JPH057340A - Imaging device - Google Patents

Abstract

(57) [Summary] [Object] To provide an image pickup apparatus having a simple structure for AE (automatic exposure control) and at low cost. [Structure] AE is performed based on the coefficient of the DC component of a DCT (discrete cosine transform) unit 18 when the image data compression unit 5 compresses the output of a solid-state image sensor CCD 2.

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 means for compressing a picked-up image, and more particularly to automatic exposure control (hereinafter referred to as AE).

[0002]

2. Description of the Related Art A conventional device of this type is shown in FIG. As shown, the image is the lens unit 1, the solid-state image sensor CC.
A digital signal (hereinafter referred to as CCD) 2 is converted into an electric signal, a video signal is converted at an image pickup processing unit 3, and an AD (analog
It is converted into a digital signal by a (digital) converter 4, compressed by an image data compressor 5, and an encoded output 6 is output.

Next, the operation of the AE will be described. CCD2
The video signal obtained by the image pickup processing unit 3 is passed through the LPF (low-pass filter) 13 and the SW (switch) 14, and
The D converter 15 converts the digital signal, and the integrator 16
Are integrated by and input to the microcomputer 9. While observing the output of the integrator 16 so that the input light amount of the CCD 2 becomes optimum, the microcomputer 9 controls the iris drive and the amplifier gain of the image pickup processing unit 3 to perform AE.

[0004]

However, in this conventional example, the LPF 13, SW 14, AD for AE are used.
Since the converter 15 and the integrator 16 are required, there is a problem that the device becomes complicated and the cost becomes high.

The present invention has been made in view of the above problems, and an object thereof is to provide an image pickup apparatus which has a simple structure for AE and is inexpensive.

[0006]

In order to achieve the above object, the present invention utilizes an orthogonal encoder for AE, and more specifically, an imaging device is constructed as shown in (1) below. (1) Image pickup means, image data compression means for performing image data compression on the output of the image pickup means using an orthogonal transform encoder, and a required exposure amount based on the coefficient of the DC component of the orthogonal transform encoder. And an exposure amount determining means for determining.

[0007]

According to the configuration of (1), the required exposure amount is determined based on the coefficient of the DC component of the orthogonal transform encoder related to the exposure amount.

[0008]

EXAMPLES The present invention will be described in detail below with reference to examples.
FIG. 1 is a block diagram of an "imaging device" that is a first embodiment of the present invention. As shown in the figure, the image is converted into an electric signal by the lens unit 1 and the CCD 2, converted into a video signal by the image pickup processing section 3, converted into a digital signal by the A / D converter 4, and then by the image data compression section 5. The image data is compressed and the encoded output 6 is output. This is a compression method that performs one two-dimensional DCT (discrete cosine transform) of orthogonal transformation. The output from the AD converter 4 is stored in the frame memory 17 for one screen, and the DCT unit 18 performs DCT from the frame memory 17 from 8 × 8 pixel data of 8 pixels each in the vertical and horizontal directions.

Image data f (i, j) of N × N pixels is set to 2
When the three-dimensional DCT transform is performed, the transform coefficient F (U, V) of the DCT
Is

[0010]

[Equation 1]

[0011] 8 × 8 coefficient matrix F (U,
V) corresponds to the conversion coefficient of the frequency component of U / 2N times and V / 2N times of the highest spatial frequency included in the image, respectively, and as shown in FIG. 2, Y ₀₀ is a component of frequency 0. That is, the average value of 8 × 8 pixels corresponding to the coefficient of the DC (direct current) component, and the top row is the coefficient of the spatial frequency component in the horizontal direction of the image, and Y ₀₇ on the right is the highest in the horizontal space. Corresponding to the coefficient of the frequency component, the leftmost column corresponds to the coefficient of the spatial frequency in the vertical direction of the image, and the lower Y ₇₀ corresponds to the coefficient of the spatial frequency component in the vertical direction having the highest value. The output of the DCT unit 18 enters the SQ linear encoder 19 and the DC component coefficient Y ₀₀
Is converted into a one-dimensional prediction code, and the coefficients except the DC component coefficient Y ₀₀ are zigzag-scanned and variable-length coded to obtain VL.
It is converted into a variable length code by the C fixed Huffman encoder 20 and the encoded output 6 is obtained.

Next, this embodiment will be described with reference to the flow chart of AE shown in FIG. When the AE is started, the memory 17 is transferred from the CCD 2 via the image pickup processing unit 3 and the AD converter 4.
The image is captured in (S301). Next, the image data is input from the memory 17 to the DCT unit 18 in the thinning pattern as shown in FIG. 4, and the coefficient Y of the DC component of the output of the DCT unit 18 is input.
₀₀ is loaded into the microcomputer 9 (S302). The microcomputer 9 integrates the coefficient Y _{00 of the} DC component (S303), and shifts to a determination (determination of the required exposure amount) whether the integrated value is within a predetermined constant level range (S304), and the constant level range is reached. If it is (YES in S304), the completion of the AE is displayed on the display unit 11 under the control of the microcomputer 9 (S308), and the AE is completed. When the integrated value is not within the predetermined level range (S304, NO),
If the level has not reached a certain level (S305, small), open the iris n steps or open the shutter for nt.
If μs is made longer (S306) and is larger than a certain level (S305, large), the iris is closed by n steps or the shutter closing time is shortened by nt μs (S306), the process proceeds to step 301, and the integral value is set to a predetermined constant. Repeat this loop until you reach the level range.

