how do i find out the perfect edge

Iam writing the code to detect the edge of a leaf in matlab code,but Iam unable to find out the clearcut edge formation my code is

clc

close all;
clear all;
a=imread('t.jpg');
figure(1);
subplot(3,3,1);
imshow(a);
title('Actual image');

g=rgb2gray(a);
subplot(3,3,2);
imshow(g);
title('Gray image');

[r c l]=size(a);
o(:,:)=a(:,:,1);
x=0;y=0;

bw=im2bw(a,0.4);
subplot(3,3,3)
imshow(bw)
title('binarized image');

s=imcomplement(bw);
subplot(3,3,4)
imshow(s)
title('complement for binarized image')
for i=1:r
    for j=1:c
        for k=1:3

                if g(i,j)<=80
                     o(i,j)=0;
                elseif g(i,j)>80
                    o(i,j)=255;
                end 
                if(s(i,j)==255)
                x=x+1;
                w=x*0.00147;
                elseif(s(i,j)==0)
                y=y+1;
                b=y*0.00147;
                end
          end
      end
  end
  c=edge(s,'canny');
  subplot(3,3,5);
  imshow(c);
  title('canny');
  p=edge(s,'log');
  subplot(3,3,6);
  imshow(p);
  title('log filter');
  p=edge(s,'roberts');
  subplot(3,3,7);
  imshow(p);
  title('roberts filter');
  p=edge(s,'sobel');
  subplot(3,3,8);
  imshow(p);
  title('sobel filter');

Answer 1

[Walter Roberson]

You cannot get perfect edge detection from a JPEG image, unless it is one of the rare lossless JPEG images. JPEG blurs edges in strange ways.