Video Calibration With A Colorimeter

[CAVX]

Hi DTV, the following is discussion about calibrating our displayes with a colorimeter and seeing what tweaks members do to give their picture that little more POP. I am posting this at the request of a forum member, so I hope this helps everyone and we get some interesting discussion.

So as per the title, you will need to have a colorimeter to be a part of this. This can range from the SENCOR right down to the humble Eye 1 and software to run this on a PC or tablet. So why a colorimeter? Well basically, our eyes (and our ears when calibrating audio) can decive us and IMO intrument based readings are going to be far more accurate than what we see or think we see as being correct. If your speedo in your car didn't work, how would you know exactly how fast you were driving? Does that make sense?

So whilst the user controls allow the adjustments of gamma (contrast/brightness) colour (colour and tint) and sharpness (or other edge enhancment) you can't get the correct colour of grey for optimal video. That colour, by the way is 6500K. This is sometimes expressed as D6500K or D65 where the D stands for Daylight and that corrosponds to a reference point (the D point) on the CIE diagram.

One of the key points I think needs discussion is screen brightness as to me, this is also a very important part of good calibrating. The SMPTE standard for digital projection (for D-Cinema) is 14 foot lambert with +/- 4 acceptable. I think in most cases in HT, if we can hit 12 we are doing OK unless you have a light cannon like my BenQW6000 where out of the box, the thing produced over 30FL.

To calibrate my BenQ W6000, I do go into the factory mode. When I used to calibrate the previous W5000, I did everything in user modes. In the factory mode, there is color temperature setting that has RGB gains and offsets with range from 1 to 1024. In the user modes, the steps are much corser with steps from 1 to 100.

I got my colorimeter back in 2008 and in the time, I have calibrated SONY, JVC, Panasonic, Epson and of course BenQ. There might be others, but I can't think of them right now.

So back to the BenQ. In user mode, the default setting for colour temp is 50 and in facotry mode, the setting is 512. In both cases this is a half way point and you can both increase or decrease RGB for both gain and offset. With all the JVCs I have calibrated, you can't push red as it is already maxed out and to get 6500K often requires the reduction of green and blue to bring their levels down to what red is reading.

Now the side effect to this is usually a drop in lumens because you are pulling down the levels of green and blue to match red. So what I want to discuss is whether or not it is acceptable to push RGB when you can.

Two things to consider -

1. GREY IN VIDEO IS EQUAL AMOUNTS OF RED GREEN and BLUE and that colour of GREY should be 6500 Kelvin.

2. We want at least 12FL on screen and dropping levels of RGB will ultimately drop FL on screen.

.

The member in questionn owns a W5000 and wants a brighter picture. I have not really tested this, but I see no problem in pushing the levels of RGB in both the gain and offset to somewhere between 512 and 1024 if required. I do thnk this will affect gamma in a big way and ther might even be a limit to how far you can push these before black levels raise to high. So these are some thing I would like to read about from other members.

The thread is open to discussion.

[Owen]

For UHP lamp projectors green will be the strongest colour, normally followed by red and blue, so green and red will have to be reduced proportionally to match blue for a 6400k gray scale, its the nature of the UHP lamp light source.

The best way to get more brightness and "pop" is to create a custom gamma curve that is sort of S shaped, levels around 75% are boosted without affecting white or black level. A colour meter is not required, the adjustments can be done purely by eye. Throwing out the gray scale accuracy simply to get more lumens is not something i would do.

I would not use a moderately priced meter to adjust primary or secondary colours via a CMS, the result will likely be less accurate than standard on most decent projectors. Gray scale adjustment should be no problem but the eye should always be the final determinant of what is correct, especially at the black end of the spectrum where colour meters tend to be inaccurate.

Simply calibrating color based on measurements taken with an inexpensive meter is not wise IMHO. It gets you close but a good eye and gray scale ramp test pattern are needed for fine tuning.

[CAVX]

For UHP lamp projectors green will be the strongest colour, normally followed by red and blue, so green and red will have to be reduced proportionally to match blue for a 6400k gray scale, its the nature of the UHP lamp light source.