As described above, the coefficient Y ₀₀ of the DCT section 18 is an average value of 8 × 8 pixels, which is calculated by the microcomputer 9
The AE can be performed so that the light amount of the input light of the CCD 2 becomes optimum by controlling the iris and the shutter so that the integrated value becomes optimum by integrating. Note that this calculation may be performed on a thinned image obtained by appropriately thinning the output of the CCD 2. 4A and 4B are patterns of thinning from the screen, where FIG. 4A is a thinning from the entire screen, FIG. 4B is a center-thinning thinning, FIG. 4C is a thinning from the entire screen of 8 × 8 pixels, and FIG. Is a center-thinning thinning of 8 × 8 pixels. In this way, the weighting of photometry is controlled by the density of sample points.

In the present embodiment, band compression is performed using DCT, but other orthogonal transform systems such as Hadamard can also be used.

Next, a second embodiment of the present invention is shown in FIG.
The flowchart will be described. The overall configuration is similar to that of the first embodiment.

The purpose of this embodiment is to shorten the time until the end of AE. First, AE for changing the iris in n steps or changing the shutter time for nt μs is performed (N ≧ 2) (S501). Y _{00 with} microcomputer 9
If the integrated value of is within the first level (for example, 60 ± 20% with respect to 100% of itself), and if it is out of the range (S502, NO), step 501, until it reaches the first level. Repeat 502. When it is within the first level (S502, YES), is it within the second level (for example,
65 ± 10%), and if it is within (S50
3, YES) Display that AE is completed (S505)
finish. If it is not within the range (S503, NO), the AE control is performed in which the iris in one step or the shutter time of tμs is changed until the second level is reached (S504). The AE for changing the iris in n steps or the shutter time for nt μs is to control the AE by changing the iris drive by n steps or changing the shutter time by nt μs as shown in FIG. .. Also, the AE for changing the shutter time of 1 step iris or t μs means that the iris is driven by 1 step or the shutter is t μs.
The AE is controlled by changing each.

As described above, in the present embodiment, the opening time of the iris or the shutter is changed greatly when the deviation of the AE level is large, and the opening time of the iris or the shutter is changed small when the deviation of the AE level is small. By doing so, it is possible to shorten the time until the AE is completed and to perform the AE accurately.

Next, the configuration of the third embodiment of the present invention is shown in FIG. As illustrated, the difference from the first embodiment is that the microcomputer 9
Data can be input to the DCT unit 18. This embodiment will be described with reference to the AE flowchart shown in FIG. An image is captured from the CCD 2 to the memory 17 via the imaging processing unit 3 and the AD converter 4 (S701), and then image data is input from the memory 17 to the DCT unit 18 in a thinning pattern as shown in FIG. 4 (S702). ), DCT unit 18
The coefficient Y ₀₀ of the DC component of the output is taken into the microcomputer 9 (S
703), the process proceeds to the determination of whether the average value of all thinned-out images has been obtained, and if not (S704, NO), the coefficient Y _{00 of the} DC component loaded into the microcomputer is transferred from the microcomputer 9 to the SW21 for every 8 × 8 data (for every 64 data). Via the DCT unit 18 (S705), and the process proceeds to step 703. If the average value of all thinned images has been obtained (S704, YES), the process proceeds to the determination whether the average value is within a predetermined constant level range, and if it is within the constant level range (S706, YES), A
The display 11 that the E is completed is controlled by the microcomputer 9.
Is displayed (S710), and the AE ends. If the average value is outside the fixed level range (S706, NO) and has not reached the fixed level (S707, small), the iris is opened n steps or the shutter opening time is lengthened by nt μs (S).
708), if it is larger than a certain level (S707,
Large), closing the iris n steps or shortening the shutter closing time by nt μs (S709), and step 701
Then, the operation is repeated until the average value falls within a predetermined level range.

As described above, in this embodiment, DC
The coefficient Y ₀₀ of the DC component of the T section 18 is the average value of the input 8 × 8 data, and the Y value of the output of the DCT section 18 is utilized.
By temporarily returning ₀₀ to the DCT unit 18 via the microcomputer 9, the DCT unit 18 can obtain the average value of all the pixels of the thinned image, and the iris and shutter are controlled so that this average value falls within a predetermined range. By doing so, AE is performed.

[0020]

As described above, in the present invention, since the AE is performed by utilizing the DC component of the image obtained during the image data compression processing, the LPF for extracting the low frequency component for the AE, The A-D converter, the integrator, etc. are not required, and the AE can be performed at a low cost.

[Brief description of drawings]

FIG. 1 is a block diagram of a first embodiment.

FIG. 2 is an explanatory diagram of the first embodiment.

FIG. 3 is a flowchart of AE according to the first embodiment.

FIG. 4 is a diagram showing an example of a thinning pattern.

FIG. 5 is a flowchart of AE of the second embodiment.

FIG. 6 is a block diagram of a third embodiment.

FIG. 7 is a flowchart of AE of the third embodiment.

FIG. 8 is a block diagram of a conventional example.

[Explanation of symbols]

 2 Solid-state image sensor CCD 5 Image data compression unit 9 Microcomputer 18 DCT unit

Claims (1)

Claim: What is claimed is: 1. An image pickup means, an image data compression means for performing image data compression on an output of the image pickup means using an orthogonal transformation encoder, and a DC component of the orthogonal transformation encoder. An image pickup apparatus comprising: an exposure amount determination means for determining a required exposure amount based on a coefficient.