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Digital Light Processing by Texas Instruments uses a Digital Micro Mirror Device (DMD). It has thousands of tiny mirrors (see below), each representing a single pixel. The mirrors move back and forth and deflect light to the screen to create the image. The estimated life expectance of a DLP projectors panels is 20,000 hours. Due to the use of one chip for all the primary colours single chip DLP is light and compact.
DMD component parts
DLP DMD mirrors close up
In a projector with only one chip, each colour has to be projected in turn, Sequentially, one after the other.
Sequential Imaging
The first generation DLP projectors, incorporated a colour wheel that rotated sixty times per second (60Hz or 3600 RPM). With one red, green and blue segments in the wheel, updates on each colour happened 60 times per second.
This baseline 60Hz rotation speed in the first generation products is also known as a "1x" speed.
The second generation doubled the rotation speed - referred to as 2x Speed (120Hz, or 7200 RPM).
Today, DLP projectors designed for the home cinema market incorporate a six-segment colour wheel which has two sequences of red, green, and blue. This wheel still spins at 120Hz or 7200 RPM, but because the red, green, and blue is refreshed twice in every rotation rather than once, the industry refers to this as a 4x speed.
The ultimate projection system. The move away from the single chip, removes all the associated issues. Occupying the very high end, Ultra Bright projector category. With a brightness 16,000 and over, suitable for 3D Mapping. Projectisle are the only Australian website authorized to sell high end Barco, Digital Projection, Panasonic 3-chip projectors
Vivid Sydney - 3D mapping
DLP implement Lasers in a number of different ways. Using single chip and three chip systems. Obviously 3 chip are far superior.
Using a single blue laser and one micro-mirror-device engine (DLP chip).
A phosphor wheel and a colour wheel generate the red, green and blue coloured parts of a picture, providing natural colour representation.
Blue Laser phosphor
3-chip projectors generate the three coloured parts of a picture in parallel. RB laser systems use two blue and a red laser. Green is produced from one dedicated blue laser via a phosphor wheel. Having two blue lasers improves colour representation and brightness uniformity.
3-chip using Red and Blue Lasers
Primary colours are created from the two blue lasers, Green created with a phosphor wheel. Generates improved colour and brightness uniformity.
3-chip using two blue Lasers
RGB laser uses the so-called ‘pure laser’ technology. Red, green and blue lasers are delivered directly to the 3 DLP image chips. The product of this technique creates a light pipe consisting of absolutely pure light that is split into the three RGB components.
The light is emitted in very narrow RGB bands with very distinct spectral frequencies. This technology allows the creation of a large colour space that easily exceeds even that of Adobe-RGB or DCI and can already cover the demanding Rec. 2020 colour space.
3-chip using Red, Green and Blue Lasers
Developed in the late 80's DLP (Digital light Processing) replaced the organic liquid crystals with inorganic mirrors. DLP have a quoted life expectancey of 20,000 hours, a considerable improvement. First shipped in 1997, DLP offered improved contrast to LCD. But there were image quality issues.
A human hair in front of a DLP mirror surface.
We are comparing single chip DLP to 3 chip LCD. This may seem unfair. Why not compare 3 chip DLP to 3 chip LCD? The reason is price.
