JP2004153315A - Image processing method and digital camera - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing method and a digital camera for improving the brightness of the face of a person by correcting the brightness for an image. <P>SOLUTION: This image processing method and the digital camera detect a half depression state of a shutter button (S103), acquire an image after being subjected to exposure and focus processing (S105), detect a full depression state of the shutter button (S106), analyze the acquired image to extract the face region of the person, calculate a correction amount at which the brightness of the extracted face region has the optimum value, and correct the brightness of the recorded image on the basis of the correction amount (S108). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image processing method and a digital camera that perform brightness correction using a face extraction technique.
[0002]
[Prior art]
In recent years, digital cameras are equipped with functions such as AE (automatic exposure) and AF (automatic focus adjustment) so that photographing can be performed more easily. Center-weighted metering is generally known as a metering method in this AE. However, in center-weighted metering, when shooting with a composition in which the main subject is not in the center, an appropriate exposure according to the main subject can be obtained. There is no problem. For example, in a composition in which the person who is the main subject is placed at the end of the frame, and the center of the background is white, the AE controls exposure according to the white color, so the amount of light is reduced and the person's face appears dark. Exposure failure such as end.
[0003]
As a means for solving the disadvantages of center-weighted metering, exposure control by so-called multi-pattern metering in which the amount of light is measured at a plurality of points is also performed. According to multi-pattern photometry, average exposure control is performed over the entire frame, and thus the problem in the case where the person who is the main subject is not in the center as described above is somewhat solved. However, for example, when a person is photographed with backlight, the AE is judged to be bright overall and exposure control is performed to reduce the amount of light regardless of the composition. The problem of being captured is not solved.
[0004]
[Problems to be solved by the invention]
As described above, center-weighted metering, multi-pattern metering, or a digital camera that can arbitrarily select them cannot perform exposure control so that the brightness of the face is appropriate depending on the situation at the time of shooting. However, in general photography where the subject of photography is a person or landscape, the person's face, especially the person's face, rather than the landscape, affects the quality of the photograph (or image data). It is desired that the part is appropriately brightened.
[0005]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image processing method and a digital camera that make a person's face have good brightness (luminance) by correcting the brightness of the image.
[0006]
[Means for Solving the Problems]
The image processing method of the present invention is an image processing method for correcting the brightness of an image, the step of analyzing the image to extract a human face area, and a correction amount at which the brightness of the extracted face area becomes an appropriate value And a step of correcting the brightness of the image based on the calculated correction amount.
[0007]
Further, in the image processing method of a digital camera that performs exposure and focus adjustment by half-pressing the shutter button, and acquires and records a recorded image after exposure and focus adjustment by fully pressing the shutter button, the half-press is detected. A step of acquiring an image after exposure and focus processing (S105), a step of detecting the full press and analyzing the image after exposure and focus processing to extract a human face region (S201), and an extracted face A step of calculating a correction amount at which the brightness of the region is an optimum value (S203), and a step of correcting the brightness of the recorded image based on the correction amount (S205) are included.
[0008]
The digital camera of the present invention detects half-press in a digital camera that performs exposure and focus adjustment by half-pressing the shutter button, and acquires and records a recorded image after exposure and focus adjustment by full-pressing the shutter button. Means for acquiring an image after exposure and focus processing (memory in the face area extraction processing unit 114) and extracting the face area of a person by detecting the full press and analyzing the image after exposure and focus processing Means (face area extraction processing unit 114), means for calculating a correction amount at which the brightness of the extracted face region is an optimum value (correction amount calculation unit 115), and brightness of the recorded image based on the correction amount And means for correcting (digital signal processing unit 107).
[0009]
According to the above-described invention, the brightness of the recorded image is corrected based on the correction amount at which the brightness of the face area extracted from the image is an optimum value, so that the face portion of the person can be recorded with good brightness (luminance). An image is obtained.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a digital camera according to an embodiment of the present invention. Mainly, a lens 101, a CCD 102, an analog signal processing unit 103, an A / D converter 104, a TG (timing generator) 105, and a control unit. 106, a digital signal processing unit 107, a memory 108, a compression / decompression unit 109, an LCD 110, a recording unit 111, a shutter button 112, an operation switch 113, a face extraction processing unit 114, and a correction amount calculation unit 115.
