JPH0898082A - Electronic still camera - Google Patents

Abstract

PURPOSE: To obtain an optimum image over the entire frame by dividing each frame and obtaining optimum focus or exposure for each block and integrating the results. CONSTITUTION: Image data stored in a frame memory 18 are divided into a prescribed block b a division circuit 20, a pulse generating circuit 14 changes an exposed time from a minimum time to a maximum time discretely and a best DC component obtained by a DCT orthogonal transformation circuit 22 and an exposure condition at that time are stored in a buffer memory A26. Then a focus is changed from infinite to a closest point, data in the memory A 26 are referenced and a focus condition evaluation circuit 28 obtains an optimum condition of each focus and exposure for minimum to maximum exposure time and stores the result in a buffer memory B30. Then data of an optimum condition of each block stored in the memories B30 and A26 are stored in a memory C32. Thus, a best image is stored in a memory C32 as consecutive data for each block subjected to orthogonal transformation and a focused image with optimum exposure is obtained over the entire screen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus and exposure control technique for an electronic digital still camera, and more particularly to an image in which an optimum focus condition and exposure condition are obtained for each part of the screen in the entire area of the screen. The present invention relates to an electronic still camera with optimized full-screen conditions that makes it possible to obtain an image.

[0002]

2. Description of the Related Art Generally, when trying to obtain an image with a high magnification while maintaining the brightness, the depth of focus becomes shallow due to the characteristics of the optical lens. Only a small area of can be focused. Further, in the general snap photography, when the flash or the like is not used under the backlight condition, the shadowed portion is crushed black or the white portion is crushed white. This is because, if the level of the luminance component is greatly different depending on the area in the screen and the exposure condition is met in either one, the local fine range contrast cannot be fully expressed in the other area.

Conventionally, optical image information of a subject is input to a solid-state image pickup device such as a CCD via an optical processing system such as a lens, and an electric signal photoelectrically converted and output is digitized.
Electronic cameras that process digital images as information have been put into practical use.

In this kind of electronic camera, a method of evaluating focus control based on a high frequency component of a digital image electric signal has been considered (JP-A-3-216078, JP-A-3-214868). The high-frequency component is obtained by a method of inputting an electric image signal into a bandpass filter (BPF) or the like, or a method of obtaining an orthogonal transformation calculation, and the focus lens is driven so that this value becomes maximum. An image of the focus position can be obtained.

Further, in an electronic camera, a method of evaluating exposure control based on a luminance component of an electronic signal or a direct current component obtained by an orthogonal transformation calculation and controlling the exposure amount by the evaluation can be considered. Since the data itself is processed and used as an evaluation target, there is no need to provide a dedicated sensor, which is advantageous for downsizing and cost reduction of the camera.

However, in the general conventional autofocus method, one optimum focus position or one optimum exposure is obtained for one screen, and the focus and exposure conditions are optimized in the entire area of the screen. It is not possible to obtain a converted image. Therefore, in Japanese Unexamined Patent Publication No. 4-83478, the screen is divided into a plurality of areas, the focus position in each area and the conditions of an appropriate exposure amount are obtained, and an image under each of these conditions is input for one screen and added, A method is disclosed in which a recovery process by spatial frequency filtering is performed on the image obtained in this way to synthesize an image in which each subject in the screen is in focus.

Further, as another technical means, for example, "S.
A. Sugimoto, Y .; Ichioka; Appl
ied Optics, vol. 24, P.I. 2073 ~
P. 2080 (1985) "or" Kouju Ohta, Kokichi Sugihara, Noboru Sugie, IEICE Transactions (D), vol.J.
66-D, No. 10, P.I. 1245-P. 1246 "
, A method using an image processing technique using a large-scale computer has been reported. This method is to pick up a small portion that is a focal point locally and synthesize it to obtain an image with a deep focal depth over the entire screen.

[0008]

However, according to the method of Japanese Patent Laid-Open No. 4-83478, an image that is totally blurred and is not focused on any part can be excluded from the addition target, but only in a part of the area. It is in-focus, so images that are out-of-focus are added to other areas, and even if recovery processing is performed later, the effect cannot be ignored and the result is an overall slightly blurred image. There was a problem of becoming. Also, how to divide the area is not clearly explained, and there is a high probability that a roughly divided area will contain a plurality of subjects, and in that case, a correct focusing condition for each subject in that area is obtained. I can't. This problem can be avoided by dividing the entire screen into small blocks by making the divided area fine, but adding a large number of images with in-focus points to each small block increases the blur of the finally obtained image. There is a problem. It is considered that the method of the prior application works effectively if the positions of a plurality of subjects within the screen are known and the screen can be optimally divided in accordance with the positions. However, it is necessary to add a focus scan process for this process, and it is very difficult to automatically optimize such work.

