## 4 Discussion  
There is currently no gold standard for assessing the effectiveness of laser dye removal. Qualitative scales are the most commonly used. These studies are based on expert evaluation of images before and after the laser dye removal procedure. It should be noted, however, that qualitative studies have a number of disadvantages, including that it depends on the expert's experience, they do not allow for a quantitative assessment of the effectiveness, and they do not allow the comparison of the effectiveness of the procedure in relation to different dyes, themes, colors. In addition, photos taken with the use of digital cameras are most often evaluated, which means that the method and quality of lighting can significantly affect the assessment of the results. Even a small change in the color temperature of the light illuminating the skin will bring significant differences in the assessment. Hyperspectral imaging is devoid of the above-mentioned disadvantages. It is independent of expert evaluation and is quantitative and repeatable. The color of the dye is significant and has a significant impact on the subjective perception of the effectiveness of permanent makeup removal. Importantly, the color of the analyzed spots (pixels) depends on the type of incident light. Thus, simple methods of statistical analysis and methods of image analysis and processing do not work well in recognizing skin/dye characteristics. In hyperspectral imaging, color is represented by the radiation reflection vector over a wide range of wavelengths. This gives a definitely different set of information than the three-component RGB system and allows for a multi-faceted and multi-perspective analysis of the assessed objects (skin surface) and, thus, very high accuracy in mapping skin/pigment features [21; 33; 34]. A relatively new method of acquiring image data is hyperspectral imaging. It provides much more information about the examined object compared to traditional digital photography because a hyperspectral image consists of several hundred individual images recorded at precisely-defined wavelengths. Data can be recorded in a wide range of electromagnetic radiation--from ultraviolet through the visible range to infrared [24]. Figure 12: Homogeneity in GLCM analysis before and after laser application. HSI has been used in the diagnosis of precancerous conditions, squamous cell carcinoma of the cervix, and gastric cancer. It is also useful for assessing tissue oxygenation in ischemic wounds and for assessing the risk of foot ulceration in diabetes [35]. It is also used to measure the content of skin chromophores: melanin and hemoglobin [36]. Apart from being used for medical research, the hyperspectral camera can be used to present the effect of cosmetic procedures, such as permanent makeup removal. Selective absorption of laser energy by the dye is a prerequisite for its effective removal without damaging the adjacent structures [25]. Regarding the variety of colors used in permanent makeup, the most effective wavelength should be selected so that the maximum level of dye absorption coincides with the wavelength of the laser. The proposed method of hyperspectral imaging allowed for a quantitative assessment of the spectral parameters of the dyes used in the study and, thus, for optimization of the laser parameters necessary for their removal. [PERSON] et al. [14] used hyperspectral imaging to select the most effective type of laser for removing the red pigment of permanent lip makeup. The minimum reflectance observed in the cited study occurred for the wavelength of 487 nm, and the maximum was observed in the range of 700-800 nm. While selecting the wavelength, it was important to determine the minimum reflectance. The higher the reflectance, the more radiation is reflected from the skin surface [14].