2_matlabtool

7/31/2019 2_matlabtool

1/16

MATLAB for Image Processing


2/16

CRD LabsCybernetics Research & Development

MATLAB Image Processing Toolbox

Built on the computation and function capabilitiesof MATLAB and the Signal Processing Toolbox.

Can read/write image data in a variety of formats.

Provides functions for image transforms, filtering,

enhancement, image registration, deblurring,feature extraction, etc.

Expandable, by adding own functions.

Command-line oriented, but adding new GUIs toaccess tools is possible.


3/16


4/16


CMY Model

Based on secondary colors

Realizes a subtractive color scheme.

Yellow results when the blue is subtracted from white

Red is realized when yellow and magenta are

removed from white.

This approach is used for hard copy devices.


5/16


YIQ Model Simple linear transform of RGB:

Used in TV broadcasting

Y component provides information for monochromedisplay.

Exploits human visual system, since we areparticularly sensitive to luminance.

0.299 0.587 0.114

0.596 0.275 0.321

0.212 0.523 0.311

Y R

I G

Q B


6/16


HIS Model Most relevant to IP is Hue,

Saturation, and Intensity

(HIS) model

Hue = perceived color

which is approximately thedominant wavelength

Saturation = dilution of

color by white light


7/16


MATLAB Image Types

Indexed Images

Intensity Images

Binary Images

RGB Images

Multiframe Image Arrays

Image data in MATLAB can be logical, double,

uint8, uint16


8/16


Indexed Images8

Consists of a data matrix,Iand a colormap matrix, C

C is an m-by-3 matrix, with each row specifying the R, G, and B

components of a single color. Values in C are floating point numbers in the range [0, 1]

Color of each pixel is determined by using the corresponding value ofI

as an index into the colormap R G B

0

1 0

Map

1

2

m

100.5 0.5 0.5

1 0.35 0.25 Example:.>> [x, map] = imread('forest.tif');>> imshow(x, map)

1 0

1

10

Image


9/16


10/16


11/16


Colormap A colormap is an m-by-3 matrix of real numbers

between 0.0 and 1.0

Each row is an RGB vector that defines one color

>> load flujet

>> figure;imagesc(X);>> figure;imagesc(X);colormap gray


12/16


Reading Images12

MATLAB can read images of various formats including BMP, HDF, JPEG, PCX, TIFF, XWD

Use function imreadto read image filesimreadreads indexed, intensity, and truecolor images

Images are read into a uint8 matrix of appropriate size

imreadautomatically determines the format of the image based oninformation in the header

You can specify a format as an optional second argument

>> Crusader = imread(Crusader.jpg');>> image(Crusader)


13/16


Writing Images MATLAB can write images of various formats including the following

BMP, HDF, JPEG, PCX, TIFF, PNG, PNM Use function imwrite to write image files

imwrite determines the format from extension of filename You can specify an optional format if extension is absent or to force a particular format

Use imfinfo(filename) to get information on an image file

13

>> Abrams = imread(Abrams.jpg');>> image(Abrams)>> whos Abrams

Name Size Bytes ClassAbrams 511x640x3 981120 uint8 arrayGrand total is 981120 elements using 981120 bytes>> AbramsGray = rgb2gray(Abrams);>> colormap gray;>> image(AbramsGray)>> imwrite(AbramsGray, 'Abrams.bmp');


14/16


Summary

imreadUsed to read images

imwriteWrite matrices to specified image format

imshow/imageDisplay images

imfinfoRetrieve information about image

colormapSet/change colormap used for

displaying image


15/16


More on image display

>> a = imread(kids.jpg);>> b = imread('SCHOT_CENTER.JPG')>> subplot(121); subimage(a);

>> subplot(122); subimage(b);

>> imshow(F,[-1 5]);>> colormap(jet),colorbar

Use to display multiple images in the

same figure.

Use colorbar to add a colorbar to the image..


16/16


Image Arithmetic

Standard MATLAB arithmetic operators are defined fordouble data. The IP toolbox provides a set of functions to do arithmetic

on other data types.

Documents

2_matlabtool