how can i detect sky

Hello

I want to detect sky in a image and chang it colour to black.How can i do that?

For example this image:

[Jan]

While this may be easy for this image, "sky" can be extremly hard for other images.

[Adam Danz]

[Adam Danz]

@Eren Aslan for your simple image of a nearly uniform background, I would start with regionprops to segment the plane and then assume everything else is sky (including the ocean in my image above). However, it will not work with more complex backgrounds.

[Sam Chak]

@Eren Aslan Are you trying to develop the MATLAB-based "Magic Wand"? Sound like an interesting project!

Answer 1

[yanqi liu]

yes，sir，for more image，may be use DeepLearning to segment

but just for this image，we can use some simple method，such as

im = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/945114/image.jpeg');
jm = rgb2lab(im);
s = imcomplement(mat2gray(jm(:,:,3)));
bw = im2bw(s, graythresh(s));
im2 = im;
% make sky to black
r = im2(:,:,1);g = im2(:,:,2);b = im2(:,:,3);
r(bw) = 0; g(bw) = 0; b(bw) = 0; 
im2 = cat(3,r,g,b);
figure; 
subplot(2,2,1); imshow(im,[]);
subplot(2,2,2); imshow(s,[]);
subplot(2,2,3); imshow(bw,[]);
subplot(2,2,4); imshow(im2,[]);

[Adam Danz]

Nice work!