Talk:Digital Light Processing
|This is the talk page for discussing improvements to the Digital Light Processing article.|
|WikiProject Electronics||(Rated C-class)|
- 1 This article has printing problem
- 2 DLP vs DMD resolution
- 3 Color primaries and mixing
- 4 The "Rainbow Effect" and three-DMD systems
- 5 Marketplace
- 6 Pros/Cons - DLP Lag?
- 7 Are there actually cons?
- 8 How do the damned things work?
- 9 NuVision LED spam and forward-looking statements
- 10 LED?
- 11 Lights Dimming With Age
- 12 Colour-absorbing screen
- 13 PIP
- 14 Fan noise
- 15 Lamps
- 16 Pro/con size/fluids?
- 17 Pro/Con = Original research
- 18 Max RPM?
- 19 Proper name?
- 20 longer life = pro compared to CRTs?
- 21 "X is used by Y" versus "Y uses X"
- 22 The color wheel "rainbow effect"
This article has printing problem
I tried to print this article, and got page 3, 4, 5 as blank pages out of total 7 pages. I tried Adobe Acrobat printer too, and got same error. Then, I switched to "Printable Version", and this problem went away. I don't know how to fix this by myself, only thing I can do is to report this. —Preceding unsigned comment added by Hoonham (talk • contribs) 04:28, 16 December 2009 (UTC)
DLP vs DMD resolution
I tried to fix some errors in the DMD section. For example the article said that each mirror represented a single pixel. That is generally not true in modern DLPs due to Wobulation. I think what I wrote better reflects the current state of DLP TVs, but it still implies that DMDs come in 1920x1080. My understanding is that the vast majority of DLPs sold as 1080p sets, do not have a 1920x1080 DMD in them, but one half that size. I could not find the website where I read this and was working from memory, so I did not want to get into too much detail about it. Maybe someone else could make it a bit clearer which sizes modern DMDs come in, and how they correspond to the HD resolutions.220.127.116.11 21:30, 24 July 2007 (UTC)
Color primaries and mixing
Actually, red, blue and green are not primary colors. They are base colors for subtractive color mixing, but by definition, the primary colors are red, blue and yellow. -Anon
Actually, neither is right. Red, green, and blue, (RGB) are the base colors for additive color mixing. Additive color mixing is commonly used when the light source is integral to the system (think television, computer monitor, LCD screen etc.).
Cyan, magenta, and yellow are the base colors for subtractive color mixing commonly used when an external light source is utilized (think paintings, printed documents etc.). It helps to think of Cyan, magenta, and yellow as being anti-red, anti-green, and anti-blue.
Yellow is often included in the list of primary colors due to a fluke in synthetic pigments. As described here: http://science.howstuffworks.com/light7.htm
I personally dislike the term 'primary colors' when it is used in reference to red, green, and blue in discussions of color science. It's use implies that color mixing is property inherit to the nature of light when in reality its root lies in the nature of human physiology and the nature of the human eye.
NPW is right. Red Green and Blue are that way because we have cones in our eyes sensitive to red, green and blue light. Some people (all of them are women due to the nature of the genetic anomaly) have a fourth set of cones sensitive to another primary color. Fortunately (or unfortunately) that fourth color is aparently very close to red. Otherwise TV would probably look very artificial to them. Nsayer 19:02, 25 July 2006 (UTC)
The "Rainbow Effect" and three-DMD systems
The article makes the claim:
- Three-chip projectors do not suffer from the "rainbow effect", since all three components are present at the same time.
While it's true that three-DMD devcies are far less prone to the "rainbow effect", it's not true that they are completely immune. Because the DMDs are (fundamentally) binary devices, they are operated as Pulse Width Modulators and the red, green, and blue beams are each individually turned on and off. This means that for certain colors, there are definite times when a (say pink) displayed object is illuminated solely by the red beam and at other times by all three beams. If your eyes are in motion, such an object could still be perceived as being striped in red and white, even in a three-DMD system. The reason the effect isn't seen as much in a 3-DMD system is that the pulse-width modulators operate a lot faster than the frame rate of the color wheel in a single-DMD system so there's less distance separating the colors when your eyes are in motion. Also, the produced color artifacts are (usually) a lot less distinguishable than the obvious red, green, and blue artifacts.
