Why does the kd34xbr960 need 1400 line of resolution. - Page 7 - AVS Forum
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post #181 of 306 Old 11-19-2004, 03:15 PM
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Quote:
Originally posted by subysouth
CRTs AFAIK have a beam spot a minimum of a the dot pitch in diameter(they have to be by nature)
And ... here we are.

A CRT's beam spot can be smaller (or larger) than the dot pitch in diameter. Much bigger ... much smaller ... doesn't matter ...
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post #182 of 306 Old 11-19-2004, 03:36 PM
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Quote:
Originally posted by dt_dc
And ... here we are.

A CRT's beam spot can be smaller (or larger) than the dot pitch in diameter. Much bigger ... much smaller ... doesn't matter ...
The tech at KDS says beam spot is fixed when the set is built and will bloom slightly based on contrast etc but not much and not without problems. The beam spot is permanently set to be slightly larger than pitch on a direct view CRT. Thats why low line counts yield scan lines. If the beam spot were variable you could increase beam spot for lower line counts and always have a full screen. It doesnt happen. You get beam spot at triad pitch plus a little over-bleed(or possibly a lot of over-bleed in an aperature grille approach.)

Even beam spot on a seperate 3 gun array is barely variable and not without ill effects. The trick to properly scaling a 3-gun CRT array is getting a line count that matches the vertical size of line x beam spot.

ss

edit: And dt if you think about it, if the beam spot is smaller than the pitch you cant light all the phosphors in a triad in one pass. You couldnt do white without two passes and then youd run smack into that angular problem. And youre scanning rate would have to exceed your vertical screen/pitch just to cover the screen. I think at minimum(and maximum) pitch and beam spot size are basically very similar and set the day the set is built.
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post #183 of 306 Old 11-19-2004, 04:01 PM - Thread Starter
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Have you reached any conclusions regarding the merits/drawbacks of Sony's new CRT technology? Or are you even talking about the Sony any more? (shadow mask, dot triad etc etc don't apply do they?)

Ps Without a basic understanding of the internal parts of a CRT you lost me a long time ago.:confused:
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post #184 of 306 Old 11-19-2004, 04:49 PM
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Quote:
Originally posted by gdg
Have you reached any conclusions regarding the merits/drawbacks of Sony's new CRT technology? Or are you even talking about the Sony any more? (shadow mask, dot triad etc etc don't apply do they?)

Ps Without a basic understanding of the internal parts of a CRT you lost me a long time ago.:confused:
Not really, but I for one have learned a lot.

The aperature grille on the Sony IMO is inherently more prone to vertical(and horizontal) bleed due to the lack of any metal dividers in the vertical(except a couple of stiffening wires) and minimal separtion in the horizontal.

However the Sony's undivided vertical stripe makes an argument of actual 1080 vertical resolution possible. Aperature grille sets are uniquely built to possibly support 1080.

The dot and slot mask sets are limited at least by the holes in their mask.

The best test would be an HD vertical resolution pattern.

ss
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post #185 of 306 Old 11-19-2004, 06:57 PM - Thread Starter
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Quote:
Originally posted by subysouth

.....The best test would be an HD vertical resolution pattern.

ss
Like I said, the guys at "Secrets" should start testing CRTs. I can't understand why they don't. There is a real niche, which they are ideally suited to fill, for rigorous technical analysis.
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post #186 of 306 Old 11-20-2004, 01:21 PM
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Quote:
Originally posted by gdg
Like I said, the guys at "Secrets" should start testing CRTs. I can't understand why they don't. There is a real niche, which they are ideally suited to fill, for rigorous technical analysis.
gdg, I read a couple of the display device reviews on their site and while they may delve deep in some other arenas, their display reviews are pretty non-technical.

In my experience so far, WSR and TPV are the most unbiased and skeptical reviewers(unless Joe Kane gets his hands on a particular device.) Maybe in the future they will ratchet up the testing to more explore actual resolution.

I sent them an e-mail asking as much. Maybe if more people did they would.

ss
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post #187 of 306 Old 11-20-2004, 03:23 PM - Thread Starter
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You're right, they don't do much in the area of TVs, or in fact in anything other than DVD players. That said, just for the heck of it, you should check out their "Benchmark" dvd tests that show virtually everthing out their in a comprehensive and ranked chart. It's absolutely outstanding, and involves the most exhaustive set of tests I've ever seen. (there is a table near the top of the page I've linked to)

http://www.hometheaterhifi.com/cgi-b...deInt=0&mpeg=0
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post #188 of 306 Old 11-21-2004, 12:12 AM
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Quote:
The beam spot is permanently set to be slightly larger than pitch on a direct view CRT.
Incorrect.

