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How to digitise oversized materials?

This part presents how to digitise large still-image like maps. Such an object will not fit into a standard scanner, so it has to be digitised piece by piece and then it can be merged using appropriate computer software.

Figure 1. Partial scanned images of a poster.

This lesson shows how to stitch 8 partial scanned images of a poster into a single image using Hugin. Hugin is a panorama photo sticher, but it can be used to stitch partial scanned images. Hugin is an opensource software available for Windows, Linux, Mac and FreeBSD. You can download it from Hugin download page.

This tutorial is based on the 0.7.0 version of Hugin.

Start by launching Hugin. This step depends on your operating system.

Figure 2. Adding files of partial scanned images.

Switch to the Images tab and add files using the Add indiviual images... button.

Figure 3. Camera and lens tab.

Switch to the Camera and Lens tab. Because we are using images from a scanner, we have to specify parameters for camera and lens. Select each image and enter 10 for the degrees of view (v) in the Lens and 0 for a, b, and c in the Radial Distrortion.

Figure 4. Stitcher tab.

Switch to the Stitcher tab and select Rectilinear for projection (f). Change the Field of View to 40 for both horizontal and vertical.

Figure 5. Control points tab.

Switch to the Control points tab. Here you have to add a series of control points for each pair of images. Use the title bar above each image to select an image on the left and right side. Make sure that both auto fine-tune and auto-add are checked. Now use your mouse to select the control points. Control points are well-defined points visible in both images. Select a point on one image. You get a magnifying glass window that allows you to carefully select the location of the point. Then click the corresponding point on the other image. You do not need to mark the exact location, Hugin will automatically select it. When you select next control points on one image, Hugin will find and select them on the second image. You have to select about 5 or 6 pairs of control points.

Now go back to the Camera and Lens tab and uncheck the link option for degrees of view (v), horizontal (d) and vertical (e) for each image. Next, for each image in turn push the New Lens button.

Figure 6. Optimizer tab.

Now select the Optimizer tab. Change the Optimize setting to the Custom parameters below. Check the roll (r), view (v), x shift (x), y shift (e) for all images except the first (with number 0). Make sure that other paramaters are not selected for optimization (yaw , pitch (p), distortion(a), barrel(b), distortion (c)).

Now push the Optimize Now! button and apply the results of optimization by the Yes button. Launch the preview window by pressing the Ctrl+P key combination. Use the Fit button and scroll bars in the preview to adjust output image.

Close the preview window and switch to the Stitcher tab save stitched images to file. Choose the output file format and push the Stitch now! button.

Figure 8. Result of stitching.