how to crop a rectangle/square out of a image when four end points are given ?

How to crop a rectangle aligned at some angle to the x axes when its four coordinates are known ?? Say for example I have a square and I want to crop out a square connecting all the mid points of the sides of the bigger square.Basically I want to make all the pixels inside the smaller square white and the remaining as black.

Answer 1

[Bruno Pop-Stefanov]

I wrote a custom function that "draws" lines onto a matrix (superimposeLines.m) and a script that use that function to draw the four sides of your tilted rectangle (Animesh.m). Then, I use the function imfill to fill all the pixels inside the small rectangle with the same color as the sides.

Here is the final result:

You can use that function to draw more complex shapes, like a polygon. All you have to do is properly write the starting and end points of each line in your polygon and pass it to superimposeLines. Look at the code in the attached files for how to properly format your matrix of point coordinates.

[Animesh]

Thanks a lot sir for helping with the code..

Answer 2

[Image Analyst]

Use poly2mask() to make a binary image from the 4 corner points:

binaryImage = poly2mask(x, y);

Then call regionprops to get the bounding box:

measurements = regionprops(binaryImage, 'BoundingBox');

Then crop out out the tilted box from the original image:

croppedImage = imcrop(originalImage, measurements.BoundingBox);

[Image Analyst]

When you say "Basically I want to make all the pixels inside the smaller square white and the remaining as black." that is not necessarily cropping. You could just set some regions black or white without cropping. You'd need to specify what you want to happen to the pixels in the region outside the larger square, the 4 triangular corner regions, and the inner small square. I'm not really sure what region you want black, white, or unchanged.

[Animesh]

Sorry for the clarity sir,I wanted the exact thing given in the above figure

Answer 3

[Doug Hull]

In MATLAB, an image is really just a matrix. You could do something like this:

m = ones(20,20,3)
m(3:8,2:17,:) = 0
imshow(m)

You get the idea.