Image Acquisitionand Proces

106 Image Acquisition Processing with LabVIEW
Therefore, an example 3 ¥ 3 image combination would be implemented as follows:
122 127 125 122 123 111 0 4 14
190 120 123 _ 187 130 113 = 3 –10 10
115 178 160 117 180 167 2 –2 –7
Source Image A Source Image B Combined Images
As intensity values less than 0 are forbidden in a 256 level image (only values
between 0 and 255 inclusive are permitted), any combined intensity values of 0 or
less (shaded cells in the previous example) are clipped to 0 (black). Therefore, the
true (distorted) output of the combination routine for this example is:
122 127 125 122 123 111 0 4 14
190 120 123 _ 187 130 113 = 3 0 10
115 178 160 117 180 167 2 0 0
Source Image A Source Image B Combined Images
The subtracted image’s intensity values are the subtracted components and are
therefore either smaller than (hence darker) or equal to that of the original pixels. The
example in Figure 5.27 shows an image of a digital clock, from which an intensitygraduated
box is subtracted. As you can see, the corresponding portions of the resulting
image located where the gray boxes image is dark are relatively unchanged, as the
subtracting factor is dark (therefore close to zero). Conversely, where the gray boxes
image is bright, the pixel intensity values are relatively high and therefore the resulting
image’s pixels are low. The example in Figure 5.28 shows the opposite scenario —
the clock image is subtracted from the gray boxes image. The examples in Figure 5.28
were implemented using IMAQ Subtract, shown in Figure 5.29.
IMAQ Subtract also allows for constant values to be subtracted from all image
pixels (Figure 5.30). As you might expect, using a constant of 100 subtracts 100
intensity units from each pixel of the source image (Figure 5.31).
(a) (b) (c)
FIGURE 5.27 (a) Clock source (b) Gray boxes source (c) Clock – boxes
(a) (b) (c)
FIGURE 5.28 (a) Gray boxes source (b) Clock source (c) Boxes – clock