MATLAB

Image Processing Toolbox

Muhammad ikram ul haq

BCS-F07-M032

5th Semester

Introduction

Collection of functions (MATLAB files) that supports a wide range of image processing operations

Documentationwww.mathworks.com

Read an Image

Read in an image Validates the graphic format

(bmp, hdf, jpeg, pcx, png, tiff, xwd)

Store it in an arrayclear, close allI = imread(‘pout.tif`);[X, map] = imread(‘pout.tif’);

Display an Image

imshow(I)

Check the Image in Memory

< Name, Size, Bytes, Class >whos

Name Size Bytes Class ans 291x240 69840 uint8 arrayGrand total is 69840 elements using 69840 bytes

uint8 [0, 255]

uint16 [0, 65535]

double [0, 1]

Histogram Equalization

Histogram: distribution of intensities

figure, imhist(I)

Equalize Image (contrast)I2 = histeq(I);

figure, imshow(I2)

figure, imhist(I2)

Histogram Equalization (cont.)

Histogram Equalization (cont.)

Write the Image

Validates the extension Writes the image to disk

imwrite(I2, ’pout2.png’);imwrite(I2, ‘pout2.png’, ‘BitDepth’, 4);

Morphological Opening

Remove objects that cannot completely contain a structuring element

Estimate background illuminationclear, close allI = imread(‘rice.tif’);imshow(I)background = imopen(I, strel(‘disk’, 15));imshow(background)

Morphological Opening (cont.)

Subtract Images

Create a more uniform backgroundI2 = imsubtract(I, background);figure, imshow(I2)

Adjust the Image Contrast

stretchlim computes [low hight] to be mapped into [bottom top]

I3 = imadjust(I2, stretchlim(I2), [0 1]);figure, imshow(I3)

Apply Thresholdingto the Image

Create a binary thresholded image1. Compute a threshold to convert the

intensity image to binary2. Perform thresholding creating a logical

matrix (binary image)level = graythresh(I3);bw = im2bw(I3, level);figure, imshow(bw)

Apply Thresholdingto the Image (cont.)

Storage Classes

double (64-bit), uint8 (8-bit), and uint16 (16-bit)

Converting (rescale or offset)doubleim2double (automatic rescale and offsetting)RGB2 = im2uint8(RGB1);im2uint16imapprox (reduce number of colors: indexed images)

Image Types

IndexData matrix (uint8, uint16, double)Colormap matrix (m x 3 array of double [0

1])

Intensity (black = 0, white = ) Binary (0, 1)

B = logical(uint8(round(A))); (logical flag on)

B = +A; (logical flag off)

RGB (m x n x 3 of truecolor)

Converting Image Types

dither gray2ind grayslice im2bw ind2gray

ind2rgb mat2gray rgb2gray rgb2ind

Multiframe Image Arrays

Same size, #planes, colormap Store separate images into one

multiframe arrayA = cat(4, A1, A2, A3, A4, A5)

Extract frames from a multiframe array

FRM3 = MULTI(:, :, :, 3)

Display a frameimshow(MULTI(:, :, :, 7))

Image Arithmetic

imabsdiff imadd imcomplement imdivide

imlincomb immultiply imsubtract

Adding Images

I = imread(‘rice.tif’);J = imread(‘cameraman.tif’);K = imadd(I, J);imshow(K)

Brighten an image results saturationRGB = imread(‘flowers.tif’);RGB2 = imadd(RGB, 50);subplot(1, 2, 1); imshow(RGB);subplot(1, 2, 2); imshow(RGB2);

Adding Images (cont.)

Adding Images (cont.)

Subtracting Images

Background of a scenerice = imread(‘rice.tif’);background = imopen(rice, strel(‘disk’,

15));rice2 = imsubtract(rice, background);imshow(rice), figure, imshow(rice2);

Negative valuesimabsdiff

Subtracting Images (cont.)

Multiplying Images

Scaling: multiply by a constant(brightens >1, darkens <1)

Preserves relative contrastI = imread(‘moon.tif’);J = immultiply(I, 1.2);imshow(I);figure, imshow(J)

Multiplying Images (cont.)

Dividing Images (Ratioing)

I = imread(‘rice.tif’);background = imopen(I, strel(‘disk’, 15));Ip = imdivide(I, background);imshow(Ip, [])

Linear combination only truncates the final result

K = imlincomb(.5, I, .5, I2);

Dividing Images (cont.)

Coordinate Systems

Pixel Coordinates Discrete unit

(integer) (r, c) = (1, 1)

Spatial Coordinates Continuous unit (x, y) = (0.5, 0.5)123

Non-default Spatial Coordinate System

A = magic(5);x = [19.5 23.5];y = [8.0 12.0];image(A, ‘xData’, x, ‘yData’, y), axis

image, colormap(jet(25))

Spatial Transformations

Map pixel locations in an input image to new locations in an output image Resizing Rotation Cropping

Resizing Images

Change the size of an imageI = imread(‘ic.tif’); J = imresize(I, 1.25);K = imresize(I, [100 150]);figure, imshow(J)figure, imshow(K)

Resizing Images (cont.)

Rotating Images

Rotate an image by an angle in degrees

I = imread(‘ic.tif’); J = imrotate(I, 35, ‘bilinear’);imshow(I)figure, imshow(J)

Rotating Images (cont.)

Cropping Images

Extract a rectangular portion of an image

imshow ic.tifI = imcrop;

Ending