value of the previous frame, is calculated as the brightness of the image. In more detail, the frame average brightness values are stored sequentially. The frame average brightness value of the current frame is compared with the frame average brightness value of the previous frame, and the difference is a predetermined value, for example, the frame average brightness value at which the luminance value differs by 6 or more from the average value in the night mode is discarded. All. This process is repeated for 30 frames for a predetermined time, for example 1 second, and the average of the frame average brightness values is obtained for the remaining frames.

Thereafter, in step S210, the average value of the remaining frame average brightness values is calculated again. From these values, the shooting mode is determined as one of the day mode, the night mode, or the dark night mode (step S230).

E.g

Y ₄ -Y ₃ = 8, Y ₁₀ -Y ₉ = 11

For other values

Y _{n + 1} -Y _n ≤ 6,

Y = (Y ₁ + Y ₂ + ... + Y ₃₀ ) / 28 (average except Y ₄ and Y ₁₀ )

= 85, the controller determines the night mode.

When the shooting mode is determined as described above, the exposure value is controlled according to the shooting mode (step S250). In one embodiment, the control of the exposure value is controlled in frames per second. The exposure controller 150 determines the number of frames per second according to each shooting mode. For example, in the dark night mode, the frames per second may be 20 frames, 30 frames in the night mode, and 40 frames in the day mode. Next, the color value is controlled according to the obtained shooting mode (step S270). The color value is controlled by selecting the mapping table according to the shooting mode and mapping the U and V values according to the selected table.

As described in detail above, the mobile communication terminal according to the present invention detects the brightness from the captured image and automatically adjusts the exposure value according to the detected brightness, thereby eliminating the need for a separate light sensor for detecting the brightness of the captured image. As a result, parts and manufacturing cost can be reduced while improving image quality.

Furthermore, since the mobile communication terminal according to the present invention suitably converts the color components of the image according to the brightness of the captured image, the captured image has a balance between brightness and color.

Furthermore, the mobile communication terminal according to the present invention can provide stable picture quality by appropriately limiting the control timing of the exposure time, monitoring the brightness change during the timing, predicting the shooting environment, and controlling the exposure time.

On the other hand, the present invention has been described with reference to the embodiments shown in the drawings, but this is only illustrative, it should be understood that those skilled in the art that various modifications are possible without departing from the scope of the present invention. Therefore, the technical protection scope of the present invention should be interpreted only by the appended claims, which are intended to cover such obvious modifications.

Claims (16)

In a mobile communication terminal, the terminal is: A camera unit for acquiring digital image data; A storage unit which stores the obtained digital image data; A display unit which displays the obtained digital image data; The obtained digital image data is monitored to obtain intra-frame average brightness values for frames for a predetermined time, and the remaining values are averaged to obtain the brightness of the image, except when the variation in the obtained frame average brightness values is abnormally large. And a control unit for outputting a control command to the camera unit to control the exposure time at predetermined time intervals according to the calculated brightness value. The method of claim 1, wherein the control unit: The obtained digital image data is monitored to obtain intra-frame average brightness values for frames for a predetermined time, and the remaining values are averaged to obtain the brightness of the image, except when the variation in the obtained frame average brightness values is abnormally large. A brightness calculator that calculates And an exposure controller for outputting a control command to the camera unit to control the exposure time at predetermined time intervals according to the brightness value calculated by the brightness calculator. The brightness of an image according to claim 2, wherein the brightness calculator calculates an average value of the remaining frame average brightness values except for a frame having a frame average brightness value larger than a frame average brightness value of a previous frame with respect to the frames for a predetermined time period. Mobile communication terminal, characterized in that to calculate. 3. The remaining frame average brightness value of claim 2, wherein the brightness calculator calculates an average value of the frame average brightness values during the predetermined time period, and excludes values having a large deviation from the calculated average value among the frame average brightness values. The average value of the mobile communication terminal, characterized in that for calculating the brightness of the image. The mobile communication terminal according to claim 3 or 4, wherein the control command output by the controller is data related to the number of frames per second. The method of claim 5, wherein the camera unit: A lens unit, an imaging unit, a conversion unit for converting and outputting analog image signals captured by the imaging unit into digital image data; And an imaging controller for outputting a control signal to the imaging unit according to a control command of the controller. The mobile terminal of claim 6, wherein the mobile communication terminal comprises: And a signal processing unit which processes the digital image data output from the camera unit and stores the signal in the storage unit, and outputs the signal processed image data or the image data read from the storage unit to the display unit. Mobile communication terminal. The apparatus of claim 7, wherein the signal processor further comprises a color converter configured to convert color component values of the digital image data. The control unit is: A brightness calculator for calculating a brightness value of the subject from the digital image data; An exposure controller which determines an exposure time of the imaging unit from the brightness value calculated by the brightness calculator and outputs an exposure time control command to the imaging controller; And a color conversion control unit controlling a color conversion method of the color conversion unit from the brightness value calculated by the brightness calculation unit. The method of claim 8, wherein the color conversion unit selects one of a plurality of conversion tables according to a control command of the color conversion control unit, and maps and outputs at least U and V signals among signals input by the selected conversion table. Characterized in a mobile communication terminal. The mobile communication terminal according to claim 3 or 4, wherein the controller controls the operation of the camera unit by using a serial bus. 12. The mobile terminal of claim 10, wherein the serial bus is an I ² C bus.  A digital photographing method for acquiring an image through an imaging unit, the method comprising: a) converting the analog image signal picked up from the image pickup unit into digital image data; b1) calculating a frame average brightness value for each of the image frames for a predetermined time; b2) calculating an average value of the remaining frame average brightness values of the frame average brightness values, except for values having a large deviation from the reference value, as an image brightness value; c) controlling an exposure time of the imaging unit according to the obtained brightness value; Digital photographing method comprising a. 13. The process of claim 12, wherein step b2) is: And calculating an average value of the remaining frame average brightness values as an image brightness except for a frame having a frame average brightness value larger than a frame average brightness value of a previous frame. 13. The process of claim 12, wherein step b2) is: Calculating an average value of the frame average brightness values during the predetermined time; Calculating an average value of the remaining frame average brightness values of the frame average brightness values except for a large value of the calculated average value as the brightness of the image; Digital photographing method comprising a. 15. The digital photographing method as claimed in any one of claims 13 to 14, wherein said step c) is a step of controlling an imaging frame rate per second of said imaging unit. The method of claim 13 or 14, wherein the digital imaging method is: and d) differently mapping a color value of the digital image data according to the obtained brightness value.

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