JPH1086696A - Method for detecting characteristic part in face image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly detect characteristic parts such as nostrils from the face image in which the information of a human face is picked up. SOLUTION: The position of the nostrils is detected from the face image, and in the next time, the search region is set based on the position of the nostrils discovered in the previous time. The nostrils need not be searched for the whole face image, and the processing load is reduced thereby. In addition, the search region of the nostrils is changed according to the consciousness level of a driver. When the consciousness level of the driver is low, the movement of the face becomes slow, and the search regions 20b, 20c in the normal condition are contracted to the search regions 20d, 20e. The nostrils can thus be rapidly detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a characteristic part in a face image obtained by photographing a human face.

[0002]

2. Description of the Related Art In recent years, a device for preventing a driver of a vehicle such as an automobile from falling asleep has been developed, and a part of the device has been put to practical use. As an example of the dozing driving prevention device, there is a device that determines a dozing state based on a movement of a characteristic portion of a driver's face, for example, a time during which eyes are closed. In this case, in order to capture the movement of the driver's eyes, it is necessary to take an image of the driver's face and identify the eyes from the face.

Japanese Patent Application Laid-Open No. Hei 7-181012 discloses that a face area is extracted by binarizing an image including a face, and the relative positions and individual positions of a plurality of blocks of black pixels in the face area are extracted. There is disclosed a technique for specifying an eye from an aspect ratio of a mass of black pixels. The black pixel clusters are eyebrows, eyes, nostrils, etc., and eye candidates are selected from relative positions such as no left and right eyebrows and nostrils outside the width of eyes, eyes are under eyebrows, etc. Then, the eyes are determined from the aspect ratio of the candidate. Also, in order to shorten the detection time, once an eye is detected, a search area is set in a narrow range around the eye from the next time.

[0004]

According to the above-mentioned publication, once an eye is detected, the search area is set to be narrow.
Sometimes I lost my eyes.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and provides a method for detecting a characteristic part in a face image that can surely and quickly detect a characteristic part in the face image. The purpose is to do.

[0006]

In order to achieve the above-mentioned object, a method for detecting a characteristic portion in a face image according to the present invention comprises: an image capturing step of capturing a human face to obtain a face image;
A search area setting step of setting an area for searching for a predetermined characteristic part from the face image; a characteristic part detection step of detecting a predetermined characteristic part in the search area; and a consciousness level of a person to be imaged And a search area changing step of changing the search area set in the search area setting step based on the calculated consciousness level.

According to this configuration, the search area is set according to the consciousness level of the person to be photographed, so that the search area suitable for the active movement of the face can be set. The activity of the human face, that is, the speed and frequency of the movement, is correlated with the consciousness level of the person, and the movement becomes less active, that is, becomes slower as the consciousness level decreases. If the movement of the face becomes slow, the possibility that the position of the characteristic portion greatly changes from the position detected last time is reduced, so that the search area can be narrowed. Further, since there is a characteristic movement depending on the consciousness level, the shape of the search area can be changed. For example, when the consciousness level is low, the movement of the face in the horizontal direction is reduced as compared with the case where the consciousness level is high, so that the width in the horizontal direction can be further reduced as compared with the vertical direction. As described above, when it is determined that the search area can be narrowed by setting the search area according to the consciousness level, the area is narrowed and the calculation processing time is reduced. In a situation where a larger search area is preferable, the search area is set wider to prevent the disappearance of the characteristic portion.

Further, the search area changing step may be a step of changing a search area in a re-search performed after losing the characteristic portion. According to this, when the characteristic part is lost, the search area is appropriately set according to the consciousness level, so that the characteristic part can be rediscovered more reliably and quickly.

