Vegetation extraction is a bit more complex than running the spatial analysis tools that you named. For better results I would suggest the following:
- run analysis on a 4 band image (e.g. R,G,B,NIR)
- change image to be symbolized as 432 for RGB not 321
- create training samples that represent vegetation and run a supervised classification
These steps will give you a fair result, however you will still get many false returns (e.g. shadows by buildings, or green water bodies...etc).
For best results you will have to use a remote sensing software (including the three bullets above) that analyzes both spectral and textual objects of the imagery. I asked a question about what free software exists that can do this type of analysis, see link below:
Land Cover Feature Extraction from Satellite Imagery