Abstract
Texture plays an important role in computer vision in expressing the characteristics of a surface. Texture complexity evaluation is important for relying not only on the mathematical properties of the digital image, but also on human perception. Human subjective perception verbally expressed is relative in time, since it can be influenced by a variety of internal or external factors, such as: Mood, tiredness, stress, noise surroundings, and so on, while closely capturing the thought processes would be more straightforward to human reasoning and perception. With the long-term goal of designing more reliable measures of perception which relate to the internal human neural processes taking place when an image is perceived, we firstly performed an electroencephalography experiment with eight healthy participants during color textural perception of natural and fractal images followed by reasoning on their complexity degree, against single color reference images. Aiming at more practical applications for easy use, we tested this entire setting with a WiFi 6 channels electroencephalography (EEG) system. The EEG responses are investigated in the temporal, spectral and spatial domains in order to assess human texture complexity perception, in comparison with both textural types. As an objective reference, the properties of the color textural images are expressed by two common image complexity metrics: Color entropy and color fractal dimension. We observed in the temporal domain, higher Event Related Potentials (ERPs) for fractal image perception, followed by the natural and one color images perception. We report good discriminations between perceptions in the parietal area over time and differences in the temporal area regarding the frequency domain, having good classification performance.
Highlights
Visual perception is a complex process, enveloping various sub-processes
Texture analysis is of particular interest in various domains like computer vision, biomedical sciences, medical imaging, geographic information systems and many more [2], while fractal models are very popular for generating synthetic color textures
We evaluate the brain responses to two distinct groups of images, natural and fractal synthetic textures, with similar complexity ranges according to Color Fractal Dimension [31], in comparison with reference images of no complexity
Summary
Visual perception is a complex process, enveloping various sub-processes. The visual information crosses through the optical system and along with light excites the retina’s photoreceptors. The definition of color image complexity requires objective compensatory measures, such as the underlying processes of the neural activity itself In this sense, one technology that proved to be suitable for recording and interpreting the neural activity is electroencephalography (EEG), technique widely used in visual perception research which records the cortical electrical activity [21,22,23,24,25]. The ERP responses provide information about the visual and cognitive processes [30] and along with investigations on the oscillations in different frequencies will shade a light into the human interpretation of the complexity of fractal and natural textures, as this research will further demonstrate. The study proposes the investigation of first visual perception triggered by subconscious processes and cognitive human interpretation over the complexity of color images (conscious), both synthetic fractal and natural texture images, in an experimental study with healthy participants.
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