JP4576027B2 - AF system - Google Patents

Description

【００１３】
小さいウィンドウのＡＦデータによりδより大きい変化が生じなければ再スキャンの必要性はない（主要被写体に変化がないと判断する）。
変化が生じた場合、大きいウィンドウのＡＦデータの変化判定も併せ選択を行う。スキャンを行う判定が示された場合は、その条件にしたがった再スキャン処理を行う。
【００１４】
【発明の効果】
以上、説明したように本発明は、山登り方式により合焦動作を行い、ピント位置を検出した後も継続的にピントを追い、合焦した後、合焦位置近傍のデータの時間的平均値を算出し、その合焦位置近傍の平均値とその合焦位置近傍のデータ最大値の差分量が第１の変化判定レベルより小さい場合には変化無しと判断し、差分量が第１の変化判定レベルより大きく第２の変化判定レベルより小さい場合には変化量が小と判断し、差分量が第２の変化判定レベルより大きいと判断した場合には変化量が大きいと判断し、その結果、変化量が大きい場合には広い範囲を間引いた荒いスキャンを行い、変化量が小さい場合には狭い範囲を細かくスキャンするものである。
したがって、継続的にピント位置を追うＡＦシステムにおいて、効率の良い再スキャン処理を実現することができるという効果がある。
【図面の簡単な説明】
【図１】本発明によるＡＦシステムの回路の実施の形態を示すブロック図である。
【図２】本発明によるＡＦシステムの動作を説明するためのフローチャートである。
【図３】被写体条件によるＡＦデータ変化率の差を説明するための概略図である。
【図４】ピント再検出用の変化判定基準値の設定を説明するための図である。
【符号の説明】
１…ズームレンズ
２…フォーカスレンズ
３…被写体光
４…ＣＣＤ
５…プロセス回路
６…ＡＦウインドウ
７…ＢＰＦ
８…絶対値回路
９…積分器
１０…ＣＰＵ
１１，１２…レンズドライバ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an AF system that performs a focusing operation by a hill-climbing method and continuously performs a focusing operation even after a focus position is detected.
[0002]
[Prior art]
In a system that continuously performs AF, after a focus is detected by a hill-climbing method, the lens is stopped until a change occurs in a subject, and scanning is performed when the change occurs.
[0003]
[Problems to be solved by the invention]
In the above scanning process, components due to noise, flicker, camera shake, and the like are included in the obtained level change, so it is difficult to distinguish them from the determination of whether or not the subject position has changed.
In addition, the system cannot distinguish between movement of a subject and scene change. For this reason, even though the subject has moved slightly, scanning may be performed up to a distance range that is unnecessary as a scene change.
In a system that continuously follows AF, when the subject position changes, it is required to quickly and surely reach the focus position.
[0004]
The present invention responds to the above request, and after detecting the focus position, it is determined whether or not the focus position detection process is performed again in response to the change of the subject, and the focus position detection process is determined to be executed. In such a case, an AF system capable of performing an optimum scanning process and performing an efficient focusing operation is provided.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the AF system according to the present invention performs a focusing operation by a hill-climbing method using a luminance signal that has passed through a filter that passes only a signal band necessary for AF control from an image signal as AF data , and is in focus position. In an AF system that continuously tracks the focus even after detection, after focusing, the temporal average value of the AF data in the vicinity of the in-focus position is taken, and the average value in the vicinity of the in-focus position and the in-focus position When the difference amount of the AF data maximum value is smaller than the first change determination level, it is determined that there is no change, and when the difference amount is larger than the first change determination level and smaller than the second change determination level, it changes. When it is determined that the amount is small and it is determined that the difference amount is larger than the second change determination level, it is determined that the amount of change is large, and when the amount of change is large, a wide range is thinned out. Performed have scan, it is configured to finely scan a narrow range when the amount of change is small.
The change determination level is defined by δ × k, and the δ can be configured to change depending on the contrast and brightness of the subject.
Where k: magnification
δ: Unit judgment level (adjacent to the peak of the scan result when focus detection is performed)
AF data difference)
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of a circuit of an AF system according to the present invention.
The subject light 3 enters the CCD 4 through the zoom lens 1 and the focus lens 2. The video signal output from the CCD 4 is processed by the camera process circuit 5 to generate a luminance signal and a color signal. FIG. 1 shows only luminance signals necessary for AF control. The luminance signal is input to the AF window circuit 6 and only the luminance signal of the area necessary for AF control is extracted.
[0007]
Thereafter, the signal is input to a band pass filter (BPF) 7 that passes only a signal band necessary for AF control. The luminance signal output from the band pass filter 7 is input to the CPU 10 via the absolute value circuit 8 and the integrator 9. The integrator 9 integrates the luminance signal for one field, and then clears the integration data by an integration clear signal CR sent from the CPU 10.
The CPU 10 determines the start of one field from the input vertical synchronizing signal (VD) and horizontal synchronizing signal (HD), sends an integration clear signal CR to the integrator 9 at the start of one field, and at the end of one field. The integration data FD is taken into the CPU 10. The CPU 10 can obtain the focus voltage by repeating this operation.
The CPU 10 drives and controls the lens driver 11 based on the focus voltage.
[0008]
FIG. 2 is a flowchart for explaining the focusing operation of the AF system according to the present invention.
When power (not shown) is turned on and the CPU 10 starts AF processing, AF scanning processing is performed (S201). Next, a change determination level is set (S202). Then, the AF data is taken and averaged (S203).
The fetched averaged AF data is compared with the change level, and it is determined whether or not the difference is larger than the first change determination level (n × δ) and the second change determination level (m × δ). Perform (S204). If it is greater than the first and second change determination levels, a coarse rescan setting is performed (S206). If it is larger than the first change determination level and smaller than the second change determination level, fine rescan setting is performed (S205).
If the difference between the averaged AF data and the maximum data value near the in-focus position is smaller than the first change determination level, it is determined that there is no change.
[0009]
Next, the determination reference value (change determination level) will be described.
When hill-climbing focus detection is performed, as shown in FIG. 3, the change rate of AF data increases when the subject is brighter than dark and when the subject has a higher contrast than low.
Therefore, if the threshold used to determine whether or not to re-detect the focus is set to a fixed value, the focus re-detection process will not be performed even if there is a change in the subject in a low-contrast or dark subject. Even if the subject is within the depth of field, a focus change that is not necessary due to slight changes or noise is performed. In order not to be affected by the difference in the AF data change rate depending on the subject condition, the following determination reference value is set based on the change in the AF data when the focus is actually detected.
[0010]
Reference value setting of change judgment level for focus re-detection (re-scan) As shown in FIG. 4, the difference between the AF data is taken on both sides of the scan result, and the larger one is set as δ as shown below. A size criterion is provided. δ varies depending on brightness and contrast.
In order to eliminate the influence of noise, camera shake, etc. as much as possible while periodically taking in the change amount detection AF data, a plurality of data are averaged (in time). That is, the data used for the change judgment is avoided by using it alone, and a plurality of data according to the passage of time are taken. For example, AF data is taken at intervals of 30 to 40 msec and averaged every 4 to 5 data.
The amount of change is the difference between the captured average data and the maximum data value near the in-focus position.
Amount of change = taken average data−DMAX
[0011]
The rescan determination is performed based on the change amount and the change determination reference value (first and second change determination levels).
Rescan determination A change determination is performed on both the AF data of a small window and the AF data of a large window, and the combination is determined.
(Judgment of change of AF data of small window)
No change: | Change amount | ≦ n × δ (1)
Small change amount: n × δ <| change amount | ≦ m × δ (2)
Large change amount: m × δ <| Change amount | (3)
(Judgment of change in AF data of large window)
The change determination of AF data of a large window is similarly performed as follows.
No change: | Change amount | ≦ n × Δ (4)
Small change amount: n × Δ <| change amount | ≦ m × Δ (5)
Large change amount: m × Δ <| Change amount | (6)
Note that n and m have a relationship of n <m.
[0012]
The processing content is determined in accordance with Table 1 together with the determination result.
[Table 1]

