Display Motion Blur - Cause and Solution

The afterimage on a display means happening distortion of image. The reason of this afterimage used to be an optical illusion or problems of a movie or a display. LCD often has a problem of afterimage and it is called 'motion blur'. It is phenomenon to be shown a blur on the edge of a video when frames are changed. The motion blur can be divided two. First is caused by that a subject is moved before a camera focuses it and it is called 'captured motion blur'. The other is 'displayed motion blur' and it is generated by driving of a display. In this article, you can get useful information why 'displayed motion blur' is happened and how pioneers can overcome this problem.

Left : Original Image,  Right : with Motion Blur

Why is motion blur happened on LCD?

The motion blur is a phenomenon to be shown a blur on the edge because of overlaping images between privios one and present one. It means than display can not divide continous images correctly. We often listen an information of motion blur that PDP is better than LCD and it is the reason that PDP is better when watching an action movie. Then why is the phenomenon of motion blur specially discussed on LCD?

1) Motion blur by responsive time of liquid crystal

LCD uses polaraizer film and liquid crystal to adjust amount of light. When a voltage is generated on liquid crystal, it moves to change direction of light and polalozers make to pass a light as an its angle. At this time, liquid crystal needs time to move where you want. For example, it is supposed to be needed as 20ms to move it's position when 5V is supplied. And there is 120Hz display needing 8ms to express a frame. Then can this display show correctly a frame? 8ms looks shorter than 20ms liquid crystal needs, isn't it? In this case, there is a problem can't show a image fully when frame is changed to other frame.

2) Motion blur by an afterimage of eyes

Almost people used to think that motion blur is mainly happened because of slow responsive time of liquid crystal, but the afterimage of eyes remebering privious an image also is playing an important role to make the motion blur. When frames are changed, eyes remember privios a frame and it is seen as motion blur to be overlaped with current frame. That's why LCD's analog driving method keeping a same image during a frame time is more fragile than PDP's digital driving showing impulsive light.

How can LCD overcome these obstacles

Aforementioned, Although LCD has a weak structure about motion blur, this display has tried to improve the problem. Thanks to these efforts, motion blur was less recognized to viewers and it positively influenced LCD which could become the strongest display on TV market. Then, look into techniques to improve morion blur.

1) Improve problem by slow responsive time of liquid crystal 

- overdriving

What is there method to improve problem by responsive time of liquid crystal?

It can come to mind firstly that making new liquid crystal with fastly responsive time. There are many tries to be related that, it is hard to improve easily when considering cost / yield / reliability. When some problem need to be improved, nomally the most easy method is which change circuit area with remaining panel area. Through this point of view changing circuit area to supply different voltage, 'Over Driving' technique is generated.

The Graph shows overdriving is how to be realized

Usally responsive time means a change time from 10% to 90%. The thing which responsive time of liquid crystal would be slow means its change time is over a frame time. So, for revising responsive time, change time of liquid crystal to change 90% makes to be in a frame. For realizing this, an idea was derivated, which generates a higer voltge to the changing frame. When high voltage is generated to the liquid crystal, it has a feature to be changed steeply. Like above fiqure, supplying high voltage is at the first frame it changes and the voltage inteneded originally is supplied when frames shows same scenes. Although slow responsive time of liquid crystal, you can reach over its 90% change in a frame time by using this technique. Actually, it looks easy but there is a problem to be implemented. Because responsive time is diffrent among grays and it means different additioanl voltage is necessary every gray value. Anyway the algorithm to be looked easily plays really important role to revise motion blur on LCD.

2) Improved problem of motion blur by afterimage of eyes - Black data insertion and frame rate doubling

Like aformentioned, there is not only liquid crystal's slow responsibe time to be problemed by motion blur. By a feature of eyes remembering static image, motion blur used to be happened. How can this problem revise? LCD approached to two different method and you can get information through the below movie.



Did you catch diffternt method to imporve the motion blur? In the movie, first, compare a movie with motion blur than original one. And there is shown techniques 'black data insertion' and 'frame rate doubleling' controbuting to improve motion blur problem.

