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Add a Percentage Column to the Attribute Editor

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The output of a classification process is a thematic file and its associated attribute table. The attribute editor (table) contains useful information such as class names, color/class, histogram, opacity, etc. This table is editable provided you have permissions on the file. Attributes (columns) may be added to the table and the cells may be edited. One such column that many users wish to add is an attribute that lists the percent that each class represents in the image. Follow the procedure below to add a percentage column to the attribute editor of a thematic file.

Software requirements: IMAGINE Essentials

1. Display a thematic image in a Viewer. A copy of lnlandc.img from the ERDAS IMAGINE examples directory will be used in this exercise.

2. Select Raster | Attributes.

3. Select the column within the Attribute Editor that will be used for the percentage (i.e., histogram) by left-clicking on the column title.

4. Select Edit | Compute Stats. A window will appear with calculated statistics.  Do not close this window yet.

5. Select Edit | Column Properties and the Column Properties dialog will open.

6. Select New In the dialog.

7. Select the Editable check-box, and change the title to the name of your choice.

8. Set the Type to Real.

9. Change the format to 0.00% by selecting the More button to the right of the Format field and then selecting 0.00% in the Number Format dialog.  Select OK.

10. Assign a formula by selecting the More button to the right of the Formula field.

11. In the Formula dialog, select the name of the column on which you performed statistics (Histogram).

12. Select the division sign ( / ) in the dialog

13. Type in the "Total" number value from the statistics window.

14. Select OK.

15. Select Apply on OK in the Column Properties dialog.

16. Select OK.

17. Examine the Raster Attribute Editor to verify that the percent column was added and populated.

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