الترشيح بالانعكاس .. كتاب التصوير الملون ، الكاتب عبد الفتاح رياض

reflection filter:

Our sense of the colors of objects is nothing more than a sense of the color of the rays reflected from them, and this can be explained more accurately if we mention that the white rays are what the body filters by reflection, not by permeation, as is the case with transparent optical filters. The object appears to us in a red color, for example, because it filters the white light that falls on it, absorbing the blue and green rays and reflecting the red rays alone. when falling on an object.

According to the foregoing, we find that the colors of objects must change if colored rays fall on them, so the body that we see is red changes color if yellow rays fall on it, for example. For example, if we shine red rays on a cyan-colored robe, it appears to us to be black, because the red color is complementary to the cyan-blue. The explanation for this is clear, as when the red filter was placed in front of the light source, it absorbed the blue and green rays, and allowed the red rays Only by passing through it, and if it falls on the blue-green robe, it will in turn absorb these red rays when they fall on it, so it will appear black, as it will not reflect rays of any color at all, and therefore it appears black.

Cyan completely. In the previous example, we assumed that the optical filter was of a pure spectral red color, and we also assumed that the color of the robe was greenish blue (that is, a color complementary to red). These are theoretical assumptions that are difficult to achieve in practice, as it is not expected that we will get colors Spectrum is always pure, whether in relation to the color of the filter or the robe, and therefore the robe often appears in a dark color, not black, when this experiment is carried out in practice.
In support of this, we mention what we see with our eyes in nature, if we look, for example, at green trees through a red filter, then these trees appear dark red, which contradicts what was previously mentioned about the red filter absorbing green and blue rays and allowing only red rays to pass through, as it was supposed to To see green trees appear black when looking through the red filter, because this filter absorbs green. However, the matter becomes clearer if we know that the trees are not completely green in nature, but rather combine green, red and yellow colours. That is why they reflect all these colors, and then they appear red when we look at them through the red filter, and they do not appear black. This is the case with most of the colors that we see in nature. It is rare to find pure spectral colors in nature, whether in relation to objects or in relation to them

for the filters themselves. And if we follow the previous method, and give another example of a blue surface on which yellow rays fall (i.e., of a color complementary to blue), and we assume that the two previous colors were completely pure and not mixed with any other colours, then this blue surface must appear black. Likewise, if we assume the opposite, that is, if we assume that the color of the surface was pure yellow, and that the rays falling on it were pure blue, then the yellow surface would appear completely black. This result is supported by what we see when lighting a blue surface with a candle or an oil lamp - the blue surface appears dark because the surface is dark. Rays in which the percentage of red or yellow rays exceeds blue rays (1). emitting light source

(1) For this reason, shops selling fabrics tend to use artificial lighting that is almost similar in color to natural daylight, and it is not recommended to examine the color of fabrics in the light of fluorescent lamps that have an increased percentage of blue rays

The difference between filtering by reflection and filtering by imagination (1) Filtering by Reflection Drop white rays on a red apple and it absorbs green and blue rays and reflects red rays

(B) Filtering by Transmission: The white rays fall on a white transparent bottle filled with a transparent red liquid, so it absorbs the green and blue rays - so only the red rays are permeated. In the figure, the red rays are symbolized by the black part of the arrow.

Mixing colored pigments with each other:

Some of the previous results may seem strange to our minds, because we are used to seeing other different results when mixing dyes, such as paint colors, for example. Therefore, we explain the following inconsistency:

White rays fall on a pigment or dye of a certain color. This dye absorbs some of the components of the white rays and reflects the rest. For example, the yellow color absorbs all blue rays (as they are complementary to its color) and reflects the rays that make up its color (which are red and green). In yellow, on the other hand, we find that the cyan color (greenish blue) also absorbs red rays and reflects blue and green rays. While Complementary

We have explained in the following table the natural result that results from mixing two dyes, one yellow and the other blue-green (cyan). We have marked with (-) the rays that the dye absorbs, and with a (+) mark for the rays that are reflected.