Touchscreens are now commonplace in electronic equipment, including cameras, but how exactly does the technology work?

Touchscreen technology is nothing new, having been around since the mid-1970s. However, changes in microelectronics mean that touchscreens are now everywhere. From ticket machines to mobile phones and checkouts to PCs, touchscreens are part of everyday life - and now the technology has started to creep its way into photography The past few years have seen more and more digital cameras making use of touch-sensitive screens that enable the user to do such things as changing exposure settings and selecting an AF point In due course we will start to see touchscreens being used in even more products, and With the Panasonic Lumix DMC-G2, GF2 and GH2 all employing one it is surely only a matter of time before the technology makes its way into a DSLR.

The two common types of touchscreen technology are known as resistive and capacitive. The overall outcome of the two technologies is the same: to detect the part of a screen that has been touched and relay this decision to a computer chip. However, they differ in how they achieve this result.

Capacitive screens use two layers positioned above the LCD panel The first layer sits on top of the LCD and is made of glass and coated with a resistive metal compound called indium tin oxide (ITO). This oxide is able to conduct electricity, yet it is transparent and colorless so it doesn't affect the ability to view the LCD screen. Above the bottom layer is a thin-air gap, on top of which sits another sheet of ITO coated glass. The ITO layers in a capacitive screen are etched to create a series of opposing lines or matching cells. Where the cells are directly above and below each other, or where the lines intersect, an extremely small capacitor is created that stores a small amount of electricity.

When the screen is touched some of the electrical charge stored in the capacitor is lost, as the user conducts electricity. The circuit around the edge of the screen detects the change in electric current across a specific row and column, and from this works out the exact coordinates of the area of the screen being touched. However, it relies on a conductive material touching the screen, which is why an Apple iPhone will not work if you are wearing a pair of gloves.

One of the major advantages of these screens is the fact that multiple points can be touched at the same time and will each give separate coordinates, which allows for multi-touch gestures to take place. The best example of this is the gestures than can be used on the Apple iPhone, where spreading your fingers apart or pinching them together Will zoom in and out of an image. Such gestures are not possible With a resistive screen.

Resistive touchscreens are similar to capacitive screens, in that they use two layers of coated in ITO, that sit above the LCD screen. The layer above the LCD screen is made of glass, while the top layer is made of a flexible plastic.

Between the two layers are a series of tiny bumps, usually made of plastic. These bumps create an air gap that separates the two layers. When the user touches the screen the flexible top layer is pressed down, which closes the air gap created by the spacers and causes the two resistive layers to make contact.

The most basic type of resistive touchscreen is a four-wire screen, in which the exact location of the touch is recorded by sending a current from left to right across the top layer. As the two layers are now touching, a voltage is created on the bottom layer, which is recorded by a control chip. The controller then sw1tches off the current on the top layer and turns on a current going vertically across the bottom layer It then records the voltage that has been created on the top layer. By sending the voltage data from each side to a computer, the exact point where the screen is being touched can be calculated. All this happens hundreds of times each second, so that if the location of the touch moves a new position can be calculated. This is how it is possible to detect movements made on the screen.

Another type of resistive screen is known as five-wire screen. In these the top ITO layer has a voltage sent through it, and then the voltage of the bottom ITO layer is read at each of the corners. The strength of the voltage detected at each of the four corners enables the coordinates of the touch to be plotted.

With touchscreens creeping into digital cameras it has the potential to change the way that we operate cameras. At a basic level it will allow menu items and settings to be quickly selected and changed. Most touchscreen cameras also allow the AF area or point to be selected, which is especially useful for focus tracking. However, this is just the start of what touch-sensitive screens will allow photographers to do.

Already some cameras have the ability to display an on-screen keyboard, much like on a mobile phone. With a touchscreen this keyboard could be used to make it easier to add keywords and copyright information to the image's Exif data, or perhaps a title or caption One of the next steps for digital cameras will be greater connectivity via Wi-Fi and, potentially, 3G phone networks. Again, a touchscreen keyboard would make it easy to send an email or images.

Currently, it is possible to use the resistive touchscreens found in digital camera to scroll left and right through images, but if they began to use capacitive screens, then multi-touch gestures could be used. This would allow images to be zoomed in to a precise level in order to judge detail, or even when using live view to quickly check the focusing. When reviewing images, it would allow them to be manually rotated to level horizons, or even to dodge and burn parts of the image. The technology to do all these things already exists in the Apple iPhone, which itself has a built-in camera. It is simply a case of when manufacturers will begin to incorporate the technology into their own cameras.

Many traditionalists will be wary of this technology, but if anything it will simplify the use of a digital camera. For those who don't want the hassle of editing images on a computer screen, a touchscreen with multi-touch functionality will allow many adjustments to be made directly in-camera.