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Whenever working with contour VOIs, the user can add or remove individual pixels as illustrated below. The initial contour 1 is filled in transparent mode. First pixel removal is activated by selecting the - button in the toolbar. The cursor shape changes accordingly, and by clicking at a shaded pixel the negative Contour 2 is created and the pixel removed (upper row). Whenever the user clicks into the image, the corresponding pixel will be removed from the VOI and a corresponding - contour is added to the list.
Pixel adding works in the same way. It is activated by selecting the + button in the toolbar, and the cursor shape changes accordingly. Whenever the user clicks into the image, the corresponding pixel will be added to the VOI and a corresponding + contour is added to the list (lower row).
Note that it is possible to create VOIs which consist of individual pixels only. The + button is available as soon as a New VOI has been created.