JP2001309393A - Imaging unit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform white balance processing at a high level without being accompanied by picture deterioration due to signal saturation or the increase of quantization noise. SOLUTION: An electronic camera provided with a white balance adjusting function is provided with a variable gain amplifier 230 for amplifying an analog video signal outputted from an imaging device 105, an A/D converter 240 for quantizing an analog signal amplified by the amplifier 230, a gain deciding circuit (the first white balance means) 252 which individually adjusting the quantization input level of the converter 240 for each color component by variably setting an amplifier gain based on the peak of the output signal of the converter 240, and the second white balance means 253 which is provided in a generating process generating a final output video signal by processing a digital video signal being the output of the converter 240 and adjusts the relative gain of each color component of the digital video signal by digital calculation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image pickup apparatus having a white balance adjustment function, and more particularly to an image pickup apparatus which performs both analog white balance and digital white balance.

[0002]

2. Description of the Related Art In an image pickup apparatus such as an electronic camera (digital still camera) or a video camera, if the color temperature of illumination light is different, the color of a video signal is biased. To correct this, various white balance processes are performed.

[0003] The white balance processing for the most basic and general RGB color signals is outlined. Although the color temperature of the illumination of the subject is unknown, (1) the subject is considered to be white (colorless) on average. The color information of the illumination light is approximately obtained by calculating and comparing the average value of each color signal by signal integration based on the assumption that the color signals are integrated. (2) Assuming that the above assumption is true, the average value of each color signal is RG to be relatively equal
The gain is adjusted for each B color. (3) Since the assumption is not true in reality, errors based on this are eliminated by various methods.

[0004] Therefore, the actual performance is particularly affected by the portion (3). For this purpose, for example, the average value calculation of (1) is performed by applying various conditions to only the portion of the subject which can be regarded as white. And then integrate it,
Regarding the gain adjustment of (2), various proposals have been made, such as limiting the kind of assumed illumination light and selecting a gain adjustment value from gain adjustment values corresponding to the illumination light.

[0005] On the other hand, considering the relationship with the signal processing method, all analog processing was initially performed.
With the digitization of the entire signal processing circuit and the advancement of white balance processing, white balance is generally performed by digital processing after A / D. That is, all digital processing is employed for the white balance processing circuit in accordance with general requirements for signal processing in an imaging device, such as miniaturization and low power consumption and elimination of circuit variations. further,
In order to realize a complicated algorithm of various judgments and processes related to the above (3), digital processing based on the use of a microcomputer is extremely suitable. From this viewpoint, all digital processing is inevitable. I can say it.

[0006]

However, since the white balance is for correcting a difference in color temperature due to illumination light as described above, it is necessary to be able to cope with the difference. Hereinafter, the RGB processing will be described as an example.

If the exposure control is properly performed in accordance with the luminance of the object, there is no problem since the control which is the main component of the luminance is sufficiently performed.
Regarding, the level relative to G greatly changes depending on the illumination color temperature. This relative level change is assumed to be 1/2 to 2 times that of G (lowest color temperature = R = 2G under reddish illumination, B = G / 2: intermediate color temperature = R = G = B under colorless illumination) : Maximum color temperature = R = G / under the most blue light
2, B = 2G). In this case, in order for none of the color signals to be saturated upon quantization by the A / D converter during the above-described proper exposure under illumination of all color temperatures, the A / D
(This is Dmax) needs to be set assuming about twice the peak level of G.

Although it is possible to avoid saturation by setting in this way, as shown in FIG. 4, for example, under colorless illumination, the maximum value of each color signal becomes Dmax / 2, and the digital bit of more than Is wasted. In other words, the relative quantization error increases twice as much as the ideal state. In addition, since the B signal under the most red illumination and the R signal under the most blue illumination are each at a half level of G, there is a problem that the relative quantization error is quadrupled.

In order to avoid this problem, A / D
Although the quantization error itself of the converter may be reduced, in other words, the number of bits is larger than the originally required number of bits (in order to be able to ignore four times the above example, +
A two-bit) A / D converter is required, which is not preferable because of the increase in cost.

The present invention has been made in consideration of the above circumstances, and has as its object to perform advanced white balance processing without deteriorating image quality due to signal saturation and increase in quantization noise. An object of the present invention is to provide an imaging device capable of performing the following.

[0011]

(Structure) In order to solve the above problem, the present invention employs the following structure.

That is, according to the present invention, in an image pickup apparatus having a white balance adjustment function, A / D conversion means for quantizing an analog video signal output from an image pickup device, A first white balance unit for individually adjusting a quantized input level for each color component of the analog video signal when the digital video signal is input to the analog video signal; and a digital video signal output from the A / D conversion unit. Second white balance means provided in a generation step of generating a typical output video signal, and adjusting a relative gain of each color component of the digital video signal by digital operation.