And Native Lamp certainly reflected that out of the box Yet once balanced up, the grey scale tracked really flat.

The best way to get more brightness and "pop" is to create a custom gamma curve that is sort of S shaped, levels around 75% are boosted without affecting white or black level. A colour meter is not required, the adjustments can be done purely by eye. Throwing out the gray scale accuracy simply to get more lumens is not something i would do.

I refer to the lumance and gamma charts when making the brightness and contrast adjustments and found that using test patterns and my eye gives me a better result for this part. I am also now using High APL test pattern for brightness rather than use the low APL like those found on the JPK disc. It just seems to work better for me because whilst the projector can hold a good black level, its level of black is not really black to start with., more like a dark grey. I don't like the DI and think I can see a colour temp shift as it kicks in and out. I tested it when the projector was new and it pumped and annoyed the hell out of me. The white light also seemed to change to a green tinge, so I turned it off.

I would not use a moderately priced meter to adjust primary or secondary colours via a CMS, the result will likely be less accurate than standard on most decent projectors. Gray scale adjustment should be no problem but the eye should always be the final determinant of what is correct, especially at the black end of the spectrum where colour meters tend to be inaccurate.

I've got the lastest FW but I don't think the CMS is even workig on my projector. I do need to re-read the manual and do more testing here. I've seen another BenQ (W20000) done this way and I was impressed with the natural look of the image. I don't seem to be able to get this.

Simply calibrating color based on measurements taken with an inexpensive meter is not wise IMHO. It gets you close but a good eye and gray scale ramp test pattern are needed for fine tuning.

The colorimeter is used to track grey scale to 6500K. I still use (not sure if I should be) blue filters (wratten 50) for colour adjustments with SMPTE colour bars at 75%. I do use the colorimeter to check and adjust foot lamberts off the screen.

[pmunger]

I got my colorimeter back in 2008 and in the time, I have calibrated SONY, JVC, Panasonic, Epson and of course BenQ. There might be others, but I can't think of them right now.

Mark,

What type of colorimeter is it? You are aware that the filters in these can drift over time making them inaccurate?

Are you proposing that contributors share their calibration settings?

Glad to see a calibration thread appear on this site.

Edited March 11, 2013 by pmunger

[pmunger]

Thanks Chopsus,

I follow the calibration thread at AVS, but good to see some local interest.

[mgrobins]

I use an Eye1 display with HCFR to calibrate my display.

I am not convinced the CMS on the W5000 is a useful tool. I like the image in general but am of the opinion that the firmware implemented by Benq is rather poor.

I have adjusted greyscale with the gain/offset for RGB and that's fine. Still seems to be a bit of a red push though and when I measure the primary colours they are all out.

Looking at the CIE diagram and measuring colours I find that the proposed methods of adjusting the baseline R,G and B colours do not work appreciably on this projector. "Colour" and "Tint" don't shift and using the fine colour control adjusting Range and saturation creates no alteration in the CIE position.

In the factory menu I can alter the DLP which has "desired" and "measured" X/Y values for primary colours. Changing these yielded no actual change in measurements so I'm not clear on what they represent (well... the XY is the coord in the CIE diagram but I find altering them makes no difference to recorded values by my sensor).

Conversely, using my Samsung TV I was able to easily change and set my primary and secondary colours using this approach. I have a number filters to view colours too and they appear to be fine after calibration. Viewing is also very nice.

I'd like to add a second aspect to this thread. Equipment offering 0 IRE and 7.5IRE (there are some other names for these too I think???). What do people find best? My system passes below black and I set my projector to 0 IRE. I'd like to hear what people think though as I also have correcponding settings in my OPPO and PCH etc.

Cheers,

Edited March 12, 2013 by mgrobins

[mgrobins]

I would not use a moderately priced meter to adjust primary or secondary colours via a CMS, the result will likely be less accurate than standard on most decent projectors. Gray scale adjustment should be no problem but the eye should always be the final determinant of what is correct, especially at the black end of the spectrum where colour meters tend to be inaccurate.