Further, the characteristic portion may be a nostril. The shape of the nostrils is represented as two parallel, substantially circular black regions in the face image, which are suitable as a characteristic portion of the face because there are relatively few individual differences.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for detecting a characteristic portion in a face image according to the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of a drowsy driving prevention device using the present invention. Infrared projector 1
Numeral 0 radiates infrared rays to a region including the driver's face, and a charge-coupled device (CCD) camera 12 photographs the region including the driver's face. In front of the lens of the CCD camera 12, an optical filter that transmits infrared light (around 870 nm) at the center is installed. The image taken by the CCD camera 12 is sent to the blink recognition unit 14, and the time of one blink, that is, the time during which the eyes are continuously closed (eye closing time) is counted. The drowsiness determination unit 16 estimates the driver's consciousness level from the length of the eye-closing time, and determines that the driver is dozing when the eye-closing time exceeds a predetermined time, that is, when the consciousness level falls below the predetermined level. . When the driver begins to fall asleep, an alarm is issued by the alarm unit 18 to call attention to the driver. The dozing determination unit 16 sends the estimated driver's consciousness level to the blink recognition unit 14 and
Then, the operator performs an arithmetic process according to the consciousness level to track the driver's eyes and measure the eye closing time.

FIG. 2 is a flow chart showing the operation of the device for preventing a dozing driving, particularly the blink recognition unit 14.
Is shown in FIG. When the present apparatus is started, it is detected where the driver's eyes are (S100). In the first search step, the position of the driver's face greatly changes depending on the driver's physique, the position of the driver's seat, and the like. Therefore, a relatively large search area is set, and the nostrils are first detected. Since the positional relationship between the nostrils and the eyes does not change much depending on the driver, an area where the eyes are assumed to have eyes is determined from the position of the nostrils, and the eyes are detected in this area. When the eyes are detected, the position of the nostrils at this time,
The positional relationship between the nostrils and the eyes is stored.

When an eye is detected, an eye tracking search is performed (S200). Once the position of the nostril is known, the position of the nostril does not change so much unless the driver performs a very large operation. Therefore, the region of the nostril search is greatly narrowed and the nostril search is performed. When a nostril is detected, an eye search area is determined from the positional relationship between the nostril and the eye, and the eye is detected.
At this time, the eye search area can be made smaller than the area at the time of the first search.

If an eye is detected (S300),
It is determined whether the eyes are closed or open (S
400). On the other hand, when no eyes are detected, re-search control for finding the eyes again is started (S500).
In this re-search, several search areas different from each other in accordance with the time elapsed since the user lost sight of the nostrils are set. If the elapsed time after losing the nostrils is short, the search area is set narrower, and if the elapsed time is longer, the search area is set wider. If no time has passed since you lost sight of the nostrils, it is unlikely that the positions of the nostrils and eyes have changed significantly. Can be shortened. Further, in the re-search, the search area is changed according to the driver's consciousness level at that time.
That is, when the consciousness level of the driver is low, the movement of the face becomes slow. Therefore, the search area is set narrow, and the processing time required for the search is reduced. On the other hand, when the consciousness level is high, the movement of the face becomes faster, so that the nostril can be found early by using a wider search area.

Then, from step S200 to step S
500 is repeated, each time it is determined whether the eyes are closed. Then, the time during which the closed state continues is measured by the dozing determination unit 16, and the dozing state is determined based on the continuous time. Hereinafter, the initial search step S
100, tracking step S200, blink determination step S4
00 and the re-search step S500 will be described in detail.

[0016] The first search routine Figure 3, the first search step S immediately after the device is activated
A detailed control flowchart of 100 is shown. First, a nostril search area is set (S102). In the first search, the position of the driver's nostril differs greatly depending on the driver's physique, seat position, etc., so that the nostril search area 20a has the entire driver's face as shown in FIG. Set to be included. Next, the first timer is set to a predetermined value, for example, 2 minutes (S104). As will be described later, this first timer is used for searching for eyes.
This timer measures the time for searching the same area while changing the binarization threshold. Further, the second timer is set to a predetermined value, for example, 10 minutes (S106). Second
The timer is a timer for measuring the time of the first search, and
If the eyes are not found even after 0 minutes, the driver is warned because there is some abnormality. At the time of the first search, it is considered that the driver has not yet fallen asleep, so that the eyes are searched for a sufficient time.

