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A trick for fixing DLP rainbows

butterworth

Standard Member
I bought the best mid-range DLP projector in the market recently, Acer X1161P. I read about the rainbow effect and suspected it might cause trouble. And yes, even with the X1161P you can see the rainbows, whenever there is fast moving white objects. You very rarely notice them, but they still cause eye strain and even slight nausea.

From reading the different forums, it seems that the main problem problem is the color separation caused by too fast updates from dark to light. People are recommending dimming the projector. The economy-mode seems to help somewhat. Less white movement means less rainbows and the projector even makes less noise.

I came up with another fix that seems to correct to issue more or less. Since the rainbows are caused by too fast dark to light pixel updates, I use software to filter the video. I'm using Ffdshow with temporal smoothing of 4. This smears the frames so that the rainbows are replaced by shadows effects from the temporal smoothing. The result is almost no eyestrain and no nausea, although the screen looks like its a plasma screen due to the slowed down pixel updates. It still looks awesome, but no discomfort from viewing.

Has anyone else tried this? I'd like to hear if other people find this useful. I know this topic will be obsolete in a couple of years with LED bulbs, but this might be useful to anyone buying a DLP now. It seems that the main problem with the old DLPs is that they tried to push it to a frame update frequency that the technology cant do without the rainbow artifacts.
 

kbfern

Distinguished Member
I bought the best mid-range DLP projector in the market recently, Acer X1161P.

:rolleyes: hardly the best mid range DLP on the market.On a scale of 1-10 I doubt it would make it past 1.

It is a presentation type pj and not a home cinema type pj.At under £300 it does not even make it to the cheapest home cinema type pj (the Optoma HD600x typical £400 price).

Rainbows are bad with presentation machines because they are so bright with their output and the colour wheel configuration is not good along with the rotation speed.

Home cinema DLP machines start at £400 and go up to over £10k so you see how ludicrous your claim is as your pj does not even make it on the radar.:D

However thanks for pointing out your fix as it may help others with similar low end pj's like yours that have an issue with rainbows. :)
 

butterworth

Standard Member
:rolleyes: hardly the best mid range DLP on the market.On a scale of 1-10 I doubt it would make it past 1.

However thanks for pointing out your fix as it may help others with similar low end pj's like yours that have an issue with rainbows. :)

Well, I am new to projectors. But, I can safely say that "On a scale of 1-10 I doubt it would make it past 1." is a bit more ludicrous. You're categorizing projectors on the basis of price. Read the specs for the thing, then what people are saying about the model. They don't rate it 1 out of 10. This model has a 6-segment wheel, it still has rainbows with the 2100 lumen economy mode, like every DLP.

Could you specifically say what features the top-end projectors have, that make the rainbow effects supposedly disappear compared to a new 6-segment DLP? That would be a useful contribution and on the topic.
 

the boots man

Well-known Member
Could you specifically say what features the top-end projectors have, that make the rainbow effects supposedly disappear compared to a new 6-segment DLP? That would be a useful contribution and on the topic.

I think they must be those new super duper diamond encrusted gold plated segment wheels :D I see rainbows quite bad on my projector so i'll try your fix out, cheers mate.
 

Paul D

Well-known Member
I'm afraid I would have to agree with kbfern.
I wouldn't class your PJ as "mid range", or even cinema class.
Please don't take offence at this, as we all have to start somewhere.
I just wouldn't want somebody else starting up, and thinking this was the "best mid range" etc.

Spec's also mean very little sometimes, and similar specs can have vast image quality differences.
You have pointed out your PJ has a six segment colour wheel. But what speed is it?
2x wheels will rainbow like mad, 6x will be much better.
Also, adding a 7th neutral (dark) section will help with the darker scenes
As you have already mentioned, lowering the projected light level really helps with rainbows.
This can be done by lowering the bulb power/iris/grey screen.
Home cinema projectors take advantage of this light lowering by using a iris that gives better contrast to boot.
DLP chips also come in different spec/quality that is rarely mentioned, and this also has an effect on final picture quality.
Finally, the quality of the lens can have a major effect on the end picture.

This all explains why two projectors which seem identical on paper, can have completely different picture/image quality...

