JPH06303490A - Camera - Google Patents

Abstract

PURPOSE:To realize high-speed and highly precise focusing while maintaining simple configuration by selecting and switching either a range made to limit to arithmetic operation for calculating the DCT coefficient of a frequency domain or the range in which this limitation is not executed. CONSTITUTION:AF control based on an obtained transformation coefficient is executed by using a feature that a coefficient value is small both in the case that a lens position is at approximately infinite distance and the in the case that it is at the closest distance, and the coefficient value shows a peak at a focusing position. The AF control is executed in this way by using an increasing and decreasing variation of the transformation coefficient value, but if the area of the coefficient to be used for the AF control is fixed, and the AC transformation coefficient of only a part to be used is determined by DCT (discrete cosine transformation) operation, focusing speed is improved. For instance, if the transformation coefficient of only a hatched part area (to show frequency domain) is used for the AF control, the DCT operation can be finished only with that of the hatched part. Namely, in this case, the range of either the DCT operation of an AF area part or the DCT operation of compression recording can be switched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a camera, and more particularly to a camera having improved focusing characteristics.

[0002]

2. Description of the Related Art In an autofocus system, a subject image obtained through an optical system such as a lens is converted into an electric signal, contrast information is detected from the electric signal, and the detected contrast information value is maximized. There is one that performs feedback control of the position of the optical system. The autofocus control according to this method is used for video cameras and the like.

The structure of a conventional still video camera is shown in FIG.
Is shown in. The position of the lens 2 is drive-controlled by the lens driving circuit 1, and the subject image is a CCD that is an image sensor.
Image to 3. The image signal converted into the electric signal by the CCD 3 is subjected to γ correction, color separation, and the like in the imaging process circuit 4, converted into digital data by the A / D converter (ADC) 5, and then the buffer memory 6 Recorded in. As is well known, block data of vertical and horizontal N pixels (for example, 8 pixels) is read from the buffer memory 6, and orthogonal transform processing is performed in a DCT (discrete cosine transform) circuit 8. The direct current (DC) conversion coefficient obtained by the orthogonal transformation by the DCT circuit 8 is supplied to the quantization circuit 9 and the lens AF control circuit 40, while the AC conversion coefficient is obtained by the quantization circuit 10 and the lens AF control circuit 40. And supplied to. The lens AF control circuit 40 receives the AC conversion coefficient, controls the lens driving circuit 1 to move the lens 2, and controls the position of the lens 2 so that the AC conversion coefficient obtained by the DCT circuit 8 becomes maximum. Focus control. The pulse generation (SSG) circuit 7 is composed of the CCD 3,
Various pulses such as horizontal and vertical synchronizing signals for controlling the imaging process circuit 4, the A / D converter 5, the buffer memory 6 and the lens AF control circuit 40 are generated.

The DC conversion coefficient quantized by the quantization circuit 9 is supplied to the delay circuit 11 and the subtraction circuit 12, and the prediction error is obtained as the output of the subtraction circuit 12. This prediction error is encoded by the encoding circuit 14 and output to the synthesis circuit 16. On the other hand, the AC transform coefficient quantized by the quantizing circuit 10 is subjected to coefficient rearrangement processing by the so-called zigzag scanning circuit 13, coded by the coding circuit 15 and output to the synthesizing circuit 16. D synthesized by the synthesis circuit 16
The prediction error of the C conversion coefficient and the AC conversion coefficient are recorded in the recording device 1.
Recorded in 7. Thus, the overall sequence of these respective components is controlled by the system control circuit 18. The DCT circuit 8 is often used at the time of image coding, and if contrast information is detected by the DCT circuit,
Since the DCT circuit can be shared, the configuration can be simplified and the cost can be reduced.

[0005]

As described above, in the conventional auto focus (AF) control of the camera, the DCT operation is performed on the entire screen area, and the obtained DCT coefficient (AC conversion coefficient or DC conversion coefficient) is obtained. Based on this, AF control is executed (for example, the method described in Japanese Patent Laid-Open No. 3-216078). However, when the DCT calculation is performed on the entire screen, there is a problem that the calculation takes time and the focusing speed becomes slow. Further, in order to reduce the amount of calculation, even when the DCT calculation is performed only on the image of the AF area that is the minimum necessary for AF control, the focusing speed delay still remains and the amount of information required for AF control is also left. As a result,
There is also a risk of false focusing.

Therefore, an object of the present invention is to provide a camera capable of high-speed and highly accurate focusing while maintaining a simple structure.