Next, a threshold value for binarizing the face image is set (S108). On the other hand, the matching between the template of the representative nostril shape and the face image is checked, and a candidate whose matching exceeds a predetermined value is selected (S110). And
A binarization process is performed on the region including each of the selected candidates using the threshold value set in step S108, and a black region is extracted (S112). Then, the two black areas arranged substantially horizontally are detected as nostrils (S114). At this time, if no nostrils are found, the process returns to step S108 (S11).
6) Re-set (change) the threshold for binarization and search for nostrils again.

If a nostril is detected in step S116, an eye search area 22 is set based on the position of the nostril (S118). If the position of the nostrils is known, the area where the eyes are present can be almost specified although there are individual differences. Therefore, the eye search area 22 is set to a slightly wider area 22a as shown in FIG. In addition, the first search area 22a is set slightly lower so as not to cover the eyebrows so that the eyebrows are not erroneously detected as eyes.

Next, in the aforementioned eye search area 22a,
An edge whose brightness changes steeply in the vertical direction is extracted (S
120). There are two types of edges: a negative edge where the brightness drops sharply from top to bottom, and a positive edge where the brightness rises sharply from top to bottom. Is formed. This pair of positive and negative edges is selected as an eye candidate (S122). Then, it is determined whether or not the selected candidate has a substantially elliptical shape as a whole (S124). If it is determined that the shape is a substantially elliptical shape, this is determined to be an eye, the position with respect to the nostril is stored (S126), and this routine ends.

If the positive / negative edge pair is not substantially elliptical in step S124, the first and second timers are counted down (S128). If the first timer is not 0 (S130), the process returns to step S108 to return to the binary Change the threshold value of the activation and start again from the detection of nostrils. First
When the timer is 0, that is, when eyes cannot be detected even after 2 minutes have passed (S130), it is further determined whether the second timer is 0 (S132). And the second timer is 0,
That is, if the eyes cannot be detected even after 10 minutes have elapsed, it is considered that the driver is wearing sunglasses or a mask or there is an obstacle in front of the camera, and the driver is warned of this ( S134), the flow ends.

If the second timer is not 0 (S1)
32), eye search area 22 set based on nostril position
The process of shifting a upward is performed (S136), and 2 minutes are set again in the first timer (S138). As described above, the eye search area 22a set in step S118
Is set lower so as not to detect the eyebrows, so the eyes may be higher depending on the driver. Therefore, the search area is shifted upward in step S136. By shifting it up little by little, only the eyes are extracted so that the eyebrows are not erroneously detected as eyes.

In the above-described initial search routine, a characteristic nostril is detected in the binarized image, and the eye is detected based on this position, so that the eye can be reliably detected. The nostrils are arranged almost horizontally, can be detected as two almost round black areas, and there is little individual difference, so that detection is easy. Also, the positional relationship between the nostrils and eyes,
Since it is possible to specify to some extent that the left eye is on the upper right of the nostril, the search area of the eye can be specified with this positional relationship with high accuracy.

Further, eye detection is performed by edge detection without performing binarization processing. This is because the edge remains even if it is affected by illumination or light from outside the vehicle, so that it is possible to reliably detect the edge. This edge detection itself slightly increases the processing time, but does not greatly affect the processing time as a whole, since the eye search area is limited from the nostril position as described above.

Also, the value 2 set in step S108
The threshold value used for the binarization process
A determination is made whether the value was appropriate. That is,
If no eyes are detected for a certain nostril candidate, it is determined that this candidate was not a nostril. Therefore, an appropriate threshold value can be set by changing the threshold value, performing an initial search, and employing the threshold value when an eye is detected. Therefore, it is possible to ultimately prevent the eyeglasses' edges and eyes from being mistaken for a nostril due to an inappropriate threshold value.

