Using the DA 7300 Digital Camera for Color Detection in Agri-Industry Processing

Per Lidén
Perten Instruments AB, Instrumentvägen 29-31, SE-126 53 Hägersten, Sweden

The DA 7300 in-line (Figure 1) incorporates a digital camera for real-time image analysis for speck detection, color measurements, and video streaming showing the product. With an advanced optical design, the camera system captures images of the same product being measured with the NIR spectrometer (Figure 2). For optimal image analysis performance, the instrument is equipped with a unique, dedicated cam LED illumination system (Figure 3).





Figure 1: DA 7300 In-line










Figure 2: Technical design with camera images taken on same object being measured with NIR

Figure 3: LED illumination

Continuous measurement stability is achieved through the use of an internal automatic reference used as white standard.

The color temperature of the illumination and camera gain per color channel is precisely controlled and ensures the measurement is stable over time and varying measurement conditions. The camera system is recording R (Red), G (Green), and B (Blue) color for all pixels, in the active color detection area. The color detection area is selectable, and is marked with a blue rectangle in the middle of the captured image field. The sensitivity of the pixels used for color measurements is factory normalized.

The DA 7300 in-line camera R, G, B values can be calibrated to present values in other color spaces and standards, e.g. L*, a*, b* color space, Hunter Lab color space or ICUMSA 420 RBU color. The instrument can be adjusted to match a specific reference spectrophotometer.

CIELAB color 

The CIELAB color space expresses colors in L*, a*, b* values in a way that approximates human vision, Figure 4. L*, a*, and b* values are mathematically defined from Tristimulus values denoted as Y/Yn, X/Xn, Z/Zn that relates to how an average person sees color across the visible spectrum at a defined illumination and viewing angle. The L* coordinate in the CIELAB definition represents the lightness of the product, a* represents green-to-red and b* represents blue-to-yellow scale.

The DA 7300 in-line camera R, G, B measurements are calibrated to Y/Yn, X/Xn, Z/Zn values. Then, the Y/Yn, X/Xn, Z/Zn are converted through the defined equations to L*, a*, b*, Figure 5.

For optimal color measurement performance, it is recommended that the calibrations are developed using similar products as those being measured and that the color range is covered.

In-process application examples

The color measurements can be used in combination with NIR measurements of chemical composition as valuable information in ensuring product quality and production within specifications, Figure 6.

Continuously displaying the color of the product to operators, and if they are within specifications, will allow for reduction of costly customer rejects.

The live camera display of the actual product stream gives additional visible information, Figure 7.

Application area examples are process steps in: durum semolina and flour milling, raw sugar processing and refining, dairy production, feed milling, oil seed processing. or corn wet and dry milling.

Figure 6: DA 7300 Process Plus web operator interface with measurements and DA 7300 in-line camera image

Figure 7: DA 7300 captured images and live video.

The DA 7300 camera can be calibrated to match a specific reference spectrophotometer. Measurements can be on products ranging in color from dark to white. Figure 8 shows the colors displayed through L*, a* and b* by the DA 7300 plotted in comparison to the reference spectrometer displayed color, making the high similarity visible.


Figure 8: The color measurement of Agri-products from the DA 7300 compared to the reference spectrophotometer