Here, the following is a preferred embodiment of the quantization input level adjustment in the first white balance means. (1) To be performed by changing the gain of an analog amplifier provided before the A / D conversion means. (2) It is performed by changing the quantization reference voltage of the A / D conversion means. (3) The maximum level of each color component of the analog video signal is set to be lower than the maximum input level of the A / D converter.

(4) Control performed by peak reference control for each color component so that each maximum value of each quantized color component is substantially equal to the maximum output value in A / D conversion. . (5) Control performed by average value reference control for each color component so that each average level of each quantized color component is relatively equal.

(Operation) According to the present invention, the first white balance processing is performed by the analog system before A / D conversion,
After the D conversion, the second white balance processing is performed by digital processing. Since the A / D is optimized in the first white balance, there is no problem of saturation and increase of quantization error. Then, advanced processing can be easily performed by the second white balance. Further, the first white balance only needs to prevent saturation or the like, and high-speed response is easy.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
FIG. 2 is a block diagram illustrating a schematic configuration of an electronic camera according to the embodiment.

Reference numeral 101 denotes a lens system including various lenses, 1
02, a lens driving mechanism for driving the lens system 101; 103, an exposure control mechanism for controlling the aperture of the lens system 101; 104, an optical filter for low-pass and infrared cut; 105, a photoelectric conversion of a subject image A CCD color image sensor with a color filter (CCD area sensor) for obtaining a color image signal by the operation, a CCD driver 106 for driving the image sensor 105, and an A 107
A pre-processing circuit including a / D converter, etc .; 108, a digital processing circuit for performing color signal generation processing, matrix conversion processing, and other various digital processing; 109, a card interface; 110, a memory card;
Is an LCD image display system.

In the figure, reference numeral 112 denotes a system controller (CPU) for overall control of each unit; 113, an operation switch system including various operation buttons; 114, an operation for displaying an operation state and a mode state; Display system, 1
Reference numeral 15 denotes a flash as a light emitting unit; 116, a lens driver for controlling the lens driving mechanism 102; 117, an exposure control driver for controlling the flash 115 and the exposure control mechanism 103; 118, which stores various setting information; 1 shows a nonvolatile memory (EEPROM).

In the digital camera 100 according to the present embodiment, the system controller 112 performs overall control, and controls the driving of the CCD image pickup device 105 by the CCD driver 106 to expose (charge accumulation) and signal. The readout is performed, the readout is taken into the digital process circuit 108 via the preprocess circuit 107, and various signal processes are performed, and thereafter, the data is recorded on the removable memory card 110 via the card interface 109. Exposure control during imaging is also performed by the system controller 112. In this case, the aperture and the C
Normal AE (automatic exposure control) for controlling the exposure period and the like of the CD image sensor 105 is used. When the strobe 115 is used for the above exposure, the system controller 112 controls the exposure control driver 117 to send each control signal for starting and stopping the strobe 115 to cause the strobe 115 to emit light.

In the digital camera 100 of the present embodiment, except for the white balance processing described in detail below,
Operations and controls similar to those of a normal digital camera are performed, and a description of such known parts will be omitted.

As shown in FIG. 2, the pre-processing circuit 10
Reference numeral 7 denotes a sample hold circuit (CDS) 210 for extracting signal information, a sample hold circuit 220 for color separation of RGB three colors, and three variable gain amplifiers 23.
0 (231, 232, 233), three A / D converters 2
40 (241, 242, 243). The system controller 112 includes a digital peak detecting unit 251 for performing peak detection independently for RGB, a gain determining unit 252 for determining the gain of the amplifier, and a digital white balance unit 253.
Here, each of the means 215, 252, and 253 may be provided with a dedicated circuit, or may be performed by software.

The analog video signal obtained by the image sensor 105 is subjected to R / R processing by sample and hold circuits 210 and 220.
After being taken out for each GB and amplified by the amplifier 230, A
The digital signal is converted by the / D converter 240. A / D
The result is digitized by the converter 240 and sent to the system controller 112 via the digital processing circuit 108. In the system controller 112, the digital peak detecting means 251 detects RGB independent peaks, and the gain determining means 252 determines the respective gains of the amplifiers 241, 242, and 243 based on the respective peak values (first white balance). processing).

Here, with respect to the above-mentioned gain setting, the gain may be set by comparing one signal data set lower, or the gain may be determined by feedback.

The former method is a method in a case where there is no time margin. First, the gain of the three amplifiers is set to a sufficiently low value (the image signal always falls within the range of Dmax for any object), and one screen is displayed. The maximum RGB value is detected, and the gain is set according to the detection result. That is, the peak value is compared with Dmax, and the peak value is slightly smaller than Dmax (about 90% of Dmax in view of a circuit margin).
Set the gain so that As a result, all of the RGB have the same level as the peak. The latter is a method in a case where there is enough time, and the gain is set by looking at information little by little by feedback of the peak value.