This isn't so important that I'm going to edit the article, but we should be aware of this.
Atlant 17:34, 28 Mar 2005 (UTC)
- I've actually been to a DLP presentation by the head of Texas Instruments UK (who's personally quite heavily involved in DLP products) and they actually have a clever way of doing the modulation that means (in your example) the blue and green would modulate very very quickly while the red stays on, meaning the interval is so small that no one could possibly see it - unlike the color wheel problem, which is (or used to be) only just outside the bounds of normal human vision, hence some people can. --Dtcdthingy 20:29, 28 Mar 2005 (UTC)
You're correct that the DMD mirror isn't simply switched on and off once per frame for a single variable-width pulse, but the switching rate of a DMD mirror isn't all that high; it's only about 5 kHz tops () so a given mirror won't switch more than (say) 82 times per field for about 41 "pulses" of light. (The switching time isn't zero and there is a wear-out mechanism in the torsion beams that suspend the mirrors.) Your eye can sweep across an entire screen width in one field, so do the math and then tell me that you wouldn't be able to see the banding for certain well-chosen colors.
As I said, the effect is far less noticeable than with a single DMD device, but it's still there.
Atlant 01:05, 29 Mar 2005 (UTC)
- Let's go with your numbers. The eye moves across the frame in 1/60th of a second, during which time 41 pulses of light are sent. The other number we need is the "shutter speed" of the eye - let's assume it's also 1/60th of a second. What you'd get is 41 images printed on top of each other on the retina during the exposure, equivalent to taking a photo, moving the film 1/41st of a frame, and repeating 40 times. If we imagine that film, the motion blur from the movement of the film would appear in 41 separate steps rather than being completely smooth. I really don't think the brain would be able to tell the difference, to be honest. --Dtcdthingy 02:01, 29 Mar 2005 (UTC)
(For ease of discussion, let's assume there's a single line of 50%-saturated pink displayed from top to bottom on an otherwise-black field.)
You don't need the "shutter speed" of the eye at all. If your eye sweeps left or right across the field in 1/60 of a second, then what you will see (thanks to persistence of vision and the like) is a screen that has 82 stripes. Half of the stripes will be white and half of the stripes will be red.
If you don't think you'll be able to see this (a pattern of 82 white-and-red stripes occupying the full field), then perhaps you need to get your eyeglass presrciption checked. :-)
The point is that your eye, in moving, "breaks up" what would otherwise be perceived (through persistence of vision and the like) as a static object. Again, the effect is nowhere as obvious as with a single-DMD system, but it is still there. Why don't you call your TI guy and ask him to contribute to our discussion?
Atlant 13:35, 29 Mar 2005 (UTC)
- Human eyes perception is around 85Hz, few might see around 100Hz, given that those 4X models of the single-ship aren't creating rainbow effects anymore, I wonder how one can perceive that in three-chip DLP? It doesn't even have color wheels. Remember that our brains interprets the signals from the eyes, and by the rule of Persistence_of_vision I found your argument "technically sound" but not "realistically" possible, because if we can actually see the Rainbow Effect in 3-chip DLP at 5kHz, then there is just no way we can settle with 24 frames per second as we will be seeing 24 frames of photos instead of a movie. Kenimaru 09:29, 13 October 2006 (UTC)
- 1. The rainbow effect occurs when an object is moving relative to your retina. This can be because the object is moving on the screen or because your eye is moving relative to the screen.
- 2. Because the light source from a DLP projector is binary (fully on or fully off) pulse width modulated, it is not continuous. Furthermore, for certain colors (I used pink in my example above), the duty cycle of the R, G, and B components is not identical. Therefore, in a three DLP projector projecting "pink" light, there are times when the "pink" light source is actually saturated red and other times when it is unsaturated white.
- 3. Therefore, if the object is moving relative to your eye (so that persistence of vision transforms a pattern in time into a pattern in space), your eye will therefore see areas of two different colors: some red and some white.
