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 Display Calibration Fundamentals : My Take, Display Calibration

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TSanfieldude
post Mar 23 2010, 08:12 AM, updated 6y ago

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A Beginner’s Guide to Display Calibration

This guide is work in progress. I will update with pictures as time goes by, please be patient.

What is Calibration?

Calibrate - To check, adjust, or determine by comparison with a standard (the graduations of a quantitative measuring instrument)

Calibration - The act or process of calibrating or the state of being calibrated.

Display calibration is centred on calibration of your display to standards.

Movie studios/directors adhere to standards when mastering movies/films.

One key feature of the standards for movies (colour) is the white point. The reference white point is defined as D65 for both North American and European standards. The white point refers to an x,y coordinate of 0.3127, 0.329 in the CIE Chromacity chart. CIE(Commission Internationale de l’Eclairage) is the international body responsible for the measurement of color.

6500K however, is a measure of the correlated colour temperature (CCT) of the white. Where D65 specifically targets a white point, the colour temperature is slightly misleading. It is possible to have a white that is 6500K in colour temperature (as it depends on whether the red and the blue channels primarily) but not hitting D65 white. For all practical purposes, D65 is a better representation of calibrating to a standard as if you do hit the 0.3127, 0.329, you automatically hit 6500K CCT.

The different standards that are available out there are:
· ITU-R Recommendation BT.709 (“Rec. 709”) – the standard for both North American and European high definition television - HD
· ITU-R Recommendation BT.601 (“Rec. 601”) and SMPTE-C – the standard for NTSC 480i/60Hz standard definition television (SMPTE-C has supplanted Rec. 601), and
· PAL/SECAM – the standard defined by the European Broadcasting Union (EBU) for 576i/50Hz standard definition television.

Once a display is calibrated to these standards (or as close to these standards as your display will allow) you do not need to wonder if the picture is accurate and tweak your settings for every movie. If your post calibration results are good, the pictures that you are viewing are as close to what the director intended for you to see.

This post has been edited by anfieldude: May 10 2010, 02:03 PM
TSanfieldude
post Mar 23 2010, 08:13 AM

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Key Components/Terminology

1. Brightness
2. Contrast
3. Sharpness
4. Colour (Hue, Saturation, Lightness)
5. Tint
6. Greyscale
7. Gamma


In order to carry out basic calibration, you would need a test disc and preferably colorimeter/spectrophotometer/lightmeter & calibration software.

Test Patterns
Test patterns or test discs are needed for you to set some of the basic stuff even without a meter. I would recommend the free AVSHD709 (for HD sources, Blu Ray and Media Players) or TomHuffmans free NTSC DVD test patterns. You can also purchase the GetGray test disc (available in PAL and NTSC), DVE HD Basic Calibration Blu Ray/DVD or the fantastic Spears and Munsil HD Benchmark

We will discuss the most basic component of display calibration, one that can be done without any meters (most of the time)

Setting Brightness
Brightness is actually the setting of the black level that for me is the basis of a proper calibration. My preference on the test pattern on setting brightness would be the brightness (PLUGE Low– Picture Line Up GEnerator) pattern on S&M Test Disc. However, since most of you would not be buying the test discs all the explanation would be based on AVSHD709 free test disc. Pull up the Basic Settings, 1st pattern (called brightness and contrast). On this pattern you will see flashing bars labeled 1-25 against a video black of 16. First check that you cannot see all the way down to the label of below 5. If you do these bars flashing, you need to check the settings of you Blu Ray player or your display. What is probably happening is that you are sending a RGB Full signal (also lookout if your display has a setting for 0 IRE, 7.5IRE, select 7.5IRE for the correct setup). For all BD or DVD material, it is based on a video level setting of 16 and above. This is the 1st setting you need to check. Once you select the correct output from your player (typically most players have an Auto setting, this setting normally sets to YCbCr it depends on the EDID that your display is sending out), you are ready to set the brightness. It is better to set the brightness in a dark environment. Turn up the brightness until you can see the bars below 16 flash. Then turn it down until 17 can barely be seen. Now go to the next pattern. The next pattern is brightness and a contrast pattern together. For displays that have different outputs based on dark/bright content in the same screen (plasmas, crt) check your brightness setting that you set earlier. Same method used here, in this case see if you can get at least 19 and above flashing and the 16 and below not flashing. The correct brightness setting is the higher one from pattern 1 and 2. ie, if using the 1st pattern you got a brightness of +1, and on the 2nd pattern you got a brightness of +2 then , use +2.