In either method, the RGB peaks can be optimized, and the quantization input levels can be made uniform. When the quantized input levels become uniform, the digital white balance unit 253 performs white balance by digital processing (second white balance processing).
As a result, digitally advanced white balance can be achieved without causing problems such as saturation and an increase in quantization error.

(Second Embodiment) FIG. 3 shows a second embodiment of the present invention.
FIG. 3 is a block diagram illustrating a main configuration of the electronic camera according to the embodiment. The same parts as those in FIG. 2 are denoted by the same reference numerals, and detailed description thereof will be omitted.

The present embodiment is different from the above-described embodiment in that the gain of the amplifier is set in a time-division manner without performing RGB color separation. Since the image signal obtained through the sample hold circuit 210 is an RGB signal output in a time-division manner, by setting the gain of the variable gain amplifier 231 in accordance with the output color, one image signal can be obtained. However, the gain can be set independently for each of RGB.

As described above, by using an amplifier capable of changing the gain at a high speed, the color separation circuit 220 becomes unnecessary, and one gain variable amplifier 231 and one A / A
It is only necessary to use the D converter 241 and the configuration can be simplified.

The present invention is not limited to the above embodiments. In the embodiment, as the first white balance processing, the output is determined digitally and the amplifier gain is controlled analogously.
The amplifier gain may be controlled based on the signal before digitization. In the embodiment, the gain of the analog amplifier is changed to adjust the quantization level. However, the gain of the amplifier may be fixed and the reference voltage of the A / D converter may be changed.

In the case where the second white balance processing does not have enough time for signal processing (moving pictures, viewfinder), a white balance faster than a highly accurate white balance is required. In such a case, it is also possible to perform only the first white balance and pass the second white balance. in this case,
The output may be determined not by peak detection but by average value detection.

In addition, various modifications can be made without departing from the spirit of the present invention.

[0033]

As described in detail above, according to the present invention, A
By performing the first white balance processing in the analog system before the / D conversion and performing the second white balance processing in the digital processing after the A / D conversion, the image quality is degraded due to an increase in signal saturation and quantization noise. And an advanced white balance process can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an electronic camera according to a first embodiment.

FIG. 2 is a view showing a specific configuration example of a pre-processing circuit and a system controller used in the electronic camera of the first embodiment.

FIG. 3 is a block diagram showing a main configuration of an electronic camera according to a second embodiment.

FIG. 4 is a diagram showing a change in RGB output due to a difference in light source.

[Explanation of symbols]

 REFERENCE SIGNS LIST 100 digital camera 101 imaging lens 103 exposure control mechanism 105 CCD image sensor 106 CCD driver 112 system controller 210 sample hold circuit (CDS) 220 sample hold circuit (color separation) 230 (231, 232, 233) ) Variable gain amplifier 240 (241, 242, 243) A / D converter 251 Digital peak detecting means 252 Gain determining means 253 Digital white balance means

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C065 AA01 AA03 BB02 CC01 CC09 DD02 EE06 GG16 GG18 GG30 5C066 AA01 CA05 EA14 GA01 HA02 HA05 KA01 KA12 KE19 KM02

Claims (6)

[Claims] An analog-to-digital (A / D) converter for quantizing an analog video signal output from an image pickup device, and a quantization input level when the analog video signal is input to the A / D converter is set to the analog video signal. First white balance means for individually adjusting each color component of the signal; and a generation step for processing a digital video signal output from the A / D conversion means to generate a final output video signal; Second white balance means for adjusting the relative gain of each color component of the digital video signal by digital operation;
An imaging device comprising: 2. The method according to claim 1, wherein the adjustment of the quantization input level in the first white balance means is performed by changing the gain of an analog amplifier provided before the A / D conversion means. The imaging device according to claim 1. 3. The apparatus according to claim 1, wherein the adjustment of the quantization input level in the first white balance means is performed by varying a quantization reference voltage of the A / D conversion means. Imaging device. 4. The adjustment of the quantization input level in the first white balance means is performed so that each maximum level of each color component of the analog video signal falls below the maximum input level of the A / D conversion means. The imaging device according to any one of claims 1 to 3, wherein the imaging device is a device. 5. The quantization input level in the first white balance means is adjusted by a peak reference control for each color component, and each of the maximum values of each of the quantized color components is A / D. 5. The image pickup apparatus according to claim 4, wherein the control is performed so as to be substantially equal to the maximum output value in the conversion. 6. The adjustment of the quantization input level in the first white balance means is performed by average value reference control for each color component, so that the average levels of the quantized color components are relatively equal. The imaging device according to any one of claims 1 to 4, wherein the imaging device is controlled.