Calculating the area of a selected region as a percentage of total image

I have an image of bone on an implant. I would like to get the percentage of the implant covered by bone. I have written code for collecting pixels with a value less than 250 and pixels greater than 250 and dividing them, but the background is all white. How can I crop the image to get rid of the background or is there a more efficient/exact way to get this value? The photo is like the one attached but with a white background and taken from straight above. Thank you!

[Luciano Garim]

Hi,Jenna Wahbeh.

You may use some image segmentation technique. Algorithms like k-means are efficient when want to segment you image.

Other option is use the Image processing toolbox. The option threshold color is a good one.

I hope helped you!

Answer 1

[Nitin Kapgate]

You can use the roipoly function to interactively specify polygonal region of interest (ROI) and create a binary mask for the same. This binary mask can be then used to calculate the area of ROI as a percentage of total image.

You can use the following code snippet to begin with:

% Load an inbuilt MATLAB image
I = imread('eight.tif');  % Read your own image here
  
% Interactively select the polygon ROI
% For more information about interactive selection of ROI, refer:  
% https://www.mathworks.com/help/images/ref/roipoly.html#mw_826b4f37-e92a-4a20-ab6f-c2aa6d12d500 
BW = roipoly(I); % Binary mask image
  
% Display input image and the binary mask image
figure;  
imshow(I);  
figure;  
imshow(BW); % The white portion is ROI
    
% number of white pixels in the binary image(Area of ROI) 
nWhite = sum(BW(:));
% number of black pixels in the binary image(Area of background)
nBlack = numel(BW) - nWhite;
   
% ROI as a percentage of Total Image  
percentageROI = (nWhite / (nWhite + nBlack)) * 100;