Question

All,

I need to know how to stretch an image for further work.

for example, I have the next two images:

I want that the numbers will fill the entire square like this:

any help will be greatly appreciated.

Answer 1

Assuming that the background is a constant value, and that the image doesn’t have any constant rows, cols, and that the useful image is a rectangle in the middle of the larger image with background:

colsWithImg = find(any(abs(diff(img)))); % idxs of cols with any img in it.
rowsWithImg = find(any(abs(diff(img'))));
imgWithNoBG = img(min(rowsWithImg):max(rowsWithImg),min(colsWithImg):max(colsWithImg));
% this will also work: but you will lose any constant rows / cols
% imgWithNoBG = img(rowsWithImg,colsWithImg);

Now that you have an image with no background it is easy to stretch it using imresize, assuming you have the imageprocessing toolbox.

resizedImg = imrezize(imgWithNoBG,newSize);

To remove the artifact, first descritize the extracted character:

descImg = floor((nDescLevels*imgWithNoBg)/max(max(imgWithNoBg)))
colsNoArtifact = find(any(abs(diff(descImg))));
rowsNoArtifact = find(any(abs(diff(descImg'))));

And then extract the correct rows from the non descritized image

img3 = imgWithNoBG(min(rowsNoArtifact):max(rowsNoArtifact),min(colsNoArtifact):max(colsNoArtifact));

Lowering the number of descritization levels will help to remove more of the artifact, but will make it more likely to mistakenly remove part of the character. I also forsee some problems with numbers like 1 or 7 where part of the character can be mistaken for artifact.