CRT - Cathode Ray Tube - The Original

The cathode ray tube (CRT) is a vacuum tube containing an electron gun (a source of electrons) and a fluorescent screen, with internal or external means to accelerate and deflect the electron beam, used to create images in the form of light emitted from the fluorescent screen. The image may represent electrical waveforms (oscilloscope), pictures (television, computer monitor), radar targets and others.

CRT Basics - How does it work?

A CRT monitor operates much like your regular television set. A cathode ray tube (CRT) uses an electron gun to shoot electron beams through a metal grille or mask on the inside of a glass monitor screen. The screen is coated with phosphor dots that glow red, green, or blue to create any colour and produce the image you see on your monitor. Shooting the gun at the appropriate colours in differing intensities produces the full colour spectrum.

CRT Screen Size - is based on the diagonal screen measurement of its picture tube and is usually an inch larger than its viewable image size. A 17" CRT, for example, typically has a 16" viewable image size, with the edge of the picture tube covered by the bezel of the monitor.

Dot Pitch - is the spacing between pixels on a CRT, measured in millimetres. Generally, the lower the number, the more detailed the image.

Resolution - a CRT screen is made up of individual dots of colour, or pixels. Resolution refers to the number of pixels contained on a display. Resolution is typically expressed by identifying the number of pixels on the horizontal axis (rows) and the number of lines on the vertical axis (columns), such as 720x576 for PAL Standard Definition (SD) or 1920x1080 for High Definition (HD).

Refresh Rate - is the number of times per second that a CRT's picture must be redrawn. The standard is a rate 50Hz but increasing this to 100Hz will avoid flicker and cause less strain to the operator's eyes during grading.

 

Sony Broadcast High Definition Monitor - BVM Series

 

LCD - Liquid Crystal Display

LCD Basics - How does it work?

LCD (liquid crystal display) monitors use liquid crystal filled grids, activated by electric fields, to create smooth, finely detailed images. The liquid crystal acts like a shutter that either blocks the backlight or lets it pass through to light up a particular colour filter. The screen has hundreds of thousands of pixels that are charged or not charged, making them reflect or not reflect light to form images. LCD technology produces the same image as a CRT, but in a much smaller package. Different types of LCD technology use different alignment modes to filter or twist incoming light, with differing results.

Resolution - an LCD screen is made up of individual dots of colour, or pixels. Resolution refers to the number of pixels contained on a display. Resolution is typically expressed by identifying the number of pixels on the horizontal axis (rows) and the number of lines on the vertical axis (columns), such as 1920 x 1200 (1920 x 1080 active video area).

Brightness - LCD brightness is calculated by measuring the greatest amount of light that comes from the screen when displaying pure white. The measure is expressed in candelas per square metre.

Contrast Ratio - refers to the difference in light intensity between the brightest white and the darkest black that an LCD can produce. Higher contrast ratios help prevent colours from washing out when you turn up the brightness and from disappearing when you turn it down.

Colour Depth - indicates how many colours can be displayed on a monitor's screen. Colourpixel. Colour depth is usually talked about in bits, describing how many bits are used for each of the three additive primary colours - red, green and blue - per pixel. So, for example, if 8 bits are dedicated to each of the three colours, the colour depth is 24-bit (8 bits x 3 colours = 24).

Pixel Pitch - is the spacing between pixels on an LCD, measured in millimetres. Generally, the lower the number, the more detailed the image.

Viewing Angle - because of the way light passes through the liquid crystals in the display, LCDs may appear to lose some brightness and image quality as you move to the side of the screen, or above or below it. An LCD's viewing angle indicates how far, in degrees, you can move from the centre of the display before the image quality deteriorates to unacceptable levels. A wider viewing angle indicates more freedom to view the monitor from the side, from above or below the screen position.

Refresh Rate - the number of times per second in which the monitor draws the data it is being given. A refresh rate that is too low can cause flickering and will be more noticeable on larger monitors. Many high-end LCD televisions now have a 120Hz (current and former NTSC countries) or 200Hz (PAL/SECAM countries) refresh rate. The rate of 120 was chosen as the least common multiple of 24 fps (cinema) and 30 fps (NTSC TV), and allows for less distortion when movies are viewed due to the elimination of telecine (3:2 pulldown). For PAL/SECAM at 25 fps, 200Hz is used as a compromise of one-third the least common multiple of 600 (24 x 25). This is most effective from a 24p-source video output (available on Blu-ray DVD).

Dead Pixels - can occur when the screen is damaged or pressure is put upon the screen; top end manufacturers only pick the best LCD displays available and should replace screens with dead pixels under warranty.

In LCD manufacture, it is common for a display to be manufactured that has a number of sub-pixel defects (each pixel is composed of three primary coloured sub-pixels). The number of faulty pixels tolerated before a screen is rejected is dependent on the class that the manufacturer has given the display. Some manufacturers have a zero tolerance policy with regard to LCD screens, rejecting all units found to have any pixel defects - obviously these are more expensive.

