The basic components of visual inspection hardware include: a processor, a camera, a lens, and a light source. Among these, the two most important parameters related to the light source are its color and shape.
Today, we'll introduce some basic knowledge about the topic of color.
First, what is color?
Color is a visual effect of light produced by the eyes, brain, and our life experience. The light we see with our naked eyes is produced by electromagnetic waves with a very narrow wavelength range. Different wavelengths of electromagnetic waves appear as different colors. The recognition of color is a visual nerve sensation caused by the stimulation of the naked eye by electromagnetic radiation energy.
Color has three characteristics: hue, saturation, and brightness.
Simply put, it's the sensation caused by light shining on an object and reflecting back to the eye, which is then perceived by the brain. It's represented by hue, saturation, and value, commonly known as HSV.
Of course, there are more than one way to represent color, and RGB is another way. But the most intuitive way for humans to perceive color is HSV.
Second, what is HSV?
Hue
If we categorize colors, we can divide them into two types: chromatic colors (containing color) and achromatic colors (black, white, gray). Among chromatic colors, the types of colors such as red, blue, and yellow are called "hues".
The primary hues are red, yellow, green, blue, and purple. Arranging these hues in a circular pattern according to the color spectrum is called a "color wheel." Using this color wheel, we can determine intermediate and complementary colors.
Saturation
Saturation refers to the vividness of a color, indicating the strength of its hue. Deeper, more vibrant colors have higher saturation, while lighter, darker colors have lower saturation. The color with the highest saturation is called a "pure color," and the color with the lowest saturation (a color with absolutely no vividness) is called an achromatic color.
Brightness Value
Brightness (Value) represents the lightness or darkness of a color. Both chromatic and achromatic colors have a value. A bright color indicates "high brightness," while a dark color indicates "low brightness." White has the highest brightness, and black has the lowest. In other words, the brightness of a chromatic color can be represented by the corresponding level of achromatic color.
The relationship between HSVs can be represented by the following diagram:
Third, complementary colors
Red and green, blue and orange, etc., are hues that are opposite each other on the color wheel and are called complementary colors. Complementary colors, when mixed, become achromatic. Pigments mixed (subtractive color mixing) produce black, while colored light mixed (additive color mixing) produces white.
example:
IV. The Relationship Between Wavelength and Color
If natural light is broken down using a prism, colorless light will appear to exhibit seven colors. The different colors of light are caused by wavelength. From shorter wavelengths to longer wavelengths, the order is violet, blue, green, yellow, and red. The wavelengths of each color are shown below.
Meanwhile, due to the wave-particle duality of light, shorter wavelength blue light is more particle-oriented, making it more suitable for detecting minute defects and scratches on products in practical applications. Red light, on the other hand, is more suitable for applications that require penetrating thin films to detect internal structures.
