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University Library, University of Illinois at Urbana-Champaign

Unwarping images using ArcMap

This guide shows how to use ArcMap to transform an image of a curled book into a flat picture. Scanned images of books are often distorted near the binding. This process can correct that.

Begin the Transformation

  1. The ArcMap Table Of Contents should have a grid or graph paper on top with transparency set to between 50 and 90%.  Below the grid should be the image that you want to uncurl.
  2. If necessary, turn on the Georeferencing toolbar in ArcMap.  Under the "Customize" menu item, hover over "Toolbars" and then be sure the "Georeferencing" toolbar has a check mark in front of it. The toolbars are moveable and yours may appear in a different location than is shown below.

  3. Set the georeferencing toolbar "Layer:" use the dropdown to select the name of the layer that contains the curled image.

  4. Under the "Georeferencing" drop down menu, uncheck "Auto Adjust".  This is important because the first few points may cause the image to warp beyond recognition. If that happens, simply remove the last point from the link table as shown in step 4), number 6.

  5. Find a corner of the image by using the hand icon  or scroll bars to move sideways and up/down. Zoom into the corner using the mouse wheel or the magnifying glass tool .
  6. Activate the Georeferencing mode by clicking the "Add Control Points" icon.

    Add Control Points
  7. Click on a corner of the paper in the curled image. We will then connect it with a corresponding point on the grid.
  8. Click on the grid location where you want that point to appear.  If you are not using a grid, click where you want that point to be stretched toward.

  9. Click on another corner in the curled image and repeat the process.  The mouse wheel, scroll bars, hand icon and magnifying glass can be used to move around.  If you switch to a different tool, you will need to click the "Add Control Points" tool again to finish placing your points.

  10. Look at the lines of text and add additional transformation points.  Click on the text first and then click where the text should appear on the grid.

  11. Spread the control points around the document. It is best to evenly spread points throughout the document so that it is stretched evenly.