How do I add custom gridlines on my image?

So I'm trying to program an image converter and trying to get some gridlines on it.

axis equal;
imagesc(secondlevelTIFF, scale) %read matrix into figure
axis equal;
colormap(jet) %makes it into jet
axis on;
grid on;
colorbar;
temp=[[sprintf('fig%03d', i)],'.tif']; %name current figure file
fpath = [I have my path here]; %set file directory
saveas(gcf, fullfile(fpath, temp));

This is my current code with the 'secondlevelTIFF' being my image. I'm trying to add custom gridlines. The image file I have is 500*500 pixels and i want gridlines at 50 and 150 pixels. How do I add these gridlines so that they are on the top of my final image file?

[Clay Swackhamer]

If you are still working on this I wrote a simple function to put a grid on an image. It is on the file exchange here

Answer 1

[Image Analyst]

Either burn the lines into your image like this:

[rows, columns, numberOfColorChannels] = size(secondlevelTIFF);
for row = 1 : 50 : rows
  secondlevelTIFF(row, :) = 255;
end
for col = 1 : 50 : columns
  secondlevelTIFF(:, col) = 255;
end

(this will change your image), or draw a line in the overlay above your image like this

hold on;
for row = 1 : 50 : rows
  line([1, columns], [row, row], 'Color', 'r');
end
for col = 1 : 50 : columns
  line([col, col], [1, rows], 'Color', 'r');
end

This will not make changes to the image array itself - it will just place lines into the graphic overlay. Adapt spacing and offset as needed.

[Hosup Song]

I'm trying to use the second method here, but having a bit trouble understanding it. How do I actually implement this method?

[Image Analyst]

You implement it by coping and pasting that code I gave you into your code in the text editor window after you've displayed your image. It's very basic MATLAB skills. You have to learn how to write code into editor windows and how to debug them. If you already know how to do that, then I really don't understand your question at all. Here is a complete m-file for you:

secondlevelTIFF = imread('moon.tif');
imshow(secondlevelTIFF);
axis on;
[rows, columns, numberOfColorChannels] = size(secondlevelTIFF);
hold on;
for row = 1 : 50 : rows
  line([1, columns], [row, row], 'Color', 'r');
end
for col = 1 : 50 : columns
  line([col, col], [1, rows], 'Color', 'r');
end

And here is what it looks like:

Answer 2

[Star Strider]

You have to create a figure object, then put the gridlines on top of the image.

figure(1)
imagesc(secondlevelTIFF, scale) %read matrix into figure
set(gca, 'Layer','top')
... REST OF YOUR CODE ...

[Walter Roberson]

The layer top is the obscure bit. Other than that you use the fact that grid lines are placed at tick positions.

[Image Analyst]

I used this:

secondlevelTIFF = imread('moon.tif');
% imshow(secondlevelTIFF);
imagesc(secondlevelTIFF) %read matrix into figure
axis on;
set(gca, 'Layer','top')

and I don't see any grid lines on top of the image.

What did I do wrong?

[Star Strider]

You didn’t toggle the grid.

figure(1)
secondlevelTIFF = imread('moon.tif');
% imshow(secondlevelTIFF);
imagesc(secondlevelTIFF) %read matrix into figure
grid
axis image
set(gca, 'GridColor','r', 'GridAlpha',1)
set(gca, 'Layer','top')

and add a few tweaks to make the grid lines more visible:

[Hosup Song]

How do I customize this grid? like I only want gridlines at x = 50 and x = 300 for the above example and nowhere else. How do I make it that some show and some don't?

[Walter Roberson]

Change the xtick to only the place you want the lunes

[Star Strider]

@Walter — Thank you.

I had to be away for a while. Life intrudes.

[Image Analyst]

Hosup, if you have R2016b you can run the new function xticks():

xticks([50,300]);

There is a similar function, yticks().