Most visual researchers will choose to generate their stimuli entirely within the computer without reference to the outside world at all but sometimes it is necessary to work with real scenes that contain natural selections of colours, luminances and spectral composition. In this case an input device of some description is needed. Exactly which one to choose depends on which parameters are important, but the questions to ask are, do I want colour, do I want moving or static images, what resolution is needed and of course how much money is available. Here is short summary of the available options:

Scanners. Scanners are very freely available now and often come in a flatbed format in which you insert the original material to be scanned, close the lid and press the button. Typical resolution is 600dots per inch and 8 bits of greyscale. Colour scanners are available but expensive. Scanners will only work with paper or flat originals and obviously can’t handle moving pictures.

CD-ROM. This is a very popular format now, particularly for high resolution images where the amount of data are very large. Pre- recorded images can be purchased from many suppliers or a better solution is to capture your own on 35mm film and have them scanned and recorded onto CD-ROM by almost any high-street processor (very cheap). Scanned photographs have a very high resolution, typically 3000x2000pixels with 24bits per pixel, so the amount of data is enormous. You will definitely need to sub-sample these and reduce the quantity of data before using them.

CCD or video. This is the only way to go if you want any kind of moving image or sequence of frames. It normally involves adding a card to your computer to digitise the image and a source of video data such as a ccd camera or VCR. Resolution is medium (256x256 pixels) and colour quality is poor, particularly when the image is obtained from a television system.

Internet. Many researchers like to use the same images as their colleagues in order to compare results more easily. These can be obtained from many sites on the internet and have the benefit of being free. Indeed it has become something of a game among the image processing fraternity to try and establish pictures of children or students as de facto standards in this area.

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