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2.3 nip for reflectogram mosaics

This section quickly builds an infrared reflectogram mosaic using the sample images that come with nip. See Chapter 3 for detailed coverage.

Click on Insert=>Image from file to get an image file load dialog. Click on the down button at the right end of the current directory line (see Figure 4.8) and select nip's main data directory from the list. It'll probably be at the end of the list and look something like /usr/local/vips-7.8/share/nip/data. The IR directory should appear in the directories list. Double click on that, and you should see six sample files. Drag with the left mouse button to select them all and click OK. See Figure 2.7.

Figure 2.7: Loading the sample images
\includegraphics[width=3in]{figs/snap14.PS}

The images have been named to match their positions in the mosaic, so for example cd2.1.v is the first image in row two. Open up viewing windows for your first two images by double clicking on the thumbnail images. Move your two opened images viewers so that they are side by side. Adjust the zoom (using the i and o keys) and the pan so that the overlap area is visible in both images.

Mark a tie-point on each image by Ctrl-left-clicking on a feature you can see in both images, see Figure 2.8. Move a point after you've marked it by dragging on the label. You don't need to be exact: nip just uses the point you select as the start point for a search. It can cope with misses of up to about 10 pixels. To mosaic the two images together click on Mosaic=>Mosaic_translate=>Left_right. See Figure 2.9.

Figure 2.8: Ready to join
\includegraphics[width=3in]{figs/snap15.PS}

Figure 2.9: Joined images
\includegraphics[width=3in]{figs/snap16.PS}

Join the rest of the pairs of sample images together left-right. Figure 3.2 shows how they should fit together. Once you have made all the rows, join the rows together in turn to make the complete image using Mosaic=>Mosaic_translate=>Top_bottom. Chapter 3 has some tips for doing this quickly.

When you've built the whole thing, you'll see that there are differences in brightness between the tiles that make up your composite image. You can fix most of problems like this automatically by selecting your final mosaiced image and clicking on Mosaic=>Mosaic_balance. This operation takes your mosaic apart, examines the overlap areas for differences in brightness, calculates a set of adjustment factors to minimise these differences, and then rebuilds the mosaic.

There can be some problems left even after mosaic balance. Use Mosaic=>Tilt_brightness to remove any left-right or up-down graduations in brightness. The mosaic balancer outputs a floating point image (each pixel is a large floating point number), which you can't save as TIFF, PNG or JPEG. Therefore as a final step, click on Format=>Convert_format_to=>unsigned_8bit to turn the image back into something you can save.

Save your mosaic workspace for future reference by clicking on File=>Save workspace. To save just the mosaiced image, right click on the thumbnail and select Save.


next up previous contents
Next: 2.4 nip for nerds Up: 2. Tutorial Previous: 2.2 Quick interface tour   Contents
John Cupitt 2003-07-21