I don't agree. Using test images and comparing the screen image I can get a much nicer setup with the assistance of my meter. Being able to see and manually control changes is a useful factor.

A lot of retail displays and projectors are horible out of the box.

[CAVX]

Mark,

What type of colorimeter is it? You are aware that the filters in these can drift over time making them inaccurate?

It is an eye one and yes I am aware that the filters can change over time. I constantly check mine against the chart I took off my lap top monitor when the meter was new and it seems nothing has changed with it and why I continue to use it.

Are you proposing that contributors share their calibration settings?

They can if they want but I see no point as each case is different where the end result is a combination of the projector and the screen merial being used. Also is the point you brought up with the meter itself. What I don't want to see is someone without a meter just copying the settings into their units and expecting perfect results.

Glad to see a calibration thread appear on this site.

Yes I thought we needed one too

[CAVX]

I'd like to add a second aspect to this thread. Equipment offering 0 IRE and 7.5IRE (there are some other names for these too I think???). What do people find best? My system passes below black and I set my projector to 0 IRE. I'd like to hear what people think though as I also have correcponding settings in my OPPO and PCH etc.

Cheers,

Having a setting that allows the end user to switch between 0IRE and 7.5IRE not always the best thing IMO because of the confusion it can cause and some manufactures getting it wrong.

0IRE is the same as absolute black or PC values of 0 for RGB. 7.5IRE is the same as Video Black or PC16 for the RGB levels. In order to see Below Video Black (also known as Blacker Than Black) and Above Video White (AKA Whiter Than White), a video system must be set to 0IRE so it can pass 0~120IRE (?) or PC values of RGB 0 ~ 255. The 7.5IRE setting limits the range from PC16~235 (or is that 231?). The video is then limited to Video Black and Video White and this result in crushing at both black and white. The most obvious example of white crush is clouds where the clouds look like a single white mass instead of having varying shades of (light) grey. On the black end, the shadows may be crushed resulting in a loss of shadow detail.

Whilst it might not nessessary to see above white and below black, it certainly helps when performing a calibration so you know what the display is doing.

The problem is some source components are also band limited and so having the video display system set correctly won't change a thing and will make setting gamma difficult.

[mgrobins]

Thanks Mark.

By spec eqwuipment should pass below black even though video may not be authored for it.

I set my PCH to 0-255 sRGB and projector to 0 IRE.

Since readjusting my calibration settings I am also using a gamma of 2.4 instead of 2.2. In a very dark light controlled room I find it works better for me. Thoughts??

Im at 1800 hours on low lamp and with my iris at 9 was measuring 8-12ft lamberts roughly. I didnt run the constant measure option to ensure I had the meter in the most intense spot.

In regard to the red running out of steam in the 90%-100% grey range you can fix this by reducing your contrast. Obviously that's a trade-off that will effect light output and image as well.

[CAVX]

Since readjusting my calibration settings I am also using a gamma of 2.4 instead of 2.2. In a very dark light controlled room I find it works better for me. Thoughts??

The specs for D-Cinerma (Dolby 3D) is Gamma 2.6. 2.2 might have been reference for CRT, but given we have all moved on from that technology, maybe settings like Gamma should change also.

HERE are my W6000 charts at 300 hours. Note that Gamma is 2.8 which I had to do just to get a decent level of black.

Im at 1800 hours on low lamp and with my iris at 9 was measuring 8-12ft lamberts roughly. I didnt run the constant measure option to ensure I had the meter in the most intense spot.

I used to measure the white background in the chart when taking a continious reading, but now I shink the HCFR window and push it to the left hand side. I then open paint in a small window that I increase to a nice large size, then click the green arrow. Having done this several times in a single night and I seem to be getting constant results.

