A monitor or display is an electronic visual display for computers. The monitor comprises the display device, circuitry, and an enclosure. The display device in modern monitors is typically a thin film transistor liquid crystal display (TFT-LCD), while older monitors use a cathode ray tube (CRT).

CRT v Flat Screen Technology

Screen size

The size of an approximately rectangular display is usually given as the distance between two opposite screen corners, that is, the diagonal of the rectangle. One problem with this method is that it does take into account the fact that when a rectangle with a given length to its diagonal, becomes more rectangular, and less square (its aspect ratio increases), and at the same time its diagonal remains the same, then the area of the rectangle decreases. That is, given the same diagonal, the area of the display decreases if its aspect ratios increases. For example, a 4:3 21 in (53 cm) monitor has an area of about 211 sq in (1,360 cm2), while a 16:9 21-inch widescreen has about 188 sq in (1,210 cm2).

This method of measurement is inherited from the method used for the first generation of CRT television, when picture tubes with circular faces were in common use. Being circular, only their diameter was needed to describe their size. Since these circular tubes were used to display rectangular images, the diagonal measurement of the rectangle was equivalent to the diameter of the tube's face. This method continued even when cathode ray tubes were manufactured as rounded rectangles.

Another problematic practice was using the size of a monitor's imaging element, rather than the size of its viewable image, when describing its size in publicity and advertising materials. Especially on CRT displays, a substantial portion of the imaging element is concealed behind the case's bezel or shroud in order to hide areas outside the monitor's safe area due to overscan. These practices were seen as deceptive, and widespread consumer objection and lawsuits eventually forced most manufacturers to instead measure viewable size.

Comparison

1. CRT

Pros:
  • High dynamic range (up to around 15,000:1 [1],) excellent color, wide gamut and low black level.
  • Can display natively in almost any resolution and refresh rate
  • No input lag
  • Sub-millisecond response times
  • Near zero color, saturation, contrast or brightness distortion. Excellent viewing angle.
  • Usually much cheaper than LCD or Plasma screens.
Cons:
  • Large size and weight, especially for bigger screens (a 20-inch unit weighs about 50 lb (23 kg))
  • High power consumption
  • Geometric distortion caused by variable beam travel distances
  • Older CRTs are prone to screen burn-in
  • Produces noticeable flicker at low refresh rates

2. LCD

Pros:
  • LCDs have no sensitive electron guns. Colours will not drift therefore no ongoing adjustments are needed
  • Lighter weight - 20" CRT weighs in at around 30kg, a 24" LCD around 10kg. No health and safety or lifting issues
  • Digital technology ensures consistent colour reproduction between monitors, making multiple monitor set ups easier.
  • Many medical imaging systems are now embracing High Definition technology. Most LCD monitors are HD Ready making them future proof.
  • Multiple inputs, both analogue and digital, ensure greater operability and flexibility. Some monitors incorporate have picture in picture feature.
  • Standard VESA Mounting holes enable easy fixing of the monitor onto an arm, something that the weight and mass of a CRT made impractical.
  • LCD monitors do not have magnets inside, like CRTs, so eliminate any magnetic interference issues.
  • LCD monitors do not suffer the eye-straining 50Hz flicker inherent in CRT monitors.
  • Non-reflective screens of LCDs eliminate reflection problems from the high light levels in operating theatres unlike the curved glass screens of CRTs
  • Unlike the curved class screen of the CRT a flat screen ensures perfect convergence and geometry.
  • CRT tubes can fade and go soft with time. An LCD has a longer operational lifetime and stays sharp.
  • High Resolution
  • Wide Range of screen sizes - 15" to 32"
  • Stable colour temperature
  • Wide viewing angle
  • Longer operational life
  • Less energy and waste heat
  • No geometric distortion
  • Rugged
  • Little or no flicker depending on backlight technology
Cons:
  • Limited viewing angle, causing color, saturation, contrast and brightness to vary, even within the intended viewing angle, by variations in posture.
  • Bleeding and uneven backlighting in some monitors, causing brightness distortion, especially toward the edges.
  • Slow response times, which cause smearing and ghosting artifacts. Modern LCDs have response times of 8 ms or less.
  • Only one native resolution. Displaying resolutions either requires a video scaler, lowering perceptual quality, or display at 1:1 pixel mapping, in which images will be physically too large or won't fill the whole screen.
  • Fixed bit depth, many cheaper LCDs are incapable of truecolor.
  • Input lag
  • Dead pixels may occur either during manufacturing or through use.
  • The first generation of medical LCD monitors was a compromise to fulfil the requirement of systems manufacturers to be first with flat screen technology. The latest generation with HD panels are far superior.
  • Early LCD monitors suffered from Image delay, where the displayed picture lagged behind the movement of the camera. With more sophisticated circuitry, this has now been virtually eliminated