[0011]
Specifically, the lens 101 is a zoom lens (focal length variable lens) having an AF (automatic focus adjustment) mechanism, and the AF mechanism and the zoom mechanism of the lens 101 are driven by a drive circuit (not shown). Instead of the zoom lens, a focal length configuration lens having only an AF mechanism may be used.
[0012]
The CCD 102 is an optical sensor having a large number of light receiving elements arranged in a matrix or honeycomb, and is arranged at a position inside the camera body corresponding to the focal position of the lens 101.
[0013]
The analog signal processing unit 103 performs predetermined analog processing on the image signal output from the CCD 102, and outputs it as R, G, and B signals for each pixel. The analog signal processing unit 103 includes a CDS (correlated double sampling) circuit, an AGC (auto gain control) circuit, and the like. The CDS circuit reduces noise of the image signal, and the AGC circuit adjusts the gain of each image signal by adjusting the gain. Level adjustment is performed.
[0014]
The A / D converter 33 converts the R, G, and B signals sequentially added from the analog signal processing unit 32 into digital R, G, and B signals and outputs them.
[0015]
The timing generator 105 gives timing signals to the CCD 102, the analog signal processing unit 103, and the A / D converter 104, and the circuits are synchronized by the timing signals.
[0016]
The control unit 106 controls the operation of each unit connected by the bus and performs overall control related to the imaging operation of the digital camera. Also, it functions as a control means for controlling AF (automatic focus adjustment), AE (automatic exposure), AW (auto white balance), and the like based on inputs from the shutter button 112 and other operation switches 113. The control unit 106 performs various functions in software as well as data transfer with the peripheral configuration and timing control.
[0017]
The digital signal processing unit 107 performs various processes such as white balance correction, gamma (γ) correction, contour correction, color correction, and YC processing on the input image data. Further, brightness correction is performed based on a brightness correction amount that optimizes the brightness of the face described later. Image data converted into a luminance signal (Y signal) and a color difference signal (Cr, Cb signal) by the digital signal processing unit 107 is stored in a memory 108 for temporary storage of image data via a bus. The YC signal is compressed in accordance with a predetermined format by the compression / decompression unit 109 and then recorded on a recording medium such as a memory card via the recording unit 111.
[0018]
The memory 108 is constituted by a DRAM or the like, and functions as a buffer memory that temporarily stores acquired image data. In order to perform various processes, the image data is read out to each unit connected via the bus, and is written again after the process.
[0019]
The compression / decompression unit 109 compresses the image data stored in the memory 108 by a predetermined compression method such as the JPEG method and records the compressed image data on a recording medium loaded in the recording unit 111 or reads the image data from the recording medium. Or stretch. Image data when the compression / decompression unit 109 performs compression processing is converted into luminance data Y and color difference data Cr and Cb (YC separation processing) and stored in the memory 37. On the other hand, when the image data recorded on the recording medium is reproduced and displayed, the luminance signal and the color difference signal generated by the YC separation are converted into RGB signals.
[0020]
The LCD 110 is a display for image display, and is driven by an LCD driver (not shown) based on RGB signals. The image data temporarily stored in the memory 108 is transferred to the LCD 110 after predetermined processing, and a color image is displayed. At the time of shooting, the shooting range can be accurately determined by using the LCD as a viewfinder.
[0021]
The recording unit 111 records the acquired image data and tag information for each image data on a recording medium such as a memory card. When recording is instructed by pressing the shutter button 112 fully (that is, acquisition of image data), the specific processing of recording is the thumbnail image of the image stored in the memory 108 after completion of the series of image processing and the JPEG method. A compressed image compressed by the above is generated, and both images together with tag information (frame number, exposure value, shutter speed, compression rate, shooting date, flash on / off data at the time of shooting, scene information, etc.) relating to the shot image Is recorded on the recording medium.