I like your other idea of trying to reduce rainbows.
But i fear it will compromise other aspects of the picture.
Smearing and lowering of intra scene contrast springs to mind.
Also, rainbows are caused by the relatively slow refresh rate of the three primary colours.
When moving your eyes across the screen, the colours break down into the component parts.
It is easier for your eyes to detect this with bright to dark objects etc.
The only real solution is either three chip or faster refresh rate afforded by tri-LED projectors etc.
 
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dovercat

Guest
I'm afraid I would have to agree with kbfern..

kbfern was not very diplomatic to put it mildly.

I wouldn't class your PJ as "mid range", or even cinema class.
Please don't take offence at this, as we all have to start somewhere.
I just wouldn't want somebody else starting up, and thinking this was the "best mid range" etc.

It is sold as home cinema and business and looks like it would give a bright, colourful, high contrast image.

It is much brighter than most home cinema projectors, much more than you would need in a light controlled bat cave.
4x3 SVGA which is high enough for no screen door with DLP, but not high enough for pixel to pixel mapping with PAL DVD or High Definition sources for the sharpest possible picture.
Does not appear to have RGB bias and gain controls to enable grey scale colour calibration.
So I as well would not call it a home cinema projector, but that rather depends on your expectations, it is certainly looks good enough to watch TV and films on.

Spec's also mean very little sometimes, and similar specs can have vast image quality differences.
You have pointed out your PJ has a six segment colour wheel. But what speed is it?
2x wheels will rainbow like mad, 6x will be much better.
That rather depends on viewer sensitivity and image brightness, originally home cinema projectors were only 2x speed and many people were happy with them.
Also, adding a 7th neutral (dark) section will help with the darker scenes
They were only needed due to increased colour wheel speeds, reducing the time the chip had to produce shades, leading to more use of temporal and spatial dithering which produces image noise.
A 7th neutral (dark) segment has disadvantages according to
http://www.cine4home.de/knowhow/DLP-Farbraeder/RGB-Farbraeder.htm cine4home.de.
They are not needed with slower colour wheels and should be unnecessary with newer faster colour wheel projectors using lamp pulsing.

Yellow colour wheel segment reduces rainbow effect due to making it Yellow/Blue rather than Green/Red, as yellow is the brightest colour on the wheel rather than green, and the difference in brightness yellow to blue is less than the difference green to red.
Some projectors using secondary as well as primary colours on their wheels are misleading because they count the number of times they can make a colour and you can make a colour using a mix of primary or secondary colours. So rather than RGBRGB segment wheel x 2 rotations = 4 speed, they are RGBYCM segment wheel x 2 rotations = 4 speed. Despite the fact they will produce rainbow effect the same as a two speed because the transition brightest segment to its opposite Yellow to Blue in their case only occurs once per rotation.
As you have already mentioned, lowering the projected light level really helps with rainbows.
This can be done by lowering the bulb power/iris/grey screen.
Or using a camera neutral density filter to tame a too bright projector. Then removing the filter when the lamp dims.
Home cinema projectors take advantage of this light lowering by using a iris that gives better contrast to boot.
DLP chips also come in different spec/quality that is rarely mentioned, and this also has an effect on final picture quality.
It is 4000:1 contrast as good as most home cinema projectors. It is dark chip 3 that is better than many home cinema projectors, higher off chip contrast.

It is a presentation type pj and not a home cinema type pj.At under £300 it does not even make it to the cheapest home cinema type pj (the Optoma HD600x typical £400 price).

It is a presentation type pj because it is 4x3 SVGA, bright and lacks the ability to fine tune the grey scale colour.

The Optoma HD600X is a proper home cinema projector because it is 16x9 720x1280 resolution and has RGB bias/gain controls for grey scale calibration.
But looks to be dark chip 1 with 350:1 ANSI checkerboard contrast low for dlp, 3500:1 peak contrast. It seems to be 6-segment, 4x colour wheel. "Brilliant color" processing so probably secondary as well as primary colour segments or white peaking using the spoke time. If it is using secondary colours on the wheel and counting how many times it can make a colour as its speed it may only be as good as 2x colour wheel as far as rainbows. Ignoring resolution I doubt there is much in it as far a picture quality is concerned. But contrast is more important than resolution, so although the Acer should look softer due to down-scaling it might still look better.
 