- Black Data Insertion / Scanning Backlight

The first method is impulse driving like CRT or PDP. It is not maintain a light for a frame time. it means showing a light during shorter time than a frame time. For the realization, black frame is inserted to between scenes. 'Scanning Backlight' is representative method to insert black frame on LCD and it is possible by turning on / off its backlight.

Black Data Insertion's basic concept

There is, however, demerit to need more light for showing same brightness during short time. (Link -> What's difference between LCD and PDP)

Like aforementioned, the technique 'Scanning Backlight' shows black image by turning off its backlight in middle of a frame time. It helps to refresh remembering image using black like impulse driving. This method is very effective and easy to implementation, but, it has a demerit to be lower power efficiency because it has to show more light as much as reducing a frame time.


- Frame Rate Doubling / MEMC

Frame Rate Doubling's basic concept. Let's compare between 60Hz and 120Hz

The other method is derived from an idea 'Raise frame refresh time to don't aware motion blur'. In other words, a number of frames are increased during same time and it means some images should insert to between existed frame. Then, input frequency is increased from 60Hz to higher frequency and it is decided by a number of insert images like 120Hz or 240Hz. For realization, there is a technique such as frame rate doubling and it is one of method MEMC. This method extracts the vector from images inputting 60Hz and estimates change of between vectors. From estimated result, a new frame is made by interpolating motion between two frames. This method needs complicated algorithom extracting the vector from images changing so fast and needs many memory ICs for buffering images. Also fast frame rate by this technique makes many demerits to raise cost and power consumption, to weak noise and to require changing many components like T-Con and Panel IC. But it has merit to get high power efficiency of backlight unit because it can maintain same brightnees for a frame time.
About competition to refresh frequency

The problem by slow responsive time of liquid crystal is almost overcomed. But motion blur by afterimage of eyes is still issue and many company are trying many technologies to jump off the obstacles. It is true the high frame rate helps to improve problems of motion blur on LCD because time previous image is shown is reduced and it means the time eyes remember image is also reduced. High frame rate of 240Hz makes considerable improvement as people don't catch this problem.

At this time, we need to detailed check about frame rate, in other words, frame refresh time. PDP uses sub filed driving method and it means 8~10EA subframe is shown through 600 times of sustain. Then they advertise it uses 600Hz driving. But, is it true to show 600EA different images?

TV set receives a frame image every 60Hz and it is also not real 60Hz. The original movie format is almost 24fps and multimedia player likes DVD player makes to change this format to 60Hz using 3:2 full down method it is just repeat image according to ratio. In other words, 60Hz TV receives is just 24frame image. Although PDP sustains 600times for a frame time, it is to shows just 24 different frames.

Then, we can get a question 240Hz makes really different 240 frames for displaying? Nobody say motion blur to PDP despite of its 60Hz driving. Then high speed driving is necessary? If it is true, what speed is suitable?

These questiones is connected to several problem from standard movie format to driving method. More detalied contents relaed above question will be shared soon. Good luck.

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Display Story2. What's Difference between LCD and PDP

I wrote an article about a display focusing on smart revolution. From now on, I am going to make a posting focusing the display by itself. There were many considerations what is selected to the first subject. And it was decided as first subject to difference driving method between LCD and PDP, which was asked at an education for incoming employees.

What's difference between LCD and PDP

What come to your mind when you have question about a difference between LCD and PDP? If you were to consider selecting a TV between LCD and PDP, you might come to mind responsive time, luminance and power consumption. When these displays were in keen competition, there were some words that if you want to see a movie, select PDP and else if you want to see a drama, you should buy LCD. Although PDP are dusky comparing LCD, PDP has merit to motion blur and it is effective when you see action movie switching scenes quickly. LCD has advantages bright luminance and low power consumption.

Why are happened these differences? It is because there is a difference of driving method between two displays. How about watching a movie comparing LCD and PDP before giving a detailed explanation? It is a movie which film a screen of LCD and PDP directly and this movie shows wide difference between two displays.