[0022]
The recording medium is not limited to a memory card such as a semiconductor recording medium, but an optical recording medium such as a DVD-RAM, DVD-RW, or CD-RW, a magnetic recording medium such as a floppy disk, or a magneto-optical such as MO. A recording medium or the like can also be used, and is not limited to an external recording medium, and may be a built-in recording medium such as a hard disk.
[0023]
The shutter button 112 is a switch for instructing the digital camera to start shooting. The shutter button 112 is a two-stage switch that can detect a half-pressed state and a fully-pressed state. Adjustment) control, AE (automatic exposure) control, and acquisition of an image for face area extraction are performed. When the shutter button 112 is fully pressed, shooting, brightness correction processing (to be described later), and image data recording are performed.
[0024]
In the AE control, a shutter speed and an aperture are automatically set based on luminance detection and luminance determination. In the luminance detection, the luminance values of the respective color components of the image data given by R, G, and B are summed over the entire image using the image data captured by the CCD 101 at predetermined intervals and stored in the memory 108. On average. The shutter speed and aperture setting are determined based on the determination result of the brightness of the subject based on the luminance determination.
[0025]
In the AF control, focusing is performed by moving the lens 101 while obtaining an approximate contrast value of the entire image data as an AF evaluation value. For example, the AF motor drive circuit drives the AF motor so that the high-frequency component of the G signal is maximized when the shutter button is half-pressed, and the lens is moved to the in-focus position to perform autofocus.
[0026]
The face area extraction processing unit 114 has a memory that holds image data acquired by half-pressing the shutter button 112, and a face extraction function that extracts an area corresponding to a human face present in the image from the image data. . The face extraction processing is performed on image data that has undergone processing such as contour correction by the digital signal processing unit 107. A known technique (Japanese Patent Laid-Open No. 9-101579) can be used as a method for extracting a face region.
[0027]
The correction amount calculation unit 115 calculates the brightness (luminance value) of the extracted face area, and calculates a correction value from the difference between the calculated brightness and the appropriate brightness.
[0028]
The face extraction process and the correction amount calculation process are not performed in a period after a half-press of the shutter button, which requires a short process, because the processing time is relatively long. Perform in the period after full pressing.
[0029]
Next, the operation of the digital camera according to the embodiment of the present invention will be described with reference to the flowchart shown in FIG.
[0030]
When the power switch of the digital camera is on (step S101) and the “shooting” mode is on (step S102), the control unit 106 detects half-pressing (S1) of the shutter button 112 (step S103). .
[0031]
When half-pressing of the shutter button 112 is detected, AE and AF are executed in accordance with an instruction from the control unit 106 (step S104), and the image data acquired by determining the in-focus and proper exposure by the AE and AF is obtained. Stored in the memory 108. The same image data is also stored in the memory in the face area extraction processing unit 114 for face area extraction (step S105). The stored image data is a reduced image (for example, an image size of about VGA) thinned out in the CCD thinning mode.
[0032]
Next, the control unit 106 detects full press (S2) of the shutter button 112 (step S106). If the shutter button 112 has not been pressed, the elapse of the predetermined time is determined in step S107, and if the predetermined time has not elapsed, the return detection in step S106 is repeated. If the predetermined time has elapsed, it is determined that the shooting operation is not performed, and the process returns to step S103.
[0033]
When the full press of the shutter button 112 is detected in step S106, brightness correction processing including image recording and brightness correction is performed according to an instruction from the control unit 106 (step S108).
[0034]
FIG. 3 is a flowchart showing the procedure of brightness correction processing performed on an image acquired for recording. When the full press of the shutter button 112 is detected, the control unit 106 performs image recording and brightness correction processing.
[0035]
In order to perform brightness correction processing, the face area extraction processing unit 114 performs face area extraction processing on the image data stored in the memory in the face area extraction processing unit in step S105 (step S201). Next, when the subject of the image data is a person and a face area exists, the brightness value of the extracted face area is calculated (step S202).
[0036]
Next, a correction value for performing brightness correction processing performed on image data acquired for recording is calculated (step S203). The correction value is a difference value between the luminance value calculated in step S202 and the luminance value at the appropriate brightness of the face.
