JPS62225088A - Digital camera - Google Patents

Abstract

PURPOSE:To apply accurate white balance and gamma correction with small circuit scale by selecting a data of the gamma correcton corresponding to the color temperature in a ROM depending on the level of the chrominance signal in picking up an object. CONSTITUTION:Signals R,G,B from an image pickup element 1 are subjected to A/D conversion 2 to form Si(R),Si(G),Si(B) and signals So(R),So(G),So(B) are formed by the signal processing at a white balance gamma correction circuit 7, the signal is converted into a color TV signal by an encoder 5, and the signal is subjected to D/A conversion 6. A maximum signal in three color signals in picking up a white object is detected (11) by the circuit 7, the ratio of the signal to the three color signal is calculated 12a-12c, and the value decrementing 1 from the value is obtained. Then a prescribed correction function and the changing range of the input signal Si are multiplied, the calculated value after gamma correction is used as the data of the ROM 8. Then the function of gamma correction of the R,G,B signals is decided and the data is written in RAMs 9a 9c.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to a digital camera.

[Technical background of the invention and its problems] The signal processing of color cameras that have been in practical use for a long time has generally been analog signal processing, but broadcasting equipment is becoming increasingly digital, and compared to analog equipment, digitalization is The benefits have been proven.

However, due to problems such as the price and power consumption of A/D, D/A converters, memory, etc., color cameras have not yet been put into practical use, but as prices decrease and LSI technology progresses, color cameras will become available. It is expected that it will become digital.

The basic configuration diagram of the digital camera currently being considered.
It is shown in FIGS. 4 and 5. First, in Fig. 4, white balance, gamma (
When digital signal processing is used to perform gamma (gamma) correction, the latter can be accurately corrected by using memory as the gamma (gamma) correction circuit 2, but the former white balance cannot be processed in real time by the white balance circuit 1. Therefore, a high-speed multiplier is required.

In other words, this makes digital cameras expensive and completely impractical. Another configuration is to process the white balance signal in an analog section before A/D conversion, as shown in Figure 5, but the analog section and digital section are mixed, making it difficult to convert the circuit into an LSI. In this case, the number of ICs increases and the cost increases.In any case, from the perspective of the widespread use of digital cameras, the above-mentioned drawbacks are quite problematic.

[Object of the Invention] The object of the present invention has been made in view of the above problems, and its purpose is to reduce the circuit scale and
Another object of the present invention is to provide a digital camera that can perform accurate white balance and γ correction.

[Summary of the Invention] The present invention provides read-only memory processing based on the magnitude of a red (R) signal, a green (G) signal, and a blue (B) signal when a white subject is projected under lighting conditions of a certain color temperature. The data of the γ correction value corresponding to the color temperature is selected from among the γ correction values stored in the ROM (ROM), and the white balance and γ correction of the image signal are performed all at once. .

[Effects of the Invention] According to the present invention, signal processing for white balance and γ correction can be performed accurately and easily, and a digital camera can be constructed at low cost.

[Embodiment of the Invention] An embodiment of the present invention will be described in detail below with reference to the drawings. First, FIG. 1 is a basic configuration diagram of the present invention.

The signals R and GSB obtained from the image sensor 1 (11) are converted into digital values S i (R) and S i by the A/D converter 2.
(G), S i (B), and is converted into S o (R) S o (
G), S o (B). These signals are converted into color television signals (MTSC) by an encoder 5 and converted into analog signals by a D/Af conversion circuit 6.

Here, the white balance/γ correction circuit 7 will be explained with reference to FIG. A case will be explained in which the bit length Ω of the input signal Si and output signal SO of the white balance/γ correction circuit 7 is 8 bits.

Signals R (W), G (W), when a white subject is shown
The largest signal S (wax) among B(ν) is detected by the maximum value detector [1, and S (IIIax) and R(
The calculation circuit 12a calculates the ratio of ν〉, G(ν), and B(W).
, 12b, 12c, and from that value 1
The value obtained by subtracting kr.

kg, kb. Here, it is assumed that kr Skg and kb are smaller than 1. Read-only memory (ROM)
Bit length of address input as g! is 15 bits (32
768 words) is used.

If γ correction is performed using a certain function, the required bit length of the address input is 8 bits, so the ROMB
When using γ correction, divide the γ correction of different functions, multiply by the change range (0 to 255) of the input signal St for each case, and use the calculated value when γ correction is applied to that value as RO.
Enter it as M8 data. Here, kr mentioned earlier,
kg 1kb12B (7 bits) accuracy, this value determines the value of m in the input/output relational expression, and is R and G, respectively.

The γ correction function of B is determined. The data indicated by this function is stored in a random access memory (RAM) 9B,
Write 9b and 9c. At this time, switch 14a
~14c is on the A side. Then switch 13a~
13c % Set 14a-14c to B side, input signal 5t
(R), S i (G), and S i (B) can be γ-corrected and output.

