1)Reading an Image
To import an image from any
supported graphics image file format, in any of the supported bit
depths, use the imread function.
Syntax A = imread(filename,fmt)
Description
A = imread(filename,fmt) reads a
greyscale or color image from the file specified by the string
filename, where the string fmt
specifies the format of the file. If the file is not in the current
directory or in a directory in
the MATLAB path, specify the full pathname of the location on
your
system.
>> b= imread('C:\Documents
and Settings\bond\My Documents\ld1 (8 x 8).jpg')\
2)Display An Image
To display iamge, use the imshow
function.
Syntax imshow(A)
Description
imshow(A) displays the image
stored in array A.
>> a = [0 0 255 0 0 0 0
255;0 0 255 0 0 0 255 0;0 0 255 0 0 255 0 0;0 0 255 0 255 0 0 0;0 0 255
255 0 0 0 0;0 0 255 0 255 0 0 0;0
0 255 0 0 255 0 0;0 0 255 0 0 0 255 0;0 0 255 0 0 0 0 255];
>>imshow(a)
3)Writing Image
Data/ Writing Image to Disk
Imwrite Write image to
graphics file
Syntax
imwrite(A,filename,fmt)
Description
It writes the image to filename,
inferring the format to use from the filename's extension. The
extension must be one of the
values.
>> a = [0 0 255 0 0 0 0
255;0 0 255 0 0 0 255 0;0 0 255 0 0 255 0 0;0 0 255 0 255 0 0 0;0 0 255 255 0 0
0 0;0 0 255 0 255 0 0 0;0 0 255 0
0 255 0 0;0 0 255 0 0 0 255 0;0 0 255 0 0 0 0 255];
>>imwrite(a,'b1.jpg','jpeg')
>>imshow(‘b1.jpg’)
4)How to get no.
of rows and columns of image
Syntax
[r,c]=size(a)
Description Function size
gives the rows and columns dimension of image
Accessing the
Pixel data
There is a one-to-one
correspondence between pixel coordinates and the coordinates MATLAB uses
for matrix subscripting. This
correspondence makes the relationship between an image's data matrix
and the way the image is
displayed easy to understand. For example, the data for the pixel in the fifth
row, second column is stored in
the matrix element (5,2). You use normal MATLAB matrix
subscripting to access values of
individual pixels.
For example, MATLAB Code A(2,15)
returns the value of the pixel at row 2, column 15 of the image A.
5)How to get Image
Information
Syntax info =
imfinfo(filename)
Description
It returns a structure, info,
whose fields contain information about an image in a graphics file.
filename is a string that
specifies the name of the graphics file.The file must be in the current
directory or in a directory on
the MATLAB path.
>> imfinfo('C:\Documents
and Settings\bond\My Documents\ld1 (8 x 8).jpg')
6)Convertion of
Image
Syntax Im2unit8
Description Convert image to
8-bit unsigned integers
I1 = im2uint8(I)
Syntax Im2bw
Description Convert image to
binary image, based on threshold.
BW = im2bw(I, level)
Syntax Im2double
Description Convert image to
double type image.
I2=im2double(I)
7)Displaying gray
scale image
Syntax
imtool(I,[low high])
Desription
It displays the grayscale image
I, specifying the display range for I in the vector [low high]. The
value low (and any value less
than low) is displayed as black, the value high (and any value greater
than high) is displayed as white.
8)Changing the
size of Image
Syntax B =
imresize(A, scale)
Description
It returns image B that is scale
times the size of A. The input image A can be a grayscale, RGB,
or binary image. If scale is
between 0 and 1.0, B is smaller than A. If scale is greater than 1.0, B
is larger than A.
Example
B=imresize(a,0.5) making image B half of the image size of A.
B=imresize(a,[512
512]) making image b with size of 512X512.
9)Rotating the
image
Syntax B =
imrotate(A,angle)
Description
It rotates image A by angle
degrees in a counter clockwise direction around its center point. To
rotate the image clockwise,
specify a negative value for angle. imrotate makes the output image B
large enough to contain the
entire rotated image. imrotate uses nearest neighbour interpolation,
setting the values of pixels in B
that are outside the rotated image to 0 (zero).
10)Reading the color
value of an Image
Syntax P =
impixel(I)
Description
impixel returns the red, green,
and blue color values of specified image pixels. In the syntax,
impixel displays the input image
and waits for you to specify the pixels with the mouse.
11)Converting color
Image to Gray scale Image
Syntax I =
rgb2gray(RGB)
Description
It converts the truecolor image
RGB to the grayscale intensity image I. rgb2gray converts RGB
images to grayscale by
eliminating the hue and saturation information while retaining the
luminance.
12)Detecting edges
of an Image
Syntax BW =
edge(I)
Description It takes a
grayscale or a binary image I as its input, and returns a binary image BW of
the
same size as I, with 1's where
the function finds edges in I and 0's elsewhere.
