Detect Colors in a white image

Greetings, for a school project I need to detect if there are nonwhite colors in this image.

http://radar.weather.gov/ridge/RadarImg/N0R/JUA_N0R_0.gif

If there are colors apart from white in the image I need to transmit a signal to a controller telling it to start working.

How do I detect colors and transmit the signal?

Answer 1

[Sean de Wolski]

in a unsigned 8bit integer image (uint8) (just example)

 I = your_image
assert(isa(I,'uint8'),'For this example I is expected to be uint8');
if(any(I(:)~=255))
   fprintf('There are non white areas');
else
   fprintf('All white!');
end

Answer 2

[Walter Roberson]

First you have to define "white" for your purposes. If a pixel is (254, 254, 254) then is that white? How about (255,255,254) ? How about (128,128,128) ?

Answer 3

[Jose]

Thank You very much Sean de... It worked. Walter Roberson, you are also right, the program was not working because 255 was not the value of white for that image, I clicked on the variable matrix of the image and it was 9, after I changed the value, it worked perfectly.