Tracking Search Routine FIG. 6 is a detailed flowchart of the tracking search step S200 performed after the initial search step S100. When the nostrils and eyes are detected in the initial search,
A routine to track these is started. First, based on the driver's consciousness level estimated by the drowsiness determination unit 16, a reduction ratio for changing the size of the nose search area is set. As shown in FIG. 7, the reduction rate is set to a low value when the consciousness level is lowered. In the case of the present embodiment, the reduction rate is normally “1”, and when the consciousness is slightly lowered, “1” is set. 0.8 ", and if further decreased, it is set to" 0.6 "(S201). When the consciousness level is lowered, the search area is narrowed according to this reduction rate as shown in FIG. That is, when the consciousness level is slightly lowered, a rectangle in which the length of each of the vertical and horizontal sides of the rectangle of the search region is 0.8 times that of the normal region is set as a new search region. In the tracking search routine, the normal nose search area 20c is reduced to the area 20e when the consciousness level is lowered.

Next, based on the position of the nostril detected in the previous search and the reduction rate set in step S201, a nostril search area 20 is set around the previous nostril position (S202). This area is a horizontally long rectangular area including the nose, as shown in FIG. 4C or 8B. The area 20c is set smaller than the area 20a at the time of the above-described first search and smaller than the area 20b of the second mode at the time of the re-search described later. This is based on the premise that if a nostril has been detected last time, the nostril can be detected without searching for such a large range this time. Further, the reason why the search area 20c is set to be wide horizontally is that, in the operation during driving, the operation of shaking the head is faster than the operation of shaking the head vertically, so that a wider area is taken in the horizontal direction, and This is to cope with the horizontal movement of the hole.

Then, the inside of the nostril search area 20c is binarized to extract a black area (S204). Then, the two black areas arranged substantially horizontally are detected as nostrils (S2).
06). If nostrils are not detected (S208),
The tracking search routine ends. If a nostril is detected,
The eye search area 22b is set based on the previous positional relationship between the nostrils and the eyes (S210). This search area 22b is shown in FIG.
As shown in (b), slightly larger than the size of the eyes,
It is slightly smaller than the area 22a at the time of the first search. This is because, in the previous search, the positional relationship between the nostrils and the eyes is known, and since the positions of the nostrils in the previous time are known, the positions of the eyes can be specified quite accurately. Then, an edge is extracted in the search area 22b as in the first search (S212). Further, an edge pair in which the positive and negative edges are vertically adjacent is searched (S214), and if there is this edge pair, the position and the position of the nostril are stored (S218). If there is no edge pair (S216), the tracking search routine ends.

As described above, since the previous nostril position and eye position and their relationship are known in the tracking search routine, the nostril and eye search regions 20c, 20e, and 22b are initially searched for in the regions 20a, 22a at the time of the initial search. It can be set smaller. At the time of the first search, it is important to reliably detect the nostrils and eyes as described above, but at the time of tracking, it is required to quickly detect the eyes. In the present apparatus, since the dozing determination is performed with the continuous time of the closed state of the eyes, if the tracking takes a long time, this determination becomes inaccurate or impossible. Therefore, in order to quickly detect the eyes, the most characteristic nostrils are first detected in the binarized image, and the eye search area 22b is narrowed based on the nostrils. Then, the edge detection time, which tends to increase the processing time, is reduced. Furthermore, when the consciousness level of the driver is low, the movement of the face, that is, the movement of the nostrils is considered to be slow. Therefore, the search area is narrowed according to the consciousness level, and the processing time is reduced.

Blink Determination Routine FIG. 9 shows a control flowchart of the blink determination step S400. The eye edge pair detected in the tracking search step S200 is read out (S40).
2) The maximum value of the vertical distance of each pair is set as the eye opening at that time (S404). Then, the degree of opening of this eye is compared with a predetermined threshold value (S406). If it is less than the threshold value, it is determined that the eye is closed (S408). (S41
0). The determination of whether the eye is open or closed is made by the dozing determination unit 1 described above.
6, the consciousness level is estimated, and the drowsiness is determined.

[0030] The re-search routine 10, are control flow chart of the re-searching step S500 is shown. When the nostrils or eyes cannot be detected in the tracking search step S200, the nostrils and eyes must be found quickly so as not to hinder the determination of dozing. Therefore, it is not possible to detect the nostrils and eyes again using the initial search routine. The initial search routine is a routine that aims to surely detect nostrils and eyes even if it takes time as described above, and is not suitable for rediscovering in a short time. In other words, by separately providing the re-searching routine, the search for the nostrils and the eyes is reliably performed over a long period of time in the initial searching routine. Also,
In the re-search routine, there are three types of search modes depending on the difference between the setting of the nostril search area and the setting of the eye search area, and by selecting an appropriate mode,
It ensures that nostrils and eye finding are more accurate. Further, a search area is set according to the driver's consciousness level, so that the nostrils can be quickly and reliably found.

