how to crop image into overlapping patches

i have an image of 720x680 and i want to extract overlapping patches. each patch has size of 16x16 and the overlapped pixels is 10. does anyone know how to do this in Matlab.

[darova]

Please show the image

Answer 1

[Image Analyst]

Try this:

% Read in image.
rgbImage = imread('peppers.png');
h1 = subplot(2, 1, 1);
imshow(rgbImage);
hLine = yline(h1, 1, 'Color', 'y', 'LineWidth', 1);

h2 = subplot(2, 1, 2);
[rows, columns, numColorChannels] = size(rgbImage);
stepSize = 10;
subImageWidth = 16;
for row = 1 : stepSize : rows
	row2 = min(row + subImageWidth - 1, rows);
	% Put a yellow line over the full size image to let us know where it's at.
	delete(hLine); % Delete old yellow line.
	hLine = yline(h1, row2, 'Color', 'y', 'LineWidth', 1);
	for col = 1 : stepSize : columns
		col2 = min(col + subImageWidth - 1, columns);
		subImage = rgbImage(row:row2, col:col2, :);
		imshow(subImage);
		drawnow;
	end
end

[ghada sandoub]

thanks a lot . but when i run this code i get this error:

Undefined function or variable

'yline'

i am using Matlab R2015a. Is this function not included in this version?

[darova]

Please use this

% hLine = yline(h1, row2, 'Color', 'y', 'LineWidth', 1);
hLine = line(h1, [1 500], [1 1]*row2, 'Color', 'y', 'LineWidth', 1);

[M J]

Hi, is there a way to save all of these individual subimages at once? Thank you very much !

[ghada sandoub]

Hello, I wanted to save each subimage individually and name it based on its order.So, I used a variable called 'count' to save the number of extracted subimages.so, every time I save the extracted image based on the value of the variable 'count'. For example : if I started with count = 0, so the name of the first extracted subimage is 0 and in the second iteration the variable 'count' will be increased by one 'i.e. count=1' so, the name of the second extracted subimage will be 1 and so on.. I added this part to the previous code in order to save the extracted subimages as jpg images. Before the for loops initialize the value of count as :

count=0;

Then, before the end of the inner for loop add the following: % define the name of each extracted subimage based on the value of variable 'count'

baseFileName = sprintf ('%d.jpg',count); 
Foldername='D:/extracted subimages'; %enter the path of the folder that you want to save the subimages in it 
fullFileName=fullfile(Foldername, baseFileName); 
imwrite(subImage,fullFileName); 
Count=count+1;

[Image Analyst]

After you define Foldername, I'd have this:

if ~isfolder(Foldername)
    mkdir(Foldername); % Create folder if it does not exist yet.
end

[M J]

Thank you so much to both of you, I appreciate it!

[sotiraw sotiroglou]

I am trying to do the same with the sliding patches, but i need it to be done only for a part of an image. For example a region of image defined by a polygon inside image.

Lets say that somehow or someway we have this region by some coordinates of its nodes. For example if the region is a triangle , we have the cooedinates of the 3 nodes. If its a polygon , more.

How could i aply this only inside this polygon? I would appreciate your help

[Image Analyst]

Use poly2mask() to create a mask from the coordinates,

mask = poly2mask(x, y, rows, columns);

where rows and columns are for the small sliding patch, not the full sized image. Then multiply it by the image patch,

grayImage = grayImage .* uint8(mask);

or use indexing,

grayImage(~mask) = 0; % Erase outside of mask

or use bsxfun()

% Mask the image using bsxfun() function to multiply the mask by each channel individually.  Works for gray scale as well as RGB Color images.
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, 'like', rgbImage));