PixelSugar's Preview Panel shows the current image.
Change the image's zoom with the slider at the toolbar's center.
Press the space bar to toggle between "fit to screen" and actual pixels zoom levels.
You can also use Cmd and the +/- keys together to zoom in past 100%, or zoom out past "fit to screen"
Use the buttons at the bottom-right to show before/after and split views of your edit.