Editing an Image

Editing is not needed or useful for morphometric analysis. Notheless, Tracer will allow you to edit and save the actual image data. You can only remove areas by setting the voxel values to zero; you cannot change voxels to intensities other than zero.

The ability to edit images was inherited from a predecessor of Tracer that was specifically designed to be an editing tool. Some of the modifications that have been made are suboptimal for editing purposes and editing will be reoptimized in a future version of Tracer. Despite these inconveniences, the editing features are fully functional

To edit an image

1. From the "Contours" menu, select "Style" and then select "Closed" from the submenu

   This is not absolutely required, but the editing consequences of closed traces are easier to predict

2. Define a structure name
3. Trace the structure
4. Modify the trace as needed
5. Click the "Erase Here..." button on the control panel. Its text should turn red indicating that you are in erasing mode
6. If you want to erase everything inside a trace, click on the inside of the trace. Otherwise click on the outside of the trace
7. Repeat the above steps until editing is complete
8. If you make a mistake, you have a window of oppportunity to undo the mistake by choosing "Revert Edited Image" from the "Edit" menu. This will restore the current slice to its state prior to the last internal save of the edits. A variety of user actions can cause an internal save that closes this window of opportunity. These include, and are not necessarily limited to:
   • changing to another plane
   • changing the orientation
   • changing the magnification
   • changing the image intensity
9. Save the image

If you want to remove everything on a plane, you can choose "Select All" from the "Edit" menu when you are in tracing mode

Depending on your magnification and voxel anisotropy, the final edits produced may not precisely match the boundaries of your contour. This is due to the fact that traces can be digitized with subvoxel accuracy with respect to the voxels in the original images. However, edits must be defined in whole voxels, hence the blocky appearance at higher resolution

Mistakes that are recognized too late to use the "Revert Edited Image" feature described above can still be corrected by loading the original image as a reference image and using it to repair the image

Modified: December 15, 2001