Further, even in the other method of using the image processing technique utilizing the large-sized computer mentioned above, although it is an extremely effective method, the apparatus becomes large in size, the algorithm is complicated, and it is practically used. There is a problem that there are many inconveniences.

The present invention has been made to solve the above-mentioned conventional problems, and it is possible to obtain an image which is in focus at each point over the entire area of the screen even when the depth of field of the lens is shallow with a relatively simple device. It is an object of the present invention to provide an electronic still camera that can obtain an image that can express a local fine contrast even under conditions such as backlight.

[0011]

According to the present invention, there is provided means for driving a focus lens to continuously obtain image data of a plurality of frames each having a discretely different focus condition, and a plurality of image data for each frame. Means for dividing into blocks, means for determining and setting the optimum focus condition for each divided block, and for each block unit,
The object is achieved by further comprising a storage unit that selectively stores the image data of the block under the optimum focus condition of the block and finally stores the image data of one frame.

The present invention also provides a means for continuously obtaining image data of a plurality of frames whose exposure conditions are discretely different by changing the exposure condition, and dividing the image data into a plurality of blocks in each frame. Means for determining and setting the optimum exposure condition for each divided block, and for each block, the image data of the block under the optimum exposure condition for the block is selectively stored and finally set. The above-described object is similarly achieved by including a storage means for storing one frame of image data.

The present invention also drives a focus lens,
Further, a means for obtaining a plurality of frame image data having different focus conditions and exposure conditions by changing the exposure conditions, a means for dividing the image data into a plurality of blocks in each frame, and a method for each divided block. ,
The conditions for determining and setting the optimum focus condition and the optimum exposure condition, and the image data of the block under the optimum focus condition and the optimum exposure condition of the block are selectively stored for each block, and finally one frame worth The above-described object is similarly achieved by including a storage unit for storing the image data.

The present invention also achieves the above-mentioned object by the fact that the content of the image data for one frame to be finally stored is the data obtained by compression-encoding the image data.

[0015]

According to the present invention, both or one of the focus and the exposure is scanned, the image data is divided into a plurality of blocks in each frame, and the focusing condition or the optimum exposure condition is determined and set for each block. By doing
Image data of optimum conditions is obtained for each block, and image data for one frame is finally obtained by integrating these. Optimum for both focus and exposure, or one condition over the entire screen area. You can get an image.

Further, when the content of the data to be finally stored is configured to be compression-encoded data, more efficient processing becomes possible.

[0017]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of the first embodiment of the present invention.

In FIG. 1, 2 is a main CPU for controlling various functions of the electronic still camera, 4 is a focus control circuit,
Reference numeral 6 is a lens drive circuit, and 10 is a lens whose focal position can be freely changed. Further, 12 is an image pickup circuit, 16 is an AD conversion circuit, 18 is a frame memory, and 14 is a pulse generation circuit for controlling them.
20 is a block dividing circuit for dividing an image into blocks, 2
Reference numeral 2 is a DCT orthogonal transform circuit that performs DCT calculation on each block to obtain a DC component and an AC component, 24 is an exposure condition evaluation circuit, and 26 is a buffer memory A that stores the optimum exposure condition for each block. , 28 is a focus condition evaluation circuit, 30 is a buffer memory B for storing the optimum focus position of each block unit, and 32 is a buffer memory C for finally storing image data satisfying the optimum condition for one frame. is there.

A series of processes is composed of "first pre-process", "second pre-process" and "main process". Therefore, the "first preprocessing" will be described first.

First, the focus position is set to an appropriate position. This is performed by driving the lens 10 from the main CPU 2 through the focus control circuit 4 and the lens drive circuit 6. The image input to the lens 10 is a CCD
An image is formed on the image pickup circuit 12 using. The pulse generation circuit 14 adjusts the exposure time to the preset minimum value.
Controls the scan timing of the CCD. The analog image data thus obtained is converted to digital by the AD conversion circuit 16 and stored in the frame memory 18. The array of this data is raster scan, and is converted by the block division circuit 20 into a block scan array of 8 × 8 pixels. DCT for each block
The DCT operation is performed by the orthogonal transformation circuit 22 to obtain a direct current component (DC) and an alternating current component (AC). Through the exposure condition evaluation circuit 24, the value of the DC component and the value indicating the exposure condition at this time are stored in the address assigned to each block of the buffer memory A26. This corresponds to the initial value for exposure condition evaluation.

