Appearance analysis of the hottest print

Editor's note: for consumers, the appearance of a product is the most direct and persuasive product information, so printers and printing customers attach great importance to the surface of a print. An important task faced by printers and designers is to correct the color of images, match samples, or use spectrophotometer and densitometer for various tests and color management. These are familiar appearance analysis concepts, in addition to subjective intuitive judgment

in fact, the appearance judgment of a product inevitably includes various subjective and customer factors. Therefore, the appearance analysis of a product can start with these factors that affect the appearance judgment, supplemented by appropriate technology, instruments and measurement methods. This is exactly what Richard Harold wants to introduce to you in this article. Harold has 30 years of research experience in the field of appearance analysis and served for GATF for two years. Harold first introduced the interaction between light and the target, which is the reason for the visual effect of the observer. Then Harold will introduce various devices and principles for analyzing appearance properties based on this visual principle

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the appearance of an object is the result of the interaction of many complex factors, including the properties of light shining on the object, the visual characteristics of the object, the perception of the observer, etc

if a product wants to achieve the expected market value, appearance is one of the most important commercial attributes of the product, which largely determines whether the product will be accepted by consumers. Because from a psychological point of view, the appearance of products is always related to the expected quality

because the appearance of products directly affects the purchase behavior of potential consumers, all manufacturers pay close attention to the appearance of their products, including visual factors such as color, gloss, shape, texture, transparency and so on. Manufacturers understand that under the condition that other performance, quality and price of products are the same, consumers will choose the one with the best appearance. The appearance of products is undoubtedly the most direct and illustrative product information

in addition to the visual appeal of the product appearance, printing customers also need to maintain the same printing effect of different batches of the same product when making the friction coefficient. Because if the appearance and packaging of a batch of products are different from those before, it is easy for consumers to suspect that they are inferior or expired products. Therefore, the consistency of product appearance is also a concern of customers

at the same time, when consumers consider the service life of products, the durability of outer packaging is also an important factor. Although the subjective evaluation is questionable, there are also some objective evaluation standards, which can test its lightfastness and stability through standardized tests. These tests help consumers make more informed purchase decisions

the interaction between light and different substances such as ink, paint, paper, fiber, plastic, metal, ceramics and so on is different, which depends on many physical factors. As long as appropriate instruments and operating methods are used, the appearance properties of various substances can be measured

I. interaction between light and objects or substances

when the light source emits visible light, the appearance of the object seen by the eye depends on the effect of the object on its own illumination. The object mentioned here can be either a printed matter or any object or substance such as a piece of paper or an apple

the wavelength range of visible light is 380 to 770nm, and light of different wavelengths presents different colors. Due to the different energy of light radiation of different wavelengths, some wavelengths of light appear to be more intense than others. Therefore, human eyes react differently to light with the same total energy but different wavelengths. It is expressed as the photometric curve of human eyes, which describes the energy of light or radiation of each wavelength

light can be emitted by objects heated to white heat, such as incandescent bulbs, or excited by atoms or molecules, such as the light emitted when the metal coil of an electronic furnace is heated to red. Fluorescence is a special case, which is produced when light changes from one spectral region to another

a pure radiation source, called "blackbody radiator", can be used as a reference standard to distinguish the color of white heat light source. The correlated color temperature (CCT) of the light source is the temperature when the blackbody radiator looks closest to the light source. For example, the CCT of a typical incandescent lamp is about 256K

although the appearance of matter is composed of many complex factors, these factors can be roughly divided into geometric attributes, color attributes and specific light attributes for analysis respectively

after the light shines on the object, several different reactions may occur, which produces different visual effects. If light is totally reflected on the surface of an object, the object will look dazzling and bright. What kind of reaction actually happens depends on the properties of the material. Metals are usually more harmful than other substances' total reflection, and smooth surfaces usually look brighter than rough surfaces

second, geometric attributes

are different from color. The geometric attributes of the object surface are usually related to its surface characteristics, which are very complex and cannot be described by some simple concepts of shape and arrangement. Fortunately, if only for a relatively balanced and uniform surface, its geometric properties can be simplified