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kbfern

Distinguished Member
I quite agree my diplomacy skills were definitely lacking in my post:) but The statement "I bought the best mid-range DLP projector in the market recently" was a wildly optimistic claim.

I mean come on 800 x 600 res no hdmi,bright enough to burn your retinas and circa £300.No way can this be described as the best mid range DLP in the market.

This machine is in very budget end classroom machine that can be used in desperation to play a dvd or standard def tv.

Of course the thread title is also a bit misleading as it suggests that it is a cure all for RBE which it plainly isn't.

Other than that I apologise for my lack of tact.:)
 

betelgeus

Active Member
@dovercat theOP's projector is not a home cinema projector in any way or form.

i was going to add to that but i think the one line sums it up perfectly.
 
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dovercat

Guest
@dovercat theOP's projector is not a home cinema projector in any way or form.

i was going to add to that but i think the one line sums it up perfectly.

It is designed as a dual use business - home cinema, but is native 4x3 SVGA so the wrong aspect ratio and too low a resolution to be what I would consider home cinema.

Still it does not mean it is not perfectly watchable.
According to SMPTE the order of importance is
1 Contrast Ratio / Dynamic Range
2 Color Saturation
3 Colorimetry / Color Temperature or Greyscale
4 Resolution.
A Home Cinema projector might win on number 2 depending on the color wheels used, and should win on number 3 and 4
 

Paul D

Well-known Member
Dovercat, I wouldn't read too much into published contrast ratios.
It may give something approaching half that at some extreme colour temperature.
Also, without even a half decent lens and light path, ANSI will be poor.

They can market it as a Work/Home Cinema projector, but that doesn't make it one!
A lot of business focussed projectors have shocking motion control. This means the picture can tear during movement. This happens as the picture updates across the screen at different times.
Fine for power point, not so clever for video with differing refresh rates and resolutions.
Fan noise also plays a part in Home Cinema projectors, this isn't even close.

Listen, I understand this PJ is cheap, but that doesn't make it good for Home Cinema.
What it does do is allow people to dip their toes, before moving on to something more suitable.
Widescreen, with Hdmi and colour controls would be a start.
 
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butterworth

Standard Member
This is sidetracking, but on the projector (Acer X1161P): it's a great find and hugely underrated. I'd recommend it to anyone starting with projectors at the moment. I'm very satisfied, so are my friends, who are projector enthusiasts. 6000h lamp life with 2100 lumen on 2.2kg book-sized projector I can bring to friend's place. Its not a HD projector, but that's about it.

I like your other idea of trying to reduce rainbows.
But i fear it will compromise other aspects of the picture.
Smearing and lowering of intra scene contrast springs to mind.
Also, rainbows are caused by the relatively slow refresh rate of the three primary colours.
When moving your eyes across the screen, the colours break down into the component parts.
It is easier for your eyes to detect this with bright to dark objects etc.

Here's the thing: the visible color separation seems to be caused mostly by too fast dark->light transitions, not other way around. And its caused by on-screen movements, not your eye movements across the screen.

If your screen size and distance is properly set up, then you shouldn't be moving your eyes too much. I pilgrimed once to the biggest screen in the world, Sidney IMAX. If the screen is too big relative to the distance, you need to move your eyes around and its not a pleasant viewing experience. (Bigger than life is ok, but when Leonardo DiCaprio's teeth are the size of your seat, then its too big.) So the perceived rainbows come primarily from the on-screen movement, not from your eye movement across the screen. Therefore, removing the on-screen rapid dark->light transitions will also remove the rainbows.

I used the Ffdshow temporal filter because it's the one video processing tweak I could find straight away. With the temporal filter of 4 smearing is still not visible, more than 4 and at least you start seeing it. Likely depends on your projector what the best option is. I'm not sure what filter the Ffdshow filter uses, but it's probably not the best way to fix this either, since it also smears the white->black transitions that are not a problem. (The Ffdshow temporal filter seems to be a phase-corrected moving average FIR filter) An asymmetric filter targeting the excessive dark->light pixel update speed should be optimal.

i presume this fix only works if your connected to a pc?

Yes, through a PC. I don't know if there's hardware boxes for doing the temporal smoothing, might be. What's needed is a simple low-pass filter operation, signal processing chips should be able to do this.

