Recognition and Perception of Images. Группа авторов
cortex is described on the basis of bottom-up processes (Figure 1.2.15). The internal test squares with the same brightness form a contrast to the gradient ground (Figure 1.2.15, from the left). Moreover, the contrast effect is remained on the ground of sole-colored vertical stripes (Figure 1.2.15, from the right).
The perception of brightness is offered to be analyzed according to two philosophical tendencies: idealistic and materialistic approaches. The theory of contrast is based on the lateral inhibition similar to the principal dialectic laws: contradictions unity, interrelation, transition from quantity to quality, negation of the negation. Some recent researches of the experimental psychophysics and application of mathematical methods of modeling are based on that. To ensure the adequacy of such models it’s necessary to apply the quantitative representation of complex psychical processes on the basis of dialectic law of interaction between the part and the whole.
In the process of perception of visual information contours play a significant role. Using contours, we recognize the shapes, edges, and borders of surrounding objects. To study the neural mechanisms of perception of the contours, you can use the visual system of the horseshoe crab. The eye of the horseshoe crab is structurally complex and consists of about 1,000 receptors (ommatidia). Each receptor has its own neuron and optic nerve, which responds to the light signal independently of the adjacent receptors. They are not related to each other; stimulation of one receptor is not transmitted to the next. However, at a higher neuronal level, adjacent receptors are connected by lateral nerve fibers, while simultaneous stimulation of neighboring receptors results in the summation of their activity.
Figure 1.2.15 Brightness assimilation [Ghosh, Bhaumik, 2010].
Illumination of one receptor reduces the sensitivity of its neighboring receptors, and lateral inhibition occurs. When simultaneously illuminated, each receptor responds less actively than in the case of individual stimulation. Similarly, the ganglion cells of the human retina function in a human; they have complex interrelationships and are not individually excited. Neural connections using lateral braking affect the activity of each other, thereby ensuring a clear perception of edges and boundaries.
1.2.6 Mach Bands, Hermann’s Grid
To demonstrate the effect of lateral inhibition, consider the stepwise stretching of gray color in Figure 1.2.16. The left side of each vertical rectangular strip will appear a little lighter than its right side, which causes an increase in edge contrast. However, each strip has the same lightness; it is filled with a uniform gray color. This can be easily seen if we examine each rectangle alternately, covering the others. The effect of changing the lightness of the marginal sections is named after the 19th-century German physiologist Ernst Mach, who first described this phenomenon [Abbasov, 2016].
Spatial frequencies
Contrast areas of the surrounding field of view can be characterized by spatial frequency, i.e., the number of luminosity variations in a certain part of space. For experimental confirmation, consider Figure 1.2.17. The left upper lattice has a relatively low spatial frequency (wide bands), and the lower one has a higher frequency (narrow bands). The spatial frequencies (bandwidths) of the grids in Figure 1.2.17, on the right are identical and they occupy an intermediate position. Cover the grids in Figure 1.2.17, on the right and for at least 60 s, carefully examine the grids in Figure 1.2.17, on the right, fixing the view on the central horizontal strip between the gratings. After completion of the adaptation period, translate the view into the strip in the center between the two gratings in Figure 1.2.17, on the right. Spatial frequencies will no longer seem identical: the spatial frequency of the upper lattice will seem higher (denser) than the spatial frequency of the lower lattice [Shiffman, 2008], [Gusev, 2007].
Figure 1.2.16 Mach bands.
Figure 1.2.17 Spatial frequency.
Consider the effects based on the phenomenon of lateral inhibition, these include the lattice of Hermann and light contrast. Figure 1.2.18 shows the German grid (German physiologist Ludimar Hermann in 1870), it consists of a white square grid pattern on a black background. The lightness of the white stripes is the same along the entire length; however, phantom gray spots will appear at their intersections. They are due to the suppression of the neural activity of neighboring cells of the retina. If we concentrate our gaze on a separate point of intersection, the gray spot will disappear. In this case, the image is projected on the central fossa, and gray spots appear on other crosshairs, which will be projected on the peripheral areas of the retina with high sensitivity.
Figure 1.2.18 Hermann’s grid.
Figure 1.2.19 “Complementary” grid of Hermann.
You can observe the colored spots on the crosshairs; for this you can choose a grid and a background complementary in color. Such a color grid is shown in Figure 1.2.19, blue spots will appear on the yellow cross hairs [Abbasov, 2019]. When scaling Hermann’s grid, the “phantom” spots will be more stable; for this it is necessary to move the pattern away to the projection of the grid on the retina. From a long distance, the stripes will narrow and phantom spots will be visible regardless of the gaze fixation.
1.2.7 Light Contrast
A further example of the spatial interaction of neighboring areas of the retina is light contrast. It lies in the fact that the lightness of a small closed figure depends on the intensity of lightness of the massive background area (Figure 1.2.20) [Abbasov, 2016]. From the point of view of light reflected by them, all four central gray circles are identical; however, it seems that they differ in lightness. A circle on a dark background (left edge) seems lighter than a physically identical circle on a light background (right edge). Therefore, this means that the perceived lightness of the surface depends on the intensity of its background.