This will be explained below using specific examples. R(ν)-G(ν)2B
(ν) Consider the case of μ5:4:3. Maximum value detector 11
The detected signal S (a+ax) is R(W) and S
(max) and R(W): G(V): 1 from the ratio of Bm
(!: k r −0000000, k
g -0100000, k b-1010101. Kokote input signals S i (R), S 1 (G)
, S i (B), data to be transferred from the ROM 8 to the RAMs 9a, 9b, and 9c is selected based on the values of kr, kg, and kb. If kr, kg, and kb correspond to m in the input/output signal relational expression, the relational expression for each signal is 5o(R)-ta RAM 9a
, 9b, 9c, switch 13a, Hb, He and switch L4 as shown above.
a, 14b, 14c switch to A side, 5t
(R), S i (G), and S i (B) from O to 255, which is the operating range, are changed by the counter 10, and S o (R), S'o shown in the previous equation are calculated.
(G), S o (B) values from ROM8 to RA
Transfer to M 9a, 9b, 9c. When the transfer is completed, the switches 13a, 13b, lie and the switches 14a, 14b, 14c are switched to the B side, and the RAMs 9a, 9b, 9c are in the read period and the image signals S i (R), S i (G), S i (
B) are each subjected to γ correction by the RAM 9as 9b19c. In this case RAM 9a, 9b, 9
Since the γ correction data included in c is the γ correction data that represents the value when white balance is taken, there is no need to provide another white balance circuit.

In the above embodiment, one ROM and three RAMs were used, but an embodiment that does not use any RAM will be described below.

A case where the bit length of the input signal Si and output signal So of the white balance/γ correction circuit 7 is 8 bits as described above will be explained. Signal R (W) when showing a white subject
), (W), B(W) +7), the largest signal 5 (IIlax) is detected by the maximum value detector 11, and this S (max) and R(W), G(W), B(
The ratio of ν) is calculated by the arithmetic circuits 12a%12b and 12c, and the values obtained by subtracting 1 from the calculated values are set as kr, kg, and kb. Here, it is assumed that kr and kgSkb are smaller than 1. Read-only memory (ROM) 8a.

Let us consider the case where the address input bit length is 15 bits (32708 words) as 8b and 8c. If γ correction is performed using a certain function, the required bit length of the address input is 8 bits, so the ROM 8
When using a, 8b, and 8c, the calculation is performed by dividing the function into γ increments of different functions, multiplying each by the change range (0 to 255) of the input signal Si, and correcting the value by γ. Enter the value as data in ROM 8as 8b18c. kr mentioned earlier here.

This value determines the value of m in the input/output relational expression, and the γ correction functions for R, G, and B are determined, and the human input signal S
i (R), S i (G), and S i (B) can be γ-corrected.

As a specific example, consider a case similar to the above case.

In other words, R(W), G(W), B(W) -5: 4
: This is the case of 3. The signal S (wax) detected by the maximum value detector 11 is R (V), and S (max)
The value obtained by subtracting 1 from the ratio of
It becomes 67. Expressing this in 7-bit binary numbers, k r-
0000000, kg -0100000, k b-
It becomes 1010101. Here, the input signal S i (R)
, S i (G), and S i (B).

8bs 8c data is selected by the values of kr, kg, , kb. The relational expression of input and output signals is 5o(R)=-il,
66431(B)l. In this way, the imaging signals S i (R), S L (G), S i (B)
is γ-corrected after white balance is taken.

As described above, according to this embodiment, the white balance and γ
Since the data for correction signal processing is written in the ROM, the circuit scale is small and accurate white balance and γ correction can be performed.

[Brief explanation of drawings]

FIG. 1 is a basic configuration diagram of the digital camera of the present invention, TS
Figure 2 is an lf4 diagram of a white balance/γ correction example according to the present invention, and Figure 3 is a white balance/γ correction example according to the present invention.
FIG. 4 is a diagram showing the basic configuration of a conventional digital camera, and FIG. 5 is a diagram showing another basic configuration of a conventional digital camera.

Claims (2)

[Claims] (1) In a digital camera that images a subject and performs white balance γ (gamma) correction processing on the R, G, and B signals extracted, γ correction value data corresponding to various color temperatures is stored. a memory; a means for detecting the R signal, G signal, and B signal when a white subject is imaged under lighting conditions of a predetermined color temperature; and the magnitude of the R signal, G signal, and B signal by this means; means for selecting γ correction value data from the memory; γ correction value corresponding to the color temperature selected by this means;
According to the data, an R signal when the subject is imaged,
A digital camera characterized by applying G signal and B signal γ correction. (2) The digital camera according to claim 1, wherein a memory is provided for each of the R signal, G signal, and B signal.