Eyeballing a Grayscale for Newbies

[guitarman]

Here's a copy of a post I just did for a new DLP user who needed to take a green bias out of the video. This was for an Optoma DLP but can be applied to your projector. Minus what you have available in your service menu.

If you have any other tips of tricks you've learned pls share?

Quote"
Gain=contrast
Bias=brightness

Also called cuts & drives with RPTV's
Drives=contrast
Cuts =brightness

The various RGB/gains/brightness in the service menu will effect all the signals while the user RGB's will just effect the one particular input you're working on.

Contrast RGB's effect the lighter part of video or 50IRE up.

Brightness RGB's effect the darker part of video or 50IRE down.

A good way to eyeball a 6500k grayscale is to freeze a vertical IRE gray pattern. This pattern will show you 10IRE steps from black to white in shades of Gray.

Any unwanted color in the darker area you work with the brightness rgb's.

Any unwanted color in the lighter area you work with the contrast rgb's.

These patterns are in Avia, not sure what DVE has. Even a needle pulse pattern will give you an idea if you need to take color out of the shades of gray.

Overall the concept is interesting. We're trying to make each shade of gray (gray) with no color tones. This will make the colors be at their best.

I posted this a few times but why not again.

Use the 50% format.

If you need to remove green lets say 4 clicks, stop make it just 2 clicks and in turn increase the red and blue 2 clicks each for balance.

The balance thing isn't written in stone either. Mostly I'll need to add a click to red while maybe cutting a click from the blue sometimes. Like if the face tones look a little purple."

[jkirk]

Now, that was helpful.

You're welcome at my table any day.

[guitarman]

I was hoping some of the real experts could also add some tips. Not just this apprentice guy guitarman. ;)

[Michael TLV]

Greetings

The 5 graybox pluge pattern from AVIA is usually fine as is the 4 gray box from VE ... or DVE.

You get to see what happens on both ends of the spectrum.

Mind you ... just because something looks too blue does not mean that you should just decrease blue ... (you can also increase red and green)

Most handy to also have a chromaticity chart on hand when you do this as it helps to tell you which direction you should make corrections toward.

Regards

[guitarman]

I remember Guy Kuo adding once that he would peak out the Red Green Blue colors buy using the saturation check in Avia. Pulling the component cables of the colors not being tested.

Hey Mike, good to hear from you here. My Toshiba RPTV days are over. :(

[guitarman]

Michael, that's excellent re pluge pattern.

Much easier to see color in the five very large boxes and the easy to see shift from low IRE to High. Also the increase first the two adjacent colors rather than pull back.

In the pluge I could see a slight red in both dark and light gray levels. So in the advanced adjustments RGB-contrast I left red at zero and increased blue and green to plus 2 each. For the RGB-brightness I also left red at zero and increased green to plus 1 and blue to minus 1.

This all took away any red and since increasing green and blue a little it opened up the image a good amount. More detail in black scenes.

Looking over the FIfth Element right now, everythings looking stellar on the H77.

[Jim Story]

Tom,
Would you please explain these terms that you used above?

"Use the 50% format."

"The balance thing "

"Pulling the component cables of the colors"

Does the below imply that there is no need to use a color chart (with the blue filter)?

"make each shade of gray (gray) with no color tones. This will make the colors be at their best."

It may be obivious that I know little..., about this.

[maxleung]

I must add that the grammar is making my eyes hurt. :)

[guitarman]

Originally posted by Jim Story
Tom,
Would you please explain these terms that you used above?

"Use the 50% format."

"The balance thing "

"Pulling the component cables of the colors"

Does the below imply that there is no need to use a color chart (with the blue filter)?

"make each shade of gray (gray) with no color tones. This will make the colors be at their best."

It may be obivious that I know little..., about this.

I think what Guy was doing is leaving just the one component color cable in that he wanted to maximize it's saturation. He would use the matching color filter and the saturation check with Avia. Whether it's a good Idea and works I don't know. I guess after setting color to full saturation you could move on to the grayscale check with the pluge pattern. Guy seemed to like the results.

Balance is if you moved green to minus 4 you would instead make it just minus 2 and increase red and blue to plus 2.

Better yet is if you see green leave it at zero and just increase red and blue to the needed spots. Reducing green cuts the picture brightness. This worked well for the Optoma H77 becuase it has such powerfull blacks and you really want to keep the video as bright as possible.

