Textile printing and dyeing color matching details

1. Light and Color Light is an electromagnetic wave with a wide range of wavelengths. The light that our eyes can see, that is, visible light, is only a very small part of the electromagnetic waves, and its wavelength is between 400 and 700nm. Light is emitted by a light source. Common light sources include the sun, lamps, flames, etc. Objects will display a variety of colors, and the fundamental reason is that they have the characteristic of selective absorption of light. When the sun shines on an object, the object can selectively absorb light in a certain wavelength range, and reflect the rest of the wavelengths of light into the human brain, thus giving an impression of what color the object displays. For example, blue objects absorb red and yellow light and reflect blue light, and yellow objects absorb red and blue light and reflect yellow light. Therefore, the color of an object can be considered as a stimulating effect on the human eye caused by the light emitted by the light source after a series of absorption, reflection and other effects of the object.

2. Basic properties of color Generally speaking, colors can be divided into two categories: chromatic and achromatic. Achromatic is also called achromatic, black, white, gray, etc. are all achromatic. All colors other than non-colors are called colors. All colors have relatively obvious absorption of a certain part of the wavelength of visible light. Through the study of color, people have discovered that all colors in nature can be described by three attributes: brightness, hue and saturation. Brightness is an attribute that indicates the brightness of an object’s surface. Among non-colors, the bright color is white, the dark color is black, and different grays are distributed in between. That is to say, the brightness of white is high, the brightness of black is low, and the brightness of gray is between white and black. Different colors also have different brightness levels. Generally, bright colors have higher brightness, while darker colors have lower brightness. If it is also red, the brightness of dark red is lower than that of light red. Hue is the property that distinguishes colors from each other. Radiation at different wavelengths of the visible spectrum appears in various visual hues, such as red, orange, yellow, green and blue, etc. The hue of the surface color of an object is determined by three aspects: one is the spectral composition of the illumination source, the other is the object’s light absorption and reflection characteristics, and the third is different observers. The hue of a luminous object is determined by the spectral composition of its light radiation. The hue of a non-luminous object is determined by the spectral composition of the illuminating light source and the spectral reflection characteristics of the object itself. Saturation refers to the purity of a color. Monochromatic light in the visible spectrum is a saturated color, which is 100%. The level of saturation can be understood from the mixture of spectral colors and white light. Any color can be regarded as a mixture of white light and spectral colors. At this time, the more components of white light, the lower the saturation. The fewer components of white light, the higher the saturation. White, standard gray, and black have low saturation, which is 0 or no saturation. Generally speaking, the brightness is determined by the shade of the colored substance, the hue is determined by the color of the colored substance, and the saturation is related to the vividness of the color. However, these relationships are often not simple linear relationships. For example, the relationship between saturation and vividness is complex, largely because saturation is a colorimetric concept, while vividness is influenced by considerable psychological factors.

For these three attributes of color, people often use a sphere-like model in three-dimensional space to represent them, as shown in Figure 2-1. The vertical axis in the figure represents brightness, the ring around the vertical axis represents hue, and the distance from the vertical axis represents saturation.

3. Mixing of Colors When two beams of light with different wavelengths are superimposed together, you will get light with different properties from the original two beams of light. Likewise, when two dyes of different colors are mixed together, the resulting mixture will be completely different in color from the original two dyes. This is the common color mixing in our daily life. After research, it was found that the rules for mixing the above two colors are completely different. For the sake of distinction, people call the mixing of light additive color mixing, while the mixing or superposition of light-absorbing substances such as dyes, pigments, filters, etc. is called subtractive color mixing.

