Next: 3.2.1 Setting up your Up: 3. Assembling infrared mosaics Previous: 3.1 Introduction Contents

# 3.2 Infrared imaging

Most museums use tube cameras (usually called Vidicons) for infrared imaging. Although they are relatively cheap, they are not very stable, and they suffer from (sometimes quite severe) geometric distortions. More modern solid-state cameras are still expensive, but are becoming more widely used because of their greater stability. This guide assumes you are using a tube camera, but almost all of it applies to solid-state cameras as well.

Whatever your camera, there are three main sources of error which have to be addressed in order to be able to make successful mosaics:

1. Tube cameras suffer very badly from distortions in the image, usually either `pin-cushioning' or `barrelling'. These distortions result in alignment errors when sub-images are joined together.

2. The sensitivity of the tube varies across its surface, causing some parts of each sub-image to be brighter than others. This is made worse by unavoidable variations in illumination. When a lot of such images are joined together, the result is a `brick wall' effect.

3. The sensitivity of the tube also varies between sub-images, partly as the overall lightness in the field of view changes, and also because the electronics in the camera change as the camera heats up. This leads to a patchy, unbalanced mosaic.

The first two problems will be different in each Vidicon and will change each time a tube is replaced. All three problems need to be addressed to create successful infrared reflectogram mosaics.

Subsections

- 3.2.1 Setting up your system
  - 3.2.1.1 Mechanical set-up
  - 3.2.1.2 Video set-up
  - 3.2.1.3 Setting the crop and aspect
- 3.2.2 Capturing the data
  - 3.2.2.1 Setting the gain and offset
  - 3.2.2.2 Grey card correction
  - 3.2.2.3 Image capture
  - 3.2.2.4 Capture tips
- 3.2.3 Correcting illumination
- 3.2.4 Correcting with the command-line tool
- 3.2.5 Correcting within `nip2`

Next: 3.2.1 Setting up your Up: 3. Assembling infrared mosaics Previous: 3.1 Introduction Contents