MATLAB VIDEO AND IMAGE PROCESSING BLOCKSET 3 Guia do Utilizador descarregar pdf (Página 179)

Feature Extraction

13 Use the Hough Lines block to find the Cartesian coordinates of lines that

are described by rho and theta pairs. Set the Sine value computation

method parameter to

Trigonometric fun ctio n.

14 Use the Draw Shapes block to draw the lines on the luminance portion of

the ROI. Set the parameters as follows:

• Shape =

Lines

• Border value = White

15 Use the Embedded MATLAB Function block to calculate the angle between

the two lines. Copy and paste the following code into the block:

function angle = compute_ angle(theta)

%Compute the angle value in degrees

angle = abs(theta(1)-t heta (2))*180/pi;

%Always return an angle value less than 90 degrees

if (angle>90)

angle = 180-angle;

end

16 Use the Display blo ck to view the a ngle between the two lines. Accept the

default parameters.

17 Use the Video Viewe r blocks to view the origin al image, the ROI, and the

annotated ROI. Accept the default parameters.

18 Connect the blocks as shown in the following figure.

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MATLAB VIDEO AND IMAGE PROCESSING BLOCKSET 3 Guia do Utilizador Página 179