9. Temperature distribution on the eyes

Relative results are demonstrated in Figure 12. A neural structure of [9 30 1] was trained using data from person 1 and tested using the data from person 2. At the left of Figure 12 the face should be black recognized as belonging to the sober person, while at the right it should be white since it corresponds to the drunk person. The depicted performance is satisfactory and an operator can discriminate the sober from the drunk easily. It is worth emphasizing that according to the images in Figure 12, the pixels on the forehead and the nose are correctly

Since the forehead is a very promising location on the face for intoxication identification, the above procedure was repeated only on the region of the forehead for all persons participated in the experiment. The area employed was shown in Figure 13. Accordingly, the neural structures are trained with the data from one person and tested with the data from the rest persons. The use of the forehead area for intoxication identification led to two significant conclusions: (a) The small neural structures have better identification performance since they achieve better generalization behavior during training. (b) Their success is on average 90%.

Figure 12. Results obtained when a neural structure of [9 30 1] was trained using data from person 1 and tested using the data from person 2. At the left the face should be black recognized as belonging to the sober person while at the right it

Figure 13. The black region on the forehead of the persons was employed to test the neural structures for identifying

classified in almost all cases.

162 Human-Robot Interaction - Theory and Application

should be white since it corresponds to the drunk person.

drunk persons.

Temperature distribution on the eyes of sober and drunk persons is studied by means of thermal infrared images (Figure 14). It is observed that the temperature difference between the sclera and the iris is zero for the sober person and increases when somebody consumes alcohol (Figure 15). For the drunk person, iris appears darker compared to sclera which means that the sclera temperature increases. This is something expected since the sclera is full of blood vessels which present increased activity when the person consumes alcohol. Thus, in a screening procedure for drunk identification, the infrared images of the sober person are not needed. Although in most cases the sclera is brighter than the iris for the drunk persons, in case that their gray level difference is very small, histogram modification algorithms can be used to enhance this difference and show off intoxication. In order to express the confidence of the method in drunk person discrimination, the Student t-test was employed. The results gave over 99% confidence of the discrimination inference.

Specifically, for the 28 among the 41 people who participated in the experimental procedure, it is evident by a simple comparison of the thermal images that the sclera becomes hotter compared to the iris after alcohol consumption. The images in Figure 15, where the iris is darker than the sclera (right), have not undergone any kind of preprocessing. This difference between the sclera and the iris becomes evident for four more persons when a histogram equalization algorithm is applied. Initially, for all these sober persons the sclera and the iris appeared with the same gray level as being in the same temperature (Figure 15, left image). Finally, four more persons presented this difference when a histogram clipping algorithm was applied which clips all values below 0.5 and above 0.75 of the gray level range and after that stretches the remaining histogram to its full range (MATLAB imadjust ([0.5 0.75], [0 1])). For five persons who used to drink alcohol and their breathalyzer indication was below 0.4 mg/L, it was not possible to show off the difference between the sclera and the iris.

Figure 14. Sclera is surrounding iris which is actually a muscle controlled part of the eye to adjust the size of the pupil. Sclera lies on a net of blood vessels.

(SVMs) are employed for feature extraction and classification. Two different approaches are employed for extracting the isothermal regions of the face giving continuous vectors for intoxication identification. In the first one, the histogram of the face is divided (both of the sober and the drunk person) into equal regions. In the second approach, we examine in which isothermal region the whole forehead lies for the sober and the drunk person and which other regions of the

Intoxication Identification Using Thermal Imaging http://dx.doi.org/10.5772/intechopen.72128 165

Anisotropic diffusion was applied on the thermal infrared images for smoothing boundaries before extracting the isothermal regions. Specifically, anisotropic diffusion [28, 34] is used for noise removal, homogenization of regions, and detail preservation. The morphological feature vector called pattern spectrum [25, 26, 35] is extracted from the isothermal regions and transferred to the SVMs [36–38] for recognition of intoxicated persons. The identification success is

Arbitrary determination of each isotherm is min and max (e.g. based on the minima of the

Figure 16 illustrated one example for each case. Experimentation on these four different types of isotherms revealed that only two of them are suitable for identifying drunk persons. Specifically, the first and the fourth type of isotherms, that is, equidistant and arbitrary determination as stated in the begging of the section. Using these two different types of isotherms in combination with anisotropic diffusion and morphology, isothermal features have been extracted for

In the first approach, the histogram of the face, both of the sober and the drunk person, is divided into equal regions. It was found that the best number of isothermal regions is eight. In this case, we have the maximum perceptual information on the different isothermal regions. The majority of the pixels on the face belong to the two higher regions with pixel values from 191.25 up to 255. These two regions (191–223.125 and 223.125–255) occupy almost the whole face and their shape will be used to discriminate between sober and drunk. The shape also of the whole isothermal region 191.25–255 will be tested for identifying intoxicated persons. In Figure 17(a) and (b), the regions 191.25–223.125, 223.125–255 and the whole region 191.25–255, respectively, are shown in red. The regions become larger in case of the drunk person as it is easily recognizable. Accordingly, someone can decide which person is the drunk, if both red images are available. The basic problem is that the images of the sober person are never

In the second approach, features that could help to recognize the drunk person without using the images of the sober counterpart, were tested. Accordingly, it is examined in which of the isotherms the forehead lies for the sober person and which other regions of the face are within

available and thus in real problems, there is not any capability of comparisons.

face are within these isotherms.

found to be over 80% which is considered satisfactory.

• Equidistant in the histogram range (0–255).

• Isolation of a single isotherm on the image.

• Equal populated in the histogram range.

identifying intoxicated persons.

histogram).

Initially, four different types of isotherms were implemented, as follows:

Figure 15. The left thermal image corresponds to the face of the sober person while the right to the face of the corresponding drunk person. For the drunk person the sclera becomes hotter from the iris.

The temperature difference between the sclera and the iris was examined [4, 6] based on the statistics of the pixels in these two regions by means of two different estimation procedures which correspond to two different discrimination features. In the first procedure, the ratio of the mean value of the pixels inside the sclera to the mean value of the pixels inside the iris was calculated. This procedure was performed on the left eye of each participant, both in the case he is sober and when he consumed alcohol. Consequently, two ratios of the mean value of the sclera to the mean value of the iris are available. It is observed that the ratio of the mean pixel value on the sclera to the mean value of the iris increases when the person has consumed alcohol. Specifically, for the 36 from the 41 cases, the specific ratio increases with alcohol consumption while only in 2 cases it decreases, and in the rest 3 it remains almost the same. The results were analyzed using the Students-t test, in order to support statistically the drunk screening capabilities of the proposed method from eye thermal images. In the second procedure, is estimated the variance of the pixels contained in the whole eye. This evaluation was performed for the left eye of each participant when the person is sober and when he is drunk. Therefore, two variances for each participant have been calculated, corresponding to sober and drunk person, respectively. It is observed that the variance increases in case that the person has consumed alcohol. Specifically, among the 41 participants only 4 presented decreased variance in the region of the eye for the drunk person compared to the sober one.

The proposed method presents the advantage that there is no need for comparison with the image of the sober person to infer for the intoxication situation. Simply, if an inspected person presents a gray level difference between the sclera and the iris, it has to be further tested for alcohol consumption with conventional means.
