	Vision Systems

Machine Vision Systems

Image Processing

Image processing converts a target image captured by a Charged Couple Device (CCD) camera into a digital signal and then performs various arithmetic operations on the signal to extract the characteristics of the target, such as area, length, quantity and position. Finally, an OK/No Good result is output based on preset tolerance limits.

Flow chart of image processing

Basics of Image Processing

Image scanning

Scanning transfers an image captured by a CCD to a CRT by tracing sequential horizontal lines starting at the upper left-hand corner of the screen and working down. Each line is called a scan line. There are two NTSC (National Television System Committee) scanning standards: non-interlaced(progressive) and interlaced.

Non-interlaced scanning (Progressive)

Scans from scan line 1 to scan line 525 sequentially and then begins again at scan line 1, 60 times per seconds, as shown in Fig. 1. This method is typically used for accurate image inspection.

Interlaced scanning

Scans the odd-numbered scan lines (odd field) first, then the even-numbered scan lines (even field), as shown in Fig. 2. The picture area is scanned 120 times per second but because only half of the lines are scanned at one time, the total screen area, called the frame, is scanned at a frame rate of 60 frames per second. This method is typically used for high-speed image inspection.

The CV Series conforms to the NTSC standard for both non-interlaced and interlaced scanning.

NTSC interlaced and non-interlaced scanning

Image output from a CCD camera

As shown on below, a target pattern focused on the image pickup element (CCD) is stored as an electric charge proportional to the brightness (incident light quantity) of each part of the image. This data is sequentially read (scanned) from its edge, and then converted into an image signal, whose level (brightness/darkness information) changes with time. The image signal is output as a video signal together with a vertical synchronization signal (which defines the starting point of a screen), and a horizontal synchronization signal (which defines the starting point of a scanning line). These synchronizing signals are required to reconstruct the image.

Flow chart of image output from CCD camera

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