- This movie is directly captured to Screen of PDP and LCD by Slow-Motion of iPhone 5s

Did you catch a difference between PDP and LCD in the movie? Is there flicker in PDP and LCD is not? And is there motion blur in LCD more than PDP? Surely, this difference doesn't mean a gap of performance fully. When you watch a TV directly, you might not catch a flicker on PDP. But, this difference of driving method is important factor to make a difference of performance between two displays. Above movie is filmed at 1/4x speed and it was possible to be supported 120FPS which mean to film 120frames per 1s. That is why you can feel a difference between these displays. If you might not catch a difference when you see it directly.

Difference between driving method of LCD and PDP

Like aforementioned, this difference is caused by different driving method. It can't help beging different driving method because these displays have different basic structure making a light source. When they had in competition, they have clear merit each other. But at now when I am writing this article, LCD seems to win on tight race with PDP. And many companies have dropped to develop PDP TV.

There was surely different and each had merit to appear to consumers. But, LCD could get a dominant position in competition with PDP because LCD had different structure and driving method which has advantage to revise its problem more easy than PDP.

Different driving method by difference of basis structure.

Then, I want introduce an elementary difference between two displays. LCD used to be called AMTFT (active-matrix thin film transistor) - LCD. This has a feature to adjust amount of light from backlight unit through tilted liquid crystal between two polarizing plates.

PDP(Plasma Display Panel) is a display making light using plasma effect. You can easily understand this technique based on a technology of fluorescent light. The display panel utilize small cells containing electrically charged ionized gases.

-Left is PDP's basic structure, right side is LCD's basic structure.-

Actually direction of this article is not detailed explain about difference of structure above mentioned because I want show display's difference from my view with different driving method. But for this explain, their basic structure has to be explained first briefly.

AMTFT has active-matrix structure by using TFTs. This structure makes to be possible to maintain a voltage as a pixel's need during over schedule time. The voltage supplying a pixel is maintained during a frame time and it tilts liquid crystal according to supplied voltage. The liquid crystal has interesting feature that a degree it is tilted adjust amount of light on a pixel. To add detailed explain, two polarizing plate play a role blocking light and tilted liquid crystal make to be possible to pass their block.

But, there is a problem to use liquid crystal it is core of LCD. When supplying voltage it, so many time is needed to move we want. That is why LCD driving needs to secure time to maintain supplying voltage and TFT and Cap play an important role on this driving method. This method use to be called 'Analog Driving' because each pixel has a different voltage to display gray-scale.

PDP is made of 2 sheets of glass with 2 gases stored between the sheets. Its driving consists of addressing and sustain. Each row of a frame needs addressing and the frame makes light after finishing whole addressing of rows. PDP's structure should need sustain which is similar way to fluorescent tubes used for lighting and it makes to be hard using method to maintain a voltage for a frame time like LCD's one. Also it needs very high voltage and a different voltage doesn't make a detailed difference of light like LCD's one. That's why PDP adapt different driving method which makes a light by fast repetition of addressing and sustain. At this time, amount of light is same every sustain and amount of light is decided by a number of sustains. Therefore this method used to be called 'Digital Driving' because amount of light is divided by time repeating number of sustain.

Let's compare driving methods

There is difference the number of image for a frame time. PDP needs 8 subframes, LCD needs just 1 frame.

1 frame time means that the time need to drive display for a frame. PDP drives a frame including 8 subframes at 60Hz and then it needs 16ms to show a full frame. And LCD changes a frame every 120Hz and it means frame time is 8ms. On this basement, PDP expresses 1frame by dividing with 8 sub frames. At example, there is a image having 8bit resolution, 256 grayscale (normally, PC generates 8bit, 256 grayscale). and these subframes make a whole frame by showing them during a frame time. Eyes used to be known to divide a image every almost 45Hz, which means that light of images would be accumulated and be combined as 1 image in this period. That is why people don't recognize 8 other images when they watch PDP. You can check this factor at an above figure. At this one, PDP has 8 different subframes but LCD has just 1 frame.

LCD can show a frame image using just one frame like aforementioned. This display can support different voltages to each pixel and it makes different light according to a voltage of a pixel. It means that LCD can control every pixel in a frame time. That's why a image which it want show corresponds to a displayed image like above figure. This different method showing a frame image between PDP and LCD aforementioned is by the difference of driving method, that is a difference between digital driving and analog driving.