This post has been edited by anfieldude: Apr 8 2010, 03:12 PM
TSanfieldude
post Mar 23 2010, 08:13 AM

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Setting Contrast.
Setting of contrast on a digital display without meters is difficult, as most digital displays do not clip white levels above digital white of 235. Pull up the contrast setting pattern on the AVS HD709, 3rd pattern on the basic setting page. You should be able to see as many bars as possible above 235. If you do not see anything above 230 then your set is clipping whites. Else adjust contrast up/down to show as many bars above 235 as possible. Most digital displays will show quite a bit above 235. Another thing to look out for is if the contrast is set too high, the whites start to look reddish, bluish or greenish. In this case, you need to set contrast in tandem with another pattern. In the Misc Patterns, go to the RGB High Clipping. This is essentially a clipping of the individual RGB channels that make up white. The problem with turning up contrast too high is that some of the individual channels get clipped. This in turn, makes the white either too green, red or blue. Turn down contrast until the all channels clip at about the same level.

If there does not seem to be any clipping at all for white, red, green & blue channels (highly unlikely as all digital displays will clip one channel or another), set contrast using a 100% white window (from either Calman window patterns or HCFR window patterns) to the level that pleases you eyes and is not uncomfortable.

Setting Colour/Tint
I am not going to go into this as unless you have a filter it is impossible to set this by eye. Even with a filter, the best way to set colour is to use a meter. I will add this if there is a need for this. I will explain this later as it is a complex matter.

Setting Sharpness
Setting sharpness is pretty subjective. Using the sharpness setting and the sharpness test patterns, play around with the sharpness settings to get as sharp a picture as you can while looking for halos or white edges near the black lines. Also look out for moiré and lines that seem to merge. Also, select the picture mode that reduces the artifacts. All displays have various modes, ie, dot by dot, just scan, full, wide etc. In most cases, dot by dot is the one that normally has zero over scan. Play around with them to see which one gives you the least artifacts with the sharpness setting. The Spears and Munsil disc has a better pattern to set sharpness and I have tested it with various displays. The adjustments you make in the display responds well to what you see in the test pattern that makes setting sharpness easier.

That about covers the basic settings that you can carry out without a proper meter. In order to carry out a complete calibration, you need to have a meter and complete the calibration of greyscale, gamma and colour.


This post has been edited by anfieldude: Mar 23 2010, 08:21 AM
TSanfieldude
post Mar 23 2010, 08:14 AM

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The next few areas require the use of a colorimeter or a spectrophotometer to set correctly. I will explain these briefly for now and add more detail when I get the time to complete the documentation

Greyscale
Greyscale is the calibration of the shades of white. White is the basis of colours, greyscale calibration is done to set the white shades correctly. Typically, the display controls that calibrate greyscale are labeled as white balance and have Red/Green/Blue bias/cut/gain/offset/high/low. They control the individual RGB channels that make up white.

Gamma
Gamma is a luminance measurement. This is a measurement or parameter that controls the light levels are different input levels. Setting gamma correctly is essential to the “3D” pop that people look for in a digital display. Gamma is commonly targeted by calibrators range from 2.2 – 2.5 but this depends purely on your viewing environment. Lower gamma is normally selected for high ambient light surroundings and higher gamma is for darker environments. I find targeting a gamma of 2.35 is best for semi dark environments and 2.15 for bright environments. In a dark room, a set that tracks gamma correctly at 2.35 with good black levels will produce an image that is very 3D, especially if the set also tracks good greyscale.