[0007]

In order to solve the above-mentioned problems, the camera according to the present invention uses an A / D converter for the output signal of the image pickup device.
DCT for each block when a screen related to the video signal is divided into a plurality of blocks in the D-converted digital video signal
DCT calculation means for performing calculation to obtain a DCT coefficient, focus recognition means for recognizing the degree of focus based on the DCT coefficient by the DCT calculation means in a specific frequency range, and the DCT The calculation execution range of the calculation means is set to a range limited to the calculation for calculating the DCT coefficient in a specific frequency domain applied for recognizing the degree of focus by the focus recognition means, or this limitation. And a calculation range switching means for selectively switching whether or not the range is not performed.

[0008]

According to the present invention, the range of calculation execution for obtaining the DCT can be selectively switched.

[0009]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a configuration block diagram showing an example of a camera related to the present invention. In FIG.
Components having the same reference numerals as those in Fig. 1 indicate components having the same function. In this example, from the buffer memory 6, for the entire screen or in the AF area, for example, 8
The pixel block data is supplied to the lens AF calculation control circuit 30. The arithmetic control circuit 30 performs a DCT operation on the supplied block data to obtain a transform coefficient. 8 pixels x 8
FIG. 2 shows an example of the transform coefficient Cuv obtained by performing the DCT operation on the block data composed of pixels. In FIG. 2, the larger u is, the higher the horizontal frequency component is, and the larger v is, the higher the vertical frequency component is. Therefore, C00 indicates the magnitude of the DC component (DC conversion coefficient), and higher high-frequency components in the horizontal direction toward the right (u: 0 to 7) also fall below C00 (from v: 0). Higher high frequency components in the vertical direction will be shown towards 7). Here, the remaining transform coefficients excluding the DC transform coefficients are called AC transform coefficients.

Referring to FIG. 3, in the AF control based on the conversion coefficient value obtained as described above, the coefficient value is small when the lens position is substantially infinity and at the closest distance, and the focusing is performed. This is done by utilizing the feature that the coefficient value shows a peak at the position.

Next, an embodiment of the camera according to the present invention will be described. As described above, the AF control is performed by using the increase / decrease of the conversion coefficient value. However, the area of the coefficient used for the AF control is fixed, and the AC conversion coefficient of only the used portion is DCT
The focusing speed can be improved by calculating. For example, as shown in FIG. 4, if only the conversion coefficient in the shaded area (which indicates the frequency domain) is used for AF control, the DCT calculation of only the shaded area is sufficient, so that the entire area DCT
The speed can be increased by about 4 times compared with the case of calculation. That is, it is possible to switch the range of the DCT calculation of the AF area portion and the DCT calculation of the compressed recording.

In the above embodiment, the area of the coefficient used for AF control is fixed, but if it is arbitrarily changed, the following advantages can be obtained. For example, when performing AF control,
Since it is not known whether the in-focus point is at infinity or at the closest distance, the lens is driven a little in any direction, the increase / decrease of the coefficient is checked, and the lens is driven in the increasing direction.
Direction determination is performed as pre-processing for F control.

In the large blur state, the amount of change in the conversion coefficient on the high frequency side is small even if the lens is driven to some extent. Therefore, when determining the direction, the conversion coefficient on the low frequency side as shown by the shaded area in FIG. 5A. In the AF control, the conversion coefficient on the high frequency side as shown by the hatched portion in FIG. As shown in FIG. 6, in the state away from the in-focus position (close to infinity and the closest point), the change in the high frequency side conversion coefficient with respect to the lens position change is small, whereas the change in the low frequency side conversion coefficient is small. The change is relatively large, and on the other hand, it is noted that the coefficient change on the high frequency side is large near the in-focus position.

In the example related to the present invention, when the AF control is started, all the DCT operations in the AF area are performed, and the distribution of the conversion coefficients is examined. For example, if a large frequency component on the vertical side is included. As shown by the hatched portion in FIG. 7, the conversion coefficient on the vertical side may be automatically changed, such as mainly used for AF control. Here, the conversion coefficient pattern is stored to some extent in the ROM or the like, and the optimum pattern is extracted for each AF control, or only the portion where the conversion coefficient value is high is extracted by using the fuzzy theory for AF control. It can also be used.

Also, for a long time, such as movies, AF
In the control, when the subject image changes due to the change of the DC and AC conversion coefficients, the area pattern of the coefficient used for the AF control can be changed to the optimum one each time.