[0037]
As described above, an image for recording is acquired from the CCD 102 simultaneously with the full press of the shutter button 112 in step S204, and the image data subjected to signal processing is temporarily stored in the memory 108. The recording image data temporarily stored in the memory 108 is read again to the digital signal processing unit 107, and the digital gain is adjusted based on the correction value calculated in step S203, and brightness correction image processing is performed. (Step S205).
[0038]
Returning to the flowchart of FIG. 2, the image data that has been subjected to the brightness correction process is temporarily stored again in the memory 108, and after performing necessary processes such as YC processing and compression processing, the recording unit 111 performs recording processing. To be recorded. In addition, an image is displayed on the LCD 110 as necessary (step S109).
[0039]
Through the above processing, the image data acquired for recording is recorded in a state where the brightness of the face of the subject is appropriately corrected. As a result, the subject is not at the center of the frame (in the case of center-weighted metering) or is backlit, and exposure control is not performed according to the subject's face, and the face is not captured when shooting (when acquiring image data). Even if the image data has an inappropriate brightness, it is automatically corrected so that the brightness of the face is appropriate when stored in a recording medium.
[0040]
In the above process, when a plurality of face areas are extracted by the face area extraction process (that is, when a plurality of persons are imaged as subjects), a luminance value is obtained in the plurality of areas and an average is calculated. Alternatively, appropriate condition setting is performed as appropriate, such as setting the luminance value of only a region having a large area as a representative value.
[0041]
Further, the face area extraction process does not always have to be performed at the time of shooting. For example, the face area extraction process is executed only at the time of shooting when a mode for shooting a person (for example, portrait shooting mode) is set. You may do it. By controlling on / off of the face area extraction processing unit in the mode setting, unnecessary operations such as performing face area extraction processing on image data in which a person has not been photographed are prevented, thereby reducing power consumption. be able to.
[0042]
【The invention's effect】
As described above, according to the present invention, the brightness of a person's face is improved by correcting the brightness of the recorded image based on the correction amount at which the brightness of the face area extracted from the image is an optimum value. A recorded image of (luminance) can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a digital camera according to an embodiment of the present invention.
FIG. 2 is a flowchart showing a procedure of image processing in the digital camera.
FIG. 3 is a flowchart showing a procedure of brightness correction in image processing.
[Explanation of symbols]
101 Lens 102 CCD
103 Analog processing unit 104 A / D converter 105 Timing generator 106 Control unit 107 Digital signal processing unit 108 Memory 109 Compression / decompression unit 110 LCD
111 Recording unit 112 Shutter button 113 Operation switch 114 Face extraction processing unit 115 Correction amount calculation unit

Claims (4)

In an image processing method for correcting the brightness of an image,
Analyzing the image to extract a person's face area; calculating a correction amount at which the brightness of the extracted face area is an appropriate value; and correcting the brightness of the image based on the calculated correction amount An image processing method. In the image processing method of a digital camera that performs exposure and focus adjustment by half-pressing the shutter button, and acquires and records a recorded image after exposure and focus adjustment by fully pressing the shutter button.
Detecting the half-press to acquire an image after exposure and focus processing; extracting the full-press to analyze the image after exposure and focus processing to extract a human face region; An image processing method comprising: calculating a correction amount at which the brightness of a face region is an optimum value; and correcting the brightness of the recorded image based on the correction amount. In a digital camera that performs exposure and focus adjustment by half-pressing the shutter button, and acquires and records the recorded image after exposure and focus adjustment by fully pressing the shutter button.
Means for detecting the half-press to acquire an image after exposure and focus processing; and means for detecting the full-press and analyzing the image after exposure and focus processing to extract a human face area; A digital camera comprising means for calculating a correction amount at which the brightness of the face area becomes an optimum value, and means for correcting the brightness of the recorded image based on the correction amount. In an image processing program for correcting the brightness of an image, the computer analyzes the image, extracts a human face area, calculates a correction amount at which the extracted face area has an appropriate brightness, and calculates An image processing program that functions as means for correcting the brightness of the image based on the corrected amount.

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