This post has been edited by anfieldude: Mar 23 2010, 08:23 AM
TSanfieldude
post Mar 23 2010, 08:15 AM

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Colour/Tint
Colour is a whole new can of worms. There are set colour points in the CIE chart for each colour. Red, Green and Blue are the primary colours and Cyan, Magenta and Yellow are the secondary colours. To do a proper calibration of Colour using a Colour Management System would require the use of a Spectrophotometer (colorimeters are okay as well, its just that the spectros are supposedly better in them). Each colour has its own theoretical Hue, Saturation and Lightness. The Hue and the Saturation are represented in the CIE Chart that I described earlier. A display with a good CMS would typically have independent controls to move all of the above.

The Colour controls on the different sets behave differently. On some sets, the colour control effects saturation and on others they only control lightness.

The Tint controls normally just rotate the secondary colours, however, it depends on the implementation of the display.

Saturation is a measure of how far away from the white point in the CIE chart is the particular colour. If the colour is over-saturated, it means that it is further away from the white and as such seems richer.

When hue is off, the colour seems to resemble more of a another colour rather than itself. Eg, Cyan’s hue seems to be shifted towards green instead of blue, meaning that the cyan seems to have more green than blue.

Lightness is a measure of how bright the colour is. It is possible for a colour to have accurate hue and saturation but because the lightness it wrong, it seems too bright.

All these parameters are those that are needed to be right in order for the colours to be correctly decoded accurately. I have seen numerous displays that have no controls for a CMS and the basic colour and tint just do not do much. Then, there are some displays that have all the controls you can imagine. I hope in the future all display manufacturers provide a full 3D CMS that the consumer can use to fine tune his display.


This post has been edited by anfieldude: Mar 23 2010, 08:25 AM
TSanfieldude
post Mar 23 2010, 08:18 AM

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The one thing that has happened in the past couple of years is the emergence of affordable home theater enthusiasts calibration packages that allow more and more people to calibrate displays. Along with this, the masses are adopting and understanding that calibration actually improves the overall home theater experience and adds to the excitement. With a properly calibrated set, you do not need to wonder if the pictures you are viewing are off and you can enjoy the movie more.

The choice is yours, you can either become and enthusiast and buy your own calibration software/hardware, or you can hire someone to do it for you so that you do not need to invest into this area.

I have been using Calman software for the past few years to calibrate displays of family and friends. I have been very happy with the support I have gotten from the team. The link is provided below and they ship to Malaysia.

SpectraCal Website

Another newcomer to the enthusiast and professional calibration arena is Chromapure. Their software is slightly different and their up and coming in the industry.

Chromapure

These are the 2 affordable solutions I know out in the market.

I have used Calman for a couple of years and have been following their growth for some time. The enthusiasts are lucky to have affordable solutions for home calibration with both of these players in the market.

This post has been edited by anfieldude: Mar 28 2010, 04:19 PM
TSanfieldude
post Mar 23 2010, 06:03 PM

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Please give me some time to improve on this thread. I will be doing bit by bit. Also if there are any questions, pls ask here and I will answer and improve on the thread documentation for ease of understanding.
TSanfieldude
post Mar 28 2010, 12:10 PM

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One question that keeps coming up is :

My picture looks good already. Will I see the benefits of calibration?

My answer is:

Calibration of the display is the same as tuning of your car. When u tune ur car correctly, you will get the best of the petrol consumption that the car is capable of. You also unlock the full power capabilities of your car. Sometimes when change ur oil filter and new engine oil, as u drive ur car out of the service centre, ur car is response is smooth and u admire ur car more. However, on another note, there are people who could not care less, they look at the car as a vehicle to take u from point A to point B, occasionally complaining about mileage and sometimes annoyed about the lack of power while driving. However, they could not care less about how it performs. So there are different kinds of people and they are sensitive to diffferent things.

