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5 Geometri c Transformation

Interpolation Overview

Video a nd Image Processing Blockset contains blocks that perform geometric

transformations. These blocks use interpolation to calculate the appropriate

pixel values so that images appear rotated, translated, resized, or s heared.

Note Theexamplesinthissectionareillustrations of in terp ol ation m ethods.

The block algorithms are implemented in a slightly different way so that they

are optimized for speed and memory.

The following secti on s illustrate the geometric transformation blocks’

interpolation methods:

• “Nearest Ne ig hbor Interpolation” on page 5-2 — Understand the basic

concepts of nearest neighbor inte rpo lation

• “Bilinear Interpolation” on page 5-3 — U nders tand the basic concepts of

bilinear interpolation

• “Bicubic Interpolation” on page 5-4 — Understand the b a s ic concepts of

bicubic interpolation

Nearest Neighbor Interpolation

For nearest neighbor interpolation, the block uses the value of nearby

translated pixel values for the output p ix el values.

For example, suppose this matrix,

123

456

789

represents

your input image. You want to translate this image 1.7 pixels in

the positi

ve horizontal direction using nearest neighbor interpolation. The

Translate

block’s nearest neighbor interpola t ion algorith m is illustrated by

the follow

ing steps:

5-2

1 2 ... 109 110 111 112 113 114 115 116 117 118 119 ... 251 252

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MATLAB VIDEO AND IMAGE PROCESSING BLOCKSET 3 Guia do Utilizador Página 114