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Home > News > seeing is believing? The visual assessment is exquisite, and the instrument use has tricks!

seeing is believing? The visual assessment is exquisite, and the instrument use has tricks!


seeing is believing? The visual assessment is exquisite,

and the instrument use has tricks!

Color is a feeling, and feeling cannot be quantified and memorized, and the same is true for the color difference between Colors. Therefore, we need to use a color detection instrument, also called a color difference meter, to help us quantify the color difference and control the color quality.

In general, the color difference data and the visual evaluation result are roughly consistent, that is, when the color difference value is small, the eyes cannot see the color difference; when the color difference value is large, the visual difference is large. But sometimes there will be inconsistencies, the chromatic aberration is very small, but the visual effect is unacceptable. There are many possible reasons for the inconsistency. Please consider the following questions.

First, analyze from the aspects of instrument selection and settings:

1. Is the optical structure of the instrument appropriate?

Common measurement structures on the market are: integrating sphere d/8°, 8°/d, 0/45° and 45°/0, where d/8° and 8°/d also include specular reflection state (SCI) and exclude mirror Reflective state (SCE). The results obtained by measuring the same sample using instruments with different optical structures are different. For samples with high specular reflection such as gold and silver, choosing the SCI structure will be closer to the visual result.

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2. Is the instrument light source type selected correctly?

The color data calculated for the same sample under different lighting sources are different. Choose a standard light source that is consistent with the type of light source used in the visual assessment to get consistent results. For example, if the visual inspection is outdoors or under D65 lighting in a light box, the corresponding D65 standard light source should be selected in the instrument.

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3. Is the viewing angle of the instrument appropriate?

The viewing angle is also called the standard observer, which refers to the projected angle of the sample in the observer's eyes when CIE formulates the standard. There are two standards, one is 2° and the other is 10°. Generally, when observing the color of an object, choose an observation angle of 10°; when observing a light source, choose an observation angle of 2°.

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4. Is the choice of instrument color space optimal?

Common color spaces include RGB color space, CMYK color space, Lch and Lab color space, etc. Among them, the Lab color space is established in accordance with an international standard for color measurement established by the Commission Internationale Eclairage (CIE) in 1931. It was improved in 1976 and named a color mode. The Lab color model makes up for the deficiencies of the RGB and CMYK color modes, and is widely used.

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When the above settings are all right, why are there still inconsistencies? That's because the data is inconsistent with the eyes, in addition to the improper selection or setting of the instrument, it may also be caused by the deviation of the visual assessment. An instrument is a detection tool, and the human eye is also a tool for our brain to detect color. Observer differences, differences in the size of the observed samples, differences in the background environment when observations are made, and differences in observation angles will all cause deviations in instrument data and visual effects.

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1. Visual assessment: Does the light source meet the standards?

The data obtained by the instrument measurement is calculated based on the standard illuminator specified by CIE, then the light source used in the visual evaluation

The corresponding light source should also be used, so that the results of the two can be consistent. In reality, the lighting sources used by everyone are uneven, and it is difficult to be consistent. For example, for daylight, the spectral energy distribution curve (used by the instrument calculation) specified by CIE and the curve of the light source in the real light box are as follows:

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This is actually a kind of metamerism of light. It looks like white light, but the energy of different colors of light inside is different, so it is not surprising that the sample sees different results below. CIE has established grade standards (A, B, C, D, E grades) for the quality of light sources. In order to obtain results consistent with the instrument data, it is necessary to choose a high-grade light box.

2. Visual assessment: Does the environment meet the requirements?

When the human eye compares and analyzes the color of the product, it is easily affected by the surrounding environment of the product, such as the surrounding environment is too bright and there are other colors nearby. According to research, it is the most accurate to evaluate the color in the background and environment of neutral gray, so the interior of most light boxes is now coated with Munsell N7 matte gray, and its L* value is about 70, a*b* Close to 0. In fact, everything you can see can be regarded as a light source, such as clothes, which have more or less influence on the evaluation of color.

The color difference between block A and block B in the picture looks very big, but when A and B are moved out separately for comparison, they look the same.

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3. Visual assessment: is the sample suitable?

Remember that funny picture? It looks like Einstein up close, and Monroe at a distance:

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It is often seen that engineers directly evaluate two samples of different sizes. This evaluation method is not standard and is prone to deviation. It is recommended that the size and shape of the sample to be evaluated are the same and placed in a symmetrical position. If the size cannot be the same, it is recommended to partially cover the large sample so that the area seen is basically the same as that of the small sample.

It is not recommended to stack the samples. If it is really necessary, it is recommended to repeat a few more samples on both sides to eliminate the influence of different levels and the surrounding environment on the evaluation.

4. Visual assessment: Are the eyes in their best condition?

There are no two identical leaves in the world, nor two identical eyes! As the color receiver, the eyes work with the brain to form color perception. This process is quite complicated.

In addition to being affected by the optical properties of the object itself, perception is also related to the structural state of the eye, the physical and psychological state, and the cultural background of the person. The most basic thing is to exclude any physical defects in the evaluator`s vision, such as color blindness or amblyopia. In this regard, there are many color recognition tools that can test and analyze the color sensitivity of individuals to prevent inappropriate personnel from participating in the color evaluation work.

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Science is endless. In order to achieve more accurate color digitization, many organizations and individuals have done in-depth research in this area to make the data more consistent with visual observation. The measurement principle of the instrument is in a very ideal state, but the light source during visual evaluation is not ideal; the instrument measurement only gives color data; the visual evaluation will feel the color and other appearance parameters (such as gloss and transparency) at the same time; Instrument measurement may be a single set of data, but visual evaluation may be to see multiple sets of results from different directions. The existence of this difference will make it difficult to completely resolve the inconsistency between the color difference data and the visual evaluation in the short term. The existing tools can be used to reduce the occurrence of this situation through appropriate settings and methods.


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