- Since, all the image processing used in the further articles is done by the software MATLAB, we will discuss the relevant concepts here.
+ Basic commands
+Let's start off by learning some basic commands in MATLAB to read, display and perform some basic operations on images such as crop, rotate and resize. To know more, or read detailed documentation for any of the commands, visit MATLAB help. You can use the following syntax for it.
+doc command_name
+doc imread
+
imread
-Reads image from the graphics file and stores it in a variable in the matrix form.
-Syntax
-varible_name = imread (‘file_location’)
-Example
-a = imread (‘object.png’)
-The above command will store an image named ‘object.png’ into matrix form in variable ‘a’. The size of matrix ‘a’ is decided by the dimensions of the image. Let us assume the size of ‘object.png’ be 757 x 1080, then the matrix ‘a’ will have 757 rows and 1080 columns.
+This command reads the image from a graphics file and stores it in a variable in the matrix form. The syntax for the imread operation is shown below.
+varible_name = imread ('file_location')
+a = imread ('object.png')
+
+The above command will store an image named 'object.png' into matrix form in the variable 'a'. The size of matrix 'a' is decided by the dimensions of the image. Let us assume the size of 'object.png' be 757 x 1080, then the matrix 'a' will have 757 rows and 1080 columns. If the object is an RGB image, the size of a will be 757x1080x3 where 3 represents the layers of red, green and blue.
+Make sure that the image 'object.png' is in your working directory for the code to work.
imshow
-Display the image.
-Syntax
-imshow (image)
-Example
-imshow (a)
-It will display the image stored in variable ‘a’ i.e. ‘object.png’
+This command is used to show the image that has been stored in the matrix form. The syntax for the imshow operation is below.
+imshow (varible_name)
+imshow (a)
+
+It will display the image stored in variable 'a' in a new window.
imcrop
-Crops the image according to the given dimensions.
-Syntax
-varible_name = imcrop (image, [x1 y1 x2 y2])
-Example
-b = imcrop (a, [100 100 500 500])
-It will crop the image ‘a’ into a 400 x 400 image and store it in another variable ‘b’.
+This command crops the image according to the specified coordinates. The following syntax can be used to crop an image from the index values (x1, y1) with the length l and width w.
+varible_name = imcrop (image, [x1 y1 l w])
+b = imcrop (a, [100 100 400 400])
+
+It will crop the image 'a' into a 400 x 400 image and store it in another variable 'b'. You can use imshow to verify that the operation was performed correctly.
imresize
-Resize the image according to the given scale
-Syntax
-variable_name = imresize (image, scale)
-variable_name = imresize (image, output_size)
-Example
-c = imresize (a, 0.5)
-Image ‘a’ will be shrinked to it’s half size and will be stored into another variable ‘c’.
-c = imresize (a, [200 300])
-Image ‘a’ will be resized to a matrix of 200 rows x 300 columns and will be stored in variable ‘c’.
+This command resizes an image according to the specified scale, or to a specified size. Here's the syntax for using imresize.
+variable_name = imresize (image, scale)
+variable_name = imresize (image, output_size)
+
+c = imresize (a, 0.5)
+
+
+c = imresize (a, [200 300])
+
imrotate
-Rotates the image by given angle (in degrees) in a counterclockwise direction around its center point. To rotate the image clockwise, specify a negative value for angle. ‘imrotate’ makes the output image large enough to contain the entire rotated image.
-Syntax
-variable_name = imrotate (image, degrees)
-Example
-d = imrotate (a, 75)
-Rotate the image ‘a’ in counterclockwise direction by 75 degrees and store it in variable ‘d’.
-NOTE :- imrotate uses nearest neighbor interpolation, setting the values of pixels in output_image that are outside the rotated image to 0 (zero).
+This command can be used rotate the image by given angle (in degrees) in a counterclockwise direction around its center point. To rotate the image clockwise, specify a negative value for angle. 'imrotate' makes the output image large enough to contain the entire rotated image. Here's the syntax for doing the same.
+variable_name = imrotate (image, degrees)
+
+
+
+d = imrotate (a, 75)
+
+NOTE: imrotate uses nearest neighbor interpolation, setting the values of pixels in output_image that are outside the rotated image to 0 (zero).
subplot
-Creates axis in tiled positions. Whenever we need to display two or more images in one window, we use subplot.
-Syntax
-subplot (m, n, p)
-It divides the current figure into an ‘m x n’ grid and creates an axes for a subplot in the position specified by ‘p’. MATLAB numbers its subplots by row, such that the first subplot is the first column of the first row, the second subplot is the second column of the first row, and so on. If the axes already exists, then the ‘subplot(m,n,p)’ makes the subplot in position p the current axes.
-Example
-subplot (2, 2, 1)
-imshow (a)
-‘subplot (2, 2, 1)’ will divide the figure into a 2 x 2 matrix. ‘1’ is representing the position where the image ‘a’ is going to be displayed since there are 4 positions.
+Creates axis in tiled positions. Whenever we need to display two or more images in one window, we use subplot. Here's the syntax.
+subplot (m, n, p)
+It divides the current figure into an 'm x n' grid and creates an axes for a subplot in the position specified by 'p'. MATLAB numbers its subplots by row, such that the first subplot is the first column of the first row, the second subplot is the second column of the first row, and so on. If the axes already exists, then the 'subplot(m,n,p)'' makes the subplot in position p the current axes.
+Example
+
+figure, subplot (2, 2, 1)
+
+imshow (a)
+
+'subplot (2, 2, 1)' will divide the figure into a 2 x 2 matrix. '1' is representing the position where the image 'a' is going to be displayed since there are 4 positions.
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