Yellow colour wheel segment reduces rainbow effect due to making it Yellow/Blue rather than Green/Red, as yellow is the brightest colour on the wheel rather than green, and the difference in brightness yellow to blue is less than the difference green to red.
Some projectors using secondary as well as primary colours on their wheels are misleading because they count the number of times they can make a colour and you can make a colour using a mix of primary or secondary colours. So rather than RGBRGB segment wheel x 2 rotations = 4 speed, they are RGBYCM segment wheel x 2 rotations = 4 speed. Despite the fact they will produce rainbow effect the same as a two speed because the transition brightest segment to its opposite Yellow to Blue in their case only occurs once per rotation.

Thanks for the detailed reply. You checked I was taking about a brand new Darkchip3, 6-segment 3xRotation DLP. Most people seem to suggest hardware is the only solution. But if its only some parts of the signal that are causing eye strain, then its just better to filter those parts of the signal out. The hardware companies might not do this because they need to deliver what the specs say, without compromising the video.

Thanks for the feedback so far. If anyone knows software to modify the video output from PC, I could try other filter types for fixing the issue.
 

betelgeus

Active Member
i dont think anybody is saying youve bought a donkey,trouble is this is a dedicated av enthusiast site,where the jvc x3 is considered an excellent mid range dlp projector,which costs £3,500,do you see our point now?.

with projectors you HAVE to match the input resolution with the output resolution and at 800x600 that is very difficult therefore it cannot be considered as a dedicated home cinema projector.

your ideas sound good but at the moment with most users using bluray or maybe sky at a push it dosent quite fit yet.
 

kbfern

Distinguished Member
the jvc x3 is considered an excellent mid range dlp projector,which costs £3,500,do you see our point now?.

Sorry mate the JVC is D-ila not DLP, but there are plenty of examples of DLP at a £2-3k price point to illustrate your point.:)
 

Paul D

Well-known Member
Here's the thing: the visible color separation seems to be caused mostly by too fast dark->light transitions, not other way around. And its caused by on-screen movements, not your eye movements across the screen.

I'm sorry but you are wrong.
You keep making sweeping statements without the knowledge to back them up.
This dangerous to other newbies who may assume you are knowledgeable and may actual waste some money copying you.

Listen, before i come across as bullying you, I will make this my last post here.
I like many on here, we have been dealing with rainbow artifacts since 1999.
We had a hard time convincing people the problem even existed at first.
We have visited the manufacturers and designers of many DLP projectors.
Various methods have been tried to eliminate or reduce rainbows.
Ultimately, they have all failed due to the fundamental reasons for rainbows in the first place.
I applaud the fact that you are at least trying something new.
But the fact is rainbows can be seen on static images, so motion isn't the cause.
If you don't believe me, try a scene from Gladiator where the emperor is writing in his tent after the first battle.
As he writes by candle light, the candles light will rainbow like mad.
Flick you eyes left and right, and you will see rainbows even though this is a static scene...;)
 
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butterworth

Standard Member
I applaud the fact that you are at least trying something new.
But the fact is rainbows can be seen on static images, so motion isn't the cause.
If you don't believe me, try a scene from Gladiator where the emperor is writing in his tent after the first battle.
As he writes by candle light, the candles light will rainbow like mad.
Flick you eyes left and right, and you will see rainbows even though this is a static scene...;)

I'm giving you a reply, since yours was at least on the topic of the thread.

You're saying that motion isn't the cause. You continue to say that you see the rainbows when you move your eyes.
 

Moolers

Active Member
I have to side with kbfern here. I've no problem with the info that the OP has taken the time to post but that first sentence is just plain ridiculous.
 
D

dovercat

Guest
Dovercat, I wouldn't read too much into published contrast ratios.
It may give something approaching half that at some extreme colour temperature.
Also, without even a half decent lens and light path, ANSI will be poor.

They can market it as a Work/Home Cinema projector, but that doesn't make it one!
A lot of business focussed projectors have shocking motion control. This means the picture can tear during movement. This happens as the picture updates across the screen at different times.
Fine for power point, not so clever for video with differing refresh rates and resolutions.
Fan noise also plays a part in Home Cinema projectors, this isn't even close.