CRT 101:
Beam spot size is based on scan rate. Height of screen / number of scan lines = ideal beam spot size*.

For example,
1280x1024p ... Hieght of screen / 1024 = beam spot size
1024x768p ... Height of screen / 768 = beam spot size

Beam spot size has absolutely nothing to do with mask / grill / pitch.

If you follow the path of a beam ... just for the heck of it, let's follow the red beam ... that beam is going to go all the way accross the screen, go down to the next line (for simplicity, we'll make this a progressive example), go all the way accross the screen ... and keep doing this for however many scan lines there are.

The beam is going to scan a line accross the screen ... scan line ...however many times neccessary ...

Like This:
http://members.cox.net/dt_dc/ScanLine1.GIF
Etc ... on down to the bottom of the screen ...

Beam spot size = height of screen / number of scan lines.

Let's say the above is the 768p example.

The 1024p example is going to have more scan lines ... smaller beam spot. Like this:
http://members.cox.net/dt_dc/ScanLine2.GIF
Note: I didn't do the exact calculations here for an exactly proportional image ... point is, beam spot is smaller for a higher scan rate.

To clear up some misconceptions from earlier in this thread ...

The red beam pictured above isn't somehow trying to 'miss' the blue and green phosphors. It isn't trying to only 'hit' the red phosphors. It isn't trying to somehow turn off and then only turn on when it's time for a red phosphor. The red beam takes the path above ... always 'on' ... all the way accross the screen ... line by line ... from top to bottom. It's the mask / grill that ENSURES that the red beam is only going to strike red phosphors ... NOT some sort of intentional aiming of the guns at red phosphors.

The red beam pictured above is hitting multiple triads at the same time! Yes, so what? We can get in to this later ... but this is actually a very good thing. It improves picture quality.
Quote:
The tech at KDS says beam spot is fixed when the set is built
Beam spot is fixed when the set is built ... for each SCAN RATE.
Quote:
beam spot is fixed when the set is built and will bloom slightly based on contrast
Blooming has absolutely NOTHING to do with beam spot size. Blooming is caused when contrast is set too high ... but not because the beam spot is 'too large'. Blooming is caused by the beam current being too high for the phosphors. I mean high as in quantity ... not location. You can think of it as the beam being too 'bright'. It over-excites the phosphors ... phosphors OUTSIDE the beam are creating light. Again, blooming is NOT because the beam spot is too large. I guess I'll have to explain this more in another post.
Quote:
Thats why low line counts yield scan lines. If the beam spot were variable you could increase beam spot for lower line counts and always have a full screen. It doesnt happen.
It does happen. However, this is where the "ideal beam spot size*" above comes in. Based on the design of the CRT, there are limits to the min/max spot beam size. It all comes down to focus. It's a (relatively) simple matter to adjust focus on the beam and ... change the beam size. However, there are limits (built in to the CRT) how much you can do this. You basically start getting in to problems of consistancy / uniformaty / and sharpness.

Now, it is pretty complex to have to change the focus accross the entire screen as the beam is sweeping accross (and for each line). This is exactly what's required from a flat screen monitor. If a CRT wasn't able to 'adjust' beam size ... CRT flat screens would be impossible. You'd have a small beam in the middle of the screen ... large beam at the top / bottom / sides.

But ... scaling the beam spot size to some degree accross the entire screen ... no problem (within limits).

HOWEVER, even if a beam spot can't be adjusted to the ideal for the scan rate, it's going to travel as drawn above. It's Going to be centered within the white lines ... and either spill over (or fail to fill) a little. There's still absolutely NO inherent relationship to pitch size.
Quote:
The trick to properly scaling a 3-gun CRT array is getting a line count that matches the vertical size of line x beam spot.
Yes ... which has absolutely nothing to do with the mask pitch.
Quote:
And dt if you think about it, if the beam spot is smaller than the pitch you cant light all the phosphors in a triad in one pass. You couldnt do white without two passes
And why wouldn't the following look white?http://members.cox.net/dt_dc/TriadsSplit.GIForhttp://members.cox.net/dt_dc/TriadsPartial.GIF

Couple questions? Why do you think a CD front projector array beam size can be variable ... and a TV / Monitor's can't? What do you think happens when you change your PC montor's can rate between two resolutions where you can't see scan lines?
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post #189 of 306 Old 11-21-2004, 12:46 AM
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Quote:
Originally posted by dt_dc
Incorrect.