[bjc]

I keep my Eye1 in a zip lock bag with the satchels with beads inside for soaking up moisture as i've heard that its moisture that destroys the main part that does the measuring? (Desicant or something comes to mind)

[CAVX]

Yeah silicone beads like you find in a shoe box would work for that

[CAVX]

Mine is kept in a small black bag along with my SPL meter and few other bits and pieces I use for calibrating my system.

[bjc]

Yeah silicone beads like you find in a shoe box would work for that

Thats the ones

[mr-happy-pants]

My wife keeps mine in her drawer beside the bed.

Oh, wait... I think you're talking about something different...!?

[pmunger]

I have an i1 Display Pro III (Chromapure pro version) that is supposably less prone to drift. I also keep it in a resealable bag with anti-moisture beads.

In addition to this meter I have a i1Pro Spectrophotometer to profile the i1 Display.

This means I get the accuracy of i1Pro and low light performance of the i1 Display and I don't need to worry about drift of the colorimeter nor the possible measurement inconsistencies using different display types with colorimeters.

I use this to calibrate an Epson TW5500 PJ, Samsung Plasma & Samsung LED TV

[CAVX]

Anyone want to post their charts? Anyone using something other HCFR?

[Owen]

I don't agree. Using test images and comparing the screen image I can get a much nicer setup with the assistance of my meter. Being able to see and manually control changes is a useful factor.

A lot of retail displays and projectors are horible out of the box.

Gray scale tracking and gamma are typically not right out of the box and its those aspects of performance that are critical as they dominate what we see. A colour meter is required for adjusting these vital parameters.

However colour gamut accuracy (the hue and saturation of primary and secondary colours) is typically very good on decent displays and projectors intended for home cinema use. Errors are typically so small they are very difficult if not impossible to see and difficult to measure accurately with an inexpensive meter. I consider colour management systems (CMS) that are needed to adjust these parameters as generally unnecessary and many cause more problems then they solve when used as linearity over the luminance range is adversely affected.

Manufacturers set primary and secondary colours the way they do for good reason. Unless you can profile the displays primary and secondary colours over the full range from black to white with a known accurate meter I suggest you would likely be better of using factory settings.

Once gray scale and gamma are properly adjusted errors in gamut have to be quite large before they significantly affect what we see.

[Owen]

The specs for D-Cinerma (Dolby 3D) is Gamma 2.6. 2.2 might have been reference for CRT, but given we have all moved on from that technology, maybe settings like Gamma should change also.

HERE are my W6000 charts at 300 hours. Note that Gamma is 2.8 which I had to do just to get a decent level of black.

It should be remembered that there is no definitive number to define what is correct for gamma. Perceived gamma is affected by the displays contrast ratio and black level. A DLP projector with relatively poor native contrast and high black level is going to look very different to a high contrast ratio projector like a JVC with the same notional gamma. The JVC will have much darker blacks and levels above black (shadows) will be much darker as well. The light level difference between each video level will also be much less with the DLP so gamma will need to be set differently to achieve a visibly similar result to a JVC for example.

I prefer to to set final gamma by eye using a wide range of source material rather than use a specific gamma number.

To get maximum contrast and “pop” out of a projector the contrast control should be set as high as possible before significant colour shift or clipping occurs. Video white is digital level 235 so its not necessary for the projector to display 255 without clipping.

I prefer to allow a slight colour shift at 235 to get the highest possible contrast, doing so has no noticeable negative affects if done properly.

If you cant drive the projector into white level clipping via the contrast control simple crank up the gain controls for each primary colour equally. The RGB colour gain controls are basically contrast controls for each individual primary colour and the bias or cut controls have the same effect as a brightness control for each individual colour. Adjusting all three equally is the same as adjusting the brightness control.

Edited March 13, 2013 by Owen

[jst01]

If you cant drive the projector in white level clipping via the contrast control simple crank up the gain controls for each primary colour equally. The RGB colour gain controls are basically contrast controls for each individual primary colour and the bias or cut controls have the same effect as a brightness control for each individual colour. Adjusting all three equally is the same as adjusting the brightness control.

