save large image/figure

I have a large mxn (~300,000 x 75) element matrix that I would like to save as an image or pdf without any compression. I'm currently using imagesc() to display. I've used the print function to set my own resolution but I'm having difficulty achieving the desired result. The image is a large time series that I would like to save in such a way that I may zoom in over a region, and transmit the complete series to others without any losses. Is there a simple method to save large , essentially banner sized, images / figures?

Answer 1

[Image Analyst]

Why not save it as a PNG format image file with imwrite()?

Or just save the variable as a .mat file with save()?

[Image Analyst]

Regarding your "Answer" on zooming, see the attached demo.

[George Valdes]

I appreciate the help. I'm unable to use a .mat as everyone I must share this with either does not posess or does not have any experience with matlab. I've used print, and export_fig to produce png's however even after setting the position pixel/paper size the largest images it will produce are still the compressed (fit in figure window) forms that have a maximum size matching the display size. As for the zoom example that you sent. Unfortunately I do not possess the image processing toolbox(but going back to the issue with being able to share it with others precludes this option)

[George Valdes]

I've tested the imwrite solution you've given with a quick random matrix, and it appears to work exactly as I need. thank you! This is a start. Now I just need to figure out how to remap my matrix into an indexed image with a color map!

[Image Analyst]

Well the easiest way to do that is with the Image Processing Toolbox which you said you don't have. You would be able to use functions like rgb2ind() and ind2rgb(). You can do it manually without too much trouble though if you know how you want to quantize your colors. rgb2ind() helps out there because it figures out the colormap and indexes for you.

Answer 2

[Ingrid]

I always use the export_fig figure for saving images since this doesn't crop the figure so you might want to look at this?

http://www.mathworks.com/matlabcentral/fileexchange/23629-export-fig

Answer 3

[George Valdes]

I'm able to get the export_fig function to output images (even though some of the options seem to have a compatibility issue with 2015a. However, the higher resolution images it's giving me are "higher resolution" of the compressed figure's image. Meaning I'm still unable to zoom in on the image and see the original data. the -native and -q options from what I've read aren't handling the 2015.

%%update: I see what's happening here I believe. when displaying the image I get a warning saying "too big to fit on screen displaying at 1%" so the data is being compressed to fit the figure size. The usual commands will only save images of this compressed data. I don't particularly care about displaying it, I need a way to save the 100% scale data as an image to view with windows photo-viewer.%%

[Ingrid]

I think you could have solved this by

figure('Position',[values of sizes required],'Visible','off')

but good to see that the other solution works.

[Keyes34]

What do you mean by [value of sizes required]? Could you give an example of the input parameters?

[Image Analyst]

It's x,y,width,height. So [0, 5., 1, .5] would be the top half of the screen, and [.5,0,.5,1] would be the right half of the screen. And [0, 0, .75, .5] would be a figure in the bottom half of the screen but going from the left edge to 3/4 of the way across the screen.

[Keyes34]

I keep getting a 2x2 8 bit image of grey.

    RGBImage = imread(file); 
    figure('Position', [0 0 1 1], 'Visible','off'), RGBImage;
    filename = sprintf('ROI_%s.bmp', Img{imageCount});
    export_fig(filename, '-a2')

What am I doing wrong?

[Image Analyst]

figure just brings up an empty figure. You never displayed anything with imshow() so the figure is blank. Then you do RGBImage, which does absolutely nothing. Then you create a filename, which is a string, and save the current figure, which is blank. Use imshow(RGBImage) and see if that fixes it.

RGBImage = imread(file); 
% Display figure with image in an axes.
imshow(RGBImage);
% Size the figure to full screen.
figure('Position', [0 0 1 1], Visible','off');
filename = sprintf('ROI_%s.bmp', Img{imageCount});
export_fig(filename, '-a2')

I don't know what the cell array Img contains. Hopefully it's a string or else you're in trouble with that sprintf() statement.

[Keyes34]

Yeah, that's what I tried before. Just tried it again, same result; 2x2 8 bit image of grey. Not a problem with the Img cell array, no errors.

I can display the image, but when the image is saved I get that 2x2 gray thing. If I remove

    figure('Position', [0 0 1 1], 'Visible','off');

Then the image is properly saved, just that I have the same problem as the OP.

[Image Analyst]

Well obviously if you set Visible to off, the figure will be not visible and so what is there for export_fig() to save???

This works:

RGBImage = imread('peppers.png'); 
% Display figure with image in an axes.
imshow(RGBImage);
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% filename = sprintf('ROI_%s.bmp', Img{imageCount})
% export_fig(filename, '-a2')

If the image is only 75 pixels high and 300 thousand wide, then it will show up on the screen as just a line because of the extreme aspect ratio. Why don't you just save it with imwrite()? I mean, there's no way you could put any annotation on that image anyway, and saving annotation is the main advantage export_fig() has over imwrite().

[Keyes34]

Oh. I see. Well then. Thought the guy's suggestion above would work.

To be honest, export_fig was mainly for this part of my code. Contour lines don't appear in imwrite, but they do in export_fig.

    figure,imshow(RGBImage); hold on;  %Hold for contour lines.
    contour(Marked_ROI,[0 0],'b','LineWidth',2);  %hold off;tried here b4
    %Marked_ROI is a binary image.    

    filename = sprintf('ROI_%s.bmp', Img{imageCount});
    imwrite(RGBImage, filename);

    hold off;