The overlay process in Revu lets you compare two or more PDFs by converting each document to a different color and stacking them on top of each other as layers in a new PDF. Each layer is transparent and blends with the layers below it. Where the colors are stacked directly over each other, they blend to create a darker color, making it easier to see which elements have changed and which ones have remained the same from revision to revision.
There is also a batch version of Overlay.
In the example below, an overlay was created from two revisions of a drawing, with the first revision converted to red and the second to green. When the same line existed in both drawings, they stacked to create a dark, nearly black line, indicating areas where no changes had been made from the one revision to the next.
Where something was in the second revision that was not in the first, a green line appeared.
Where something was present in the first revision and was not in the second, a red line appeared.
This made it easy not only to see changes made from one drawing to the next, but to know what had been added and what had been removed.
In general, when you run an overlay comparison Revu assumes that you wish to do so on PDFs that are currently open, so you might want to open the PDFs you plan to overlay first. It's not required, however.
Go to Document > Comparison > Overlay Pages. The Overlay Pages dialog box appears and the open PDFs are automatically added to the Layers list.
Select a page range from the Pages dropdown menu to determine which pages of the source file will be added. Options are:
For example: 1-3, 5, 9 will include pages 1, 2, 3, 5 and 9.
On the first drawing, click three points that will act as anchor points between the drawings. It is recommended to use points near the edges of the drawing.
Tip: Enable Snap to Content on the Status bar to help you get a precise definition.
The default overlay settings in Revu are changeable. To access the default settings,