To use preview, simply click (the Preview
button). This will select an area in the image and automatically apply filtration
to this area.
Or you can manually select any image area: press the left button, drag the mouse and then release the button. When an area is selected, Neat Image will (if auto recalculate preview is checked; see Filtration options) automatically apply filtration to the selected image area. You can also manually invoke preview recalculation with the Preview button, or the Filter | Preview menu item, or the F5 hotkey.
As soon as the preview is ready, you can left-click on the selected area to temporarily switch back to the original image for comparison.