- Feel free to argue that my example is pathological, but there is no doubt that if you try my example you will produce some degree of the rainbow effect, even on a three DLP projector; it's a natural fallout of the technology. Three DLPs helps compared to one DLP and a color wheel. Better (smarter) PWM algorithms helps also, but there's an upper bound on how fast you can cycle the mirrors and it's only in the low KHz range. Given a carefully-designed experiment, you'll still see the rainbow effect.
- There's another good way to demonstrate the effect I'm describing. Take a set of LED Christmas lights. These flicker at the mains frequency (so 50Hz in most of the world and 60 Hz in North America) and spend about 50% of their time "off". Sweep your eyes across the lights and see if you don't get a pattern of dots.
- Alternatively, go to the Boston's Museum of Science and go look at the line of red LEDs in the Thompson Electrical Theatre. That is, they look like a plain line of LEDs until you sweep your eyes across them rapidly. THEN you find that you're looking at dinosaurs, fish, and other objects. (I think the Exploratorium has an even better version of this in red and green.) This is because the motion of your eyes provides the X-axis scan that allows full fields of light to be painted across your retina. The DLP experiment I'm proposing exploits exactly this same effect.
- Atlant 13:41, 13 October 2006 (UTC)
- I exploited this once when debugging a bit-banged serial line and I didn't have an oscilloscope. I hooked it to an LED and quickly swept my eyes across it. Persistence of vision acted like the oscilloscope screen, and I could easily see the waveform and debug it. This was probably running at 1200 bits/sec. You can do this with many Mac power LEDs, as they use PWM for brightness control. Hell, every time you look at a CRT and see a complete image rather than a tiny spot moving, your eyes are demonstrating massive persistence of vision, as the electron beam "moves" extremely fast and paints the entire image. 18.104.22.168 (talk) 16:48, 12 November 2011 (UTC)
Additionally, the statement "Studies have long shown that only a small number of people ever experience the phenomenon" is questionably vague and needs a citation at least. 22.214.171.124 (talk) 16:59, 8 July 2013 (UTC)
I really like this segment, could people who know add it to other television types. Especially the pros/cons. I'll start researching it, but it may be a while before I get it done.
Pros/Cons - DLP Lag?
An item on the Cons list says, "Lag time between input and display with video consoles such as the PlayStation 2, making video game play nearly impossible."
Do we have a citation for this? - I can't see how this problem would be a consequence of using a DLP element in a display. My guess would be that since most DLP displays are very high resolution (and most consoles very low) the lag would be coming from upscaling the video. Either way I suppose the point could use some clarification?
— Mobius 08:32, 8 July 2006 (UTC)
- That entire thing was worded oddly. I hope I did a decent job rewriting it, but I ended up removing the statement to the effect of "TI's new stuff is better" because I can find no supporting statements anywhere. This article was the first return on one search on the matter. If anyone can find a citation, feel free to re-add it.
- Also, I put in a citation to a faq posted on a forum. I don't have any clue as to its permanence, this might be a bad citation.
- - GTMoogle 03:21, 16 August 2006 (UTC)
- I think it needs to be added that this was only an issue with the 1st generation DLP chips, and hasn't been a problem in DLP sets for 2 years now.--Indiearmy 03:19, 6 November 2006 (UTC)
- DLPs buffer the entire frame and then display it all at once, as opposed to CRTs (and maybe LCDs?) which start displaying the frame as soon as it is recieved. Therefore there is at least an additional half frame of lag on average.4hodmt 17:37, 29 November 2006 (UTC)
- I'm not sure that's a technically-accurate statement. DLPs are organized just like Dynamic RAM chips and are accessed in much the same way, so the "write" doesn't take place "all at once". And, of course, since they are using pulse width modulation to achieve grey scales, any given pixel can be written many times in a given display frame. It wouldn't surprise me if the video processors only delay the data as much as they need to finish the processing algorithms (so the initial RAM write takes place a few video linetimes after the actual video data first appears).
- Atlant 17:55, 29 November 2006 (UTC)
- That's not accurate. Each frame is loaded into a buffer within the DMD chip and then loaded onto the mirrors themselves all at once by removing the bias charge. Also, video processors need to buffer a frame or two to do de-interlacing/scaling/motion interpolation properly. --Dtcdthingy 18:20, 1 December 2006 (UTC)
Are there actually cons?
