What is a Color Sensor and What is a Mark Sensor? What are the Differences?

Many people confuse mark sensors and color sensors. A more precise classification shows two broad types:

1) Contrast sensors (used to detect and compare surface gray levels)

2) Color sensors (used to identify and compare surface color values in RGB)

What are mark sensors and what are color sensors?

Mark sensors detect gray level differences on a surface and are focused on contrast detection. They are well suited for locating repetitive patterns on moving materials, and are often referred to as contrast sensors.

Integrated Mark Sensor

Color sensors use the RGB color model to compare reflected signals against reference R, G and B values to identify and classify surface colors.

What is the practical difference between contrast sensors and color sensors?

A simple analogy is a black-and-white camera versus a color camera. Mark sensors only detect gray level, so they cannot distinguish different colors that share the same gray value. Color sensors measure RGB ratios and can precisely identify color differences.

Mark sensors are used to detect the presence and position of marks by comparing measured gray level with a threshold, helping systems determine timing and location of marks. For materials with repeating patterns, mark sensors provide a simple, robust solution: place marks with sufficient contrast at fixed pattern positions.

For multicolor printed materials where multiple patterns must be distinguished, color sensors are required. Color sensors measure RGB values and compare them to target color values to identify specific colored marks. Although color sensors can identify more complex patterns, they typically have slower response speeds due to higher data processing requirements and are thus used when color discrimination is essential, such as quality inspection and sorting.

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