MATLAB: How to save the image WITHOUT the white background using imwrite (advanced problem)

backgroundimwritesave image

RGB = imread('bird1.png');
figure
imshow(RGB)

Then I get:

Then:

s = size(RGB);
rectangle('position',[1 1 s(2) s(1)], 'edgecolor', [1 0 0])
rectangle('position',[0 0 s(2) s(1)], 'edgecolor', [1 0 0])

I get:

Now I would like to save this image WITHOUT the white background, only the content within the red box (including the red box).

Imwrite needs to use 'RGB', however after the red box been added onto the image, RGB is no longer the original RGB. It WON'T be correct just to use

imwrite(RGB, 'bird1.png');

Could anyone provide correct solution to this question please?

Best Answer

Try this:

% To burn the color into the image itself.
[rows, columns, numberOfCOlorChannels] = size(RGB)
RGB(:, 1, 1:3) = repmat([255, 0, 0], rows, 1);
RGB(:, end, 1:3) = repmat([255, 0, 0], rows, 1);
RGB(1, :, 1:3) = repmat([255, 0, 0], columns, 1);
RGB(end, :, 1:3) = repmat([255, 0, 0], columns, 1);
imshow(RGB);
imwrite(RGB, filename);

It's much more robust than saving the bitmap in the overlay, which is subject to change whenever you resize the figure window.

Related Solutions

MATLAB: R g b components of an image

That should work. The only reason it wouldn't is if i is a floating point array, in which case you'd have to use imshow(i, []) to see it. By the way, use a variable name other than i (the imaginary variable) for your image name, such as rgbImage or something descriptive like that. If you have a floating point image and values exceed 1 they will appear as white and if they are less than 0 they will appear as black. Not sure if you meant a black and white image like you said, or if you really meant a gray scale (monochrome) image that has 256 gray levels, not just 2 levels, those being pure black and pure white.

Of course you know that each color channel by itself is a gray scale image , don't you? In other words if I extract each color channel:

% Extract the individual red, green, and blue color channels.
redChannel = rgbImage(:, :, 1);
greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);

each one of those arrays is just a simple monochrome gray scale array, and will appear as gray scale if you use imshow(). If you want to see it appear in the color of the color channel that it represents then you'd have to either use cat() to make an RGB image out of it:

z = zeros(size(redChannel));
redAppearingImage = cat(3, redChannel, z, z);
imshow(redAppearingImage);

or use colormap() to apply a color to it (which will use less memory).

imshow(redChannel);
myColorMap = [[0:255]', zeros(256,1), zeros(256,1)];
colormap(myColorMap);
colorbar;

Finally you might have fun running my RGB histogram demo attached below.

MATLAB: How to add box to an image

If the bad lines are always the rightmost one and the bottom one, you can simply crop the image to not include those:

rgbImage = rgbImage(1:end-1, 1:end-1, :);

To pad the image with certain color, you can use padarray() on each color channel. There are other ways. Let me know if it's still a problem for you.

Best Answer

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MATLAB: R g b components of an image

MATLAB: How to add box to an image

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