MATLAB - How to avoid a jagged image?

Question

How do I avoid a jagged image in MATLAB?

I have a 600 x 600 pixels image opened in MATLAB and do some processing on the image. However, when I save it, it looks so blurred and jagged. What should I do?

(This question is related to my previous question, MATLAB - How to plot x,y on an image and save?)

fid = fopen(datafile.txt);
A = textscan(fid,'%f%f%f'); %read data from the file
code = A{1};
xfix = A{2};
yfix = A{3};

for k=1:length(code)
    imagefile=code(k);
    rgb = imread([num2str(imagefile) '.jpg']);
    imshow(rgb);
    hold on;
    x = xfix2(k);
    y = yfix2(k);
    plot(x,y,'-+ b'); % plot x,y on the
    saveas(([num2str(imagefile) '.jpg'])) % Save the image with the same name as it open.
end
hold off

Are you using imwrite or imsave to save the image? What options are given to imwrite? — Vitor Py, Jul 05 '10 at 18:13
@Jessy: see also http://stackoverflow.com/questions/2487692/save-plot-into-image-file-in-matlab-difference-between-saveas-and-print — rwong, Jul 05 '10 at 18:40
when I look on the file that I saved from that code, the size and resolution of the image changed. How to maintain the size and pixel? — Jessy, Jul 05 '10 at 18:54
To make it not blur, either save as svg (a vector image format) or use a large size and high resolution. — rwong, Jul 05 '10 at 21:27

score 0 · Answer 1 · answered Jul 07 '10 at 01:13

0

If it is just a resolution issue, perhaps using the print command (as listed below) with an explicit resolution option may fix it.

print(gcf,'-djpeg','-r600',[num2str(imagefile)])

answered Jul 07 '10 at 01:13

arun

105
6

score 0 · Answer 2 · answered Jul 07 '10 at 13:45

0

My guess would be JPEG compression artifacts. JPEG isn't a great format for data with a lot of high frequency components. Have you tried turning the compression down? Like so:

imwrite(f.cdata,([num2str(imagefile) '.jpg']),'Quality',100);

The default for the quality parameter is only 75. That's plenty for a lot of cases, but you might need more.

answered Jul 07 '10 at 13:45

MPG

835
4
10

thanks the image are more clear now :) ...but the "+" which I used to plot the xy coordinate, which I set in blue color, turn into black color when I saved it. Why? – Jessy Jul 07 '10 at 13:53

MATLAB - How to avoid a jagged image?

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