[JimmyR]

No, the component input doesn't work that way. You can only disable any TWO colors when your input is RGB/HV (five wire hookup).
With component (3 wire) you can disconnect Red and/or Blue but the Green always has to be plugged in because it also carries the sync signal. If Red and Blue componetnt wires are pulled you'll get a monochrome image without the chroma signal (no color, Black and White image).

[Michael TLV]

Greetings

Don't you mean pulling the red and blue leaves you with a black and white image via component?

There is no green signal via component ... it is derived by the display.

Regards

[guitarman]

I'm guessing on what Guy was talking about. The main key he was trying to convey is getting each color to be at it's highest saturation point. I thought he said something about pulling a color cable. This was from the old LT150 threads, I'd hate to even think about trying to find it. :)

Maybe Guy will break away from the Tivo watching on his HT1000 and clear it up. :)

[JimmyR]

Edited the typo :)Michael TLV, thank you.

[Cinemaphile]

Guy was talking about maximizing the dynamic range that can be achieved by the DLP chip. For maximum on-off contrast in a digital display, one should ideally set the R/G/B gains at levels just below clipping and then correct the gray scale optically. This is achieved by displaying something like the THX contrast pattern, or any pattern which has a 100 IRE box and a couple of boxes at around 98 to 96 IRE. Then by isolating each colour (either by disconnecting signal cables, using a service menu, or as I do it by using the coloured film filters that came with the Avia DVD), increase its gain until there is no difference between the 98 IRE and 100 IRE boxes, i.e. colour is being clipped, and then back off the gain a tad until the difference is again visible. Repeat the procedure for the other two primary colours. If there is a colour cast at the higher IREs after this procedure, use a gel correction filter of the appropriate colour and strength to get back to a gray level close to the desired reference.

The same procedure should be done with black levels, i.e. the R/G/B bias values should be individually set such that a 2 IRE bar first disappears into the surrounding 0 IRE background, and then the bias is notched up a bit such that the 2 IRE bar is just visible. One then prays that if there is any colour cast at low IREs, it is the same as the cast at high IREs, so that the same colour correction filter will do the job at both ends of the gray scale.

I use a Kodak CCR20 filter with my LT150 and the grayscale 'looks' quite neutral at all IRE values (it probably doesn't measure very flat around D65 though, but I like what I see).

[guitarman]

That was it, took an LT150 owner to bring the info back. thx

I don't think this would be helpful with the H77 but I may try it with the H30. I have a few Day filters around to test. I'll see if I can get the CR level up for the little guy.

[Guy Kuo]

Yes, that was with RGB signals, not component.

Grayscale on a display is one of those details that needs to be correct to make the picture look right. It's hard to explain the effect if you haven't seen a display that actually is adjusted to D65. The display's colors just have a better balance and realism after the display is calibrated. Sadly, this was until recently something very few hobbyists could really achieve. We've all gone through the myriad of attempted solutions to get a good grayscale cheaply. Home-built optical comparators, photo cells with filters, and even plain old eye-balling the grayscale usually leaves one still doubting if the calibration is actually correct or if the picture actually is as good as possible. It's not a spur of the moment thing to obtain a good colorimetry system. Current ones are expensive, albeit much less expensive than metering systems once were. On the other hand, those who do own a good colorimetry solution don't dwell on how much they spent on the meter, but will tell you instead they would never go back to leaving their displays incompletely or incorrectly calibrated. They use their colorimeter periodically and keep their image tuned even as the projector (and bulb) age. If a colorimeter is able to work with multiple types of displays accurately, it continues to add quality and value to your viewing experience as you move through different types of displays in your home theater. Without a good colorimeter, you are left wondering if the picture is done right. With a colorimeter actually set grayscale correctly rather than just an approximation. Approximations ARE better than nothing, but once you see a properly calibrated display, you too will understand how much more "right" an image looks when the grayscale and primaries/secodaries are correct.

[guitarman]

True, I started this talk in the budget forum where not many will opt for the equipment. Small things can be fixed by eye. Like sometimes I have a new projector and bring up a pluge type pattern and see things look pink. Very easy to fix with the RGB's. Make the boxes look black to gray again. It helps :)

[Kevin R. Anderson]

A number of years ago, I purchased on the Internet a broadcast quality gray-scale chip card for about $30 (8.5 x 11). It's not perfect, but it is better than nothing when using your eyes to compare a gray-scale pattern on DVE or Avia. I've always called it my "poor-man's colorimeter."

Now that I'm older and richer, I'm about to spring for the Opticone or ColorFacts.

