Image Acquisitionand Proces

178 Image Acquisition Processing with LabVIEW
7.3 MATHEMATICAL MANIPULATION OF IMAGES
If you are not able to Þnd a VI within the Vision Toolkit that will perform the
function that you need, and deÞning a custom Þlter (see Chapter 5) is not appropriate,
then breaking an image into a two-dimensional array of intensity values and performing
a custom mathematical process on them may be the only option available.
7.3.1 IMAGE TO TWO-DIMENSIONAL ARRAY
Converting an image to an array is quite simple using IMAQ ImageToArray (Figure
7.16), which parses the image, and returns a two-dimensional array of 8-bit integers
that represent the intensity levels across the image (Figure 7.17). IMAQ ImageToArray
also has an optional rectangle input, so the user can deÞne a rectangular ROI
of intensities to be returned.
FIGURE 7.16 Convert grayscale image to two-dimensional array.
7.3.2 IMAGE PORTIONS
Rather than returning a two-dimensional array of a complete image or a rectangular
ROI, IMAQ GetPixelValue, IMAQ GetRowCol and IMAQ GetPixelLine are
useful when you need to extract particular predeÞned portions of an image. In the
example shown in Figure 7.18, the user has selected a pixel in the middle of the
image, and IMAQ GetPixelValue has returned the intensity value of that pixel.
IMAQ GetRowCol has also been used to return intensity contours of the horizontal
row and vertical column that intersect at the PUI, and IMAQ GetPixelLine returns
the intensity values along an arbitrary line from the top left corner of the image to
the bottom right (Figure 7.19).
IMAQ SetPixelValue, IMAQ SetRowCol and IMAQ SetPixelLine accept
new intensity value inputs, allowing you to set the intensity values of image portions
(Figure 7.20). As you can see in Figure 7.21, the user can set the new intensity