Find yellow pixels in an image

So I have an image, jpg file, which means it is RGB?

I want to find out how many pixels are yellow, the following code is what I have now. Shouldn't be too hard except I don't know the syntax

img=imread('MyImage');
[a,b,c]=size(img);
count_y=0;
for i=1:a
    for j=1:b
        if img(a,b)==yellow   %%% How do I write this line??
            count_y=count_y+1;
        end
    end
end

Thanks folks!

[Jan]

if img(a, b, :) == yellow
   %         ^

You have to consider the RGB values, therefore you need to extract the [1x3] RGB vector for each pixel.

How do you define "yellow" exactly? There are different RGB colors looking very yellowish, so "yellow" means a range of colors usually. Then the HSV color space is smarter. There are different methods to determine the distance between colors in the HSV space, but it is your turn to define, what "yellow" is for your needs.

[Yingxiu Guo]

Hi Jan, thanks for your reply. I want bright yellow, a little bit greenish

Right now in the loop I have

if img(i,j,1) > 200 && img(i,j,2) > 200 && img(i,j,3) < 50

So the first component is red, the second is green, and the third is blue? Does this selects the yellow colors?

Thanks again!

Answer 1

[Image Analyst]

Use the Color Thresholder on the Apps tab of the tool ribbon. Select HSV color space and load your image then select thresholds and then export the function.

[Yingxiu Guo]

Hey thanks for your reply.

I think I made some progress here.

Cheers!

[Image Analyst]

If you want, you can use my code from here: my File Exchange

Answer 2

[KSSV]

Loop not required...refer this https://in.mathworks.com/matlabcentral/answers/4508-modify-this-code-to-detect-yellow-colour

[Yingxiu Guo]

I tried that. Not sure it works for my purpose

[Image Analyst]

How could we know? -- you forgot to attach your image.