first of all, some of the light shining on the object is reflected, some is transmitted, and the reflected light is reflected from the surface of the object, which becomes a luminous object in the eyes of the person who sees the reflected light. Transmitted light means that light passes through an object and is seen by people outside the object. Both reflected light and transmitted light can be further divided into complete reflection and diffuse reflection, and complete transmission and diffuse transmission. Such a division lays a foundation for analyzing the geometric properties of reflected light or transmitted light

selective absorption of specific wavelength light leads to the perception of color by human eyes. When the absorbed light accounts for the vast majority, the color also looks weak. When the light of all wavelengths and adjustment pointer is absorbed, the human eye sees black. When all wavelengths of light are reflected, you see white

there are four main motion processes of light shining on an object: complete reflection, diffuse reflection, complete transmission or partial transmission and partial reflection. These physical changes of light can be measured by photometric spectrometer and angular spectrometer

spectrophotometer curve is to measure the reflection and transmission of various lights one by one according to the wavelength within the visible spectrum range. Therefore, the spectral curve can be associated with various colors to help identify the pigment or dye part that produces a certain color

the angle spectrometer curve describes how light is reflected on the surface of an object or through an object at different angles, which are related to the geometric properties of the object. Although the measurement results of photometer and angle spectrometer cannot give a conclusive description of the appearance of the object, they illustrate how light interacts with the object in the observation environment

III. color attribute

color is related to light waves, especially the wavelength of light. Visible light refers to the light from infrared to the end of the spectrum, and their wavelength range is 400 to 700nm. Selective absorption of light of different wavelengths in this range usually determines the color of objects. The light reflected or transmitted without being absorbed by the object can be seen by the human eye. In other words, yellow objects absorb blue light, red objects absorb green light, and so on

in reality, the color of an object is measured and expressed by the photometric curve. In a typical spectrophotometer curve, the white, gray and black curves are almost straight horizontal lines. I have various answers to this question at the top, middle and bottom of the curve. The curve representing various colors is at the highest point in the corresponding spectral region of the color, and at a lower value in the region of other wavelengths

4. Psychological factors of color

from the perspective of psychology, color is the consciousness of the brain, which is generated from the signal transmitted by the light receiver of the human eye to the brain. The color of any object is the result of the effect of dyes, pigments or other absorbent substances on the light shining on it. Although the eye itself cannot complete wavelength analysis, it can integrate the response of three color receivers (red, green and blue light) to light waves. Therefore, due to the different sensitivity and proficiency of different people to color, there will be great differences in color analysis ability. A skilled color analyst can estimate the color effect of a sample after printing according to the photometric curve, which is difficult for a non professional

v. color attributes seen by the observer

when an artist examines a work, what he considers is not the color photometric curve or the response of the human eye's red, green and blue receivers to color. When distinguishing colors, he first considers the hue of the color, that is, whether it is red, yellow, blue or purple. In short, what color the object is. This attribute is in art Hue ring is usually used in color technology and decoration industry

the second attribute of color is saturation. The size of a certain color saturation depends on the gap between the outer edge of the pure hue of the color and the gray axis. For example, a light color has low saturation and high pure color saturation

the third attribute of color is related to the luminous intensity of the object (usually called the ability of reflection and light transmission). There are many names for this attribute, which can be called brightness or light value

so there are three attributes of object color: hue, lightness and chroma. In color analysis, especially when comparing color differences, light value, chromaticity and hue (LCH) are the most commonly used terms

VI. illuminant (light source)

light source will also affect people's perception of color. When actually examining the colors of different objects, you can either use natural sunlight first or choose artificial simulated sunlight. Indirect sunlight (such as sunlight from windows facing north) is usually selected in natural sunlight, which is commonly referred to as "North" light in art. However, natural sunlight has one drawback, that is, it is unstable. There are great differences in sunlight in different seasons, places and times. Therefore, the development trend of industrial detection is to use simulated sunlight, which can realize standardization and ensure the relative stability of spectral quality

in order to define different artificial light sources, CIE established a group of standard luminaries whose spectral characteristics are similar to natural light sources and can be reproduced in the laboratory (CIE, 1931): light source a represents a typical incandescent light; Light source B represents direct sunlight; Light source C represents the average value of sunlight in the whole sky

d series light sources are usually based on their correlation