The first re-search mode is a mode corresponding to a case where nostrils have been detected in the previous tracking mode but no eyes have been detected. This mode is for the case where the face movement is not so large because the nostrils are detected, and mainly corresponds to the case where the eyes cannot be detected instantaneously mainly due to lighting conditions etc. . Therefore, the search area of the nostrils and eyes is also the narrow area used in the tracking routine, the area 20 in FIGS. 4 (c) and 5 (b).
c, 22b are used.

The second re-search mode is a mode corresponding to a case where nostrils are not detected in the previous tracking mode. At this time, there is a high possibility that the face is moving, and the search area of the nostrils and eyes is set larger than in the tracking routine. That is, as shown in FIG. 4B, the nostril search area 20b in the second re-search mode is larger than the area 20c in the first re-search mode. However, it is smaller than the area 20a at the time of the first search. Also, as shown in FIG. 5A, the eye search area 22a in the second re-search mode is larger than the area 22b in the first re-search mode, and has the same size as the area in the first search. .

The third re-search mode is a mode corresponding to a case where an eye cannot be found despite searching for a predetermined time in the first re-search mode. In this case, the nostril search area is the same area 20c as in the first re-search mode.
And only the eye search area is enlarged and set to the same area 22a as in the second re-search mode.

Further, the search area in each mode is reduced according to the driver's consciousness level estimated by the drowsiness judging section 16. The reduction rate is set as shown in FIG. 7, as in the case of the above-described tracking search routine. And
In the first and third re-search modes, as shown in FIG. 8B, the search area 20c when the consciousness level is normal is reduced like the area 20e according to the reduction rate. Furthermore, the second
In the re-search mode, as shown in FIG. 8A, the search area 20b when the consciousness level is normal is reduced to the area 20d according to the reduction rate.

When the re-searching routine is started, vertical acceleration is read from an acceleration sensor installed on the vehicle body (S502), and the vertical acceleration is compared with a predetermined threshold (S504). When it is determined that the threshold value is equal to or less than the threshold value, it is further determined whether a nostril is detected in the previous tracking routine (S506). And
If there is a nostril, that is, if no eye (edge pair) is detected in step S216 even though the nostril was detected in the previous tracking routine, the first re-search mode is set (S508). . Then, the first re-search mode timer is set (S510). The set time at this time is a time for shifting from the first re-search mode to the third search mode, and can be changed according to the driver's consciousness level. Since the operation of the driver is early in the awake state and slowed down with a decrease in the consciousness level, when the consciousness level is low, it is unlikely that the nostrils will be lost even if the timer is set for a long time. The set time of the first re-search mode timer is
The consciousness level in the normal state is set to, for example, 200 ms, and is set to a longer time as the consciousness level becomes lower.

On the other hand, if the vertical acceleration of the vehicle body is larger than the predetermined threshold value in step S504, and if nostrils were not detected in the previous tracking routine, the second re-search mode is set. (S512).

Next, based on the driver's consciousness level estimated by the drowsiness determination unit 16, a reduction ratio for changing the size of the nose search area is set (S513). As shown in FIG. 7, the reduction rate is set to a low value when the consciousness level is lowered, as in the tracking search routine. The nostril search area is changed thereafter according to the reduction rate.

After the reduction ratio of the search area is set in step S513, the set re-search mode is set to the second search mode.
It is determined whether the mode is the re-search mode (S514). Second
When the search mode is not the re-search mode, a nostril search area 20c is set around the previous nostril position if the consciousness level is normal, and a smaller area 20e is set if the consciousness level is lowered (S51).
6). These areas 20c and 20e are the same as the nostril search area of the tracking routine as described above. Then, a binarization process is performed in this area to extract a black area (S51).
8).

On the other hand, if it is determined in step S514 that the mode is the second re-search mode, in the first search, the position of the detected nostril is centered and if the consciousness level is normal, the nostril search area 20b Is reduced to the area 20d
Is set (S520). These areas 20b and 20d are
As described above, each of the tracking routine and the regions 20c and 20e in the first re-search mode is set to be slightly larger and smaller than that in the first search. And this area 20
Nose candidates are selected by template matching from b and 20d (S522), and a binarization process is performed on each candidate to extract a black region (S524). As the threshold value at the time of the binarization processing, the value at the time when an eye is found in the initial search routine is used, and the binarization processing can be performed using an appropriate value.

Then, of the black regions extracted in steps S518 and S524, two black regions arranged substantially horizontally are selected as nostrils (S526). At this time, if the nostrils could not be selected (S528), the second search mode is set (S530), and the process returns to step S514. On the other hand, if it is determined in step S528 that there is a nostril, it is determined whether the first re-search mode is set (S532). If the first re-search mode is set,
The eye search area is set to the area 22b, that is, a small area (S534). If a mode other than the first re-search mode is set, the area is set to the area 22a, that is, a large area (S536). Therefore, when the third re-search mode described later is set, the region 22a is set in step S536.

When the eye search area is set in steps S534 and S536, step S1 of the initial search routine is performed.
Edge extraction is performed in the same manner as in Step 20 (S538). Then, in the case of the first re-search mode (S540), similarly to steps S214 to S218 of the tracking routine, a positive / negative edge pair is searched (S542), and if there is an edge pair (S544), its position and nostril are found. Is stored (S546). On the other hand, if it is determined in step S540 that a mode other than the first re-search mode has been set, a positive / negative edge pair is selected as an eye candidate as in steps S122 to S126 of the first search routine (S548). When these candidates are arranged in an elliptical shape (S550), the candidates are detected as eyes, and their positions and nostril positions are stored (S552). When the positions of the nostrils and eyes are detected in steps S546 and S552, the present routine ends.

On the other hand, if no eye is detected, the search is continued. If it is determined in step S544 that there is no edge pair, the first re-search mode timer is counted down (S554), and it is determined whether this timer is 0 (S556). If the timer is not 0, the process returns to step S514 and the search is performed again in the first re-search mode. Timer is 0
, The third search mode is set (S55).
8). The third re-search mode is for expanding the eye search area when no eyes are found within a predetermined time in the first search mode even though a nostril is detected. The probability of detection increases. After setting the third re-search mode, the process returns to step S514, and the search is performed again. If no eye is detected in a mode other than the first re-search mode, the process proceeds from step S550 to step S550.
Returning to 514, a re-search is performed.

As described above, in the re-searching routine, the nostrils and the nostrils are determined based on whether the nostrils have been detected up to the previous time and how long the eyes have not been detected even if the nostrils have been detected. The size of the eye search area is changing. The size of the nostril search area is changed according to the driver's consciousness level. This allows the search area to be narrowed down and re-discovered in a short time when the face is not considered to be moving significantly, while expanding the search area when the face is considered to be moving significantly. Is increasing. In addition, by providing a re-search routine independent of the initial search, the time required for finding an eye during the re-search can be reduced.

Estimation of Eye Position When Face Is Tilt In this embodiment, the eye position is estimated based on the position of the nostrils.
The eye search area is set centering on the estimated position. In particular, a method of estimating the eye position when the driver tilts his / her face will be described below.

FIG. 11 shows the relationship between the position of the nostrils and the position of the eyes when the face is tilted. In the horizontal state (a), the eye position E ₀ (X _E0 , Y _E0 ) is in the direction θ ₀ at a distance r with respect to the center point N ₀ (X _N0 , Y _N0 ) of the two nostrils. At this time, the distance r and the direction θ ₀ are represented by the following equations.

