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Discussion Starter · #1 ·
The biggest gripe with my otherwise excellent 5 year old Sony KP-53HS10 CRT-RPTV is its poor black level stability. Now, I will be buying a new bigscreen 16:9 RPTV soon (either CRT, LCD, DLP, LCOS, ???) and I'd like to know how the current batch of these TV's do with "holding black". I have AVIA, and when comparing the clips that show the moving vertical "blacker-than-black" bars on a black background, followed by a half-gray background, followed by a half-white background, my black level shows how unstable it is. Can anyone who has looked at these clips on their current model bigscreen RPTV tell me how their TV holds black? Now, I'm not talking about how "black" a CRT can get compared to an LCD. I'm talking about the TV's ability to keep the same black level independent of the brightness of the rest of the image.
 

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Discussion Starter · #2 ·
Anyone?
 

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well...for crt's...the image quality decreases over time. therefore...black levels will definately deteriorate. however, in lcd and dlp, all you have to do is change the bulb, and u've got brand new picture quality. blacks will not fade once u change to new bulbs.
 

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Quote:
Originally posted by Jim Banville
The biggest gripe with my otherwise excellent 5 year old Sony KP-53HS10 CRT-RPTV is its poor black level stability. . . . I'm talking about the TV's ability to keep the same black level independent of the brightness of the rest of the image.
What you seem to be describing is variation in black level with APL (Average Picture Level). In other words, black and near-black elements in the picture shifting brightness level with scene changes. This is an issue that should be confined to analog sets (CRT's) where there is poor voltage regulation or DC restoration. Blacks are not clamped very well in Toshiba CRT RPTV's, for example, unless User Preferences are set up from the Cinema mode. Once set up properly, black levels on the Toshibas are rock-solid. Unfortunately, this isn't documented anywhere so some folks see black levels shift all over the place and assume that it's normal for the set. There is no reason to see this in most digital, fixed pixel displays (LCD, DLP, etc.).
 

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Discussion Starter · #5 ·
xilinx, I don't think you uderstand what I'm describing. My TV has always had this issue.


Thanks Old Fogey! That seems to make sense. My TV has lots of DC settings in the service menu, but none seem affect "DC restoration".
 

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Quote:
Originally posted by Jim Banville
xilinx, I don't think you uderstand what I'm describing. My TV has always had this issue.


Thanks Old Fogey! That seems to make sense. My TV has lots of DC settings in the service menu, but none seem affect "DC restoration".
Jim,


I've owned 4 rptvs, 2 Sonys and 2 Hitachis. All had the exact same problem you describe when displaying the black with half/white vs black with half/gray.


This is not dc restoration or any other electronic problem. It is the result of internal reflection inside the rptv cabinet. When displaying the half/white pattern the white half is very bright and some of the brightness is reflected back into the set and washes out the black half to the extent that if you adjust using the half gray pattern and switch to the half white, the moving black bars totally disappear.


Next time you play a 1:85 widescreen anamorphic dvd on your set, note that during very bright scenes the black bars above and below the image are not as black as they are during dark scenes. Since your set has squeezed raster for widescreen anamorphic dvd, these black bars are not even being scanned on the crts. The lighter black during bright scenes can not therefore be dc restoration problems but can only be the result of internal reflection. If your bright scene is primarily a color other than white, say a bright blue or red, you'll note that not only are the unscanned black bars lighter but they are also slightly tinted blue or red.


I have noted that each new set I get has progressively less of this internal reflection effect, and also that it can be reduced just by cleaning the crt lenses. Some ISF calibrators and adventurous rptv owners have lined the set's interiors with duvetyne non-reflective fabric and made hoods for the crt lenses to further reduce this effect.


In any case it's pretty much a characteristic of rear-projection tv, and is not an electronic malfunction but an optical anomaly.


I've always used the black with half gray pattern exclusively for brightness adjustment, after turning contrast down to about 30-50%. I store 30% contrast and the appropriate brightness under Pro, and progressively higher contrast settings under Movie and Standard and switch between the various picture modes according to the ambient light variation in the room for daytime vs nighttime viewing.


Usint only the half gray pattern gives me the best overall compromise.
 

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Discussion Starter · #8 ·
Quote:
Next time you play a 1:85 widescreen anamorphic dvd on your set, note that during very bright scenes the black bars above and below the image are not as black as they are during dark scenes.
I see the opposite on my TV. When in 16:9 mode (vertically squeezed raster) and watching a really wide aspect movie, I get dark gray black bars above and below the main image when the image is dark, such as a night scene. So from top to bottom is: black bar, gray bar, main image, gray bar, black bar. When the image is bright, the "black bars" blend in with the truly black areas above and below the actual 16:9 area. So from top to bottom is thick black bar, main image, thick black bar. Does that make sense?
 

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Quote:
Originally posted by Steve S
Jim,


I've owned 4 rptvs, 2 Sonys and 2 Hitachis. All had the exact same problem you describe when displaying the black with half/white vs black with half/gray.


This is not dc restoration or any other electronic problem. It is the result of internal reflection inside the rptv cabinet. When displaying the half/white pattern the white half is very bright and some of the brightness is reflected back into the set and washes out the black half to the extent that if you adjust using the half gray pattern and switch to the half white, the moving black bars totally disappear.
This is DC restoration. The differences between the black, half gray, and half white levels are not all attibuted to internal reflections. All sets are not created equal when it comes to DC restoration.