[madpoet]

I would love to actually own one of the big packages, but I just can't justify it ;). If I did, I'd have to go to class to learn how to do this professionally ;)

[JimmyR]

Sure you can justify it P... :). Unless you plan giving up quality display devices forever or don't mind wondering if the display you have is giving you the best image it can.

[madpoet]

Stop it Jimmy... leave my poor buying itch alone! :)

[GetGray]

[QUOTE=Cinemaphile]Guy was talking about maximizing the dynamic range that can be achieved by the DLP chip. For maximum on-off contrast in a digital display, one should ideally set the R/G/B gains at levels just below clipping and then correct the gray scale optically. This is achieved by displaying something like the THX contrast pattern, or any pattern which has a 100 IRE box and a couple of boxes at around 98 to 96 IRE. Then by isolating each colour (either by disconnecting signal cables, using a service menu, or as I do it by using the coloured film filters that came with the Avia DVD), increase its gain until there is no difference between the 98 IRE and 100 IRE boxes, i.e. colour is being clipped, and then back off the gain a tad until the difference is again visible. Repeat the procedure for the other two primary colours. If there is a colour cast at the higher IREs after this procedure, use a gel correction filter of the appropriate colour and strength to get back to a gray level close to the desired reference.

The same procedure should be done with black levels, i.e. the R/G/B bias values should be individually set such that a 2 IRE bar first disappears into the surrounding 0 IRE background, and then the bias is notched up a bit such that the 2 IRE bar is just visible. One then prays that if there is any colour cast at low IREs, it is the same as the cast at high IREs, so that the same colour correction filter will do the job at both ends of the gray scale.[/QUOTE]

oooo baby. The new firmware on the lumagen HDP allows you to turn off all colors except the one you are working on, R, G, or B. I've been trying to think of a accurate way to find where red really peaks on my H79 since it really tapers off. I've got a OpticOne but even with it, it's hard to find the "spot" I never thought to look at a pattern with say 98 and 100 IRE to compare. This sounds like an interesting combo to try out. Maybe squeeze in some time to try weekend after next....

Cool.

[chengka]

[QUOTE=Cinemaphile]Guy was talking about maximizing the dynamic range that can be achieved by the DLP chip. For maximum on-off contrast in a digital display, one should ideally set the R/G/B gains at levels just below clipping and then correct the gray scale optically. This is achieved by displaying something like the THX contrast pattern, or any pattern which has a 100 IRE box and a couple of boxes at around 98 to 96 IRE. Then by isolating each colour (either by disconnecting signal cables, using a service menu, or as I do it by using the coloured film filters that came with the Avia DVD), increase its gain until there is no difference between the 98 IRE and 100 IRE boxes, i.e. colour is being clipped, and then back off the gain a tad until the difference is again visible. Repeat the procedure for the other two primary colours. If there is a colour cast at the higher IREs after this procedure, use a gel correction filter of the appropriate colour and strength to get back to a gray level close to the desired reference.

The same procedure should be done with black levels, i.e. the R/G/B bias values should be individually set such that a 2 IRE bar first disappears into the surrounding 0 IRE background, and then the bias is notched up a bit such that the 2 IRE bar is just visible. One then prays that if there is any colour cast at low IREs, it is the same as the cast at high IREs, so that the same colour correction filter will do the job at both ends of the gray scale.

I use a Kodak CCR20 filter with my LT150 and the grayscale 'looks' quite neutral at all IRE values (it probably doesn't measure very flat around D65 though, but I like what I see).[/QUOTE]
This system sounds easy to me. I've eyeballed my greyscale before and I never have a high degree of certainty I've done it correctly. Since this is a "newbie, I'll display my ignorance - When looking through the red filter, are you adjusting the red levels? Blue for blue, green for green?

[GetGray]

I guess I was getting off-topic. I arrived here from a link in someone elses thread. I'm using a meter to to RGB gains so not for Newbies (without a meter). Sorry about that.

[guitarman]

[QUOTE=chengka]This system sounds easy to me. I've eyeballed my greyscale before and I never have a high degree of certainty I've done it correctly. Since this is a "newbie, I'll display my ignorance - When looking through the red filter, are you adjusting the red levels? Blue for blue, green for green?[/QUOTE]

Since you can't isolate the colors. Use the pluge, large boxes of gray and tune the RGB-contrasts and RGB-brightness. It's a good idea to first tune the basics with Avia or DVE. Then first take a look at which color temp makes the pluge boxes look best. From there use the RGB's to fine tune.