What is a difference of feature between two display.

Did you remember a difference feature between PDP and LCD aforementioned in front of this article? At repetition, almost TV seller would compare lists like responsive time, luminance, power consumption and etc to show a difference.

	PDP	LCD
Responsive Time	●
Luminance		●
Power Consumption		●

- Each merit s of PDP and LCD

I have explained that different driving method cause difference of display's feature. And from now on, I want to focus why different driving method makes other results.

1. Responsive Time : In the display, responsive time means how much fast showing a image. Aforementioned, eyes have feature to remember before image according to its duration on display. If a image's switching time were slower and slower, it would to be increase probability to be happened as blur. It used to be called motion blur and PDP has a merit this blur because this display shows 8 different sub frame with over hundreds sustain during a frame time. It isn't to compare that LCD shows just 1frame during same time. These difference makes different responsive time between them and it makes PDP is better than LCD when watching action movie passing scene quickly.

2. Luminance : Luminance means brightness on the display. When you drop by shop for comparing TVs, you may easily recognize display's difference through their brightness. The brighter display tempts consumers effectively and LCD has a strong merit at this point. These difference of brightness is hard to see it's by only difference of driving method because they are have different basic structure to make a light. But, it is fact that the difference of driving method make a different time showing light during a frame time and it affect their brightness. As aforementioned, eyes have a feature to recognize something by accumulating light in specific period. For example, if there are 100nit (luminance's unit) for a 8ms and 200nit for 4ms (0nit for other 4ms), they would be recognized as same luminance. PDP has a relative short time to make a light because it should be initialize voltage every addressing of a subframe. The limitation about amount of light during short time can't help being existed and this factor makes PDP can't make brighter screen than LCD.

Amount of light which eyes can recognize is decided by time and its brightness 

3. Power Consumption : Power consumption is on extension line of the luminance. First, there is a huge difference using voltages. PDP use 60V at data sourcing part and us 180~200V at gate addressing part. On the other hand, LCD use 24V at backlight part and use 10V at data sourcing. Already there is difference between voltages to generate default structure of each displays and beside, LCD use hold-type driving method which needs low voltage to maintain voltage during a frame time. For example, if LCD have a just 1/10 frame time to make a luminance according to 1 frame, there would be huge difference of voltage and current comparing conventional method.
( The luminance of backlight is proportional to current, which mean that 10x current is needed to make same brightness like hold-type method and it require high voltage according increase current. These would reduce power efficiency and need a high performance power system. PDP use digital driving method which have a short time to make a luminance and it is one of reasons that PDP get worser power efficiency than LCD.

How can walk ahead LCD on intense competition with PDP.

The display has taken innovation to give an experience like seeing real things to people and it is necessary to natural movement and bright screen like on genial weather. In order to implement these feature, PDP has been also to make an effort for bright screen and low power consumption but it couldn't page off its limitation. Contrastively, LCD's effort which change backlight unit to LED make its merit more strong and widen a gab with PDP. Also its demerit which is response time can be overcame by revising driving frequency (60Hz → 240Hz) and overdriving technique. It could be possible that LCD have different basic structure and driving method with PDP.

Bottom Line

I organize contents which have remained in my brain through this article. This subject can be interesting because it reflects many techniques to drive a display circuit and gives other point of view as driving method comparing between LCD and PDP. Postings which is going to be wrote would connects up this subject because this posting include overall concept related on from techniques fixing aforementioned problem to novel 3D driving and OLED driving method.

In above mention, there seems to a next item. I have a plan to write about motion blur which is demerit to LCD. Then I want finish this article now and I wish meet you with better posting.

