How to convrt parts of grayscale to RGB

It's not simply convert a whole figure.

I just want to use a simple methods to finish a line trace. Like mark the air flow on a photo of wind tunnel experiment

The idea is convert the photo to grayscale first

Then check the grayscale of each pixel in a specific area

If the grascale is in a specific range (eg: 210 to 230)

Then convert it to red or blue

So that the air flow will be some colorful line on a grarscale figure.

But I don't know hot to check the pixel and convert them.

Answer 1

[ME]

This should do the trick:

A = rgb2gray(imread('image.png'));
A = cat(3, A, A, A);
s=size(A);
for i=1:s(1)
    for j=1:s(2)
        if(A(i,j,1)<=230 && A(i,j,1)>=210)
            A(i,j,1:3) = [255 0 0];
        end
    end
end

It will convert any grayscale sections in the range 210 to 230 to red. You could also add another similar if statement if you wanted to also add an additional condition to make some of it blue.

[Yubin ZHONG]

Yep it works. Thx-:)

[ME]

No problem. If this does what you want then could you perhaps accept my answer?

[Yubin ZHONG]

Oh my first time use mathwork,,,, didnt notice that

[ME]

No problem at all. Thanks for accepting my answer and I’m glad I could help.