Studying the Zapruder Film by the Overlay Method

The overlay method adjusts the position of one frame relative to another. Four buttons, Left, Right, Up and Down, enable the viewer to eliminate apparent motion caused by panning errors. Once properly aligned, successive frames show small changes in the size of objects due to their varying distances from the camera. Four adjustments, Heighten, Narrow, Shorten and Widen compensate for these changes in the apparent sizes of objects. These corrections reveal frequent buckling of the film as the cause of anomalous changes in the apparent shapes of subjects.

This program provides a drop-down list of popular frames. Clicking on any pair places the selected frames in the download text box. You may bypass this shortcut and manually enter any combination of frames. The drop-down illustrates the required syntax. A lowercase zee preceds the frame number and a forward slash separates the first from the second frame. A click on the Select and wait button starts downloading of the frames. With Internet Explorer the frames run automatically after downloading. On other browsers, you should wait until the status bar displays Done before clicking the Run button. Premature clicking on the Run button will display partial frames and slow the downloading.

All buttons support keyboard navigation. The Tab key moves focus from left to right and from top to bottom. Pressing Enter when a button has focus is equivalent to clicking it. This feature enables keystrokes to select adjustments and frees the mouse pointer to highlight graphic details. Alternately the Shift Tab combination moves focus from the right to the left and scrolls from bottom to top of the page.