MATLAB: How to “remove” a certain part of a colored image? (Double Edges??)

color segmentationedge detectionimage analysisimage processingImage Processing Toolboximage segmentation

Okay, So I have hundreds of images that I need to analyze using MATLAB. The Images are of the underside of a turtle. The images looks something like this (not the image im using, but just for reference) http://upload.wikimedia.org/wikipedia/commons/2/28/B3_Southern_painted_turtle_underside.jpg.
I want to get rid of the "body of the turtle, and just have the shell to work with (if you know turtle parts, i just want to use the plastron). I have tried using many edge detection codes, but i cant seem to just get rid of the "body" of the turtle.
Here's an example of what im trying to do/have so far.
f = imread('IMG_0003.jpg');
g = imcrop(f,[750 500 1800 1300]);
imshow(g)
% % % reads and crops
B=rgb2gray(g);
D=double(B);
for i=1:size(D,1)-2
    for j=1:size(D,2)-2
        %Sobel mask for x-direction:
        Gx=((2*D(i+2,j+1)+D(i+2,j)+D(i+2,j+2))-(2*D(i,j+1)+D(i,j)+D(i,j+2)));
        %Sobel mask for y-direction:
        Gy=((2*D(i+1,j+2)+D(i,j+2)+D(i+2,j+2))-(2*D(i+1,j)+D(i,j)+D(i+2,j)));
          %The gradient of the image
          %B(i,j)=abs(Gx)+abs(Gy);
          B(i,j)=sqrt(Gx.^2+Gy.^2);
      end
  end
  figure,imshow(B); title('Sobel gradient');
% % % Converts it to gray scale, edge detection.
C = num2cell(D);
C(~D) = {{}};
imagesc(D, 'AlphaData', D)
colormap(gray)
set(gca, 'color', 'none')
Z = cell2mat(C);
% % % % Removes the background
q = double(Z);
im=mat2gray(q);
level = graythresh(im);
imb = im2bw(im,level);
imb = ~imb;
hope = imfill(imb,'holes');
figure,imshow(hope); title('HOPE');
A = numel(hope(hope==0))
B = numel(hope(hope==1))
******* I am a beginner at Matlab, so sorry for that. But, if you look at the image "hope", you can see that i can get an image of the entire turtle and shell to be white while discluding the background. I then counted the pixels of white to find how many made up the turtle. I WANT TO DO THIS WITH ONLY THE SHELL! (So maybe theres a way to highlight both the inner and outer edge and then cut out that middle part??? I dont know).
Please, any help would be greatly appreciated!! 🙂 THANKS!
PS: I'm doing this so I can eventually find a proportion of "orange colored pixels on the turtle shell" to the "whole shell" of the turtle. I'm doing this for analytical purposes, so i can corolate this value to the same ratio on the top of the turtle shell. So once again, Just want to cut out the "body of the turtle" and be left with the shell. Thank you!

Best Answer

% Demo to write an ellipse and a line into the overlay of an image,
% and then to burn those overlays into the image.
%----- Initializing steps -----
% Clean up
clc;
clear all;
close all;
workspace; % Display the workspace panel.
hasIPT = license('test', 'image_toolbox');
if ~hasIPT
  % User does not have the toolbox installed.
  message = sprintf('Sorry, but you do not seem to have the Image Processing Toolbox.\nDo you want to try to continue anyway?');
  reply = questdlg(message, 'Toolbox missing', 'Yes', 'No', 'Yes');
  if strcmpi(reply, 'No')
    % User said No, so exit.
    return;
  end
end
% Display images to prepare for the demo.
monochromeImage = imread('pout.tif');
subplot(2, 4, 1);
imshow(monochromeImage);
title('Original Image');
subplot(2, 4, 2);
imshow(monochromeImage);
title('Original Image with ellipse in overlay');
subplot(2, 4, 5);
imshow(monochromeImage);
title('Original Image');
subplot(2, 4, 6);
imshow(monochromeImage);
title('Original Image with line in overlay');
set(gcf, 'units','normalized','outerposition',[0 0 1 1]); % Maximize figure.
set(gcf,'name','Image Analysis Demo','numbertitle','off') 
%----- Burn ellipse into image -----
% Create elliptical mask, h, as an ROI object over the second image.
subplot(2, 4, 2);
hEllipse = imellipse(gca,[10 10 50 150]); % Second argument defines ellipse shape and position.
% Create a binary image ("mask") from the ROI object.

binaryImage = hEllipse.createMask();
% Display the ellipse mask.
subplot(2, 4, 3);
imshow(binaryImage);
title('Binary mask of the ellipse');
% Let's try to add some text.  (Doesn't work)
% hText = text(50, 100, 'Line of Text');
% textMask = hText.createMask();
% binaryImage = binaryImage & textMask;
% imshow(binaryImage);
% Burn ellipse into image by setting it to 255 wherever the mask is true.
monochromeImage(binaryImage) = 255;
% Display the image with the "burned in" ellipse.
subplot(2, 4, 4);
imshow(monochromeImage);
title('New image with ellipse burned into image');
%----- Burn line into image -----
burnedImage = imread('pout.tif');
% Create line mask, h, as an ROI object over the second image in the bottom row.
subplot(2, 4, 6);
hLine = imline(gca,[10 100],[10 100]); % Second argument defines line endpoints.
% Create a binary image ("mask") from the ROI object.
binaryImage2 = hLine.createMask();
% Display the line mask.
subplot(2, 4, 7);
imshow(binaryImage2);
title('Binary mask of the line');
% Burn line into image by setting it to 255 wherever the mask is true.
burnedImage(binaryImage2) = 255;
% Display the image with the "burned in" line.
subplot(2, 4, 8);
imshow(burnedImage);
title('New image with line burned into image');
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