Denso RC5 Specifications download pdf (Page 144)

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5-4

5.1.1.5 Binarization

[ 1 ] Binarization

Image data taken in the µVision board from the camera has 256 levels of

brightness for each pixel. Binarization rewrites each pixel’s brightness to white

(1) and black (0) with a threshold value as the boundary. This threshold value

is called the binarization level. The µVision board designates binarization

levels with two values, a lower binary limit and a upper binary limit. The levels

for values between the lower binary limit and the upper binary limit are

binarized to white (1) and other levels to black (0).

fter binarization

Before binarization

Fig. 5-5 Binarization

[ 2 ] Histogram

A histogram counts the occurrence frequency of brightness values in a

designated range of a window of the image data taken from the camera.

Drawing the histogram as a graph helps you easily understand the distribution

of brightness values and you can therefore, easily determine the binarization

level. The µVision board provides an automatic binarization level decision

function. This function uses histograms to decide the binarization level. Fig. 5-

6 is a histogram of image data before binarization. You can see 2 images

separated into an object and a background. Fig. 5-7 shows the result of

binarization with different binarization levels. By adjusting the lower binary limit

and the upper binary limit, you can achieve different binarization results.

Fig. 5-6 Before Binarization Fig. 5-7 After Binarization

0 255

Number of pixels

Binarization level

Brightness

value

Object area Sx

Lower Upper Lower Upper

limit limit limit limit

fter binarization

Before Binarization

Decide

Binarization

Brightness

1 2 ... 139 140 141 142 143 144 145 146 147 148 149 ... 691 692

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Denso RC5 Specifications Page 144

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