Colour cast
Under color cast is understood in the color theory, a hue, a shift of one color to another color stimulus. The term is defined in DIN 55980.
Color theory
In general, variations of colors by the color names of the primary colors are described to the tendency of the present color.
- Blue tint, a color cast into the blue, also referred to as bluish, the color offered is bluer than desired.
- Green tint, which is greenish,
- Reddish tint, which is reddish,
- Yellow tinge, which is yellowish.
- Turquoise engraving, or even Cyanstich is less common.
The names purplish or magenta tint are not used in practice. Instead, blue-violet color casts as bluish and accordingly the red tones (ie ultimately to the blue side of the color wheel ) have a coloring for magenta are referred to as blue.
The gray hue called in bright colors less saturated colors, the achromatic there is a darker white or a lighter black. So has a white piece of fabric after repeated wash a gray tinge.
Brown stitch is used as a name in muted shades for the warmer shade.
As color tipping a color cast is called, vary in the different gray values to different colors with different intensity back.
The definition and use of color cast is not uniform. In common parlance, in the description of color variations that term is used in addition to the adjective form for the type of color names. The fresh leaves in May, the May Green is a yellowish green or yellowish green, it has " a stitch more into the Yellow " as the foliage in summer.
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A yellow tinge in textiles, paper and plastics is also referred to as the " yellowing ". In addition to yellowish substances that already exist in the crude, yellow products when molecules are broken down and decomposed by aging processes. Particularly disturbing is the one-sided yellowing, as it occurs on edges or exposed areas.
Earlier it was this yellow tinge or brownish tinge, so the yellow discoloration particularly of achromatic surfaces, fixed with laundry blue. A surface degradation products are removed by bleach. A current path are preventive additives of optical brighteners or additives that prevent degradation and are used especially in plastics.
Determination of the measure
The Stichigkeit While theoretically colorimetrically detectable, but is subject to personal variations in color perception, as in the case of turquoise (as blue or green ). Nevertheless, the recognition of color casts part of the basic requirement in the use of colors and can be trained.
Reproduction
In the color reproduction, a deviation in color matching the desired color pattern is to be avoided. This is attempted by color standards, as
- Standard light types,
- Standard color systems CMYK Euro scale in four-color printing
- Color calibration as through color management in the IT field
- Color profiles for monitors
Color cast in photography
In a photograph of a deviation in the tone of the image of the natural colors is usually undesirable. Most common cause of color casts that occur when recording, is a non-matching to illuminate color sensitization of the photographic film and an incorrect white balance for digital cameras. Another typical cause is too warm or far beyond the best before date mounted footage. In addition, the Schwarzschild and the short-term effect at extremely long or short exposure times.
Too dark or artificial lighting is a common cause for the color cast in a photo. Modern digital cameras have a built-in correction of the colors in order to avoid a color cast. This automatic fix works but not always accurate and not in any lighting. The color cast can be corrected or eliminated subsequently by means of digital image processing.
Also, a wrongly chosen temperature in the development of color photos can cause a change in hue. Color casts can also result from incorrect elaborations, storage and aging of the film material, transportation, x-rays or aging of the paper image.
In addition, the digital photography process and color spaces used by the camera, the monitor and the setters and printers have a decisive influence on the correct color reproduction.
Causes a color cast
Different types of tint are possible:
It can also occur several types of tint: Has photographed with a daylight film under incandescent light, for example, first images are expected, which are yellowish in the light areas. Now the machine for the production of prints used but foolishly the overall impression of the image to pick out the " perfect " filter. This creates additionally a blue tint in the dark areas of the image.
A color cast also occurs when the identity color is not accurately represented, but still acceptable.
Ways to correct
With relatively little effort, a color cast correction of an image-editing software is possible. As long as none of the color channels will be overridden, good results are obtained. However, it should be trying to avoid a color cast during recording to produce the negative, the file or other original image, in the best possible quality.
A color cast correction by optical means is associated with high costs. Cheap supplier of paper prints prefer an automatic setting, so that the overall impression of the image is neutral gray. Through very hard contrasts of color cast in the light and dark areas is removed, however, arise with gaudy surfaces without drawing. The image information is permanently damaged in such a case and can no longer be restored by image processing software. For this purpose, then scanning the negatives and the calculated reversal is better.