How to set specific color in an image as transparent?

In this image:

I would like to set the blue color rgb = [61 38 168] as transparent and save it to a new png. How can I do this? Thanks a lot

EDIT: additional information

Thanks to your answers. Because you ask yourself, what I want with this transparency I want to give you more information: First, I want to define the blue color as transparent:

to be able to georeference it like this:

Again, thanks for your help (I did this using Photoshop, but I would prefer doing this with Matlab... )

Answer 1

[Adam Danz]

Load image

img = 'image.png';
I = imread(img); 

figure()
tiledlayout(1,2)
ax1 = nexttile();
imshow(I,'Parent',ax1)

Isolate target color

targetColor = [61 38 168]; 
isTarget = I(:,:,1) == targetColor(1) & I(:,:,2) == targetColor(2) & I(:,:,3) == targetColor(3);
isTargetArray = repelem(isTarget, 1,1,3);

Updated: Plot isolated section on top of another image

ax2 = nexttile(); 
hold(ax2, 'on')
imshow(rand(size(I)),'Parent',ax2) % noise image

% Isolate section
img2 = imshow(I,'Parent',ax2);
% Set transparency
set(img2, 'AlphaDataMapping', 'none', 'AlphaData', double(~isTargetArray(:,:,1)));

[Image Analyst]

I'm wondering what he want the transparent parts to be over. Like is it over another image inthe same axes, or he's hoping for some kind of floating, irregularly shaped image that shows the OS's desktop (like wallpaper, icons, and other open applications) through the transparent regions of the image?

[Adam Danz]

Also wondering....

I have a feeling OP wants to isolate the blue section and treat it as a patch object which, of course, is more complex than what my answer provides.

[Harald von der Osten]

thanks for your help. I have extended my question to give you some more information for what I want to use this transparency...

[Adam Danz]

I've updated my answer to show how to selectively add transparency to sections of the image.

[Harald von der Osten]

thanks a lot, dear Adam Danz

Answer 2

[Image Analyst]

Use imoverlay

maskColor = [61 38 168];
% Create a new image where the mask is the specified color over the original rgb image.
image2 = imoverlay(originalRGBImage, maskImage, 'Color', maskColor);
imshow(image2);

where mask is your image and it's 0 where you want the original image to show through, the mask is 1 where you want the specified color. The color will be solid, 100% opaque.