CRT 101:
Beam spot size is based on scan rate. Height of screen / number of scan lines = ideal beam spot size*.

For example,
1280x1024p ... Hieght of screen / 1024 = beam spot size
1024x768p ... Height of screen / 768 = beam spot size

Beam spot size has absolutely nothing to do with mask / grill / pitch.

If you follow the path of a beam ... just for the heck of it, let's follow the red beam ... that beam is going to go all the way accross the screen, go down to the next line (for simplicity, we'll make this a progressive example), go all the way accross the screen ... and keep doing this for however many scan lines there are.

The beam is going to scan a line accross the screen ... scan line ...however many times neccessary ...

Like This:
http://members.cox.net/dt_dc/ScanLine1.GIF
Etc ... on down to the bottom of the screen ...

Beam spot size = height of screen / number of scan lines.

Let's say the above is the 768p example.

The 1024p example is going to have more scan lines ... smaller beam spot. Like this:
http://members.cox.net/dt_dc/ScanLine2.GIF
Note: I didn't do the exact calculations here for an exactly proportional image ... point is, beam spot is smaller for a higher scan rate.

To clear up some misconceptions from earlier in this thread ...

The red beam pictured above isn't somehow trying to 'miss' the blue and green phosphors. It isn't trying to only 'hit' the red phosphors. It isn't trying to somehow turn off and then only turn on when it's time for a red phosphor. The red beam takes the path above ... always 'on' ... all the way accross the screen ... line by line ... from top to bottom. It's the mask / grill that ENSURES that the red beam is only going to strike red phosphors ... NOT some sort of intentional aiming of the guns at red phosphors.

The red beam pictured above is hitting multiple triads at the same time! Yes, so what? We can get in to this later ... but this is actually a very good thing. It improves picture quality.
Beam spot is fixed when the set is built ... for each SCAN RATE.Blooming has absolutely NOTHING to do with beam spot size. Blooming is caused when contrast is set too high ... but not because the beam spot is 'too large'. Blooming is caused by the beam current being too high for the phosphors. I mean high as in quantity ... not location. You can think of it as the beam being too 'bright'. It over-excites the phosphors ... phosphors OUTSIDE the beam are creating light. Again, blooming is NOT because the beam spot is too large. I guess I'll have to explain this more in another post.It does happen. However, this is where the "ideal beam spot size*" above comes in. Based on the design of the CRT, there are limits to the min/max spot beam size. It all comes down to focus. It's a (relatively) simple matter to adjust focus on the beam and ... change the beam size. However, there are limits (built in to the CRT) how much you can do this. You basically start getting in to problems of consistancy / uniformaty / and sharpness.

Now, it is pretty complex to have to change the focus accross the entire screen as the beam is sweeping accross (and for each line). This is exactly what's required from a flat screen monitor. If a CRT wasn't able to 'adjust' beam size ... CRT flat screens would be impossible. You'd have a small beam in the middle of the screen ... large beam at the top / bottom / sides.

But ... scaling the beam spot size to some degree accross the entire screen ... no problem (within limits).

HOWEVER, even if a beam spot can't be adjusted to the ideal for the scan rate, it's going to travel as drawn above. It's Going to be centered within the white lines ... and either spill over (or fail to fill) a little. There's still absolutely NO inherent relationship to pitch size.Yes ... which has absolutely nothing to do with the mask pitch.And why wouldn't the following look white?http://members.cox.net/dt_dc/TriadsSplit.GIForhttp://members.cox.net/dt_dc/TriadsPartial.GIF

Couple questions? Why do you think a CD front projector array beam size can be variable ... and a TV / Monitor's can't? What do you think happens when you change your PC montor's can rate between two resolutions where you can't see scan lines?
I dont think a CRT front projector changes beam spot size in a meaningful way except when you change power to it. The more power the more of the surrounding phosphors get washed with stray energy because of the lack of a mask to refine the beam. However there is an ideal line count on a FP that is a combo of no line overlap based on an essentially fixed beam spot size and a given color balance. Ask any ISF tuner what the possible resolution of a CRT front projector is and he'll tell you it depends on beam spot size inherent to the calibrated gun vs tube size.

