Practical Guide to Machine Vision Software: An Introduction with LabVIEW

1Basics of Machine Vision

1.1 Digital Images

1.1.1 Grayscale Image

The basic digital image is composed of a two-dimensional array of numbers. Each number in the array represents a value of the smallest visual element, a pixel. The indexed location of the pixel value in the array corresponds to the X and Y locations of the pixel within the image, as measured from the top-left corner. The values of a pixel in an X and a Y location in the digital grayscale image, f(x,y), represent the brightness of the pixel in a range from black to white, as seen in Figure 1.1. Let us assume that total number of pixels are 300 (0–299) and 250 (0–249) in the X and Y locations, respectively. Each image can be represented by the array of size 300 × 250 that has a value for each pixel.

Figure 1.1 Grayscale image.

Each image pixel value is related to the brightness of the image at that specific location. For a given camera device, the maximum value recorded for the image pixels is generally related to a characteristic of the camera referred to as the bit depth. For example, if bit depth is k, then there will be as much as 2^k levels of brightness that can be defined. For example, if the bit depth is 8 bits, then a pixel can have 256 values (2⁸) in the range between 0 and 255.

A grayscale image pixel most often only has brightness information that can be represented in 8 bit values and as such the ...