How can i find distance between two subtracted bwboundry image like (imean, jmean)?

Hi, i am doing an experimental study with a vision camera. There are two metal plate and i want to measure the gap between these two plates. I can subtract the edges with a selection ROI and then unfill command to clear my image...You can find an initial and after run photo with the links below:

Processing image

After unfill command

Black region lines

After that, i need to find mean value of x-y pixels of black gap...Here is the ROI part...

s=imread('gap1.jpg');
I=rgb2gray(s);
BW = roipoly(I);
% manually select region here
BW1 = not(BW);
J = roifill(I,BW1); imshow(J)
Y = medfilt2(J,[10 10]); %filter the noise %best result
BWs = edge(Y, 'sobel', (graythresh(J) * .15));
cr=[ 50, 50, 400, 300];
I2 = imcrop(BWs,[cr]);
figure, imshow(I2), title('binary gradient mask');

Answer 1

[Image Analyst]

Just threshold, find the area, and divide by the number of rows. The attached m-file will create this:

[Emre]

thank you for your quick answer, but i would ask one more thing...

What about if i want to get max and min [Width(imin,imax)]?

cause i want to draw a plot in a roi about min,max width change...