Paint Color Difference: How to Check and Determine Criteria | MachineMFG

Paint Color Difference: How to Check and Determine Criteria


In the actual production process, when a product is composed of multiple parts and components, which are provided by multiple suppliers, and we require the overall appearance color of the product to be consistent, we will encounter the chromatic aberration problem of the product appearance paint color.

What to do after encountering the chromatic aberration problem of the product appearance paint?

How can we judge whether the product color provided by the supplier meets our requirements?

How many colors are there?

Human eyes distinguish colors according to the wavelength of visible light, and colors vary with different wavelengths (such as rainbow).

In the spectrum, most colors can be mixed with red, green and blue according to different proportions.

Therefore, the color can be represented by RGB value.

In the computer, we use bytes (1byte=8bit) to represent the color component.

When converted to decimal, one byte can represent 256 colors.

The color represented by RGB is R (0-255), G(0-255), B (0-255), and RGB can express 256 × 256 × 256 = 16777216 colors.

How many colors are there

In addition to the commonly used RGB representation of color, there is also HSV color space: hue (H), saturation (S), lightness (V).

The value range of hue (H) is 0 ° ~ 360 °, and the value range of saturation (S) and lightness (V) is 0-1.

hsv color space

In addition to the above two color representation methods, there is also the Lab color space representation method.

Lab color space is based on the perception of color by human eyes, and can represent all colors that human eyes can feel.

Lab color space can make up for the uneven color distribution of RGB color model, and is the color representation mode covering the widest range of colors at present.

Lab color space

L: represents lightness and darkness (black and white), △ L Large indicates partial white, △L small indicates partial black;

a: represents red and green, △a large indicates partial red, △a small indicates partial green;

b: represents yellow and blue, △b large indicates yellowish, and △b small indicates bluish;

In addition, the Lab color space also defines the color difference valueΔE.

Color difference value is used to represent the difference of colors.

ΔE=0~0.5 extremely small difference, which can hardly be determined by naked eyes;

ΔE=0.5~1.0 small difference, which is the allowable range of general color difference;

ΔE=1.0~1.5 small difference, acceptable in specific applications;

ΔE=1.5~3.0 the difference in the degree of perception by the naked eye is acceptable in specific applications;

ΔE=3.0~6.0, quite significant difference.

How to check the color difference of the product appearance paint? What are the criteria?

In product drawings, the requirements for paint color generally use the color number of the color card provided by the manufacturer to indicate the specific color of the paint, commonly used are ral color card and Panton color card.

In the inspection of paint color, we often use standard color plates to judge whether the color can meet our requirements through sensory comparison.

When using color board comparison, we can only judge whether the colors are consistent, but we can’t feed back an accurate color difference information to the supplier.

Therefore, in order to quantify the difference between the paint color and the color we require, we need to use a color difference meter to judge.

standard color plates

The lab value, △L, △a, △b,ΔE value of paint can be read quickly by using the color difference meter.

The following is the meaning of color difference.

For comprehensive color difference valueΔE the general acceptance requirement is less than 0.5. If the requirement is not strict, it can be relaxed appropriately ΔE.

Chromatic aberration value<-4-4~0.2-0.2~0.20.2~4.0>4.0
△LBlack and whiteSlightly black and less whitenormalSlightly white and slightly blackWhite and black
△aGreenish red deficiencySlightly green and less rednormalSlightly red and less greenRed and green
△bBluish and yellowishSlightly blue and less yellownormalSlightly yellow and less blueYellowish and bluish

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