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Discussion Starter · #1 ·
Howdy gang...


Traditional calibration methods for contrast/white levels on a CRT may be different for DLP.


On a CRT you would push the contrast until some specific image distortion occurs. On a DLP there is no image distortion, but I have made another observation.


I put together an IRE test disk with 5 IRE steps from 0-90 IRE and then it has IRE values of 92, 94, 96, 98 and 100. The idea was to see when the DLP stops being able to differentiate white values as contrast is increased.


On my NEC HT1000 I found increasing the contrast evetually made the 100 IRE and 98 IRE merge, then also the 96, 94, 92, and so on. The projector being in economy or normal bulb power modes did not make a difference. The DLP chip has an upper white value range it can display, and the brighter bulb mode simply increases the image brigthness on the screen. Screen reflectivity does not matter either, as the reflected signal value is simply higher or lower.


On the HT1000, the factory setting for contrast is 32. I found increasing to 39 made the 100 & 98 IRE merge.


I have also noticed any other gamma, black or contrast enhancement settings, also play a part in taking the white levels beyond the DLP's reproduction range. So if I used black enhancing gamma, some more black expansion and contrast expansion, I would have to lower the contrast below the 32 setting to be able to get back my 100 & 98 IRE discrimination.


I haven't been able to make any observations regardng the handling of the IRE scale with and without the gamma, black and contrast tweaks. But I assume there are some sublte shifts perhaps worth the effort.


And I am also wondering about a DVD running hot. Can a DVD player that is well calibrated and producing a flat IRE scale, output greater than 100 IRE? I assume the DVD range is at best 0-100 and a DVD couldn't be poorly mastered with a 110 IRE signal.


I would love to hear your comments on how you calibrate your DLP for the best reproduction of white levels.


cheers


RJ

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RJ,


Very interesting.


"I have also noticed any other gamma, black or contrast enhancement settings, also play a part in taking the white levels beyond the DLP's reproduction range. So if I used black enhancing gamma, some more black expansion and contrast expansion, I would have to lower the contrast below the 32 setting to be able to get back my 100 & 98 IRE discrimination."


Can the HT1000 store different combinations of gamma, black expansion, and contrast, so that you could all presets wouldn't clip whites?


"I haven't been able to make any observations regardng the handling of the IRE scale with and without the gamma, black and contrast tweaks."


I don't understand; why not?


Thanks
 

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Discussion Starter · #3 ·
Quote:
Can the HT1000 store different combinations of gamma, black expansion, and contrast, so that you could all presets wouldn't clip whites?


I don't understand; why not?


Thanks [/b]
Yes... The HT1000 has (4) programmable user modes, providing for the storge of a range of settings.


I have not tried setting the user modes with extreme but tweaked gamma, black and contrast enhance variations, but I will give that a try.


more later


RJ

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RJ,

It sounds like you are a more organized tweaker than I am. Have you come across what settings on the HT1000 seem to produce the best image with DVD's? You or someone posted some settings soon after the HT1000 hit the market, which looked good on my projector. However, this PJ has just so many different possible combinations of settings, if wonder if there might be something better than I'm now using.


I was watching a movie last night and enjoying it throughly when I looked up thought--no way could that little box be producing the image I'm seeing.

MIKE
 

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Discussion Starter · #5 ·
Quote:
It sounds like you are a more organized tweaker than I am. [/b]
Boy, have I got you fooled! ;-)


So far for me, the best settings for DVD watching has been...


... A user mode configured from a "movie" starting position.

... Gamma = Normal

... Color = 7800

... SweetVision = Off or Low

... Interlaced = On

... Black = Off

... Contrast enhance = 0

Pictures settings

... Brightness = -17

... Contrast = 32 (and I can push safely this to 38, but I leave it at 32 for the headroom)

... Color = 40

... Sharpness = 10


I am experimenting to find the the strongest setup the gives the whites a little more room. So far, these setup have nice blacks and good detail on the highend with clouds.


I don't know if the (3) "gamma" choices are simply linear adjustments of contrast and brightness, or maybe something more complex. When I get a minute, I'll rig up a camera view of the projector to my waveform monitor and then I'll be able to see what's what. Hopefully I'll get to do that by tomorrow night.


More later...


RJ

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Thanks, RJ. I'll give them a try.


You don't seem too impressed with "Sweetvision." NEC seemed rather proud of it, though I'm not exactly sure what it does, since NEC's sales literature is a bit vague on this point. What does Sweetvision do at higher settings that you don't like?


MIKE
 

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Discussion Starter · #7 ·
Quote:
What does Sweetvision do at higher settings that you don't like?


MIKE [/b]
Hi Mike...


SweetVision adds edge detail as one of it's functions. Depending on the source image, it can appear as an acceptable sharpening of the image. But it can also take high contrast edges between bright white and dark black objects, and make the edges overly dramatic, IMHO.


