Your choice of monitor is crucial, as you are likely to spend as much time in front of the screen as you do taking photographs. The best advice is to buy the best and biggest monitor you can afford. Poor quality screens may flicker and cause eye-strain, colour and brightness will be uneven across the image area, and they may be difficult to calibrate.
For image manipulation, minimum screen size is 38-43cm, and you should ensure that the screen is capable of displaying millions of colours, which may require the installation of a suitable video card or board to help the computer run the best vertical monitor. The screen resolution should be 1,024 x 768 pixels or better: many professionals work at 1,600 x 1,200 pixels.
Many cathode-ray tube (CRT) monitors offer a perfectly flat screen. A slightly curved type may be much less costly but a flat screen reduces reflections from other light sources and is a mark of a high-quality monitor. Liquid-crystal display (LCD) screens are also available: these are light¬weight and slim, but expensive. Nonetheless, if you are prone to eye-strain they are worth considering as they exhibit zero flicker. For all but the most critical applications, a good-quality, modern LCD screen, displaying millions of colours, is perfectly suitable for image manipulation.
A modern monitor should allow you to adjust the size of the image on the screen and to alter such factors as the shape and position of the image. An important control is convergence, which ensures that images do not display coloured fringes.