FIG. 8 shows the procedure of the AF control operation and the recording operation of the DCT coefficient as image information.
First, the first stage trigger input for AF operation is waited for (step S1), and only the DCT coefficient necessary for AF control is calculated.
After performing the F control (step S2), it waits for the AF control to end (step S3). Next, the second stage trigger input for recording operation instruction is waited (step S4), the DCT coefficient of the entire area is calculated (step S5), and the coefficient is recorded in a storage medium such as a memory card (step S6). finish. As a result, the minimum necessary calculation is performed during AF, so that the transition to the recording operation is performed quickly, and therefore the risk of missing a photo opportunity or the like can be reduced.

Although the above-mentioned DCT processing is software-processed in the lens AF arithmetic control circuit 30, it goes without saying that the DCT processing can be configured by hardware.

Next, as another example related to the present invention, an example of reducing the adverse effect of flicker will be described. This effect is due to the fact that the coefficient obtained by the DCT calculation is affected by the flicker of the light source. The false focusing operation due to the flicker will be described with reference to FIG. The curve shown by the broken line in the figure is the characteristic showing the relationship between the lens position and the coefficient value change when there is no flicker. The characteristic curve shown by the solid line shows the characteristic when flicker exists, but due to flicker, the characteristic curve is highly uneven and a false peak occurs at the lens position deviated from the accurate focus position, resulting in False focusing operation will occur.

In this example, the flicker is suppressed by using the DC conversion coefficient for the variation of the light source. That is, the fact that the DC conversion coefficient is large when it is bright and small when it is dark is used to perform AF control by using the coefficient x obtained by the following equation that reflects the change in the DC coefficient. x = (AC conversion coefficient used for AF control) × (DC conversion coefficient at the start of AF control) / (DC conversion coefficient of current field) According to the AF control using such a coefficient x, the dotted line in FIG. A smooth characteristic curve without flicker as shown by is obtained, and stable and reliable AF control is possible. Further, if a coefficient y represented by y = x × β is used instead of x, the influence of flicker can be further suppressed. Here, β is obtained from the conversion table as an example shown in FIG. 10 based on the coefficient α defined by the following equation. α = {(DC coefficient at the start of AF control)-(DC coefficient at the current field)} / (DC coefficient at the start of AF control) × 100 [%] β is a DC conversion coefficient that changes according to brightness. Since the AC coefficient does not always change in accordance with the change in accordance with the change, the AC coefficient is compensated and can be experimentally obtained.

Next, as still another example related to the present invention,
An example of obtaining data for moving object tracking and camera shake correction using a conversion coefficient obtained by DCT will be described. As a moving body tracking method, Japanese Patent Publication No. Sho 59-32743 discloses a method of projecting a two-dimensional video signal of a tracking area into a one-dimensional image, checking the correlation of each image, and tracking to a highly correlated portion. There is.
With this method, if the tracking area is increased, the amount of data used for correlation increases, which increases the time for correlation calculation, which may deteriorate tracking performance, or when the shape of the subject changes rapidly. Sometimes it becomes impossible to track and it becomes impossible to track.

In this example, in FIG. 11, the DCT operation is performed on the image of one screen, and the tracking area is locked to the subject to be tracked. Next, the sum of the absolute values of all the AC conversion coefficients in the DCT coefficient is obtained for each block, and a portion where the sum is equal to or greater than a predetermined threshold value (Th) is regarded as a subject to be tracked. In addition, for noise suppression, only continuous areas are extracted.
As a result, the main subject can be extracted.

Blocks that satisfy the relationship with the threshold value Th shown in the equation in FIG. 12 are shown by the shaded areas in FIG. Of these shaded areas, the portion within the tracking area shown in FIG. 11 is the portion g, so that the subject in the portion g may be tracked from the next screen. Further, when the size of the subject g is changed, the tracking area can be sequentially changed along with the change. In addition, full screen DCT for higher speed
DCT only the tracking area and the area around the tracking area without conversion
You may make it calculate. Further, the threshold Th may be an arbitrary fixed value, or all ACs inside and outside the tracking area.
The difference amount of the total sum of the absolute values of the conversion coefficients may be checked, and automatically calculated by, for example, fuzzy calculation or the like, and may be sequentially changed.

