Reduce loss of quality when using imfill and imfuse

I have to fill some regions of a black and white map, whose regions are black and are delimited by white borders.

This is the code

fill_regions = [   128    58
   280    80
   335   292
   430   430
   470   475
   525   525
   550   655
   680   610
   770   380
   785   480];
I = imread('https://i.imgur.com/4kWRWDV.png'); % black italy with white borders
BW = imbinarize(I,.1); % turn I into a black-white image...I had to use .1 threshold to prevent the filling of multiple adiacent regions
T = imread('https://i.imgur.com/1QY6Qw0.png'); % transparent italy, has only the borders
for i = 1:size(fill_regions,1)
    BW = imfill(BW,fill_regions(i,:));
end
imshow( imfuse(BW,T,'diff') ); % add the erased borders to BW
saveas(gcf, 'test.png')

and here is a comparison between original image (left) and filled one (right)

as you can see, the filled image has poor quality (but also the original image has not the same quality as the source image...why this happens?).

Is there a way to preserve the same quality as the source image or, at least, to reduce the loss of quality?

[darova]

I saved your boundary image, it's poor quality. Look

You don't need for loop in this case, just imfill

I1 = imfill(BW,fill_regions);

[giannit]

thank you, it works without the for loop. yes the original image is not high quality, but matlab seems to worsen it even more (borders are cut in some parts)

Answer 1

[giannit]

By placing the following command right before the saveas one

set(gcf, 'Position', get(0, 'Screensize'))

the size of the output image is increased, in my case from 853x827 to 2134x1103, and the quality of the image is increased too. However, since my screen size is 1366x768, I don't know why the size is set to 2134x1103.

EDIT

another option is to use the export_fig toolbox

export_fig test.png -m2

where -m2 produces an image double the size (in pixels) of the on screen figure

[Image Analyst]

Or exportgraphics() in r2020a or later.