How to set the value for thresholding for detecting trees in Matlab?

I am new in Matlab. I have a picture which includes a building,a person, a small river and some trees. I need to threshold the green band (I guess) to detect trees with erosion dilation etc. However, I can't seem to even make an histogram of the image's colors. All the other objec开发者_如何学Pythonts in the picture also have some green in it I think (i used myImage(:,:,2) < 130 ) and not only greens, but almost all the other objects were there in the binary picture (the person's black coat, river etc.). Can you tell me a way to do this? I want to get a histogram first, not sure how to use it though.

myImage = imread('myIm.JPG');

?? imhist(myImage); doesn't work.

Any help would be appreciated.

If I even manage to get an histogram, how can I use it to detect the trees? Can I both threshold green and other colors?

You probably want to first convert your image into another color space, like the HSV. You could do something like:

myImage = imread('myIm.JPG');
hsv_myImage = rgb2hsv(myImage);
imhist(hsv_myImage(:,:,1));         %just look at the hue component of the image

Then your histogram will indicate all the different hues.

use the hist() function in matlab for color images