img = imread('ImageProcessing_1/BerkeleyTower.png');

 

MATLAB TUTORIAL : DIGITAL IMAGE PROCESSING I

Introduction

In this chapter, we'll scan through the key features/functions of image processing from A to Z. It won't be a comprehensive but a very short while we can grasp what's going on Matlab's image processing very quickly. In later chapters, we'll go deeper.

We'll use the following basic image processing functions:

1. imread()

2. imshow()

3. imwrite()

4. rgb2gray()

5. imhist()

6. imadjust()

7. im2bw()

imread()

The imread() command will read an image into a matrix:

img = imread('ImageProcessing_1/BerkeleyTower.png');

>> size(img)

ans =

499 748 3

It's a 499x748 matrix with 3 RGB channels. The matrix looks like this:

24 40 73 108 129 108 96 100 109 114 108 109 62

29 56 97 107 110 104 103 105 106 110 110 111 105

...

3 2 2 1 0 0 1 1 0 1 2 4 2

1 0 1 3 2 0 0 0 1 1 2 1 0

...

Input file : BerkeleyTower.png.

imshow()

To show our image, we the imshow() or imagesc() command. The imshow() command shows an image in standard 8-bit format, like it would appear in a web browser. The imagesc()command displays the image on scaled axes with the min value as black and the max value as white.

Using imshow():

Using imagesc():

 

We can check the RGB values with (x,y) coordinates of a pixel:

1. Select "Data Cursor" icon from the top menu

2. Click the mouse on the image

Notice each pixel is a 3-dimensional vector with values in the range [0,255]. The 3 numbers displayed is the amount of RGB.

 

Actually, a color image is a combined image of 3 grayscale images. So, we can display the individual RGB components of the image using the following script: