I guess you are use getframe to save the image with 3 lines. getframe cannot keep the resolution of the original image. You may use imresize(), but that will modify your original image to some extent. If you have computer vision toolbox, then you can use insertShape() to fuse the lines into the pixel of the image directly.
img = imread('crop_row_001.JPG');
data = load('crop_row_001.tmg').';
data2 = zeros(size(data,1), size(data,2)*2);
data2(:,1:2:end) = data;
data2(:,2:2:end) = repmat(1:size(data,2), size(data,1), 1);
img = insertShape(img, 'Line', data2, 'Color', 'r', 'LineWidth', 1);
P.S.: I used the image and data file from your other question, which I answered.
The attached image has resolution of 320 * 240.