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5 Guidelines for Success in Image Capture

This project has demonstrated that it is important to attempt to maximise spatial resolution, colour quality and contrast ratio in image capture regardless of medium or system. Distinctions arise between media in the ways of achieving optimal quality in these areas, but as ideals to be aimed at they are standard to all media. The values obtained for these three criteria are the combined product of the effects imposed by the choice of equipment for capture and manipulation, and the expertise of the operator(s) involved.

Three main skills areas are indicated for the capture of images:

Photographic

Electronic (Video)

Computer The same skills are relevant for the post-digitisation manipulation of images and their incorporation into computer assisted learning software packages, although it has not been the remit of this report to consider that stage. On the basis of the results reported the following guidelines have been drawn up to assist staff capture high quality images for use in multimedia applications.

Selection of Source material

The first requirement is to select high quality source material for capture.

Capture

Successful capture depends on the operator having good photographic skills and an awareness of lighting techniques.

Analogue Choices 1 (35mm Slide, 35mm Negative, Colour Print)
In some photographic areas there is a trade-off between

Slides which give faithful colour but no opportunity for manipulation of colour and contrast ratio until after digitisation
Negatives plus prints which allow more control of colour and contrast ratio before and after digitisation, but require a reference (such as the Grey Scale chart or the original source material) for accurate reproduction

Analogue Choices 2 (Rostrum Camera, Still Video, Videotape frame)
Beyond photography, choices for analogue capture require some familiarity with video operations. These considerations are not intended to put off inexperienced lecturers who wish to process images - rather they indicate that an operator who gains experience processing images regularly should produce higher quality routinely.

Rostrum Camera Pros Immediate access to captured image. Easy to adjust the quality of the image at time of capture. High quality colour. Superior contrast ratio. No recurrent costs. Cons Generally poorer resolution than scanner. Re-sizing may require recapture. Needs digitiser board to capture image.
Still Video and Videotape frame Pros Speed of access. Portability Cons Overall quality (resolution, colour, contrast ratio) poor compared with other media.

Digital Choices: (PhotoCD, Digitiser Board, Scanner)
Familiarity with image capture skills are an asset, specifically familiarity with digitisation software.

PhotoCD Pros 5 grades of resolution, allowing effective zoom to detail without return to original image. Excellent resolution colour, contrast ratio. Excellent results with slides or negatives, but negatives easier for operator because of inherent flexibility. Cons Loss of control for user. Takes longer. Recurrent cost per image. Requires slides or negatives, no direct capture of source material.
Digitiser Board Pros and Cons as per Rostrum Camera.
Scanner Pros Generally superior resolution to rostrum camera. Most straightforward to use. Fast. Cons Colour generally poorer than rostrum camera. Inferior contrast ratio.

Taking account of these guidelines the preferred paths for capture of specific classes of image were as follows:

Photomicrography: Image - Microscope - Video Rostrum Camera - Digitiser Board
3 dimensional subjects using natural or artificial light: Image - Slide/Negative - PhotoCD or; Image - Video Rostrum Camera - Digitiser Board
Flat Art: Image- Slide/Negative - PhotoCD

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