JPH11275452A - Shading correction device for digital camera - Google Patents

Abstract

[PROBLEMS] To provide a shading correction device for a digital camera that can correct image deterioration due to insufficient peripheral light quantity due to reduction in size and weight of an imaging lens and can obtain high-quality imaging data with a simple configuration. A horizontal direction and a vertical direction of a pixel group of an image sensor are divided into blocks each having a predetermined number, and shading correction is performed only on each block which is a center position in the vertical direction and is divided into m / p in the horizontal direction. The coefficients are calculated and stored in the nonvolatile memory 11. At the time of photographing, shading correction is performed by reading a correction coefficient from the nonvolatile memory 11 and setting the correction coefficient in a register of the signal processing processor 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to correction of shading caused by uneven sensitivity of an image sensor, inclination of mounting, and insufficient peripheral light amount of an image pickup lens, and more particularly, to a shading correction apparatus for a digital camera which compresses image data by JPEG. .

[0002]

2. Description of the Related Art Heretofore, there has been proposed a technique for correcting shading by using a shading correction coefficient approximated by an Nth-order surface function and multiplying the output of an image sensor by the correction coefficient (for example, Japanese Patent Application Laid-Open No. H8-79773). ). In this conventional technique, the R data and the B data of the RGB data output from the image sensor are multiplied by a shading correction coefficient so as to substantially match the shading of the G data.

[0003]

However, in the prior art, the sensitivity unevenness of the image sensor can be corrected, but the shading based on the inclination of the mounting of the image sensor or the insufficient peripheral light amount of the image sensor cannot be corrected. There is.

An object of the present invention is to convert captured image data to JPE
It is an object of the present invention to provide a shading correction unit that can be easily incorporated into a recording processing algorithm in a digital camera that performs G compression.

[0005]

In order to achieve the above object, the present invention provides an image pickup optical system, an image pickup device having m pixels in the horizontal direction and n pixels in the vertical direction, and calculating a shading correction coefficient. Correction coefficient calculation means, storage means for storing the calculated shading correction coefficient, and a shading correction coefficient read from the storage means at the time of photographing, and output from the image sensor using the read shading correction coefficient. In a digital camera provided with shading correction means for shading correction of an imaging signal, the correction coefficient calculation means blocks the horizontal and vertical directions of a pixel group of the image sensor so that each of the horizontal and vertical directions has a predetermined number. The shading correction coefficient is calculated only for each block at the position. Providing shading correction apparatus Tarukamera.

In the above-described shading correction device for a digital camera, the shading correction coefficient is calculated for each zoom position and / or aperture diameter at the time of photographing.

According to the above configuration, the sensitivity unevenness of the image pickup device,
It is possible to easily correct the mounting inclination and the peripheral light quantity shortage of the imaging lens, and obtain a high-definition image.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of a digital camera according to an embodiment of the present invention. In the figure, 1 is a zoom lens block, 2 is an aperture unit, 3
Is an image sensor, 4 is a CDS that double-samples an image signal to reduce noise, 5 is an analog-to-digital converter that converts an image analog signal into digital data, 6 is a vertical driver that drives the image sensor, and 7 is an aperture unit Is a ZOOM driver that drives the zoom lens block. Reference numeral 10 denotes a signal processor for performing signal processing of image data, 11 denotes a DRAM for storing image data, 12 denotes a liquid crystal monitor used for a viewfinder function, 13 denotes a VIDEO amplifier which is a video signal amplifier for television, and 14 denotes a video signal amplifier. A serial driver 15 for communicating digital data with a personal computer or the like is a memory card 15 for storing photographing data. 20 is a system controller for displaying main system control, key input, shooting mode, number of recorded images, etc.
Reference numeral 21 denotes various keys, and reference numeral 22 denotes a mode LCD for displaying a shooting mode and the number of recordings.

Next, the operation in such a configuration will be described. In FIG. 1, light passing through one lens is photoelectrically converted by three imaging devices, and is input to a signal processor 10 through a CDS circuit 4 and an analog-to-digital converter 5. The signal processor 10 performs digital clamp, limiter processing, shading correction, white balance correction, and γ correction, and stores the result in the DRAM 11. At this time, the signal processor 10 performs exposure control using an electronic shutter function of two apertures and three CCDs. The digital imaging data stored in the 11 DRAMs is read out by 8 signal units of 8 × 8 pixels by the 10 signal processors, color space conversion processing is performed, luminance signals and color difference signals are generated, and JPEG compression processing is performed. JPEG
The compressed data is stored in the DRAM 11 again.

FIG. 2 is a conceptual diagram showing an insufficient peripheral light amount of the imaging lens. The lens has the best performance at the center, and the performance deteriorates toward the periphery. Therefore, the amount of light input to the image sensor is darker in the peripheral portion than in the central portion. This is called the cos4 power law. When reducing the size and weight of a lens, performance may have to be sacrificed to some extent.

The present invention realizes a simple and high-performance shading correction function by digitally correcting the peripheral light amount of a lens by a signal processing processor. The shading correction of the present invention will be described below. In the digital camera of the present invention, a shading correction coefficient is calculated by adjustment at the time of production, and stored as a correction coefficient in a nonvolatile memory.