 

CineTal - The Cinemage product family revolutionises critical monitoring for digital cinema acquisition, post production and DI by combining Cine-tal's leading edge IDS (Intelligent Display Server) technology and a calibrated full resolution LCD display. Cinemage provides quantitative video analysis, colour pre-visualisation, video signal quality assurance, real time collaboration between acquisition and post production, and an integrated Omnitek™ Dual Link Waveform Monitor and Vectorscope. With Cinemage you can conduct both critical visual analysis and digital quantitative analysis of HD-SDI or HD-SDI Dual Link signals in either YPbPr or RGB, linear or logarithmic, at 8 or 10 bits.

 

Cine-Tal's Cinemage LCD Technology Is Bringing Broadcast Quality to LCD

 

DLP - Projectors

Digital Light Processing (DLP) is a trademark owned by Texas Instruments, representing a technology used in projectors and video projectors. It was originally developed in 1987 by Dr. Larry Hornbeck of Texas Instruments. DLP is also one of the leading technologies used in digital cinema projection. Also because digital projection closely mirrors the theatre presentation, many feel more comfortable and trusting towards a full theatre presentation and screening. I have to say, by preference, I personally prefer to work in a dedicated theatre but not all facilities have the space.

DLP Basics - How does it work?

Digital Micromirror Device - in DLP projectors, the image is created by microscopically small mirrors laid out in a matrix on a semiconductor chip, known as a Digital Micromirror Device (DMD). Each mirror represents one or more pixels in the projected image. The number of mirrors corresponds to the resolution of the projected image (often half as many mirrors as the advertised resolution due to wobulation). 800x600, 1024x768, 1280x720, and 1920x1080 (HDTV) matrices are some common DMD sizes. These mirrors can be repositioned rapidly to reflect light either through the lens or on to a heatsink (called a light dump in Barco terminology).

Rapidly toggling the mirror between these two orientations (essentially on and off) produces grayscales, controlled by the ratio of on time to off time.

Colour in DLP projection - here are two primary methods by which DLP projection systems create a colour image, those utilised by single-chip DLP projectors, and those used by three-chip projectors. A third method, sequential illumination by three coloured light emitting diodes, is being developed and is currently used in televisions manufactured by Samsung.

 

Single-chip projectors - in a projector with a single DLP chip, colours are either produced by placing a colour wheel between the lamp and the DLP chip or by using individual light sources to produce the primary colours, LEDs for example. The colour wheel is divided into multiple sectors: the primary colours: red, green, and blue, and in many cases secondary colours including cyan, magenta, yellow and white. The use of the secondary colours is part of the new colour performance system called BrilliantColor™ which processes the primary colours along with the secondary colours to create a broader spectrum of possible colour combinations on the screen.

The DLP chip is synchronised with the rotating motion of the colour wheel so that the green component is displayed on the DMD when the green section of the colour wheel is in front of the lamp. The same is true for the red, blue and other sections. The colours are thus displayed sequentially at a sufficiently high rate that the observer sees a composite "full colour" image. In early models, this was one rotation per frame. Now, most systems operate at up to 10x the frame rate.

Older DLP systems exhibit an anomaly known as the rainbow effect. While this has been improved with faster colour wheels over the years, some people will still be able to notice this effect. This is best described as brief flashes of perceived red, blue, and green observed most often when the projected content features bright/white objects on a mostly dark/black background (the scrolling end credits of many movies are a common example). Some people would perceive these rainbow artefacts frequently, while others may never see them at all. With the advent of increased colour wheel speeds or projectors featuring LED illumination, the 'rainbow effect' has been virtually eliminated.

 

Three-chip projectors - a three-chip DLP projector uses a prism to split light from the lamp, and each primary colour of light is then routed to its own DLP chip, then recombined and routed out through the lens. Three chip systems are found in higher-end home theatre projectors, large venue projectors and DLP Cinema® projection systems found in digital movie theatres or a DI theatre.

According to DLP.com, the three-chip projectors used in movie theatres can produce 35 trillion colours, which many suggest is more than the human eye can detect. The human eye is suggested to be able to detect around 16 million colours, which is theoretically possible with the single chip solution. However, this high colour precision does not mean that DLP projectors are capable of displaying the entire gamut of colours we can distinguish.

Digital Cinema - DLP is the current market-share leader in professional digital movie projection, largely because of its high contrast ratio and available resolution as compared to other digital front-projection technologies. As of December 2008, there are over 6,000 DLP-based Digital Cinema Systems installed worldwide. DLP projectors are also used in Real D Cinema for 3-D films (Stereoscope).

 

BARCO 2k Digital Cinema Projector (20 metre screen)

 

Manufacturers

eCinema Systems - Their DPX line of LCDs offers true black reproduction with a greater than 15,000:1 contrast ratio.