Best Regards
gungs

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Display Story1. Smart Revolution and Display's Importance

[ Original Page in Official LG Display Blog (Korean)] 

Recently I watched a drama got a background 20 years ago and I thought the world had changed with many things. Actually, It is unnecessary for comparing 20years ago. Just for 5 years, so many things have changed but these changes are not made by a need of people. These made needs for a people. I can illustrate a smartphone as a representative example. When I entered to a company, iPhone 3gs was just released and other gadgets were at the ready. Almost people seemed to be attracted at unprecedentedness of a smart phone rather than it was indispensable. In particular, It leaded a trend to be called an augmented reality application which can show weather information when you see the sky through a camera of smartphone. I would imagine interesting future through a new function of the smart phone and it has been realized with numerous developers. At now, it is unfamiliar to use a conventional phone and an indefinite future is going to walk in the real world through a smart phone.

▲ Smartphone and SmartTV

Pioneers drawn a image of future and users had absorbed a change with giving praise to an innovation. At present, we are living in the innovation which it was hard to be imagine 10 years ago. If It is ture that I feel like this just because of reaching old age, I seem to live in the best rapid change until now. This change which can be just a beginning used to be called the smart revolution. The reason of what the smart revolution was possible beyond smartphone to smart-TV, smart-watch and the internet of things is because there is a base on the number of revolutions. From now on, I want to tell based revolutions and the future of our lives in the smart revolution because there is a worth and roll of displays in the furure including a direction of my article.

What Make to be Possible the Smart Revolution?

These changes it is based on the smart revolution can be categorized like that user experience(UX) / IC of hardware / battery / communication / display.

▲ UX, AP, Battery, Communication, Display

UX : What smart phone becomes really smart is thanks to be able to operate many functions supporting conventional PC. The operating system(OS) getting bigger and bigger can be lighter by an optimization based on a compatiblitity of between hardware and application and the expandability among various gadget . At last, users can have been able to get PC' experiences through a small gadget. Becoming light is got other expression such as a time reduction for operation OS with application or power reduction for longer battery. Just becoming light don't include all revolutions. On this basement, it was added to multi-touch function called a revolution of UI and sensors such as GPS, gyroscope and etc, which takes an important roll of smart revolution. The user experience (UX) is built by combining aforementioned hardware basement and the big data.

Hardware component : The core value of success of a small gadget is miniature IC called MCU or AP which operates OS , image processing, memory controlling and etc. And it is thanks to advanced semiconductor technique and it results miniature ICs including memories and sensors as well as AP. Through combining an integrated IC, which is based on ASIC technology and semiconductor process called 'nano technique', it is to be possible to a smaller chip than a nail of human and it become based on changes . In here, combining sensors play really important roll to implement UX as on a small thing called smart gadget. 

Battery : The stable power system must be necessary for operating hardware and software.. And it has to be small, chargeable, durable to meet a condition of a small gadget. These were possible by developing lithium ion battery which gets high energy density and supports a charge and reuse.

Communication : At the center of the smart revolution, there were a progress of communication technique. WCDMA build an environment can communicate each other whenever they need it. Also WIFI made stable communication system in the home or office. At now, LTE's day is arrived and whoever can communicate high-capacity multimedia data using a small gadget.

Display : A cellular phone was possible thanks to development of TFT LCD which support display screen on the small device. And a smartphone which support full screen could be made by loading high resolution display. Thanks to the display, a gap of environment which users connect contents was decreased dramatically between mobile and PC.

How these contents are going to be changed

When the first concept of the ubiquitous computing was proposed by Mark Weiser at 1998, it meant "when technology recedes into the background of our lives" and it also meant "whenever, wherever, there is computing" which is possible to be every things on the internet. But the smart phone shakes a border of ubiquitous computing. At now, UX of the smart phone becomes on the each electronic machine and it moves future's one to the present.

How will have changed aforementioned categories of smart revolution? UX will be developed to the direction getting rid of a border between reality and virtual reality. It means that people can touch something, can feel surroundings and can control everything by their sense organ like real life in the virtual world. You can see many examples in the sense of a movie that computing natural gesture and moving a matter through just thinking about that. Presently, there has been many meaningful tries to implement future UX. From now on, it looks to be important to dear with getting data smartly from each sensor rather than making more sensitive sensors.

