How to make image background white?

I have a binary image. I want to make the background white keeping the black straight lines intact.I mean those lines which intersecting image objects will remain intact. Picture has attached.

Answer 1

[Jeff E]

I would start by closing in small gaps to get a solid hand.

imgin_close = imclose(imgin, strel('square', 3));

Then I would find the overlap between that solid hand, and the inverse of the original image, leaving me with just white lines on a black background. You may have some additional noise around the edges of the hand. The could be filtered out with something like bwareaopen, depending on your application.

imgin_lines = imgin_close & ~imgin;
imgin_lines = bwareaopen(imgin_lines, 3);

I would then take the inverse of that image to get just the black lines.

imgout = ~imgin_lines;

[Zara Khan]

using imshow(imgout) showing me this error.

Error in imshow (line 227)
  [common_args,specific_args] = ...

Error in prog1 (line 10)
imshow(imgin_lines);

[Image Analyst]

This is what his code gives for me:

imgin = imread('image.png');
subplot(2, 3, 1);
imshow(imgin);
% Make a binary image
if ~isa(imgin, 'logical')
	imgin = imgin(:, :, 1) > 128;
end
imgin_close = imclose(imgin, strel('square', 3));
subplot(2, 3, 2);
imshow(imgin_close);
imgin_lines = imgin_close & ~imgin;
subplot(2, 3, 3);
imshow(imgin_lines);
imgin_lines = bwareaopen(imgin_lines, 3);
subplot(2, 3, 4);
imshow(imgin_lines);
% I would then take the inverse of that image to get just the black lines.
imgout = ~imgin_lines;
subplot(2, 3, 5);
imshow(imgout);

[Zara Khan]

Image Analyst: Thank you. It has solved my problem. Can I give black lines to any other colours ??

Jeff E: thank you. I have accepted your answer.

[Image Analyst]

Zara, I'm not sure what your question means. What do you want to give black lines "to"? What other colours are there that should receive/get black lines?

Or do you mean "how can I display the black lines in a variety of colors?" If that is what you mean, then label the lines-only image and call label2rgb().

% Label each line with a unique ID number.
labeledImage = bwlabel(imgin_lines)
% Let's assign each blob a different color to visually show the user the distinct blobs.
coloredLabels = label2rgb (labeledImage, 'hsv', 'k', 'shuffle'); % pseudo random color labels
% coloredLabels is an RGB image.  We could have applied a colormap instead (but only with R2014b and later)
imshow(coloredLabels);

[Zara Khan]

Image Analyst: Wonderful. Exactly this is what I was asking for.