The same applies to display calibration. Calibrating ur display brings the best out of display that it is capable of producing. In most cases, it helps to save electricity consumption as u calibrate the display to the optimum based on ur environment. When a display is properly calibrated (this depends on different display capabilities, u cannot compare a Ferrari to a local car, same applies to displays), u get proper flesh tones, u do not need to wonder if the director purposely skewed the hues of the colours or not, since ur display is calibrated to HD standards. U then get the best of ur display.

Can it be seen by ur eyes? If u look and pay attention, of course it can, same like when u get ur car tuned.

Some people choose to ignore it. Some don't. It's ur choice.


TSanfieldude
post Mar 28 2010, 04:01 PM

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QUOTE(gocitygo @ Mar 28 2010, 12:57 PM)
Anfield, I'm using Xrite i1 with ColorHCFR on my projector.  While doing greyscale calibration, I found out the Red too high in the original setting.  I have to adjust the Red and Blue (RGB Gain/Offset) to get the 6500K target.  The RGB post calibration looks OK but the Gamma is about 1.9 instead target 2.2.  Is there anything missing here?  notworthy.gif

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gocitygo,

What picture mode did u start with on the optoma? What gamma did u select?

I believe ur initial gamma that u selected was averaging 1.8 to start. I think u either choose Cinema or PC gamma. I believe Cinema starts at 2.35 and PC is closer to 2.2.

Check and let me know and I will help u with it.

I have calibrated a HD65 b4 and could easily track a gamma of 2.35 for a dark room.
TSanfieldude
post Mar 28 2010, 04:25 PM

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QUOTE(gocitygo @ Mar 28 2010, 04:16 PM)
Thanks for grand sifu help. 

Original setting:
display mode = cinema
degamma = film

New setting;
display mode = cinema
degamma = video

Is that always tunes with R/B instead of G (RGB gains/offset) in greyscale calibration?  In my case, I cutdown R gain a lots (-22).  Not sure it will cause the color composition to off red?  I'm not able to do Color calibration due to HD-65 limitation of CMS.
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gocitygo,

I believe I used cinema and film as well. Try PC in gamma and it should be better.

Is this a i2 display lt?

There are 2 trains of thought on what is the best way to achieve D65. I normally follow the "not touching green" camp but occasionally I add +1/-1 to green to improve on the cals.

U can try adding green as well.

What is the life of ur lamp? Are u using eco mode?

Can u refresh my memory on what other display modes were there?
TSanfieldude
post Mar 28 2010, 05:16 PM

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QUOTE(gocitygo @ Mar 28 2010, 04:42 PM)
The lamp is about 200hrs (STD mode).  Yes, I'm using i1 Display LT, the affordable version smile.gif

Display mode = Cinema/Bright/Photo/TV/User.

Degamma = Film/Video/Graphic/PC.  I tried Film before but giving unstable D65 across IRE.  Will try PC mode as you suggest.

BTW, I set ZERO both Brilliant Color & True Vivid setting.  Image AI = Off and Color Temp = Medium.
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Another thing to try would be colour temperature low as it would be more red to start with.
TSanfieldude
post Mar 28 2010, 09:16 PM

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QUOTE(pierreye @ Mar 28 2010, 05:24 PM)
Just my 2 cents, normally I'll try to find out the display deficiency in which color. That would be your cap. For example, majority of the UHP lamp is red deficient. You will see that it will run out of red when approaching 100% White. In this case as an example, if +512 is the highest number, I'll cap red at +512 and adjust Green and Blue to match D65. This would ensure you have the smoothest D65 greyscale tracking. Another option is just ignore the red deficiency issue as long as 90% white is D65. This is to get good greyscale up to 90% white but give you a bit more brightness at 100% white (You seldom have movies with lots of 100% white on screen).
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If u r running out of any particular colour, u r probably clipping that channel. The easiest way to fix that would be to reduce contrast until u stop clipping. Of course, if that is reducing ur luminance too much, then u need to compromise. I agree with you that I would compromise on the higher end rather than the mid and low end.
TSanfieldude
post Apr 1 2010, 01:29 PM

