The left and right viewport windows can be moved to a certain area of the image, by clicking in either the left or right viewport window and dragging it.
The right viewport window is updated after a slider is dragged and released.
Checking the Update box updates the whole image with the changes (not final until the green check button is clicked!). Unchecking it returns the image to unchanged.
The - and + square magnification buttons, located under the viewport windows, enable the viewport to zoom in or out. The magnification levels are: 25%, 50%, 100%, 200% and 300%.
The - and + round buttons, located on either side of a slider, change the slider value by 1(value).
The numeric values to the right of each slider, can be highlighted and overwritten.
The green check button applies whatever changes were made with the sliders, to the original image (whether the update box is checked or not). The red X button cancels the filter and returns to the image.