The advantages of this form of output are that they make use of the high quality of photographic materials for their output, which includes the high sensitivity for rapid writing of data, high resolution, colour reproduction and light stability of conventional, dye-bleach or dye-diffusion media. The main disadvantage is the need for wet processing chemicals other than for dye-diffusion materials (Pictrography).

Laser printers use analogous technology for indirectly transferring toner particles to a receiving layer. Lasers are used to form colour output in four channels: red, green, blue and black. These are scanned on to charged photoconductive drum, web or belt which becomes discharged on exposure. The unexposed areas carry charges to which toner particles adhere and are then transferred to a receiving sheet to which they are fused. This process is repeated four times, once for each channel.

The advantages of laser printers are that they are well proved technology, rapid and can print to plain paper, but their disadvantages are their high cost and that their quality is not as good as that from photographic, thermal dye-diffusion or sublimation or ink-jet printers, although they are capable of producing high quality 24-bit colour images. Also, like other computer output devices, such as ink-jet printers, the RGB additive data must be transformed to CMY(K) densities (K is black) that conform to the specific printer. Dithering (see Figure 1.4) has to be used to reproduce grey levels adequately.

Thermal printing

Thermal output media were described in the previous chapter (for terminology see Table 20.3). Currently there are two main types that provide high-quality output. These are Fujifilm's Thermo-Auto chrome (D1T1) and Kodak's dye diffusion thermal transfer (D2T2), often called dye sublimation (see Plate 25), which can produce continually varying amounts of dye and hence continuous tone images of photographic quality. This has the highest image quality and is a true professional system, capable of printing very large images, but has the disadvantages of high capital cost, requiring consumables and relatively high running costs. Similar disadvantages apply to the Thermo-Autochrome system, which is designed mainly for personal use.

Ink-jet printing

For photographic quality output special paper is required (see Chapter 20). This is perhaps the most versatile of the newer technologies for providing hard copy. There are two basic types, one is drop-on-demand, in which a drop of ink is emitted according to a signal received, and the other is continuous jet, in which droplets of ink are continuously emitted from a nozzle and deflected by an electric field to produce an image. Most desktop applications involve the former and some make use of the piezo-electric effect in certain crystals which generate a pressure pulse to emit droplets of ink. Other printers use thermal ink-jet or bubble-jet in which ink droplets are formed on evaporation of the ink in the printhead by current flowing through resistive elements. This forces the ink through nozzles to form droplets which are propelled towards the paper.

Printing devices are available in wide range of sizes for most applications, from simple and inex pensive forms for personal use to very large-scale printers for printing advertising material. Generally printing speeds are slow but they are capable of providing photographic quality with low cost consumables, although the special photographic quality paper is relatively expensive.

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Digital Camera and Digital Photography

Digital Camera and Digital Photography

Compared to film cameras, digital cameras are easy to use, fun and extremely versatile. Every day there’s more features being designed. Whether you have the cheapest model or a high end model, digital cameras can do an endless number of things. Let’s look at how to get the most out of your digital camera.

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