how do i set image of picture to have white border on the left side?

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How do I set image of picture to have white border on the left side?

b = imread('peppers.png');
b = im2double(b)
b(:,1:100) = 255;
imshow(b);

gives me like red border which doesn't have 100% opacity, how do i get white?

matlab
1 Answers

It seems likely based on your question that the image loaded from 'peppers.png' is a color image.

You can check by typing

size(b)

into the command line. If it's a grayscale image, then the size will probably be something like

ans =

    200    100

assuming your image is 200 x 100 in size. But if it's a color image, as I suspect, then the size will be something like

ans =

    200    100     3

That third dimension holds the three color channels (red, green, and blue).

When you execute

b(:, 1:100) = 255;

you haven't specified which of the color channels you're indexing, so MATLAB implicitly assumes you're indexing the first channel, which is the red channel. So you are effectively doing this:

b(:, 1:100, 1) = 255;

But you don't want to just set the red channel to 255. To get a white border, you need the red, green, and blue channels to all be 255. Thus what you should do to get a white border is this:

b(:, 1:100, :) = 255;

That way you're indexing across all three color channels when you assign a value of 255, not just the red one.

user_14600570
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