Next, the exposure condition is discretely changed up to the maximum value, and image data under each exposure condition is continuously obtained. The following processing is performed on each of the image data. A DCT operation is performed on the blocks obtained in the same manner as above to obtain a DC component and an AC component. The direct current component at this time is compared with the direct current component already stored in the buffer memory A26, and the value of the direct current component evaluated to give better brightness and the value indicating the exposure condition at that time are newly buffered. It is stored in the memory A26. If the newer condition is evaluated as better, the memory A2
6 will be updated.

As a condition for evaluation at this time, a method of selecting a value closer to a preset optimum DC component value can be considered. It is considered that the optimum DC component value in this case is an intermediate value 50 between the dynamic range of brightness 0 to 100. At this time, if the value exceeds 50,
Therefore, if the comparison is stopped and a value closer to 50 out of the value and the previous value is taken, the processing for the subsequent data can be omitted and the time can be shortened.
In this way, the provisional optimum value of the exposure amount in each block is obtained.

Next, the "second preprocessing" will be described. First, the focus position is set to infinity. The exposure condition is discretely changed from the maximum value to the minimum value of the temporary optimum value of each block obtained as described above, and the image data under each exposure condition is continuously obtained. The following processing is performed on each of the image data. Buffer memory A26
With reference to, the DCT conversion is performed on the block having the exposure condition at this time as the optimum value to obtain the DC component and the AC component. The contrast is evaluated based on the AC component at this time, and the score is obtained. Focus condition evaluation circuit 28
The score and the value indicating the focus position at that time are stored in the address assigned to the block in the buffer memory B30 via. This corresponds to the initial value for focus condition evaluation. The method of obtaining the score is not particularly specified, but a method of calculating by using the fact that the value of the high frequency component in the AC component becomes large if it is the focus point can be considered.

Next, the focal position is discretely changed up to the closest point, and the exposure condition is discretely changed from the maximum value of the provisional optimum value of each block to the maximum value as described above. , Image data under each focus condition and exposure condition is obtained. Referring to the buffer memory A26, for the block having the exposure condition at that time as the optimum value,
Similar to the above, the DC component and the AC component of the image data for each block are obtained. The contrast is evaluated based on the AC component at this time, and the score is obtained. Buffer memory B3
The score already stored at the address assigned to the block of 0 is compared with the current score, and the value of the score evaluated as the better score and the focus condition at that time are shown. The value is stored again in the buffer memory B30. In this way, the provisional focus position in each block is obtained.

When the optimum focus condition of each block is used as it is as the final focus condition of each block, the process proceeds to the next "main processing", but before that, the exposure in each block obtained as described above is performed. The final optimum exposure amount and focus position of each block are obtained from the main CPU 2 based on the provisional optimum value of the amount and the provisional focus position of each block, and stored again in the buffer memories A and B, respectively. It is also possible to keep it. As the processing at that time, smoothing processing is performed so that the difference in focus condition between adjacent blocks does not become too large, and the focus condition is set only for the frame so that the number of blocks that the focus condition has becomes the largest. A method of setting the optimum focus condition can be considered. That is, if the latter method is adopted, even if the configuration of the present invention is adopted, it is possible to obtain one optimum focus condition for one frame as in the conventional autofocus camera.

Next, the "main processing" will be described. The focus position is discretely changed from the maximum value to the minimum value of the final focus position of each block stored in the buffer memory B30. At each focus position, the exposure condition is discretely changed from the maximum value to the minimum value of the final optimum exposure condition of each block stored in the buffer memory A26. In this way, image data under various conditions are sequentially obtained, but data under conditions suitable for each block is stored in the buffer memory C32. Finally, the image data for one frame is stored in the buffer memory C32. That is, the final best image is orthogonally transformed in the buffer memory C32, and continuous data is stored for each block.
The block order of this data is the same as the block order of the image data.

In this way, image data is obtained which is in focus and has optimum exposure over the entire screen.
In this embodiment, only the case where both the focus condition and the exposure condition are optimized has been described, but it is possible to easily achieve a configuration in which either one is omitted and only one is optimized.

Next, a second embodiment of the present invention will be described. The processing of the second embodiment is also performed with the configuration of FIG. Although at least one "pretreatment" and "main processing" are required in the first embodiment, this second embodiment shows a method of ending all the processing only by "main processing".