The tech at KDS said beam spot size does not change and is similar to but slightly larger than pitch Do you have a link to something documenting this changing beam spot size? I cant take your word for it. I Google varying beam spot size and return zero hits. Thats a big deal so lets back that one up.

Lemme show you what I mean by blooming relative to power. The higher the intensity the beam the more it disperses outward from the edges of the hole in the shadow mask. I had never thought about it but, that may indeed be what causes blooming in the sense youre using it, I dont know. In any event blooming is not limited to that one use, I dont know If theyre linked but your reference is not how I intended it. Here's a pic of what I am talking about:

http://www.infocellar.com/hardware/m...dispersion.jpg

Also CRT color monitors existed before shadow masks so your statement that the mask is key to hitting any color phopshor is incorrect. The mask cleans up the shot but isnt key to it. The need for clear text on computer monitors lead to the development of the shadow mask.

ss

edit: What happens when the CRT increases resolution on the computer monitor? More of the entire field is covered. On my monitor in particular its rated to a maximum 1600x1200 but the lines fully overlap at about 1280x1024. Beyond that they over-overlap. So the beam spot size is a bit large for the actual pitch(typical btw per the KDS guy so the lower resolutions dont look to line deficient.) If you back the line count down, more and more of the screen goes black and the scan lines become larger. That wouldnt be happening if your graphs were correct. The screen IMO is acting in a way consistent with a slightly oversized compared to pitch but consistent beam spot size. The tech at KDS could be wrong or didnt understand my question but he seemed pretty firm about it. I asked him three times and made him explain it to me three times. This should be an answerable question though.

Also there are several tricks that CRT manufacurers use to equalize response across the screen. The beam spot naturally changes around the screen(flashlight effect) and the manufacturers try to reduce this as much as possible, I dont think they change the beam spot in a vertical resize like you are describing though. Here's some techniques for countering beam splatter:

-Make the back of the screen curved even though the front is flat.
-Reduce power to the center pixels of the screen
-Space the pixels at the edges farther apart but supply more power than the middle so the ovate beam spot creates a similar effect.
-Various proprietary techniques for focusing the beam spot away from ovate, not changing its size vertically across the screen though.
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post #190 of 306 Old 11-21-2004, 09:09 AM
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Quote:
Originally posted by dt_dc
HOWEVER, even if a beam spot can't be adjusted to the ideal for the scan rate, it's going to travel as drawn above. It's Going to be centered within the white lines ... and either spill over (or fail to fill) a little. There's still absolutely NO inherent relationship to pitch size.Yes ... which has absolutely nothing to do with the mask pitch.And why wouldn't the following look white?http://members.cox.net/dt_dc/TriadsSplit.GIForhttp://members.cox.net/dt_dc/TriadsPartial.GIF

Just continuing to try to sort this out.

I am assuming based on your pictures that these are both images of a dot mask screen.

I for one have been using beam spot size inappropriately. A better term would be beams strike area. The beam spot size on a direct view CRT is close to the opening size in the dot mask. The strike area is quite a bit larger than this and similar to pitch due to the spread caused by the locations of the guns to each other in space and being converged at the mask.

I am realizing another reason the above pics are impossible. The area lit by the electron beams at their fullest is limited by the unchanging hole in the shadow mask. Thats why no matter what it is, it cant be smaller than at least a pitch tall(again built in at the fixed gun locations and converged at the mask) because if it ever was lower than a pitch tall it would require the electron guns themselves relocating themselves closer to each other in space and changing the angles of incidence. And this would also require the beams to be smaller and converged inside the diameter of the shadow mask opening, something none of us have been willing to give the crt credit for doing.