The Cons section essentially states that "LED is the end of all troubles." Does someone have a citation for this? Supposedly according to a different part of the article LED DLP projectors are not even released yet. Iamthebob 02:17, 28 July 2006 (UTC)
- LED DLPs are released. I just got my Samsung HL-S5679W yesterday. It is the end of all of those troubled listed in the CON section, but my particular set introduced some new problems in Color banding which probably has more to do with the image processing than the fact that the light source is LEDs. Eric.frederich 16:31, 24 August 2006 (UTC)
- The article makes a zillion references to LED driven DLPs eliminating rainbow effect, but is this actually true? All the LEDs do are replace the color wheel with a sequence of flashing lights. The image is still an additive process with different colors being projected at different times. I'm sure that the LEDS can flash faster than a color wheel, so as to even further minimize the rainbow effect except for those with superhuman vision, but the way the article is worded implies that the rainbow effect is just not even possible with LED DLPs. I don't believe that to be true. 126.96.36.199 00:22, 12 September 2006 (UTC)
- The preceding comment is actually me before logging in. adavidw 00:23, 12 September 2006 (UTC)
- I added that material. Your understanding is basically correct -- you'd need superhuman vision to see a rainbow effect with a LED DLP. Feel free to edit if you feel I didn't get that across clearly. Jerry Kindall 20:50, 25 October 2006 (UTC)
- That's really excellent wording. Thanks! adavidw 02:32, 26 October 2006 (UTC)
I have the last LED DLP model (HL61A750) that Samsung produced before abandoning DLP rear projection. It's harder, but if I blink or move my eyes across the screen I can still perceive color flashes. Of course, I once tried a 2005 DLP set, and it gave me such terrible headaches and eye strain that I had to return the set. The new set is much, much better, but it is still noticeably less stable than an SXRD-style projection set, an LCD, or a plasma. Jonabbey (talk) 23:39, 7 May 2009 (UTC)
How do the damned things work?
I came here hoping to find something more than the marketroid stuff written by TI/DLP themselves, after discovering that practically everything on the web is just a regurgitation of that: was disappointed, of course. Well, there is additional material, including the pro/con stuff, but what's missing, at least for me, is some basic information, like: how does this technology work? What operates the hinged mirrors? Some kind of tiny electrostatic motor? I'm very curious to know this. +ILike2BeAnonymous 00:36, 10 September 2006 (UTC)
- To partly answer my own question, I did find some stuff on the How Stuff Works page on the subject; it has an intriguing illustration of the mirror assembly, but a totally inadequate explanation. Apparently, it does operate electrostatically as I had guessed, but I need details, man, details! +ILike2BeAnonymous 00:47, 10 September 2006 (UTC)
- Yes, electrostaics drive the tiny mirrors. The mirrors themselves are made from a layer of aluminum metalization which is then etched into the required shape and then under-etched to make the space for the mirrors to tilt. The mirrors are suspended by tiny portions of the aluminum metalization that are left to remain as a sort of "taut band" hinge (like a taut band-suspended d'Arsonval meter movement). Because the suspension bands are very thin, they have an adequate life before metal fatigue sets in. Because the distance between the mirrors and the substrate is so small, the voltage required to flip the mirror is also miniscule, so when we say "electrostatics", we're still only talking about IC-level voltages.
- By tipping a few degrees left or right (and banging up against a mechanical stop), each mirror simply steers its portion of the light to the screen or to a "light sink". The switches are purely binary; grey scales are achieved by pulse width modulating the mirrors, with the mirrors switching thousands of times per second.
- All of this is documented in technical papers that you can find somewhere on the the TI site; Google found them for me once and can probably find them for you as well.
- Atlant 01:46, 10 September 2006 (UTC)
- The details you're looking for are in Digital Micromirror Device --Dtcdthingy 18:16, 1 December 2006 (UTC)
NuVision LED spam and forward-looking statements
All the contributions of User:188.8.131.52  are about a not-yet-out NuVision DLP projector with LEDs, and therefore probably classifiable as commerical spam. That's why I marked some of them with citation needed (fact) tags. They should probably just be removed unless somehas has a published source. Dicklyon 21:42, 12 September 2006 (UTC)
Looks like the Samsung LED stuff was also all forward-looking spam, since these still don't exist. Please put correct info back when it becomes verifiable, not before. Dicklyon 13:53, 24 September 2006 (UTC)
- wasn't me in the 1st place, but looks like there are some. 