The Mits Diamonds and Pioneer Elites are probably the best out there in this regard (still not perfect). Hitachi's are pretty poor in this regard.
 

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Discussion Starter · #10 ·
Marc, I think Old Fogey may be onto something about this whole issue being relegated to analog sets. Do you agree? And as much as I like crt RPTV's, another check in the digital set column is lack of "smearing" since they don't draw the image by horizontally scanning the screen. I'm referring to light objects on black backgrounds, such as a rolling end-credits. Even good analog sets, such as mine, will put some horizontal smear to the right of the light colored objects on black backgrounds:(
 

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Quote:
Originally posted by Jim Banville
I'm referring to light objects on black backgrounds, such as a rolling end-credits. Even good analog sets, such as mine, will put some horizontal smear to the right of the light colored objects on black backgrounds:(
This is an artifact of any rear projection set (internal reflections) and I see it on digital sets too.
 

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Discussion Starter · #12 ·
Quote:
This is an artifact of any rear projection set (internal reflections) and I see it on digital sets too.
How is that possible? Why would internal reflections only show smearing to the right of the image (which also happens to be the same direction that the image is being "drawn" on the CRT face)?. I thought horizontal smearing was only due to either flaws or misadjusted parameters the CRT scanning the face of the picture tube. The flat LCD panel monitor on my PC doesn't show the slight horizontal smearing that can be seen on my CRT-RPTV when playing the exact same DVD.
 

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Jim


I used a Accupel HD signal generator to set black level on my Sony GWIII, LCD based rear projector.


Depending on which pattern I use, the blacker than black bar comes and goes. I basically had to find a brightness setting that was a compromize. Its a little too light with mostly a dark scene, but O.K. the rest of the time.
 

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Discussion Starter · #14 ·
JimP, my issue isn't how "black" the TV gets or what is the "best" setting for black, but how the blackest parts of the picture fluctuate in brightness depending on the changing brightness of the rest of the image.
 

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Quote:
Originally posted by Jim Banville
Marc, I think Old Fogey may be onto something about this whole issue being relegated to analog sets. Do you agree? And as much as I like crt RPTV's, another check in the digital set column is lack of "smearing" since they don't draw the image by horizontally scanning the screen. I'm referring to light objects on black backgrounds, such as a rolling end-credits. Even good analog sets, such as mine, will put some horizontal smear to the right of the light colored objects on black backgrounds:(
I've seen this smearing on direct view crt sets and a few crt rptvs, including a little on an analog Hitachi I once had. I don't see it on my current Sony, nor did the Hitachi HD ready model I had for 3 weeks have this problem.
 

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Jim


Perhaps I wasn't clear enough.


The point I was trying to get across is on a GWIII, which may or may not be typical of other rear projection LCDs, the blackest blacks fluctuates with the average screen brightness. That's the same problem you're experiencing, isn't it??
 

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Discussion Starter · #17 ·
Quote:
Originally posted by JimP
Jim


Perhaps I wasn't clear enough.


The point I was trying to get across is on a GWIII, which may or may not be typical of other rear projection LCDs, the blackest blacks fluctuates with the average screen brightness. That's the same problem you're experiencing, isn't it??
Thanks JimP. I didn't get that from your first message. That is not good news at all, BUT the KEY is: do the black parts of the image get brighter when the rest of the image gets brighter or do the black parts of the image get darker? If the black parts get brighter, then it is probably just internal reflections. If the black parts get darker as the rest of the image gets brighter, then that is a real problem.
 

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Jim


The blacks appear to get darker as the screen's average brightness increases.


I'm not sure, but this might be due to the human eye's adjustment for the screen brightness making the blacks appear darker. I could put a light meter on it. Give me a day or two to try that out. It would be interesting to find out.
 

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Discussion Starter · #19 ·
It is easy to seel that the "blacks" get darker on my TV when the average brightness level increases. I have a Sony 4x3 HD-RPTV. It has a 16x9 "squeeze" mode. In that mode, the picture squeezes down vertically and you are left with black "bars" on the TV's screen above and below the 16x9 image where the CRT's are not even scanning, so it is absolute, complete black. When I watch a film that has a wider aspect than 16x9, such as 1.85:1), I see the black bars that are actually part of the image. In bright scenes, these black bars closely match the unscanned areas ("black bars") above and below the 16:9 image. When the main image gets dark, the black bars that are actually part of the 16x9 picture on the DVD get lighter when compared to the unscanned areas of the screen. If I had a 16x9 TV, I probably would have had a harder time noticing this. I suppose that this is probably some sort of "feature" that is supposed to make it less likely that you lose shadow detail in dark scenes.
 

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Quote:
Originally posted by Jim Banville
Why would internal reflections only show smearing to the right of the image (which also happens to be the same direction that the image is being "drawn" on the CRT face)?. I thought horizontal smearing was only due to either flaws or misadjusted parameters the CRT scanning the face of the picture tube. The flat LCD panel monitor on my PC doesn't show the slight horizontal smearing that can be seen on my CRT-RPTV when playing the exact same DVD.
I'm not familiar with this "smearing"
 
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