R = {(X _E0 −X _N0 ) ² + (Y _E0 −Y _N0 ) ² } ^1/2 θ ₀ = tan ⁻¹ {(Y _N0 −Y _E0 ) / (X _E0 −X _N0 )場合 When the face is tilted, the orientation of the two nostrils slightly deviates from horizontal as shown in (b). In this case, the nostril position N
_{Even if 0} does not change, the eye position is shifted. If the directions of the two nostrils deviate from the horizontal by an angle δ, the nostril position N
₁ (X _N1 , Y _N1 ) and eye position E ₁ (X _E1 , Y _E1 ) have a relationship represented by the following equation.

X _E1 = X _N1 + r · cos (θ ₀ −δ) Y _E1 = Y _N1 −r · sin (θ ₀ −δ) The position of the eye is estimated as in the above equation, and the eye is centered on this position. By setting the search area of, eyes can be detected more reliably.

Other Embodiments In the above embodiment, the size of the search area is changed according to the driver's consciousness level in both the tracking search routine and the re-search routine. The area may be changed. In this case, the control flow of the tracking search routine is obtained by deleting step S201 from the flowchart of FIG. Once re-discovering a missing characteristic part, even if the characteristic part is lost in the tracking search routine, the routine immediately returns to the routine, so that the processing load of the tracking search routine can be reduced. For example, in the tracking search routine, a search is performed in a narrow area regardless of the driver's consciousness level. If the search cannot be performed in this area, the re-searching routine using the consciousness level is performed again in a shorter time. You can also make a discovery.

In the above-described embodiment, the reduction ratio is set to three stages of "1", "0.8", and "0.6". However, two stages smaller than this and two or more stages are set. It is also possible. It is also possible to set a separate reduction ratio for each routine and each mode. As a result, a more appropriate search area can be set, and the tracking performance and re-discovery performance of a characteristic portion can be improved.

Further, it is possible to make the reduction ratio different between the vertical direction and the horizontal direction of the face image. Thereby, it is possible to cope with the movement of the driver's face showing a characteristic movement according to the consciousness level. For example, when the consciousness level is reduced, the movement of the face in the horizontal direction is reduced, so that the direction can be set to be further reduced.

In the above-described embodiment, the consciousness level is determined based on the behavior of the characteristic portion of the face image such as the eyes.
The consciousness level may be obtained by other means, for example, it can be determined from the frequency and speed of the steering operation. In addition, the consciousness level can be obtained based on the heart rate and brain waves.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a drowsy driving prevention device according to an embodiment of the present invention.

FIG. 2 is a basic control flowchart for blink detection and eye detection according to the embodiment;

FIG. 3 is a control flowchart of an initial eye search routine of the embodiment.

FIG. 4 is a diagram showing a nostril search area.

FIG. 5 is a diagram showing an eye search area.

FIG. 6 is a control flowchart of a tracking routine according to the embodiment.

FIG. 7 is a diagram illustrating a relationship between a consciousness level and a reduction ratio of a search area.

FIG. 8 is a diagram showing a search area changed according to the consciousness level.

FIG. 9 is a control flowchart of a blink determination routine according to the embodiment.

FIG. 10 is a control flowchart of a re-search routine of the embodiment.

FIG. 11 is a diagram for describing estimation of the position of the eyes when the face is tilted in the present embodiment.

[Explanation of symbols]

10 Infrared light projector, 12 CCD camera, 14 Blink recognition part, 16 Drowsiness determination part, 18 Alarm part.

Claims (3)

[Claims] An imaging step of capturing a human face to obtain a face image, a search area setting step of setting an area for searching for a predetermined characteristic part from the face image, and a predetermined characteristic part in the search area A characteristic site detecting step of detecting
A face having a consciousness level calculating step of calculating a consciousness level of a person to be imaged, and a search area changing step of changing a search area set in the search area setting step based on the calculated consciousness level A method for detecting a characteristic part in an image. 2. The method for detecting a characteristic part in a face image according to claim 1, wherein the search area changing step includes:
A method for detecting a characteristic portion in a face image, comprising the step of changing the search region when performing a re-search performed after losing the characteristic portion. 3. The method for detecting a characteristic part in a face image according to claim 1, wherein the characteristic part is a nostril.