Burn Grid onto a Series of Images

Hi all-I have a lot of image files and onto each I am trying to place a grid. I'd like to save the grid onto the file, and so produce a new image with the grid in a separate folder. In the end I will have one folder with the original files and a second with the files+grid.

Just now I have this:

for i = 1:fileCount2
    png=d2(i).name;
  
    image = imread(png);
    
    imshow(image);
    axis on;
    [rows, columns, numberOfColorChannels] = size(image);

    hold on; 
       stepSize = 20; % Whatever you want.
        for row = 1 : stepSize : rows
        line([1, columns], [row, row], 'Color', 'r', 'LineWidth', 1);
        end
        for col = 1 : stepSize : columns
        line([col, col], [1, rows], 'Color', 'r', 'LineWidth', 1);
        end
    
    
   % for x=1:length(fileCount2)
   % outputBaseFileName = sprintf('-%4.4d.png', x); %output filename, each frame numbered from 0001
    outputFullFileName = fullfile(strcat(outputFolder, '\FramesGrids'), strcat(baseFileName, outputBaseFileName)); %full output filename with .avi file number
    imwrite(image, outputFullFileName, 'png'); %write output png file
   
         
end

This successfully adds a grid onto the first photo in the folder, and saves a new photo in a separate folder, but the grid is not saved. The grid only shows up when I run the code and produce the figure within Matlab.

So, any advice on how to save the grid? And how to fix my loop so that every photo has a grid added, not just the first?

Thanks in advance!!

[Walter Roberson]

Computer Vision insertShape

[Louise Wilson]

Hi Walter, thank you. This looks useful but to use it I need to know the points in the photo where the gridlines go and I don't know how I could get this to control the size of the grid lines so that a square grid is produced?

[Walter Roberson]

There is a linewidth option for insertshape

You know, it might be easiest to just

%red
YourArray(1:StepSize:Columns, 1:StepSize:Rows, 1) = 255;
YourArray(1:StepSize:Columns, 1:StepSize:Rows, [2 3]) = 0;

if your line width is 1.

[Louise Wilson]

Thanks! This doesn't give me lines though, it gives me a dotted grid? Kind of looks like the skeleton of a grid. How do I join the dots?

I don't mean linewidth, I mean the distance between the lines, and where exactly the lines go? How do I specify this accurately so the spacing is consistent.

Answer 1

[Image Analyst]

Simply burn it into the image itself:

grayImage = imread('cameraman.tif');
[rows, columns, numberOfColorchannels] = size(grayImage);
% Make grid every 64 rows
for row = 8 : 64 : rows
	grayImage(row, :, :) = 255;
end
% Make grid every 32 columns
for col = 8 : 32 : rows
	grayImage(:, col, :) = 255;
end
imshow(grayImage);

[Louise Wilson]

Thank you!! I am getting much closer to getting this to work :-)

Can you tell me why the first line works but the second doesn't, when they appear to be doing the same? I am trying to write my code so I can apply it in a for loop:

 [folder, baseFileName, extentions] = fileparts('02052019-0006.png');

image = imread('02052019-0006.png');
[folder, baseFileName, extentions] = fileparts(image);
    

[Image Analyst]

I think the second line

image = imread('02052019-0006.png');

should work but it's a very bad idea to assign the output image variable with a name of "image" since that's the name of a built in function. Call it grayImage or rgbImage like I did.

The third line

[folder, baseFileName, extentions] = fileparts(image);

is wrong because fileparts() takes a filename string, not a matrix of uint8 gray level values.

[Louise Wilson]

Thanks, I think the error is basically that I need to extract the information from the file before I then read it in. If I switch the commands around in the 2 and 3 lines it works.

[Louise Wilson]

Thanks so much for your help!! I finished this code and everything is working great, thanks very much to you.

[Image Analyst]

No, swapping positions wouldn't do it because then the badly-named image would not have been defined yet by the time you call fileparts().

[folder, baseFileName, extentions] = fileparts(image); % Will throw error because image is not defined yet.
image = imread('02052019-0006.png');

But whatever, glad you got it working and thanks for accepting.