how to identify the threshold of an image?

I need to quantify the threshold of the green color in the attached image to remove everything around it.

I started with something like this:

imshow(img(:,:,1))

[x1, y1] = ginput(1)

buffer = 1.5

img = buffer * (round(x1), round(y1) )

Answer 1

[Cris LaPierre]

If you have the Image Processing toolbox installed, I would use the Color Thresholder app in MATLAB. I would then export the results to the workspace, and import that into the image viewer app to make measurements.