Lights Dimming With Age
I've done a few searches on this online. I've found a few pages here and there that say that Halogen/incandescent lights do not dim with age and a few that say they do dim with age. This, to me, means that the evidence is very inconclusive. Now, I've read on a few forums that people complain about dimming lights after they've used their bulbs for a few months (the same complaint holds true with rear projection), but that dust collects on the bulb and wiping the dust off on a regular basis will alleviate the dimming problem. For the time being, I've removed "* The picture dims as the lamp deteriorates with age." statement from the cons, because I've found no concrete evidence to suggest that the halogen bulbs used in such TVs do, in fact, dim with age.Kakomu 12:22, 27 September 2006 (UTC)
- Plus, that "con" also applies to other projection technologies such as LCD. Not specific to DLP. Dicklyon 12:17, 27 September 2006 (UTC)
- So, as you can see, there's a general disagreement. Especially considering two websites, talking about halogens in car headlights, saying two completely opposite things.Kakomu 12:22, 27 September 2006 (UTC)
- I know this post is quite old, but just to clear it up so no one else becomes confused.
- The lamps found in DLP (and LCD) projectors and TVs are not halogen or incandescent. They are arc lamps, usually some form of metal halide. Light output does decrease on these types of lamps, it's all covered in the main page. Brock1912 (talk) 06:16, 28 May 2012 (UTC)
One con that seems to not have been mentioned is the DLP's poor performance when there is a lot of light in the room (eg from windows). Apparently this can now be fixed - Sony's developed a screen which absorbs all colours except for red, green and blue, which means that almost all of the ambient light (only a small part of which consists of those exact wavelengths) is absorbed into the screen. Link: . Anyway, I just thought that maybe this info and the link could be added into the article somehow. Esn 12:08, 23 November 2006 (UTC)
- This problem is not unique to DLP projectors, of course. Jerry Kindall 00:18, 28 November 2006 (UTC)
- Since light is only made up from Red, Green, and Blue, how does this magic screen work? The ambient light would be made from the same three colors unless your neighborhood uses an alternate form of physics.
- Um, how about you do your own research! Sony have indeed developed a 'black' screen which uses a different technology to the DNP screens. This is all already mentioned in the Projection Screen article. 184.108.40.206 (talk) 01:41, 10 June 2008 (UTC)
- PIP is done by the video signal generator; it doesn't matter if you display it on DLP or something else. Dicklyon 06:35, 29 November 2006 (UTC)
A recent editor changed the "con" "Fan noise" to "Some devices may have fan noise"
Are there any DLP devices that don't have fans and fan noise?
Atlant 17:40, 21 December 2006 (UTC)
- I'm sure all devices have fans (although I guess it's possible for the LED driven ones to not use one). However, it's entirely possible to have a fan without noticeable fan noise, depending on how they build the cabinet. Additionally, whether or not the noise is a con is a subjective judgement that would depend entirely on the noise level and one's own tolerance. adavidw 07:12, 22 December 2006 (UTC)
- Noise is not particular to LCD or DLP, but in general bigger projectors can have bigger fans. Larger fans can spin more slowly and move more air than a tiny fan spinning at high speed. Also a big projector can have larger internal air ducts for less air resistance so the fan doesn't have to work so hard, compared to a compact projector with very small air channels.
- Expensive professional projectors costing thousands usually have large slow whisper-quiet fans. Meanwhile the cheap compact portable projectors usually have whiny high-speed fans with lots of airflow noise.
- It's a type of mercury vapor arc-lamp, similar to a yard/security light, but very high gas pressure and about 10mm in diameter, enclosed within a huge thick ceramic support frame that is also used to dissipate heat, focus the light with a ceramic parabolic mirror, and to keep the bulb from exploding from the heat and pressure of running.
- Since everything gets so extremely hot, the ceramics are all basically heat-fused to the tiny quartz bulb and cannot be removed without cracking or destroying the whole assembly. All of this gets thrown away every time the lamp is replaced, and there's no way to salvage the parabola mirrors.
