Let's start with this image:
Select number 1 in the curve Segments list
Add Vertical curves and set them like in the image below. There are 8 curves in the image:
Press the button "Straighten":
Press the button "Set to Initial W x H Ratio":
The image is set to the initial Width x Height ratio. If a user finds that this ratio is inappropriate, set a new ratio with a slider.
Button "Set to Initial W x H Ratio" in the "Ratio Adjustment" toolbox is for rescaling processed image by Width to achieve the initial Width x Height ratio. The button "Set to Initial H x W Ratio" is for rescaling processed image by Height to achieve the initial Height x Width ratio. There are also sliders for manual ratio settings.
Every processed image can be saved with the File Save menu. Shift Lens App saves processed image in uncompressed TIFF file format.
Every action can be undone and redone.
If many curves are present on the image and if the "Actual Size" view is in use, only the selected curve is drawn while the changing shape is in progress. When the user releases the mouse button, all curves will be drawn. To move the image in the Actual size view, use sliders.