[0013]
If there is no change larger than δ due to AF data of a small window, there is no need for rescanning (determining that there is no change in the main subject).
When a change occurs, selection is also performed for determining a change in AF data of a large window. If it is determined that scanning is to be performed, rescan processing is performed in accordance with the conditions.
[0014]
【The invention's effect】
As described above, the present invention performs the focusing operation by the hill-climbing method, continuously follows the focus after detecting the focus position, and after focusing, the temporal average value of the data in the vicinity of the focus position is obtained. When the difference amount between the average value in the vicinity of the in-focus position and the maximum data value in the vicinity of the in-focus position is smaller than the first change determination level, it is determined that there is no change, and the difference amount is the first change determination. If it is greater than the level and smaller than the second change determination level, it is determined that the change amount is small, and if it is determined that the difference amount is greater than the second change determination level, it is determined that the change amount is large. When the amount of change is large, a rough scan is performed by thinning out a wide range, and when the amount of change is small, a narrow range is finely scanned.
Accordingly, there is an effect that an efficient rescan process can be realized in an AF system that continuously tracks the focus position.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a circuit of an AF system according to the present invention.
FIG. 2 is a flowchart for explaining the operation of the AF system according to the present invention.
FIG. 3 is a schematic diagram for explaining a difference in an AF data change rate depending on a subject condition.
FIG. 4 is a diagram for explaining setting of a change determination reference value for focus re-detection.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Zoom lens 2 ... Focus lens 3 ... Subject light 4 ... CCD
5 ... Process circuit 6 ... AF window 7 ... BPF
8 ... Absolute value circuit 9 ... Integrator 10 ... CPU
11, 12 ... Lens driver

Claims (2)

In an AF system that performs focusing operation by a hill-climbing method using a luminance signal that passes through a filter that passes only a signal band necessary for AF control from an image signal as AF data , and continuously follows the focus after detecting the focus position ,
After focusing, take the time average value of the AF data near the focus position,
If the difference between the average value in the vicinity of the in-focus position and the AF data maximum value in the vicinity of the in-focus position is smaller than the first change determination level, it is determined that there is no change,
When the difference amount is larger than the first change determination level and smaller than the second change determination level, it is determined that the change amount is small;
If it is determined that the difference amount is greater than the second change determination level, it is determined that the change amount is large;
If the amount of change is large, perform a rough scan with a wide range thinned out,
An AF system that scans a narrow range finely when the change amount is small. The change determination level is defined by δ × k,
2. The AF system according to claim 1, wherein δ varies depending on a contrast and brightness of a subject.
Where k: magnification
δ: Unit judgment level (adjacent to the peak of the scan result when focus detection is performed)
AF data difference)

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