- The outer plastic/metal shroud assembly (usually with a spring and metal clips) aligns the ceramics in the projector, and provides shock absorption. It can be removed and separated from the lamp, and it is possible to buy the ceramic lamp/parabola separate from the housing at a lower cost than the whole works. Often the ceramic lamps are a general part, but put inside differently shaped housings from different manufacturers.
- But it's not so simple as that. The housing power wires cannot be soldered onto the bulb because solder would melt at the operating temp of the bulb. The wires have to be spot-welded to the lamp terminals, and you're not going to have a tiny spot welder like this just lying around to use for lamp replacement.
- It hurts to pay practically half the projector cost for a new lamp but it apparently can't be done any cheaper. DMahalko (talk) 04:16, 5 June 2009 (UTC)
In this section of the pro/con area, it says plasma displays use fluid as the projection medium...
"Unlike their LCD and plasma counterparts, DLP screens do not rely on fluids as their projection medium and are therefore not limited in size by their inherent mirror mechanisms, making them ideal for increasingly larger high-definition theater and venue screens."
That doesn't make a bit of sense. It seems like two different points are being made at once. Might be clearer said this way??:
"DLP displays are limited in size only by the power of the projection lamp and the mechanism's ability to dissipate the heat from a higher powered lamp. This is in contrast to LCD projectors, which create an image by using liquid crystals to block unwanted light. They are size limited by their ability to adequately block that light, and their ability to function with the higher levels of heat a higher powered lamp would generate. LCD and plasma direct view panels are size limited by manufacturing constraints and the physical constraints of maintaining the integrity of the panel."
I mean, plasma displays aren't actually fluid based as the original paragraph claims. They are just a grid of (in essence) tiny fluorescent tubes. Instead of using a white phosphor as in fluorescent lighting, they use colored phosphors.220.127.116.11 (talk) 22:02, 19 December 2009 (UTC)
Pro/Con = Original research
Guys, i'm sorry, but I think the pros/cons section is definitely original research. At very least with the things that can be said sourced and objectively, change the title of the sections to be more neutral. JoeSmack Talk 17:51, 20 December 2009 (UTC)
The article reads "There is a maximum rotational speed limit for the wheel, typically 10,000 to 15,000 RPM." and goes on to describe how this is related to framerate. Is repeating the colour pattern on the colour wheel not an obvious solution to this problem? It also contradicts an earlier passage that says up to 10x rotation speed is available. This passage seems out of date or just plain incorrect, but I'm not an expert and don't have a primary source to reference.
- Repeating the color pattern would require a bigger wheel, and there is a limit to wheel size for a given projector size. 18.104.22.168 (talk) 16:56, 12 November 2011 (UTC)
- The DLP® trademark is not an acronym for the words 'digital light processing' and should never be followed by '(digital light processing)'.
On the other hand, a paper by Hornbeck puts a TM after Digital Light Processing.
It looks to me like the opening paragraph should draw some appropriate distinction - perhaps, for instance, it should refer to digital light processing as a technology and DLP® as a TI trademark for its line of products implementing that technology. However I don't know enough of the whole picture to write it myself.
- It looks simpler to me to simply ignore the DLP® trademark. In fact, it should never be followed by '(digital light processing)', as TI puts it. This clarifies that we are not talking about the DLP® trademark in this page. --Pot (talk) 22:40, 14 November 2010 (UTC)
longer life = pro compared to CRTs?
The use of a replaceable light source means a potentially longer life than CRTs and plasma displays (this may also be a con as listed below).
"X is used by Y" versus "Y uses X"
The entire opening section is mainly of an X is Y form, rather than Y <verb> X form. It comes across as stilted and verbose. Compare:
- The single-chip version of DLP and 3LCD are the two main technologies used in modern colour digital projectors, with the two technologies being used in over 95% of the projectors sold in 2008.
Rewritten without is:
- Modern color digital projectors mainly use single-chip DLP and 3LCD devices; in 2008, over 95% used them.
The color wheel "rainbow effect"
I am quite sure this or a similar effect happens with plasma TV/monitors, because when I look at them, sometimes I see flashes of green and some other colours.Bolegash (talk) 22:36, 22 December 2011 (UTC)