1. Additive color mixing Additive color mixing refers to the addition of light of various colors. The three primary colors of light are red (R), green (G), and blue (B). White light can be obtained by mixing these three kinds of light in appropriate proportions. The basic law in additive color mixing was proposed by H. Grassman in 1854 and is called Grassman’s law of color mixing. Color mixing on a color TV screen is a typical example of additive color mixing in daily life. A typical example of additive color mixing in printing and dyeing is the fluorescent whitening of textiles. The fabric after scouring and bleaching still has a certain yellow color, that is, the reflected light of the fabric lacks blue-violet light, and the fluorescent whitening agent can absorb ultraviolet light to excite blue-violet visible light, and the blue-violet light adds to the yellow light. , white light can be obtained, so the whiteness of the fabric increases. 2. Subtractive color mixing A common example of subtractive color mixing is the mixing of dyes during the dyeing process. The three primary colors in subtractive color mixing are yellow, magenta, and cyan (often called “red,” “yellow,” and “blue”). Dyed textiles appear a certain color, such as blue, because the dyes in them convert illuminating white light into Most of the red, yellow, and green light is absorbed, so the blue light is mainly reflected. Color is because most of the blue and purple in white light are absorbed. Therefore, mixing blue and yellow dyes is equivalent to white light passing through blue and yellow filters successively, thereby converting red, yellow, and blue. , purple and other colors of light are absorbed, and what is left is green. Subtraction of the three primary colors is often used in the textile industry. Many colors can be obtained by subtractive color mixing. Figure 2-2 shows the color changes in the additive color method and the subtractive color method. The three primary colors of the additive color method are mixed by addition to obtain the three primary colors of the subtractive color method. The three primary colors of the subtractive color method are mixed by subtraction to obtain the additive three primary colors. One of the important differences between additive color mixing and subtractive color mixing is that the brightness of additive color mixing increases. , while the brightness of subtractive color mixing decreases.

3. In addition to additive color mixing and subtractive color mixing, there is another method called average color mixing. The average mixing of colors can be illustrated with the example of a top. Paste several colors on the surface of the top, such as yellow and blue, and then spin the top quicklyUp, the color we see at this time will be green, which is an effect produced by the two colors yellow and blue frequently acting on the retina within the visual reaction time of the human eye. Since the result of this mixing only changes the hue, but the overall brightness does not change, it is an average mixing.

4. The quantitative measurement of object color in the CIE standard chromaticity system is very complex. It involves many issues such as the observer’s visual physiology, visual psychology, lighting conditions, and observation conditions. In order to obtain consistent To measure the effect, the International Commission on Illumination (CIE) stipulates a standard colorimetric system, called the CIE standard colorimetric system. According to Glassmann’s color mixing law, colors with the same appearance can replace each other, and colors that replace each other can be found through color matching experiments. The method of adjusting two colors to be visually the same or equal is called color matching. In the color matching experiment, the number of three primary colors required to achieve color matching with the measured color is called the tristimulus value. That is, the R, G, and B values. A color corresponds to a set of R, G, and B values, and color perception can be quantitatively expressed through tristimulus values. As long as the R, G, and B values ​​of any two colors are the same, the color feeling will be the same. In order to measure the tristimulus value of an object’s color, we must first study the color visual characteristics of the human eye and measure the spectral tristimulus value. This data is called the “standard colorimetric observer spectral tristimulus value” to represent the human eye. Average color vision properties. In 1931, CIE proposed the earliest major recommendation – the CIE standard colorimetric observer and chromaticity coordinate system; and stipulated the standard light source and lighting observation conditions, and established the CIE standard colorimetric system, thus laying the foundation for modern colorimetry. .

5. Different objects have different colors because of their different absorption and reflection characteristics of light. However, sometimes we find that two color samples with different absorption and reflection characteristics (such as different formulas) can match each other under a specific light source. This phenomenon is called “same light and different spectrum”. Such two light stimuli The phenomenon of metamerism cannot be distinguished by the human eye. The spectral components in the mixed color are related. Therefore, when the observer and the light source change, or one of the two changes, the properties of isochromatic light will be destroyed. At the same time, the degree of mismatch will also be different due to the different spectral reflectance of the sample. It can be measured by the size of the color difference caused by changing the observer or changing the lighting source. To measure the degree of metamerism of two samples. In order to quantitatively evaluate the degree of metamerism of colors, in 1971, CIE published a method for calculating the “special metamerism index (changing illuminant)”. The principle is that for a specific reference illuminant and the observer have the same tristimulus value For two metamer samples, the color difference between the two samples caused by test illuminants with different relative spectral power distributions is used as the special metamer index Mt. CIE recommends the use of standard illuminant D65 as the reference illuminant for testing. Use standard lighting body A or lighting body F.