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QUOTE(chewkl @ Apr 1 2010, 09:46 AM)
Bro Anfieldude, what do U think about the new Panny S2 calibrated results on the 2nd post here?

http://www.avsforum.com/avs-vb/showthread.php?t=1232441
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Slightly better than last year. However, the gamma is the same and that is a major issue in my book. Colour decoding slightly better, greyscale slightly better. Green cast still there and needs calibration to remove.
TSanfieldude
post Apr 1 2010, 04:06 PM

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QUOTE(chewkl @ Apr 1 2010, 02:12 PM)
Thanks bro. Will be waiting for Sammy's 2010 plasma panel then. biggrin.gif
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I hope u find what u r looking for. Just remember, there is no perfect display. All have their strengths and weaknesses.
TSanfieldude
post Apr 1 2010, 05:32 PM

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QUOTE(chewkl @ Apr 1 2010, 04:13 PM)
With all due respect, U are wrong bro. KRP is perfect to me, just that I can't afford it. cry.gif
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The KRP also has its flaws...
TSanfieldude
post Apr 2 2010, 04:39 PM

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QUOTE(pierreye @ Apr 2 2010, 04:12 PM)
If your projector had  blue only mode (which turn off red and green) then you don't need the filter. Even the tint/color  control is not accurate based on the Calman reading. If you have CMS, just leave tint/color at default. It's very easy to screw up the color using tint/saturation control.
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My personal opinion is that for getting colours right, u need a meter (preferably a spectro). Also a working CMS is a must, else the display must track Rec 709 accurately. But a 3D CMS is the way to go.
TSanfieldude
post Apr 9 2010, 03:08 PM

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QUOTE(formalin @ Apr 9 2010, 02:12 PM)
Bro anfieldude,

It is possible to post the best possible setting for KRP-500A ??  icon_question.gif
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I don't have a KRP-500A to do that.
TSanfieldude
post Apr 21 2010, 09:11 PM

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All,

Do let me know what other stuff you would like me to cover in Display Calibration or anything related to something that is not brand or technology specific. I will try to put more details in the 1st page. If there is enuf interest, I don't mind adding a step by step calibration guide to use a meter to calibrate. However, there are others that do it well.
TSanfieldude
post Apr 27 2010, 06:02 PM

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QUOTE(junwei @ Apr 24 2010, 11:03 PM)
Bro anfieldude can setup a team to train video calibration in Penang and those interested can fly there, pay a fee n attend the course n share ideas together. and if anfieldude doesn't wanna to collect the fee, we can donate it to charity :)hehe


Added on April 24, 2010, 11:09 pmFrom what I've read so far in this thread, people who is interested and have technical knowledge will probably understand at least 60% and above of what is mentioned here.

The rest are probably scratching their heads trying to figure out what those terms (d65,rec 709, +512, 3D CMS, etc).

Maybe do a simple definitions on what these terms and meanings are.
like, why we need to get D65 and what it means, etc tongue.gif

Then everyone will understand further.
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Thanks for the suggestion. I will update the material when I get the chance.
TSanfieldude
post Apr 29 2010, 11:42 AM

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QUOTE(Alias @ Apr 28 2010, 10:02 PM)
anfielddude,
apart from the sizes (600m & 500a), is there any more difference in terms of specs and hardware between those two?
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I posted the reply in the Pioneer Thread. See link below.

Link to Pioneer Thread

This post has been edited by anfieldude: Apr 29 2010, 11:44 AM

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