MATLAB VIDEO AND IMAGE PROCESSING BLOCKSET 3 Guide de l'utilisateur télécharger pdf (Page 149)

Correcting for Nonuniform Illumination

Global threshold techniques, which areoftenthefirststepinobject

measurement, cannot be applied to unevenly illuminated images. To correct

this problem, you can change the lighting conditions and take another picture,

or you can use morphological operators to even out the lighting in the image.

Once you have corrected for nonuniform illumination, you can pick a global

threshold that delineates every object from the background. In this topic, you

use the Opening block to correct for uneven lighting in an intensity image:

1 Define an intensity image in the MATLAB workspace. To read in an

intensity image from a PNG file, at the M ATLAB command prom pt, type

I= imread('rice.png');

I is a 256-by-256 matrix of 8-bit unsigned integer values.

2 To view the image this matrix represents, at the MATLAB command

prompt, type

imshow(I)

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MATLAB VIDEO AND IMAGE PROCESSING BLOCKSET 3 Guide de l'utilisateur Page 149