JPH1127684A - Automatic color temperature correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost increase, to attain color temperature correction with high accuracy and to apply color temperature correction again to a video signal once converted into a digital signal by obtaining a deviation of a mean value of a red color signal with respect to a mean value of a green color signal and obtaining a deviation of a mean value of the blue color signal with respect to the mean value of the green color signal and providing an output of red and blue correction color signals corresponding to the obtained deviations. SOLUTION: An AGC 3 is a voltage controlled amplifier circuit to control the amplitude serial red, green and blue signals. A microcomputer 9 detects how much deviation the mean value of the red signals and the mean value of the blue signals have from the mean value of the green signals, generates a correction control signal in response to the deviation and gives the correction signal to a LUT 6. The correction color signal from the LUT 6 is stored in a recording medium 7 in a form of 8-bit digital signals. Then highly accurate color temperature is corrected for the color temperature correction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for automatically correcting a color temperature of a color signal from an electronic image sensor.

[0002]

2. Description of the Related Art In electronic still cameras and TV cameras, an optical image signal is converted into an electric signal by an electronic image pickup device such as a CCD device. In a camera that captures a color image, a color filter is provided in front of the CCD element to obtain R (red), G (green), and B (blue) color signals.

Since the CCD elements have different sensitivity characteristics for each of red, green and blue colors as shown in FIG. 4, it is necessary to make corrections so that the respective sensitivities become the same for correct color reproduction. is there. In FIG. 4, the horizontal axis is wavelength,
The vertical axis indicates the relative sensitivity as a percentage when the peak of the output sensitivity of the green pixel CCD is 100.

The wavelength distribution of light is different between sunlight and indoor artificial light, and the fluorescent light and incandescent light have different light source wavelength distributions even for the same artificial light. Even when the image is captured by the CCD image sensor, the image may be captured in a different color depending on the type of light source. For example, color temperature correction is performed to adjust the gain of a color signal in accordance with the color temperature in order to maintain a constant color reproducibility so that a white object can be photographed as white under any photographing conditions.

FIG. 3 shows a configuration of a conventional automatic color temperature correction circuit. The principle of this automatic color temperature correction is based on an empirical rule that natural colors have almost the same average value of each of the three primary colors. In FIG. 3, light from a subject (not shown) passes through a lens 20 and an aperture 21 to form an image on a CCD image sensor 22 including a plurality of pixels. Color filters such as red, green, and blue are arranged in the pixels. CCD2
2 is scanned and input to a double correlation sampling circuit (CDS) 23. The CDS 23 includes a sample and hold circuit, and simultaneously outputs RGB signals serially input from the CCD 22. The amplification circuit 24
It includes three voltage controlled amplifiers controlling the respective amplitudes of the signal, the G signal and the B signal. The R, G, and B signals output from the amplifying circuit 24 are combined into one signal in a signal processing circuit 25 and are converted into an analog / digital converter (A / D) 2.
At step 6, it is converted into a digital signal. The output of the A / D 26 is subjected to predetermined digital signal processing such as color separation in a signal processing circuit 27.

On the other hand, the output of the A / D 26 is input to a tint detection circuit 28. In the tint detection circuit 28, the average value of the red, green, and blue color signals of all the pixels is obtained. Next, the microcomputer (MPU) 29 detects how much the average value of the R signal and the average value of the B signal differ from the reference value by using the average value of the G signal as a reference. A control signal is generated such that the deviation approaches zero according to the deviation. By controlling the gain of the voltage-controlled amplifier of the R signal and the gain of the voltage-controlled amplifier of the B signal of the amplifier circuit 24 by the control signal,
Feedback control is performed so that the average values of the R, G, and B signals are always the same. Thereby, natural color reproduction is always performed. The above processing is called color temperature correction.

