I'm working on digitising aerial images of saltmarshes onto ArcGIS, so that I can measure change in extent over time.
To do this, I had a georeferenced image loaded on Adobe Photoshop Elements (figure 1). There, I extracted the 'saltmarsh', and subsequently re-georeferenced that image back into ArcGIS 9, but this time with only the parts that I'm interested in (figure 2).
Now, I want to convert all the greenish stuff into a shapefile. What is the best way to do this? I didn't want to create a new polygon by hand because as you can see, the structure is rather complex and it would be time consuming to draw it accurately (I have many more images to process after this).
Any ideas? Your help would be really appreciated?
Figure 1: Saltmarsh image.
Figure 2: Saltmarsh aera removed from background - I now want to convert this section of image into a shapefile. How do I do this?