3. Plasma

Pros:
  • Compact and light.
  • High contrast ratios (10,000:1 or greater,) excellent colour, wide gamut and low black level.
  • High speed response.
  • Near zero color, saturation, contrast or brightness distortion. Excellent viewing angle.
  • No geometric distortion.
  • Highly scalable, with less weight gain per increase in size (from less than 30 in (760 mm) wide to the world's largest at 150 in (3,800 mm)).
Cons:
  • Large pixel pitch, meaning either low resolution or a large screen.
  • Noticeable flicker when viewed at close range
  • High operating temperature and power consumption
  • Only has one native resolution. Displaying other resolutions requires a video scaler, which degrades image quality at lower resolutions.
  • Fixed bit depth
  • Input lag
  • Older PDPs are prone to burn-in
  • Dead pixels are possible during manufacturing


Since manufacturers such as Sony and Panasonic discontinued CRT production, all major medical equipment suppliers now provide flat screen LCD monitors with their endoscopic systems. The LCD monitor is now the modern standard for medical stacks, outperforming both CRT and Plasma monitors.

Most popular suppliers: Sony and Panasonic

Sony
with full 1920 x 1080 HD resolution has been designed for endoscopic, surgical reference and educational applications. The new 32" display supersedes the current top-of-the-line LMD-2450MD 24-inch model with an expanded viewing area and a range of additional advanced features. The new display offers a much increased available screen size and a host of advanced features offering surgeons the highest quality visual peripherals. Providing enhanced side-by-side image display, the HD LCD supports simultaneous viewing of multiple modalities and maximises use of the available screen to significantly expand the size of the image. Similarly, the picture-in-picture mode delivers larger inset images with enhanced use of space. Additionally, in dual monitor configurations, an innovative mirror image feature inverts the image display on one of the monitors to present clinicians with an image orientation consistent with their view of the surgical field wherever they are situated. These monitors have 10-bit signal processing and Sony ChromaTRU™ colour management technology for high detail, brightness and colour accuracy. Designed for easy integration and operation in surgical environments, the 32-inch LMD-3250MD is compatible with a full range of surgical mountings and features a front bezel control panel with touch-sensitive backlighting.

Panasonic EJ-MLA32U-W 32" Class Full HD Widescreen Medical Monitor

  • Designed and certified for medical operating room environment
  • User selectable picture-in-picture or picture-out-of-picture
  • Side-by-side display of 2 HD images; independent adjustment of each
  • Three simultaneous screen display possible, such as surgical image, vital signs, etc.
  • Multiple HD inputs are standard, no need to purchase optional input board(s)


In-Plane-Switching Technology (IPS-Pro)
The new Panasonic medical displays implement the latest evolution of In-Plane-Switching technology, IPS-Pro, which provides excellent colour images with a very high contrast ratio from almost all viewing angles.

Medical imaging applications require highly consistent performance and accurate image reproduction. IPS-Pro substantially improves viewing angle, brightness, contrast, black levels and switching speed, producing the best solution on the market for multi-modality medical imaging.

When viewed from a wide angle, a monitor with non IPS-Pro display will exhibit a poor contrast and inaccurate colorimetry. In a non-medical environment, this performance limitation is not critical, but in medical imaging systems, color accuracy is vital and aids medical professionals during surgery. IPS-Pro TFT technology defeats the restrictions of conventional LCD display technology in terms of wide viewing angle, contrast ratio, brightness, and color accuracy.

http://www.sony.co.uk
http://www.panasonic.com
http://en.wikipedia.org/wiki/Computer_monitor

Compiled and edited by John Sandham
July 2010

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