A pristine 1080i quality image is as sharp as you would like. A 480i image can sometimes be very soft, and SweetVision can help make the presentation a little sharper to the eye that has become spoiled by a pristine 1080i source. But SweetVision is not a "set it and forget it" option.


If there are other things going on with SweetVision besides detail/edge enhancement, I would love to hear some comments. So far, I have not noticed the setting at work in any other image esthetic. But to be honest, I have not spent a great deal of time with it, because I'm a person who dials back the sharpness control to eliminate any artifical edge detail.


As I have said in some other posts, I would love to see what lies under the hood of the HT1000, in the service menu. Perhaps there is an adjustment to dial back the edge detail of the SweetVision settings, while leaving the other processing intact.


I have been searching for a service manual, but so far no joy. If anyone on the list can order me a HT1000 service manual, please drop me an email.


RJ

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Can anyone outline any special steps or considerations to keep in mind when calibrating a pj with Video Essentials?


Last time I did this on my older NEC SVGA display I was a bit confused by the setting of the contrast because the white in the contrast would not bloom! And believe me, this is far from top quality pj so I know its not because the pjs cababilities. I keep taking the contrast up, but there was no blooming. I went all the way to the highest setting, and still no blooming.


So I wound up just backing it down until it "looked" right, but I no that is not the idea. I can't recall exactly what pattern I was using for the test, but its the standard pattern they show in the instructional part of VE where they say "ok now its time to set your contrast". There was just no blooming and the lines remained straight.


So perhaps would it be better to use the IRE pattern found later in the disk and set the contrast so that each bar was a distinct shade of white - just like described in the first post in this thread? Thanks.
 

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Correct me if I'm wrong, but I don't believe digital projectors "bloom" To set the contrast use the two moving bars until the lighter one just disappears.


Scott
 

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I don't think VE has the moving bars; AVIA has that feature.


MIKE
 

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lovingdvd:


Digital projectors do not bloom nor bend the straight lines as contrast is cranked up. This is because digital projectors don't use CRTs. Those 2 characteristics only apply to CRT based display devices.
 

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Quote:
Originally posted by VPC
lovingdvd:


Digital projectors do not bloom nor bend the straight lines as contrast is cranked up. This is because digital projectors don't use CRTs. Those 2 characteristics only apply to CRT based display devices.
Thanks - that confirms what I was seeing.


So with that in mind, how am I supposed to calibrate the contrast then? Their instructions and pattern they show is not designed to set contrast on a pj then? As mraub pointed out above VE does not have any moving lines, etc.


Am I just supposed to use the IRE bars and eye ball it so that none of the bars are the same color - like as was discussed in the first post in this thread? Please advise. Thanks.
 

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That's really the only way with VE. Put up the grey scale and eyeball the last few IRE steps. That's why I purchased AVIA after I already had VE. VE was produced to calibrate CRT based displays.
 

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Yes, Avia is much better for calibration of digital devices as they simply crush detail rather than display any of the charateristics of CRT's that are being pushed to hard. RJM's test pattern is a great idea and probably the best way to calibrate a digital display. It would be perfect if similar close steps were added at the bottom end of the range to help adjust black level and shadow detail. 10 IRE steps is really too large for fine tuning.
 

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Thanks for the update - I didn't realize Avia had a big advantage like that but obviously it does. Does Avia have any other advantages over VE when it comes to front pj calibration?


I should have a copy of Avia available to play with. Can you provide an overview of what the Avia pattern is like and how it is used to set the contrast?


Also do you have any experience with doing the color decoder accuracy? I assume this involves the use of all three filters. I'm very curious to know how this test/tweak is performed. If you notice that red, for example, is off, what pj control do you typically adjust for a specific color - the gamma for red? Thanks - your information has been ver helpful!
 

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Well, if you were going to use Avia to set contrast and brightness, I would start with the moving bars and log steps pattern to set the black level. Then I would move on to the vertical (or horizontal) 10 IRE steps and calibrate to have maximum brightness and detail at the upper end, without crushing the blacks at the lower end. Brightness, contrast and gamma will all have an effect here.


You should check color decoder accuracy after calibrating saturation and hue using the blue filter. The pattern is three columns of color (R G B)of varying intensities on a light grey background. Use one of the colored filters to match the colored boxes to the grey background intensity. The number next to the box shows you how much it's off. Correcting this is tricky. You might be able to correct minor errors with the bias and gain controls, but too much correction will through off your greyscale. The service menu may contain direct access to the decoder controls, which is where you should make these corrections if at all possible.
 

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For people without Avia, the contrast pattern in the THX optimiser suite on most new THX DVDs can also be used to determine if the projector is clipping the high end of the IRE scale (however, I still recommend Avia). Additionally, it is important to check whether each of the red, blue, and green components is individually clipping. LT150 tweakers have discussed these techniques to exacting detail in earlier posts. Do a search for a wealth of calibration information.
 
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