نصوع اللون .. كتاب التصوير الملون ، الكاتب عبد الفتاح رياض

(-) - Brightness: An explanation of what we mean by color brightness. For example, a colored object reflects light waves within the wavelengths of pure red spectral rays, and this body is lit by a light source 50 cm away from it, and it emits completely white rays, so what happens? If that distance increased gradually?

So we say that the origin of the hue color is to change, as the lengths of the reflected light waves have not changed, and the degree of color saturation will not change, as no new amount of neutral color has been added to it, but the degree of brightness of the color will gradually change as the light source is far from the colored object. , as a result of the decrease in the light energy falling on it, either due to the distance of the light source or the decrease in the light energy it emits, although there has been no change in the spectral characteristics of the rays. The answer for y

This, if the source of light continues to move away gradually from the body to a very large distance, then darkness will prevail, so that all colors appear black. If these rays decrease or disappear completely after the light source is completely gone, there will be no reflected rays, and therefore no visible colors will appear to us.

As for the developments that occur during the stage of moving away from the light source, gradually moving away from these colored surfaces or objects; It depends on the origin of the color, and it will appear from our observations that:- (1) The red color will appear red-brown, then gradually darken until it reaches the stage of blackness. (b) The orange color will appear brown, gradually darkening until it reaches the stage of blackening.

His sight, which until now we have overlooked another factor that directly affects our visual report of the brightness of the color, and this factor is e and e) the subjectivity of the seer, and the extent of his safety. depends on him for judgment.

(c) The yellow color will appear yellow-brown, and will gradually darken until it reaches the stage of blackening.

(d) The green will appear olive green, gradually darkening until it reaches

blackening stage.

(e) White will appear light gray, then gradually darken until it reaches

blackening stage

We have relied on the above-mentioned objective factor in judging color luminance. This factor is the amount of light energy reflected from the object or colored surface, and the extent to which this quantity increases or decreases as a result of the distance or proximity of the light source, or as a result of its strength or weakness.

Therefore, we must differentiate between two types of color brightness: Objective brightness.

Apparant brightness (1) True color brightness:

That property that characterizes colors and that can be measured as by physical means, so that no two people differ in its assessment, even if the one who estimates it is visually impaired, and therefore we can call it Objective Brightness. he

(b) apparent luminance of colours:

It is the brightness that appears to the eye, and it cannot be relied upon as a basis for judgment. Judgment on it may differ from one person to another.
From that, the judgment of a single individual with sound vision may differ if the light level is weak from his judgment if the light is strong, as this is subject to psychological factors related to each individual in particular, and the extent of his ability to express. The name of a color that he sees or the degree of apparent brightness that he senses, as it is subject to physiological factors related to the nature of vision in humans in general, because there are (in general) two types of cells in the follicles of the retina in the human eye.

In the eye, Fovea centralis, these two types are rods, and cones, and the first is used when the light level is low, and they are cells that are not sensitive to colors, and therefore we are unable to perceive colors in the dark. . The second is due to the sense of color

When the additional level is high. High Brightness level. It follows from the different characteristics and function of each of these two types of cells that the color luminance differs in the two cases of vision in strong light, and vision in weak light. The inability of the eye to estimate the ratio between the apparent luminance of two different colors (yellow and green (for example) is manifested if the vision is in the two light conditions referred to in Figure 23, and these two light conditions are: - A - vision in strong light such as sunlight) and in this case the cells work Cone vision) and this case is known as Cone Vision with vision in weak light (in this case the rod cells work) and it is known as Rod Vision. We conclude from Figure (23) that the relative estimate of the luminance of two different colors in changing light conditions is to be a correct estimate.

Now that we have reviewed both cases of color luminance, you will find that the correct judgment is the one that is based on methods of measurement by natural means by means of optical devices.