I wouldn't do this. Some displays will not clip 101% white even with the Contrast at 100. Unless the Green gain is set way off, which would be very unusual out of the box, I wouldn't go yanking up the gains to try to make the display clip white.

Edited March 13, 2013 by jamiet

[CAVX]

I prefer to to set final gamma by eye using a wide range of source material rather than use a specific gamma number.

I have been doing this myself using a PLUGE pattern for brightness and similar striped pattern in white for contrast. I am now at 460 hours and my gamma reading is off the chart. It doesn't bother me because the image looks good.

To get maximum contrast and “pop” out of a projector the contrast control should be set as high as possible before significant colour shift or clipping occurs. Video white is digital level 235 so its not necessary for the projector to display 255 without clipping.

I prefer to allow a slight colour shift at 235 to get the highest possible contrast, doing so has no noticeable negative affects if done properly.

I agree with this....

If you cant drive the projector in white level clipping via the contrast control simple crank up the gain controls for each primary colour equally. The RGB colour gain controls are basically contrast controls for each individual primary colour and the bias or cut controls have the same effect as a brightness control for each individual colour. Adjusting all three equally is the same as adjusting the brightness control.

Wouldn't this also affect the grey scale?

[Owen]

Wouldn't this also affect the grey scale?

Normally with a three chip systems one colour tops out or becomes non linear at the bright end before the others resulting in a colour shift at peak output. I like to keep the grey scale accurate up to 90% stimulus and let it drift off a little at 100% to maximize contrast.

There is no reason adjusting for full output with an input level of 235 should cause any problems as the projector was designed to provide that output. If there is not enough adjustment in the contrast control to get peak output with an input level of 235 adjusting up all three gain controls to achieve that end really should not course any problems. All you are doing in moving all levels up so that 235 gives the same output as a 255 stimulus would. Its only when you push beyond what the projector would have provided with a 255 stimulus that colour shifts or clipping may set in.

Single chip DLP is a different animal and one I have no experience with so I cant comment on how they behave when asked to provide more output then would be available with 255.

[Owen]

I wouldn't do this. Some displays will not clip 101% white even with the Contrast at 100. Unless the Green gain is set way off, which would be very unusual out of the box, I wouldn't go yanking up the gains to try to make the display clip white.

Maybe you wouldn't but I've been doing it since the days of CRT with no problems. All we are doing is getting maximum output with an input level of 235 (video white) rather than 255 (PC white). Its not really any different to calibrating the black point to 16 (video black) in stead of 0 (PC black). We are not asking the display to operate outside its limits.

Some displays have unused headroom above what a 255 input would give with the contrast control set to 100% and utilizing it by adjusting the gains can definitely be helpful, at least for three chip systems.

I have no idea how single chip DLP behaves when over driven, and I would not be surprised if there where issues.

[CAVX]

Normally with a three chip systems one colour tops out or becomes non linear at the bright end before the others resulting in a colour shift at peak output. I like to keep the grey scale accurate up to 90% stimulus and let it drift off a little at 100% to maximize contrast.

There is no reason adjusting for full output with an input level of 235 should cause any problems as the projector was designed to provide that output. If there is not enough adjustment in the contrast control to get peak output with an input level of 235 adjusting up all three gain controls to achieve that end really should not course any problems. All you are doing in moving all levels up so that 235 gives the same output as a 255 stimulus would. Its only when you push beyond what the projector would have provided with a 255 stimulus that colour shifts or clipping may set in.

Single chip DLP is a different animal and one I have no experience with so I cant comment on how they behave when asked to provide more output then would be available with 255.

I have calibrated all three technologies and I don't see pushing gains an issue with DLP. With the JVC DiLA units I have calibrated, I generally find red is already maxed out and the only way to bring color temp back down to 6500K is to pull green and blue (blue more than green) down. So whilst you get a nice flat grey scale, you also get a drop in FL on screen.

With LCD like my old SONY, there was a point when pushing the gains/bias that the image just turned to crap. It was like there was a clear limit here one could go.

Edited March 13, 2013 by MarkTecher