Perspective transformation of images via touch signals

An example calibration device includes a projector to project a first image onto a touch screen. The first image includes a first set of four corner coordinates. A processor is to perform a first perspective transformation of the first image into a second image for projection onto the touch screen by the projector. The second image includes a second set of four corner coordinates. The processor is to receive at least one touch signal associated with a second set of four corner coordinates associated with the second image from the touch screen. The processor is to perform a second perspective transformation of the second image using the second set of four corner coordinates to resize the second image based on the first set of four corner coordinates.