In the formula of FIG. 12, the sum of the absolute values of all AC conversion coefficients is used, but various conditions (picture of subject, background,
The subject brightness, the degree of focus, etc.) may be taken into consideration, and the sum of the absolute values of only the AC conversion coefficients relating to the optimum region for each condition may be used. Further, it may be the sum of absolute values of the AC conversion coefficients in the area used during AF control. AC related to this optimum area
The conversion coefficient can be calculated by the distribution of the AC conversion coefficient or an arbitrary fixed coefficient can be used. Further, in the above description, the threshold value (Th) or more is regarded as the subject, but the condition (Th) or less may be regarded as the subject depending on conditions. Also, D
Although the C coefficient is not used, the subject may be extracted by focusing only on the change of the DC coefficient, or the subject may be extracted by comprehensively judging both the changes of the DC coefficient and the AC coefficient.

As described above, it is possible to track a moving body and extract an arbitrary subject. By using such subject extraction, it is possible to detect the amount of screen shift (for example, the amount of camera shake). For example, as shown in FIG. 13A, appropriate areas i, j, k, and 1 are defined at the four corners of the screen, and the subject at each of the four corners is extracted by the formula in FIG. 12 (FIG. 14B) and the next screen (FIG. 14A), the same processing is performed to obtain a subject pattern as shown in FIG. 14B. Next, pattern matching processing is performed on each of the four corners of FIGS. 13B and 14B to detect the amount of screen misalignment.

In the above example, the four corners are set as the DCT target areas, but it is clear that at least one area is enough for detecting the image shift amount, and the number and the block for performing DCT. (8 × 8 pixels in this example) is also arbitrary, and can be set in consideration of cost and accuracy.

As described above, according to this embodiment, high-speed and accurate focusing control can be performed without adding special hardware. It is obvious that the present invention can be applied not only to electronic still cameras, but also to other cameras such as movie cameras.

[0027]

As described above, according to the camera of the present invention, not only the focusing operation can be speeded up and the accuracy can be improved, but also the DCT calculation range can be arbitrarily set.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an example of a camera related to the present invention.

FIG. 2 is a diagram showing transform coefficients obtained by performing a DCT operation on block data of vertical and horizontal 8 pixels.

FIG. 3 is a diagram for explaining AF control based on a conversion coefficient obtained by DCT.

FIG. 4 is a diagram showing an example of fixing a coefficient region used for AF control in the embodiment of the present invention.

FIG. 5 is a diagram showing conversion coefficient regions used at the time of determining a lens drive direction and at the time of AF control in AF control in an example related to the present invention.

FIG. 6 is a diagram showing a relationship between a lens position and a high frequency conversion coefficient and a low frequency conversion coefficient.

FIG. 7 is a diagram showing an example of distribution of transform coefficients in an example related to the present invention.

FIG. 8 is a diagram showing an AF control operation and an image information recording operation processing procedure in an example related to the present invention.

FIG. 9 is a diagram showing a relationship between a lens position and a conversion coefficient in AF control depending on the presence or absence of flicker.

FIG. 10 shows coefficients α and β in another example related to the present invention.
It is a figure which shows an example of the conversion table with.

FIG. 11 is a diagram for explaining an operation tracking method in still another example related to the present invention.

FIG. 12 is a diagram for explaining the operation of the example shown in FIG. 11.

FIG. 13 is a diagram for explaining the operation of the example shown in FIG. 11.

FIG. 14 is a diagram for explaining the operation of the example shown in FIG.

FIG. 15 is a configuration block diagram of a conventional camera based on AF control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 lens drive circuit 2 lens 3 CCD 4 imaging process circuit 5 A / D converter 6, 21 buffer memory 7 pulse generation circuit 8 DCT circuit 9, 10 quantization circuit 11 delay circuit 12 subtraction circuit 13 zigzag scanning circuit 14, 15 encoding Circuit 16 Composite circuit 17 Recording device 18 System control circuit 30, 40 Lens AF control circuit

Claims (1)

[Claims] 1. A digital video signal obtained by A / D converting an output signal of an image pickup device is subjected to a DCT operation for each block when a screen relating to the video signal is divided into a plurality of blocks, and D
DCT calculating means for obtaining a CT coefficient, focus recognizing means for recognizing the degree of focusing on the basis of the DCT coefficient by the DCT calculating means in a specific frequency range, and calculation by the DCT calculating means The range of execution is set to a range limited to the calculation for calculating the DCT coefficient in a specific frequency domain applied for recognizing the degree of focusing by the focus recognizing means, or a range not performing this limitation. A camera, comprising: a calculation range switching means for selectively switching whether or not to set.