Another frequent cause of the apparent absence of contrast is the presence of narrow dark intermediate fields, such as are formed by bordering a field with black lines, or by the shaded contours of objects.When such fields interfere with the contrast, it is because black and white can absorb much color without themselves becoming clearly colored; and because such lines separate other fields too far for them to distinctly influence one another.Even weak objective differences in color may be made imperceptible by such means.
A third case where contrast does not clearly appear is where the color of the contrasting fields is too weak or too intense, or where there is much difference in brightness between the two fields.In the latter case, as can easily be shown, it is the contrast of brightness which interferes with the color contrast and makes it imperceptible.
For this reason contrast shows best between fields of about equal brightness.
But the intensity of the color must not be too great, for then its very darkness necessitates a dark contrasting field which is too absorbent of induced color to allow the contrast to appear strongly.The case is similar if the fields are too light.
To obtain the best contrast-effects, therefore, the contrasting fields should be near together, should not be separated by shadows or black lines, should be of homogeneous texture, and should be about equal brightness and medium intensity of color.
Such conditions do not often occur naturally, the disturbing influences being present in case of almost all ordinary objects thus making the effects of contrast far less evident.To eliminate these disturbances and to produce the condition most favorable for the appearance of good contrast-effects, various experiments have been devised, which will be explained in comparing the rival theories of explanation.
There are two theories -- the psychological and the physiological -- which attempt to explain the phenomena of contrast Of these the psychological one was the first to gain prominence.Its most notable advocate has been Helmholtz.
It explains contrast as a DECEPTION OF JUDGMENT.In ordinary life our sensations have interest for us only so far as they give us practical knowledge.
Our chief concern is to recognize objects, and we have no occasion to estimate exactly their absolute brightness and color.Hence we gain no facility in so doing, but neglect the constant changes in their shade, and are very uncertain as to the exact degree of their brightness or tone of their color.
When objects are near one another "we are inclined to consider those differences which are clearly and surely perceived as greater than those which appear uncertain in perception or which must be judged by aid of memory,"
just as we see a medium sized man taller than he really is when he stands beside a short man.Such deceptions are more easily possible in the judgment of small differences than of large ones; also where there is but one element of difference instead of many.In a large number of cases of contrast, in all of which a whitish spot is surrounded on all sides by a colored surface -- Meyer's experiment, the mirror experiment, colored shadows, etc., soon to be described -- the contrast is produced, according to Helmholtz, by the fact that "a colored illumination or a transparent colored covering appears to be spread out over the field, and observation does not show directly that it fails on the white spot." We therefore believe that we see the latter through the former color.Now "Colors have their greatest importance for us in so far as they are properties of bodies and can serve as signs for the recognition of bodies....We have become accustomed, in forming a judgment in regard to the colors of bodies, to eliminate the varying brightness and color of the illumination.We have sufficient opportunity to investigate the same colors of objects in full sunshine, in the blue light of the clear sky, in the weak white light of a cloudy day, in the reddish-yellow light of the sinking sun or of the candle.Moreover the colored reflections of surrounding objects are involved.Since we see the same colored objects under these varying illuminations, we learn to form a correct conception of the color of the object in spite of the difference in illumination, i.e.to judge how such an object would appear in white illumination; and since only the constant color of the object interests us, we do not become conscious of the particular sensations on which our judgment rests.So also we are at no loss, when we see an object through a colored covering, to distinguish what belongs to the color of the covering and what to the object.In the experiments mentioned we do the same also where the covering over the object is not at all colored, because of the deception into which we fall, and in consequence of which we ascribe to the body a false color, the color complementary to the colored portion of the covering."
We think that we see the complementary color through the colored covering, -- for these two colors together would give the sensation of white which is actually experienced.If, however, in any way the white spot is recognized as an independent object, or if it is compared with another object known to be white, our judgment is no longer deceived and the contrast does not appear.
"As soon as the contrasting field is recognized as an independent body which lies above the colored ground, or even through an adequate tracing of its outlines is seen to be a separate field, the contrast disappears.Since, then, the judgment of the spatial position, the material independence, of the object in question is decisive for the determination of its color, it follows that the contrast-color arises not through an act of sensation but through an act of judgment.
