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6.6 Computer Vision
Note that the output of a thresholded color image is a two-dimensional
array, since there is no need to have more than one value attached at each
pixel. Also, in theory a binary image would permit only values of 0 and
1. However, on many compilers there is no particular benefit to doing a bit
level representation, and it can complicate code reuse. Also, most display
software is used to displaying at least 256 values. The difference between 1
and 0 is not detectable by the human eye. Therefore, it is more common to
replace the 1 with a 255 and use a full byte per pixel.
Thresholding works better in theory than in practice due to the lack of
color constancy. The shape of an object will mean that even though a human
sees the object as a solid color, the computer will see it as a set of similar
colors. The common solution is to specify a range of high and low values on
each color plane. The C/C++ code would now become:

for (i= = 0; i< numberRows; i++)
for (j= = 0; j<numberColumns; j++) {
if (((ImageIn[i][j][RED] >= redValueLow)
&& (ImageIn[i][j][RED] <= redValueHigh))
&&((ImageIn[i][j][GREEN]>=greenValueLow)
&&(ImageIn[i][j][GREEN] <= greenValueHigh))
&&((ImageIn[i][j][BLUDE]>=blueValueLow)
&&(ImageIn[i][j][BLUE] <= blueValueHigh))) {
ImageOut[i][j] = 255;
}
else {
ImageOut[i][j] = 0;
}
}

The change in viewpoints and lighting means that the range which de-
fines the object from the robot’s current position is likely to change. The
color range for the object has to be made even wider to include the set of
color values the object will take. If the object color is unique for that envi-
ronment, this increase in the color range is acceptable. Otherwise, if there
are objects which have a color close enough to the object of interest, those
objects may be mistaken for the target. In some circles, the object of interest
FOREGROUND is called the foreground, while everything else in the image is called the back-
BACKGROUND
ground. Thresholding an image requires a significant contrast between the
background and foreground to be successful.