The calculation of the correction coefficient is performed as follows. A luminance box is set to the determined luminance, and an image is taken with a camera. As shown in FIG. 3, the image sensor has a color filter arranged for each pixel, and the sensitivity differs for each pixel. Before performing shading correction adjustment, white balance adjustment is performed, and a gain coefficient for the R pixel and a gain coefficient for the B pixel are calculated from the difference between the data of the R pixel and the data of the G pixel. In the shading correction adjustment, it is necessary to calculate shading correction data using a white balance adjustment value. By doing so, it becomes possible to obtain a shading correction coefficient in which the variation in the sensitivity of the image sensor has been corrected.

The shading correction coefficient when the number of pixels of the image sensor is horizontal m = 1280 and vertical n = 960 is calculated as follows. The number of horizontal correction coefficients is obtained from m / p (p is an integer of 8 or more). In this embodiment, p = 20
Has 64 correction coefficients in the horizontal direction. Since the processing system is an 8 × 8 block, it is ideal that the correction coefficient in the vertical direction is provided for every 8 lines in the vertical direction. However, the configuration is such that a block including the vertical n / 2 line at the center is provided as a representative value. doing.

FIG. 5 shows a shading correction coefficient block of the image pickup device. Therefore, there are 64 shading correction coefficients in the horizontal direction.

Next, a method of obtaining a shading correction coefficient will be described. First, the average luminance of the block divided into 64 in the horizontal direction is calculated. Let the average luminance data of each block be DAT_SHADE i. i is 0 ≦ i ≦ 63. Data having the maximum value in DAT_SHADE i is referred to as SHADE_MAX. In FIG. 4, N blocks have the maximum value. Therefore, SHADE_MAX = SHADE_DATN. In FIG. 4, black circles indicate SHADE_DAT. The shading correction coefficient ADJ_SHADE i is obtained by the following equation. The obtained shading correction coefficient is stored in an FLSH memory which is a nonvolatile memory.

[0016]

(Equation 1)

Next, shading correction in photographing by a camera will be described. In the photographing mode, the signal processor 10 reads initial data necessary for photographing from the flash memory 16. When the photographing is executed, the signal processor 10 sets the setting value read from the flash memory 16 to the register of each processing module. The shading correction is set there since there are 64 correction coefficient registers in the horizontal direction. Although it is possible to have fine correction data in the vertical direction, it is necessary to perform critical timing control such as increasing the cost of the FLASH memory and increasing the rewriting of correction coefficients during the horizontal blanking period. In the embodiment, the correction coefficient is calculated using representative center data.

In a zoom lens camera, the amount of peripheral light deficiency varies depending on the zoom position. Therefore, shading correction can be realized by having a correction coefficient at each zoom position. Further, since the amount of insufficient peripheral light varies depending on the diameter of the aperture, shading correction can be performed by providing a correction coefficient for each aperture diameter.

[0019]

As described above, according to the configuration and method of the present invention, the shading correction coefficient is calculated by dividing the center of the image pickup device into 64 parts in the horizontal direction by the signal processor during production adjustment. Is stored in a non-volatile memory, and at the time of photographing, the correction coefficient is read out from the non-volatile memory to perform shading correction. Therefore, shading correction can be performed with a simple configuration, and a structured image can be obtained.

Further, by having shading correction data divided into 64 for each zoom position and aperture diameter,
It is possible to correct unevenness in sensitivity of the image sensor, inclination of the mounting, and insufficient peripheral light amount of the imaging lens only by setting the correction coefficient register without rewriting the correction coefficient at a critical timing or increasing the cost.

As a result, the size and weight of the imaging lens can be reduced without increasing the cost, and the size and weight of the camera can be reduced.

[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 conceptual explanatory view showing a state in which the amount of peripheral light is insufficient.

FIG. 3 is a schematic diagram showing a pixel array of the image sensor of the present invention.

FIG. 4 is a graph illustrating the relationship of shading correction according to the present invention.

FIG. 5 is a schematic diagram showing a block for shading correction according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lens block 2 Aperture unit 3 Image sensor 4 CDS 5 ADC 6 Vertical driver 7 Aperture drive unit 8 Zoom lens drive unit 10 Signal processor 11 DRAM 12 LCD monitor 13 Video amplifier 14 Serial driver 15 Memory card 16 FLASH memory 20 System controller 21 Key input section 22 Mode display LCD

Claims (2)

[Claims] An image pickup optical system, an image sensor having m pixels in the horizontal direction and n pixels in the vertical direction, a correction coefficient calculating means for calculating a shading correction coefficient, and storing the calculated shading correction coefficient. And a shading correction means for reading a shading correction coefficient from the storage means at the time of photographing, and shading correction of an imaging signal output from an imaging element using the read shading correction coefficient. The correction coefficient calculation unit may be configured such that the horizontal direction and the vertical direction of the pixel group of the image sensor are divided into blocks each having a predetermined number, and the shading correction coefficient is calculated only for each block at the center position in the vertical direction. A shading correction device for a digital camera. 2. A shading correction device for a digital still camera according to claim 1, wherein said shading correction coefficient is calculated for each zoom position and / or for each aperture diameter during photographing.