Listen, I understand this PJ is cheap, but that doesn't make it good for Home Cinema.
What it does do is allow people to dip their toes, before moving on to something more suitable.
Widescreen, with Hdmi and colour controls would be a start.

I agree I would not call the Acer a home cinema projector. Personally due to the lower than standard definition anamorphic widescreen PAL DVD resolution, let alone Blu-rays. It also lacks the calibration optimization options on most home cinema projectors.

It is however dark chip 3 and alot of dlp projectors are stock designs with stock components, it is not difficult to make a good quality single chip dlp projectors so I would be unsure about how far below the standard of a budget dedicated home cinema projector it is as far as light path design, motion processing and lens quality, as I would not expect much difference as things are built to a price. As for fan noise it is not that loud 26dB in low lamp mode, the proper home cinema projector mentioned by kbfern Optoma HD600X is louder 29dB.
I could be being over optomistic as the only business-home cinema projectors I have seen are 2006 models xga resolution $5500 back in 2006, worth around £100 second hand these days.

It is not that long ago it would of been considered an outstanding projector for home cinema. Just look at the much worse specs of the 2002-2004 Infocus X1 svga dlp business projector that led to dual use business-home cinema projectors being marketed. At the time it was heralded for its outstanding picture quality and raved about on forums, but these days would not even be deemed suitable for home cinema use by many.

I expect current LCD, DLP home cinema projectors will be viewed as very sub-par in five years as more manufactures make LCOS projectors that have massively higher native contrast and better fill factor. But just because they will no longer be anywhere near state of the art does not mean their picture quality will suddenly become unwatchable, unless you get tainted by viewing the latest LCOS projector in a dedicated bat cave room.
 
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dovercat

Guest
Here's the thing: the visible color separation seems to be caused mostly by too fast dark->light transitions, not other way around. And its caused by on-screen movements, not your eye movements across the screen.

As I understand it the brighter the image the faster the eye/brain will process it, if the eye/brain is faster than the colour wheel you may see rainbows.
Rapid eye movement increases the likelyhood of seeing rainbow effect as the eyes dart about the screen missing colour refreshes. The eyes naturally keep track of bright moving objects, it is subconscious involuntary eye movement, so high contrast moving images are the most likely to induce rainbow effect.
High contrast especially moving objects in the peripheral vision will trigger eye movement, so I expect screen size can play a part.
A example of a worse case image is the THX test screen for geometry on most THX certified DVDs, in the THX optomizer usually in the language submenu if not in the main menu. It is a white circle on a black screen, the eyes naturally trace the circle round. I would expect most people to easily see rainbows on the THX geometry test pattern or to be able to induce rainbows with the pattern by blinking or moving their head.

Thanks for the detailed reply. You checked I was taking about a brand new Darkchip3, 6-segment 3xRotation DLP.

How did you find out it is a 3xRotation. I looked up the projector but could not find how fast the colour wheel was or what the segments are in the colour wheel RGBRGB or RGBYCM or whatever.
 
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Moolers

Active Member
As I understand it the brighter the image the faster the eye/brain will process it, if the eye/brain is faster than the colour wheel you may see rainbows.
Rapid eye movement increases the likelyhood of seeing rainbow effect as the eyes dart about the screen missing color refreshes. The eyes naturally keep track of bright moving objects, it is subconscious involuntary eye movement, so high contrast moving images are the most likely to induce rainbow effect.
High contrast especially moving objects in the peripheral vision will trigger eye movement, so I expect screen size can play a part.
A example of a worse case image is the THX test screen for geometry on most THX certified DVDs, in the THX optomizer usually in the language submenu if not in the main menu. It is a white circle on a black screen, the eyes naturally trace the circle round. I would expect most people to easily see rainbows on the THX geometry test pattern or to be able to induce rainbows with the pattern by blinking or moving their head.

How did you find out it is a 3xRotation. I looked up the projector but could not find how fast the colour wheel was or what the segments are in the colour wheel RGBRGB or RGBYCM or whatever.



This is the only time I ever noticed the rainbow effect on my PJ. I must give Sin City a spin to see if I notice it while watching an actual movie.
 
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kbfern

Distinguished Member
If you are susceptible to rainbows Sin City will deffo show them also any B&W film or the beginning of Casino Royale (the B&W section).
 

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