The hardware component is going to develop smaller and smaller and it will disappear from eyes. The high integration technology makes a performance users want despite of reduction its size as users can't see well. And on this component, a cloud computing technology was graft , which have made to reduce a burden of the hardware's performance. Surely, the performance is important, but it has been developed as that users don't recognize its differences comparing than battery performance's development.

▲ Intel Edison

The Intel announced a computer named 'Edison' which has small size according to a SD Card. And it looks to a finished computer because of operating based on Linux and offering Wifi, Bluetooth and etc function. It is representative example to show that hardware is going to disappear and it has sufficient condition to combine other small gadget. This combination called IoT(internet on things) makes needs of small computing.

The battery has been developed to reduce its size like the hardware component. A need of small size makes to advance low-power technique, a technology increasing battery life and wireless charging method. The battery is so important to be operated on the small thing, but aforementioned future example can be realization using existing power .

The communication has developed the direction operating faster and faster and keeping its communication state. And it requires advanced security technique and new communication system like LI-FI in the ubiquitous period.

Eventually I deal with the display. The display can be categorized in hardware like other component, but it has beed developed as other direction. The people requires its direction to increase size bigger and bigger because they want to see a vivid screen and want feel the reality. And it has advanced its appearance with curved, transparent and supporting 3D. It seems that display's final direction is what support hologram to feel like real-life.

Display Plays Important Roll in Future Technology

In brief, the direction of evolution will be proceeded to actualize the virtual thing and it makes feeling like in the real-life. Almost hardware has became smaller and it will disappear finally by results of advanced technology. But the display has a different tendency comparing other hardware above mentioned. The the display will be bigger and be other shape to give users experience like real-life.

Why did I give a long-winded explanation like aforementioned? The UX and display will have a shape can be felt like real after beyonding threshold of a change. Although the hardware and communication aforementioned are very important in the future, they will get a moment which its perpormance is over its need. And after this mement, these are hard to make a change got impact and it called just advanced specification rather than inovation. The battery has get a hurdle to be flexible, but it's going to be possible with many advanced tries at once. And it's going to walk a way like other hardware component. UX needs more experiences and technologies and its way to be a realization of virtualization. For developing UX, something has to be a prerequisite and it is just the display.

I think that the display's developemt play important roll to make advanced gadgets in the future. Already, so many media deals with the shape of the future and they have a common thing which is based on a display like transparent, curved or whole display of a wall.

Somethimes ago, I watched impressive TV-advertisement of a communication company which is not related on display company. The ad drawn future's image and it was look like future of the display company. As well as this ad, medias aforementined shown display's future. Actually, I majored a uniquitous system and its field closes software rather than hardware. But I selected a display which is near hardware's field because I belived the display will become the criterion can prove the future's development.

▲ Advertisement of some communication company

 

How Much Do You Know the Display

Todays, the display is always nearby you. The smartphone, TV, washing machine, refrigerator and other gadgets having some scareen have the display. TV have advantaged from CRT to PDP, LCD and OLED at now. The smartphone has became to get over retina display having high resolution. 3D technology has been developed to give more sense of reality and it has advanced to many image prossesing for displaying vivid screen. Also there is an effort to meet colors with eyes and there is so many agreement between from making a movie to displaying it.

You might heard a diffrence between PDP and LCD or see 3D dirving technology from some pages of internet . And you might come into contact many information about display's superiority or its future but you might be hard to know detailed information how it is possible or why this changes happend.

Although it can be difficult to know the display well, there are so many interesting story on the process to analize phenomenon and to follow traces. As mentioned above, since the display will be center of various inovations for making advanced future, it can make to afford much food for thought.

I Want to Share an Information of Display 

So I have a plan to give helpful stories for understanding the display to those who have interest and those who will have interest it. This contents divided with 3 categories which are issue , theory and future. The posting is going to fill these categories with new contents related on seminar or exhibition. There is an indefinite part in this plan as ever, but I beleive that its result which is steadily stacked make to guide advanced ways.

▲ Posting Plan

How much do you know the display? I am not an expert who knows everyting about display. But, I know the display how much more interesing it is. Fortunately, I am working in the company giving many chances to get various experiences related on the display. And on my work, I could get special experience with great co-workers and it will help you can understand easily and get interesting.

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