| LCD(3) | DLP(1) | ||
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No rainbow effect | Rainbow effect experienced by small proportion of users. Virtually eliminated with new DDR chip. | |
| More panels, a higher price | Value for Money | |
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No Dithering Artifacts | Inherent in all DLP systems, Due to the way DLP renders greys | |
| Small gap between pixels, have larger panels to reduce this. | Much finer gap between pixels (99% fill factor), resulting in smoother overall image | |
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Better colour reproduction with up to 216 Billion colours | Less saturated colour, but improving significantly, especially with new DDR chip. | |
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Achieve contrast up to 2500000:1 | Achieve contrast up to 1800000:1 | |
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Smooth movement easy on the eye | May see blurry images in rapid motion video | |
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Higher Lumen output per Watt | The Colour wheel reduces brightness | |
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Brightness of Colours match the light output of White | Brightness disparity when a data projector has a white segment. i.e. colours have lower brightness than the white parts of the image. | |
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Better Lens Systems - offer better lens shift range. | Sealed lens system restricts lens movement. Most DLP projectors don't offer lens shift. | |
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Filters are used to prevent dust and debris entering the projector, projecting circuitry LCD panels and Lamp. | Filter Free design - The DLP panel is a sealed unit. while this is touted as a design benefit. Electronics produce static, that attracts dust, dust collects over time and can arc causing components to fail. | |
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LCD Panels are Organic and can discolour over time. The latest iLCD panels are inorganic and don't have this problem and have a life span of 20,000 hrs plus | DLP image does not deteriorate - recommended for long running 24/7 applications. Estimated panel life is 20,000 hours | |
Unfortunately, the downside to the single chip system is that a colour wheel projects the primary colours sequentially (one after the other). This means that in any one instant, there is only one colour on the projection screen, unlike 3LCD systems that project all three primary colours in one hit. Single chip DLP relies on the slow response of the human eye to combined the colours to create the full colour image in the viewers mind.
Upon release of the first generation machines, it became apparent that a small but vocal percentage of the population were experiencing headaches from either seeing colour breakup more commonly known as the "Rainbow Effect" or from the sequencing of the colours. One point that must be considered with public projection systems using
Although not always visible to the naked eye. The rapid flashing Due to the sequencing of colours produced by the single chip system, has been noted to make some epileptics feel ill.
The color wheel speed improvements have reduced this considerably.Yet there is still a small fraction of the population who are sensitive to them.
To see the rainbow artifacts, spread your fingers and wave your hand in front of your face. While watching a DLP image or move your eyes (see diagram 1) quickly from left to right, as if watching a Tennis match. Picture 2 shows a bad case, this is created from the projection of a single white circle and using the eye movement technique. For those of you that don't have the classic white circle DVD, picture 3 shows an example of when the rainbow effect is most visible compared to an LCD projector.
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Diagram:1
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Pic: 2
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Pic: 3
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The introduction of the colour wheel to the light path also reduces the brightness of the projector. This means that more powerful lamps must be used to achieve the same lumens as similar LCD machines. The increased lamp power subsequently produces more heat which is dissipate with faster fans - producing more noise.
If we consider the opration during projection. The light switches on and off between each segment. More segments mean more off time and the percentage of the wheel that is coloured glass is higher. A four segment colour wheel, gives higher brightness than using six segments with the same wattage lamp. In fact a six segment colour wheel can be 75% of the brightness of a 4 segment colour wheel
To reduce the brightness drop a white (clear) segment has been added. This is fine for data presentations, but it creates a disparity between the brightness of colours and the white content of the image. People in the industry often deny this. But it was introduced to boost brightness, QED it is brighter than the existing system.
This disparity can be seen more when the data projector is used for video. DLP home theatre projectors do not have the white segment. Although some cheaper brands are using them in Home theater machines.
If the white segment is passing through the full lumens of the projector the colour segments may only be passing 50% of this. LCD projectors do not have this disparity and subsequently colours look more vibrant.
NEC NP4100 which has the option of 6 or 4 segment wheels. The 6 segment producing softer images for video.The mirrors on the digital micro mirror device have two positions on or off. Unlike LCD which can project shades by varying the light transmission of the LCD panels DLP can not be partially on. In the on position the mirror reflects light. In the off position no light is reflected - black is projected. DLP systems uses Dithering to project Grey. The process involves increasing the DLP mirrors switching speed. So that only a partial amount of light is projected compared to the normal on time. As with the sequential colour projection, your eye is not supposed to perceive this rapid switching and only see the desired grey. The side effect of dithering is that it can produce some visible instability in solid colours especially in darker areas of the image. This instability is commonly referred to as dithering artifacts.
