How can I modify this code so that canny edge detector can detect this red mark line ?

I take image using Microsoft kinect. But all time canny edge detector missed that line. I dont know why ?how can i detect this line? I attached here raw depth image & output of canny. Don't hesitate about black depth image. it works. When u run my code u will see that in red arrow area of raw depth image has an edge but after canny operation it vanished.

 A_depth_distance=imread(raw_depth_image);
  figure,imshow(A_depth_distance,[0 4500]);

%Filtering the raw depth image Median
filtered_depth_distance=medfilt2(A_depth_distance,[3 3]);
figure,imshow(filtered_depth_distance,[0 4500]);
title('Filtering the raw depth image Median');

%Edge Detection Using Canny Operator
edges_depth_distance=edge(filtered_depth_distance,'canny',[0 .02],4);
figure, imshow(edges_depth_distance); 
title('Image obtained using Canny Operator');

Raw Depth Image:

Canny output: