Hi, I am using Matlab version 7.9.0(R2009b). I need to select a rectangular region of interest for my tif image. I tried imrect but the rectangular appeared on an empty coordinat system, not in my tif image. Could you please help me on this?

mathworks

[Image Analyst]

Help with what? You forgot to post the code.

[Lisa]

imshow(image); h=imrect;

[Abioye Samson]

okay, you didnt speciify the the co-ordinates of the rectanglar region of interest e.g

figure(1), imshow(image)

h=imrect(gca,[10 10 100 100])

where 10 10 is the x1 and y1 (i.e initial position) and 100 100 is x2 and y2(i.e distance to travel on x axis and y axis respectively) Hope it works.

[Image Analyst]

What does that mean? Do you mean improfile() to get a 1D line profile? Or do you mean surf() to get a 2.5D perspective image? See my code below for info on how to use imrect. You could also use rbbox() if you don't want the user to have to confirm the position of the box.

[Lisa]

yes, I meant 1D line profile from the roi.

[Image Analyst]

What's wrong with improfile()? Or extract the rectangular RIO with imrect() or rbbox() and take the mean in the horizontal or vertical direction and plot that? Try something.

[Lisa]

imrofile() gives only the profile of a line but I need to profile of the rectangular roi area. thanks in advance.

[Image Analyst]

Did you see my responses below, in the Answer section of this page???

[Image Analyst]

Lisa, please put your comments after my answer. Then I'll continue the discussion.

Answer 1

[Image Analyst]

Try this:

  txtInfo = sprintf('Draw a box over the image by clicking and dragging over the image.\nDouble click inside the box to finish drawing.');
  text(10, 40, txtInfo, 'color', 'r', 'FontSize', 24);

      % Prompt user to draw a region on the image.
    msgboxw(txtInfo);
    
    hBox = imrect;
    roiPosition = wait(hBox);
    roiPosition % Echo coordinates to the command window.
    % Erase all previous lines.
    if ~enlargeForDrawing
      axes(handleToImage);
  %     ClearLinesFromAxes(handles);
    end

  xCoords = [roiPosition(1), roiPosition(1)+roiPosition(3), roiPosition(1)+roiPosition(3), roiPosition(1), roiPosition(1)];
  yCoords = [roiPosition(2), roiPosition(2), roiPosition(2)+roiPosition(4), roiPosition(2)+roiPosition(4), roiPosition(2)];

  % Plot the mask as an outline over the image.
  hold on;
  plot(xCoords, yCoords, 'linewidth', 2);

[Image Analyst]

Regarding your comment on your question above:

redChannel = rgbImage(:,:,1);
croppedRed = redChannel(10:560, 300:400)
verticalProfile = mean(croppedRed, 2);
horizontalProfile = mean(croppedRed, 1);
plot(verticalProfile, 'r-');
hold on;
plot(horizontalProfile , 'b-');
grid on;

[Lisa]

This one worked, thank you very much.

[Image Analyst]

You're welcome. Then please mark my Answer as "Accepted".

[Image Analyst]

The second argument of mean says what direction (dimension) to do the averaging over. Look up mean, or any other function, in the help documentation if you have any questions on what the arguments mean or want more in-depth explanations.

[Image Analyst]

After you get each profile, plot it:

hold on;
plot(horizontalProfile);

Don't use 'r-' or else all plots will be in red and you won't be able to tell them apart.

[Image Analyst]

Unless you share you actual code - not pseudocode - we can't help.