[0007]

The above-mentioned conventional automatic color temperature correction circuit requires three expensive voltage control amplifiers to control the gain of each of the R, G, and B color signals, resulting in an increase in cost. became. Furthermore, feedback color temperature correction for follow-up adjustment is common due to the low calculation speed of a microcomputer, and so it has been difficult to correct the color temperature of an image signal once converted into digital data. In addition, when color temperature correction of an image signal converted into digital data is performed, there is a disadvantage that a quantization step becomes coarse and image quality deteriorates.

An object of the present invention is to provide an improved color temperature correction apparatus capable of suppressing an increase in cost, performing high-accuracy color temperature correction, and performing color temperature correction on a once digitized video signal again. It is to be.

[0009]

A color temperature compensating apparatus according to the present invention comprises means for calculating an average value of color signals of all colors of all pixels based on red, green and blue color signals obtained from an electronic image pickup device. Means for determining the deviation of the average value of the red color signal and the deviation of the average value of the blue color signal with respect to the average value of the green color signal, and a data table storing a corrected color signal corresponding to the deviation value. Means for reading and outputting, from the data table, red and blue correction color signals corresponding to the obtained deviation.

[0010]

The average value of the color signals of all the pixels is detected based on the color signals. A correction color signal corresponding to the deviation of the average value of the red and blue color signals from the average value of the green color signal is stored in the data table in advance. The color signal corrected correspondingly according to the deviation is read from the table.

[0011]

FIG. 1 is a block diagram of a color electronic camera to which a color temperature correction device according to an embodiment of the present invention is applied. An image of a subject is formed on a CCD image sensor 1 including a plurality of pixels. Color filters such as red, green, and blue are arranged in the pixels. An output signal from the CCD 1 is scanned and input to the CDS 2. The CDS2 amplifies and outputs the R, G, B signals as they are serially. The AGC 3 is one voltage control amplifier circuit, and controls the amplitude of a serial R signal, G signal, and B signal. The serial RGB signal output from the AGC 3 is converted to an analog / digital converter (A / D).
In step 4, it is converted to a digital signal. The output of A / D4 is 10
Bit digital data.

The output of the A / D 4 is a microcomputer 8
Exposure evaluation and exposure control are performed. The gain of the AGC 3 is controlled by the control signal of the microcomputer 8, and the feedback control is performed so that the level of the serial RGB signal is kept constant.

On the other hand, the data of the 10-bit digital color signal output from the A / D 4 is stored in the memory 5 for one screen.
The 10-bit color signal data stored in the memory 5 is read out according to a read control signal from the microcomputer 9 and input to the look-up table (LUT) 6 and the microcomputer 9.

The LUT 6 stores 10-bit image data in 8
This is a conversion table that converts the image data into bit image data and outputs the image data. At the time of conversion, color temperature correction is also performed according to the correction control signal. FIG. 2 shows an example of the conversion table of the LUT 6.
The horizontal axis is the input signal. The vertical axis is the output signal. The slope of the conversion line in the table indicates the color temperature correction rate. The signal of the G pixel is the reference, and the signal of the G pixel does not perform color temperature correction. In the conversion table of FIG. 2, when the input of the average value of the G signal is 1024, the input of the average value of the R signal is 51
2 shows a case where the input of the average value of the B signal is 256. Therefore, since the average value of the B signal is the lowest, the conversion characteristics as shown in the drawing are obtained in order for the R, G, and B signals to be corrected to 8-bit outputs having the same value. Several such conversion tables are experimentally created in advance in accordance with the value of the correction control signal, and stored in a memory as a lookup table.

The above average value is the average value of all pixels in one screen. That is, for each pixel, each color signal is summed and divided by the number of pixels. For example, if the average value of the G signal is 1
28, the average value of the R signal is 64, and the average value of the B signal is 32. In that case, to match the average value of the G signal, the lookup table 6
The B signal is quadrupled and output. That is, for each pixel, the G signal is output by multiplying it by 1, the R signal is output by doubling, and the B signal is output by doubling.

The look-up table 6 receives a 10-bit signal and outputs an 8-bit signal. If the number of bits is reduced by two bits, the input signal can be easily doubled or quadrupled, although the signal accuracy is reduced. For example, as shown in FIG. 2, the G pixel table simply converts a G signal from 10 bits to 8 bits. With reference to the G pixel table, the R pixel table is a table for doubling the input signal, and the B pixel table is a table for doubling the input signal.

Specifically, the G pixel table is a table for multiplying by 1, and outputs the upper 8 bits of a 10-bit input signal. The R pixel table is a table that doubles,
It outputs 8 bits excluding the most significant bit and the least significant bit of the 10-bit input signal. The B pixel table is a table for multiplying by four, and outputs the lower 8 bits of a 10-bit input signal. As described above, the lookup table 6
By converting a 10-bit signal to an 8-bit signal, the R, G, and B balances (white balance) can be easily obtained by changing the magnification.

On the other hand, in the microcomputer 9, based on the input 10-bit signal from the memory 5, the average value of the R signal and the average value of the B signal are respectively set with respect to the average value of the G signal. The degree of deviation is detected, and a correction control signal corresponding to the deviation is generated.
The correction signal is input to LUT6.

The correction color signal from the LUT 6 is stored in a recording medium 7 such as a semiconductor memory or a magnetic memory medium in the form of an 8-bit digital signal. Further, the processing circuit 10 performs color processing for synthesizing the corrected color signal and the luminance signal from the LUT 6, and an image can be reproduced on the monitor screen 11.

The present invention is not limited to the embodiment described above, and it is obvious that those skilled in the art can make various changes and improvements based on the disclosure of the embodiment.

[0021]

According to the present invention, the voltage controlled amplifier circuit is
The cost can be reduced because only one circuit for GC is required. In addition, since the image data converted to digital data is written to the memory, the color temperature is calculated from the written data, and the color temperature is corrected when the data is read from the memory, a sufficient color temperature calculation time can be secured. Accurate color temperature correction becomes possible. Further, even for an image signal for which color temperature correction was insufficient, the color temperature can be corrected again because the data is stored in the memory.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an electronic color camera to which a color temperature correction device according to an embodiment of the present invention is applied.

FIG. 2 is a diagram showing an example of the contents of a lookup table according to an embodiment of the present invention.

FIG. 3 is a block diagram of a conventional automatic color temperature correction circuit.

FIG. 4 is a graph showing a spectral sensitivity characteristic of a CCD.

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 1 CCD imaging device 2 CDS 3 AGC circuit 4 A / D converter 5 Memory 6 Look-up table 7 Recording medium 8, 9 Microcomputer 10 Processing circuit 11 Monitor

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Keisuke Uchida 1-6-6 Matsuzakadaira, Yamato-cho, Kurokawa-gun, Miyagi Prefecture Inside Fujifilm Micro Device Co., Ltd.

Claims (5)

[Claims] A means for calculating an average value of color signals of respective colors of all pixels based on respective color signals of red, green and blue obtained from an electronic image pickup device; and a red color signal for the average value of the green color signal. Means for calculating the deviation of the average value of the blue color signal and the deviation of the average value of the blue color signal; a data table storing a correction color signal corresponding to the deviation value; Means for reading and outputting a color signal from the data table. 2. The electronic image pickup device according to claim 1, wherein the electronic image pickup device includes a CCD equipped with a color filter, and further comprises an analog / digital converter for converting an analog output color signal of the CCD into a digital signal. Color temperature correction device. 3. The image processing apparatus further includes a memory unit for storing a color signal obtained from the electronic imaging device, wherein the color signal stored in the memory unit is n-bit (n is an integer of 2 or more) data. 3. The color temperature according to claim 2, wherein when the n-bit red and blue color signals and the deviation are input to the data table, a corrected color signal having fewer bits than n is output. Correction device. 4. The color temperature correction device according to claim 3, further comprising a feedback circuit for controlling the output color signal of the analog / digital converter to maintain a predetermined level. 5. The color temperature correction device according to claim 3, wherein the data table converts a 10-bit color signal into an 8-bit correction color signal.