Most of the processing is the same as in the first embodiment. The focus condition is changed discretely from infinity to the closest point, and the exposure condition is changed from the maximum value to the minimum value each time, and image data under all conditions are successively obtained.

The second embodiment differs from the first embodiment in the following points. That is, in the process of sequentially inputting image data in the “main processing”, when the focus condition or the exposure condition is better than the past condition, the image data at that time is overwritten in the buffer memory C32 one after another, and at the same time, the buffer memory C32 is simultaneously overwritten. The high scores of the focus condition and the exposure condition stored in A26 and the buffer memory B32 are also updated.

At this time, if the data rewriting due to the improvement of the exposure condition is permitted only under the same focus condition, the focus priority processing is performed, and if the data rewriting due to the improvement of the focus condition is permitted only under the same exposure condition, the exposure is performed. It is a priority process. In this way, the image data in which the focus is over the entire screen and the optimum exposure is obtained during one focus scan can be obtained. In the second embodiment, only the case where both the focus condition and the exposure condition are optimized has been described, but a configuration in which one of them is omitted and only one is optimized can be easily achieved.

Next, a third embodiment of the present invention will be described. FIG. 2 is a block diagram showing a schematic configuration of the third embodiment. The third embodiment is shown in FIG. 1 showing the first and second embodiments.
In comparison with the above configuration, the quantization circuit 40 and the Huffman coding circuit 4
2. A compressed data storage circuit 44 is added to the circuit for data compression processing.

That is, in the third embodiment, the DC component and the AC component of each block are obtained by the DCT calculation in both the first embodiment and the second embodiment. Therefore, the image data is used as compression encoded data. Is stored as. As the compression encoding method at this time, JPE using DCT operation is used.
G method is suitable.

That is, the compression processing signal for one frame is received from the main CPU 2, and the buffer memory C32 outputs 1
The image data for the frame is read out, the quantization circuit 40 quantizes it, the Huffman coding circuit 42 subsequently performs Huffman coding, and the compressed data storage circuit 44 stores it.
Further, in the present invention, the image data is divided into blocks of 8 × 8 pixels, but since this is the same as the input format at the time of the image data compression, the pipeline processing enables efficient processing. It will be possible.

[0036]

As described above, according to the present invention, the optimum focus, the optimum exposure, or the image data of the optimum focus and the optimum exposure can be obtained for each block. It is possible to obtain an image in which the above conditions are optimal over the region.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of a first embodiment of the present invention.

FIG. 2 is a block diagram showing a schematic configuration of a third embodiment of the present invention.

[Explanation of symbols]

 2 ... Main CPU 10 ... Lens 12 ... Imaging circuit 14 ... Pulse generation circuit 16 ... AD conversion circuit 18 ... Frame memory 20 ... Block division circuit 22 ... DCT orthogonal transformation circuit 24 ... Exposure condition evaluation circuit 26 ... Buffer memory A 28 ... Focus Condition evaluation circuit 30 ... Buffer memory B 32 ... Buffer memory C 40 ... Quantization circuit 42 ... Huffman coding circuit 44 ... Compressed data storage circuit

Claims (4)

[Claims] 1. A means for driving a focus lens to continuously obtain image data of a plurality of frames each having a discretely different focus condition, and a means for dividing the image data into a plurality of blocks in each frame. Means for determining and setting the optimum focus condition for each of the divided blocks, and image data of the block under the optimum focus condition of the block is selectively stored for each block, and finally, for one frame. An electronic still camera, comprising: storage means for storing image data of. 2. A means for continuously obtaining image data of a plurality of frames whose exposure conditions are discretely different by changing the exposure condition, and a means for dividing the image data into a plurality of blocks in each frame. Means for determining and setting the optimum exposure condition for each of the divided blocks, and image data of the block under the optimum exposure condition of the block is selectively stored for each block, and finally one frame An electronic still camera comprising: a storage unit for storing minute image data. 3. A means for obtaining a plurality of frame image data having different focus conditions and exposure conditions by driving a focus lens and changing an exposure condition, and image data is divided into a plurality of blocks in each frame. Dividing means, conditions for determining and setting the optimum focus condition and the optimum exposure condition for each of the divided blocks, and image data of the block under the optimum focus condition and the optimum exposure condition of the block for each block. An electronic still camera, comprising: storage means for selectively storing and finally storing image data for one frame. 4. The method according to any one of claims 1 to 3,
The content of the image data for one frame to be finally stored is
An electronic still camera, which is data obtained by compression-encoding image data.