Sony - Makes the de facto standard reference monitor in their BVM line of CRTs (now being discontinued sadly). Their CRTs are being replaced by their BVM-L line of CRTs.

Ikegami - Makes broadcast-grade CRTs and LCDs.

Barco - Barco is re-entering the broadcast monitor market with their RHDM-2301 LCD. Integrated calibration probe tailored for the monitor. Colours match very closely with Barco CRT. They also make D-Cinema projectors.

Cinetal - Makes the Cinemage, known for its software capabilities that add various monitoring options and 3D LUTs.

CHRISTIE - One of the forefront projector manufacturers within the industry.

 

 

Displays - The Future

Artificial Muscles - Source: Optical Society of America

Scientists have unveiled a new technology that could lead to video displays that faithfully reproduce a fuller range of colours than current models, giving such a life-like viewing experience that it could be hard to go back to your old TV. The invention, based on fine-tuning light using microscopic artificial muscles, could turn into competitively priced consumer products in eight years, the scientists say.

The research appears online in Optics Letters, a journal of the Optical Society of America, and will also be published in the September 1 print issue of the journal.

In ordinary displays such as TV tubes, flat-screen LCDs, or plasma screens, each pixel is composed of three light-emitting elements, one for each of the fundamental colours red, green, and blue. For example, shades of orange and yellow are displayed by mixing different amounts of red and green. Unless you look closely, the colour elements in a pixel are indistinguishable: the eye sees a single, composite colour.

The fundamental colours in each pixel are fixed, and only their amounts can change -- by adjusting the brightness of the colour elements -- to create different composite colours. That way, existing displays can reproduce most visible colours -- but not all. For example, current displays do not faithfully reproduce the hues of blue one can see in the sky or in the sea.

"State-of-the-art displays such as LCD displays can only reproduce a limited range of colours because the three mixing colours red, green and blue are determined during the time of production," said Manuel Aschwanden, a nanotechnology expert at the Swiss Federal Institute of Technology (Eidgenössische Technische Hochschule, or ETH) in Zurich, Switzerland. Aschwanden and his colleague Andreas Stemmer figured that one can overcome such limitations by changing the fundamental colours themselves, not just their brightness. To obtain different colours, they used an optical trick called diffraction.

Tunable diffraction grating. The vertical membrane is made of artificial muscle, and has carbon electrodes attached to its sides. The membrane has one side moulded into a diffraction grating and coated with gold to increase reflectivity. As the applied voltage varies, so does the periodicity of the diffraction grating, changing the angle of the diffracted light.

In their setup, white light hits a so-called diffraction grating, a pattern of equally spaced grooves on a surface. Their grating is a rubbery, one-tenth of a millimetre wide membrane, with one side moulded into a shape that resembles microscopic pleated window shades. The membrane consists of an "artificial muscle," a polymer that contracts when voltage is applied.

White light contains the full spectrum of colours of the rainbow, which correspond to all wavelengths of light. But when white light hits a diffraction grating, different wavelengths fan out at different angles.

"It's like when you hold a CD in direct sunlight, and you rotate it," Aschwanden said. Like the microscopic tracks on a CD surface, the grooves on the artificial muscle split white light into a rainbow of colours. But instead of rotating the surface to obtain different colours, the ETH team adjusts the light's angle by applying different voltages to the artificial muscle. As the membrane stretches or relaxes, he incoming light "sees" the grooves spaced closer or tighter. All the angles of reflection change, so the entire fan of wavelengths turns as a whole. The desired colour can then be isolated by passing the light through a hole: As the hole stays fixed, different parts of the spectrum will hit it and go through it.

To obtain composite colours, every pixel would use two or more diffraction gratings. By this method, a display could produce the full range of colours that the human eye can perceive, Aschwanden said.

Tunable diffraction gratings are routinely used in applications such as fibre optic telecommunications and video projectors, but existing technologies are based on hard materials rather than artificial muscles, limiting their stretchability to less than a percentage point. By contrast, artificial muscles can change their length by large amounts. Correspondingly, the fan of reflected light will move enough for the part of the beam going through a hole to change from one end of the spectrum to the other.

Getting a full range of colours requires a source of "true" white light to begin with -- rather than a mere combination of red, green and blue that looks like white light to the human eye. For that purpose, the technology could exploit a new generation of white LED lights that have recently been developed, Aschwanden said.

Though Aschwanden and Stemmer have so far just a proof of concept, it demonstrates the feasibility of the technology, Aschwanden said. With enough investment, it could turn into consumer products, perhaps in less than eight years, he said. "Once you have one pixel, it doesn't take too long to develop a new product."

The team is now improving the technology to bring it closer to industrial application. In particular, the artificial muscles described in the Optics Letters paper operated at several thousand volts, while in a consumer product that would have to come closer to the 120 volts of household AC. Since the paper was accepted, the team has already reduced the voltage to 300 volts, and new materials currently being developed could allow voltage to drop further, Aschwanden said.

 

Source: Optical Society of America