General notes on the electronic manipulation of images using computers.

• A scanner - a device to enable you to get the image into the computer.
• A computer - on which to work when manipulating the image.
• A printer - to enable the manipulated image to be outputted as a print.

The type and quality of these items will effect the final image as well as the ease and speed with which the process can be carried out.
The choice of equipment used will depend on the nature of the work, the availability of the equipment and the budget!

Scanners
A scanner works by converting the light reflected from the image (or passing through it) into an electronic map of that image. A scanner is linked to a computer which is used to control the scanning operation.
There are four main types of scanner:

Hand scanners Flat bed scanners Film scanners Drum scanners

The first two are designed for use with prints; the main practical differences are that the hand scanner is limited to scanning images up to 6"x4" while most flat bed scanners will scan from up to A4 size originals. Both are available as black/white or colour versions. For photographic work in black/white a 256 grey scale scanner is minimum requirement:
A colour scanner will also work in colour or black/white.
Film scanners will scan at very high resolution from negative or transparencies.
Drum scanners can work from prints or transparency at very high quality.

Computers
Although AppleMac computers still retain the lead in terms of popularity in the field of graphic design, PC based systems are increasingly used. A relatively new machine is required; in the PC sector a fast 486 is minimum, and a 586 (Pentium) will work faster. Most newer Apple Mac computers will be suitable.
Requirements on both systems are:

Good quality colour monitor Plenty of memory (RAM) and hard disk capacity Software designed for photo-manipulation: Adobe Photoshop one example but alternatives can be effective.

Printers

There are three types of printer worth mentioning: Inkjet printers are comparatively cheap to purchase and use: they also offer the possibility of printing onto a variety of papers types (one drawback of inkjet printers is that the image is not waterproof). Laser printers although more expensive to purchase are cheap to run are can be capable of high definition printing. Dye sublimation printing is the version that is almost indistinguishable from photographic prints. The cost is much greater than the other two both in initial equipment and in cost per print.

One of the advantages of digital darkroom working is that you do not need to own all the equipment (only have access to it). It is possible to have images scanned commercially and put onto disk, and to have them printed elsewhere requiring you to need only the computer. It may also be possible to hire time on a suitable computer.

Scanning
The process of scanning is carried out on the scanner attached to the computer:
As scanning takes place so the image appears on the computer monitor. The resolution or dpi (dots per inch) of the scan will determine the quality.
Scans from large images take up large quantities of storage space on disks and at high resolution they take up vast quantities. In general you should scan at the lowest dpi that you can whilst still maintaining the quality required.
Most printers will print at 300-600 dpi and in general you should aim to work with an image that is the size you require the print to be at 150 - 300 dpi.
A 35mm slide is usually scanned at 2700 dpi which is the equivalent of about 10" x 8" at 300 dpi.
A 10"x8" colour image at 300 dpi will create a file about 21mb (megabytes)
Depending on your computer and operating system; you will need about 40mb of ram available to work on a 21mb image.
The more RAM your computer has, the larger the file size you can use and the quicker it will work.

Image manipulation
Stage one
Once the initial scan has been made it is usual to 'tidy-up' the image: this might involve straightening the edges and cropping it to the size required.
Stage two
Will be about basic control of brightness, contrast and colour to recreate the picture as close to the original as possible. Experience will play a part in this process as the printed image will not always look the same as the image on the monitor: screens can be set-up to match the characteristics of printers but a little interpretation will usually be required.
Stage three
Software will determine the options open to you as regards manipulation of the image.
Most software designed for image manipulation will have control over the following:

• Brightness and contrast.
• Colour and saturation.
• Burning and dodging.
• Cropping and re-sizing the image.
• Copying the whole image or parts of it.
• Pasting in sections copied (cloning)
• Filters: to sharpen or soften the image

Printing
Once you have an image that you feel happy with, the final stage will usually be to print it.
Most image manipulation software will only give you a very basic control over the size and position of the image on the paper. They are designed to be used in conjunction with other software packages that will control the positioning of the image and allow you to combine it with either other pictures or with text. These packages are usually referred to as Desk Top Publishing or DTP software.
The software has to work with the printer to give you the control and quality you require.

Most printers commonly available are restricted to printing on A4 size paper although commercially it is possible to get work outputted in much larger sizes (at a price!).
Inkjet printers usually offer the most choice in terms of the finished print quality as they can be made to print in different ways. Most have the ability to offer a variety of print halftones. Because they all work by printing black, cyan, yellow and magenta ink onto paper they have to have a method of dealing with shades when printing photographs. To achieve other colours they print a fine pattern of ink with gaps between which from a distance will merge and look like other colours. The pattern (known either as halftoning or dithering) can usually be varied.
Inkjet printers will also print on a variety of paper surfaces and colours: different surfaces will give surprisingly different results. Some paper will act like blotting paper and the ink will spread losing the fine detail; some will appear to give better blacks than others.
Laser printers are usually black and white and only work at their best on smooth coated paper.
Dye sublimation printers are the ones designed to output photographs from computers. Prints made this way are often indistinguishable from traditional photographs and are printed onto the same paper that is used as the base for resin coated photographic paper. The main drawback is the cost which is higher than traditional photographic printing at around £5 per A4 print whilst the printers cost in the region of £10,000 to buy.
A new development in this field is the Kodak Vision printing process that uses computers to 'write' a digital image on to standard photographic paper which is then processed in the normal way to give a traditional print.
This list of printers is not complete and there are hybrid printers offering slightly different results.