As the use of computers has become so much more common and their power has increased, so the cost has fallen dramatically, and previously unheard of computing power and extremely useful programmes are now available in the home.
Enhancement by computer is a valuable tool for improving an image for publication purposes. The process has two stages, the acquisition of the image by scanning the document into the computer, and the second, the manipulation of the image by special image editing software under the control of the operator.
Image acquisition is carried out using a scanner, which inserts a digital image of the material into the computer. There are many types on the market, either small and hand held and moved over the page, or a large piece of equipment, something like a photocopier, into which the document can be placed for the scanning process.
Three types of images can be scanned - line art, continuous tone images, and half tones.
Text, Architectural plans, sketches and bar charts are line art images. They consist of black and white lines or areas of one density (the colour of the lines can be black or green or any other colour). All will be represented as black, as long as they are similar in density. The best line art images have good contrast.
A black and white or colour photograph printed on photographic paper is a continuous tone image. Black and white photographs are composed of gradient tones from black and white, whereas colour photographs are composed of gradient tones with distinguishable colour attributes or hue. The best continuous tone images have a broad, even distribution of tones.
Black or white or colour photographs printed in a book or magazine or newspaper are halftone images. Halftoning is a process that allows non-continuous tone output devices, such as linotronic image-setters and laser printers to reproduce continuous tone images. Halftoning reproduces a continuous tone image as dots of various sizes. The eye merges these dots with surrounding white area and perceives continuous tones. Use a magnifying glass to look at a photograph in a book or magazine or newspaper. You will see the fine dot pattern. The best halftone images are ones with a very fine halftone dot pattern, which are found in high quality publications.
A scanner takes these different images into account, and it must be set accordingly. A pixel is the smallest element in a document that can be displayed or printed. The more computer bits of information that can be stored for each pixel, the more the grey values can be represented. A document with 1 bit per pixel is line art (black and white). A document with 16 bits per pixel can represent many shades of gray. The scanner can also be set for brightness, a feature which adjusts the gray density of a document. The number of dots per inch also determines its visible quality. A document with a higher resolution appears smooth, realistic, and finely defined.
Image quality can be optimised if the original image is prepared properly. This may save hours of editing later. One can use a pen or pencil to repair broken lines, or use correction fluid to remove unwanted spots. It may be possible to make a photocopy and work from that. Glossy paper images and those of low contrast or on textured paper can be copied but corrections must be applied.
The size of a scanned image file is partially dependant on the size of the original image, but also on the document mode (black and white or gray scale), resolution and file format. A 1 inch by 1 inch image stored at a resolution of 100 dots per inch (dpi) may require 1.2 kilobytes (k) of memory. A similar size image at 400 dpi may require 160k. If the scanned image measures 4 inches by 6 inches at 400 dpi and 256 gray-scale, then the file size may be 3.8 megabytes, which is very large indeed.
The image looks best on the screen if your computer has a super VGA monitor and 256-colour display mode. The image may be scrolled across the screen using the mouse and parts can be selected to zoom in and out to adjust magnification from 800% to no smaller than 100 by 100 pixels.
The retouching feature is one of the most powerful applications. One can make subtle retouches or completely remake the entire document. Individual features can be altered by darkening or lightening, blemishes removed, out of focus areas sharpened, background or foreground areas changed or removed. One can select a number of brush sizes and styles as well as erasers to achieve these changes. The whole picture can be enhanced in terms of brightness, contrast and tone with the press of a button, as well as overall sharpness. Gray shades can be equalised, converting the lightest pixels to white, the darkest to black, and evenly distributing the remaining pixels in between automatically. The effect after skilled manipulation is to produce a picture which is clear and sharp, and with good contrast and detail.
Parts of a picture can be easily selected both for duplication or for printing. Any selected image can be rotated or skewed and one can add lines, boxes, frames and text.
The resulting digital image can be saved in a number of ways. It can be transferred to other computer programmes such as word processors or desk top publishing, but it can also be sent down the telephone line using a modem to a remote computer.
A laser printer should be used for the best results, as very high quality printouts can be obtained.
The minimum system requirements for this type of software are a 386 type computer running under DOS 3.1 or later and Windows, 1 to 4 megabytes of on board memory, and a hard drive. A pointing device such as a mouse is essential, and a windows compatible laser printer and colour monitor.
The practical application of this process for Meccano publications is invaluable. Meccano models have always been difficult to photograph and to draw, particularly when it comes to a complex mechanism hidden away inside a structure, and annoying metal reflexion. Great attention must be paid to the lighting and the exposure, and yet the result frequently disappoints. With computer enhancement, a significantly enhanced picture can be achieved, and one good picture saves a thousand words.