how to cut part of an image ?

I have a image

I have created boundary for the necessary part of my image using bwboundaries();

Now i want to remove rest of the image and make it black like :

how will i do this?

Answer 1

[Image Analyst]

OK. Seems like you're having trouble so I made a full blown demo for you. See attached m-file below this image it creates. Be sure to change the folder and image file name to whatever you have on your computer.

Answer 2

[Ahmet Cecen]

This might not be the most robust way to do it, but create a mask matrix with that red boundary as 1s and everywhere else 0. Then use imfill with holes argument to fill inside that boundary, then multiply the mask with the image element-wise.

Answer 3

[Image Analyst]

Assuming it's a gray scale image, not color, create a mask and assign it

mask = grayImage > 138;  % Whatever value gives you the flower.
mask = bwareaopen(mask, 1000); % Get rid of any small specks that might be there.
maskedImage = grayImage; % Initialize
maskedImage(~mask) = 0;  % Zero outside the mask.

If it's a color image, you can mask like this:

% Mask the image using bsxfun() function
maskedRgbImage = bsxfun(@times, rgbImage, cast(mask, class(rgbImage)));