Also in order for a dot mask set to generate white in the way you are displaying it it would take inter-line collaboration to resolve sub single triad height white lines and a sub triad beam strike size. That would seen to fly in the face of a the way a CRT is built. The partial two and single line shots above are impossible unless there is interline collaboration which opens up a whole seperate can of worms. The design of the dot mask set inherently as kdb descibed above interlaces the lines together, the signal processing I dont think views the lines that way, it views them as vertically stacked lines of a complete image. I cant see how it would know to take advantage of that overlap to create a wide version of white uses triads from seperate lines.

dt can you give us a field of one line on - one line off on the dot mask matrix? It will make what kdb described much clearer and show which parts go with which lines. Use red as the top of all triads for simplicity. I dont know which color is the actual to of each triad.

ss
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post #191 of 306 Old 11-21-2004, 01:45 PM - Thread Starter
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[quote]Originally posted by subysouth
about:

http://www.infocellar.com/hardware/m...dispersion.jpg

QUOTE]

I'm just following along here, mostly in a fog, since I have no basic technical. knowledge of how a CRT works. On the other hand I do have a BSc in Physics (from years ago) and, if memory serves me correctly, the concept of blooming, at least the way it's presented above, is fundamentally flawed. Photons and electrons behave like particles and travel in STRAIGHT lines. It could be argued that they do exhibit wave properties as well, but the behavior of electrons, when "fired" from an electron gun, can be most closely modeled along the lines of discrete particles (projectiles).

The misconception probably arises when viewing the way a spotlight appears to spread out from the source. This is an atmospheric effect and is actually a result of photons being scattered by particles in the atmosphere (and indeed the molecules that make up the atmosphere). As I understand it a CRT tube is a VACUUM.

Note: Another factor which results in a beam "appearing " to spread would be related to the construction of the reflecting surface used to project light from a point source. (not applicable in this case)
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post #192 of 306 Old 11-21-2004, 04:45 PM
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There are so many different thoughts on how a CRT actually works it scares me to think anyone would come to this forum for CRT advice :D I wish just one person here could be a CRT engineer, that would end all this :)

All posts and no replies make Geise a dull boy.
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post #193 of 306 Old 11-21-2004, 06:12 PM
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gdg even in a vaccuum I think I could see the effect pictured although not as much as pictured. I think its physically feasible. I dont think its as pronounced as the picture though.

I think we are pecking away at it, but I agree it would be nice for an engineer to just come in and lay it all out.

ss
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post #194 of 306 Old 11-21-2004, 10:41 PM
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Quote:
Originally posted by subysouth
edit: What happens when the CRT increases resolution on the computer monitor? More of the entire field is covered. On my monitor in particular its rated to a maximum 1600x1200 but the lines fully overlap at about 1280x1024. Beyond that they over-overlap. So the beam spot size is a bit large for the actual pitch(typical btw per the KDS guy so the lower resolutions dont look to line deficient.) If you back the line count down, more and more of the screen goes black and the scan lines become larger. That wouldnt be happening if your graphs were correct. The screen IMO is acting in a way consistent with a slightly oversized compared to pitch but consistent beam spot size.
Yes ... your perfect world is something like this?
http://members.cox.net/dt_dc/TriadsPerfect.gif
And you're saying that when you run 1280x1024 ... the above is what it SHOULD look like ... however the beam is a little wider than pictured above ... so you're getting overlap? Is that correct so far?

I'm asking ... describe the path of the beam when you then run 1280x1024.
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post #195 of 306 Old 11-21-2004, 11:21 PM - Thread Starter
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Quote:
Originally posted by subysouth
even in a vaccuum I think I could see the effect pictured although not as much as pictured. I think its physically feasible.

ss
Actually no. The wave behavior of subatomic particles is manifest at the level of of the particles wavelength. This is many magnitudes smaller than what you are describing here. I only brought up the fact that sub atomic particles display both particle and wave properties because I figured someone might erroneously make the wrong connection. For our purposes and at the level CRT's are engineered at, for all intents and purposes, an electron may be considered a particle. Particles travel in straight paths unless influenced by an outside force (Newton). The edges of an opening cannot deflect a particle as you have described. ( A very small number of particles could conceivably bounce off one edge and across to the other side. A few might even go beyond the edge of the beam at the other side, but the flux density would be utterly insignificant.
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post #196 of 306 Old 11-22-2004, 08:15 AM
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Quote:
Originally posted by subysouth
Also CRT color monitors existed before shadow masks so your statement that the mask is key to hitting any color phopshor is incorrect. The mask cleans up the shot but isnt key to it. The need for clear text on computer monitors lead to the development of the shadow mask.
A direct view CRT without a shadow mask is called ... a black and white TV or monochrome monitor.

There were a few prototypes of other systems back when they were first implementing color TV.

However, when the first color TVs arrived in stores from RCA ... they contained ... shadow masks. Shadow masks were part of the 'RCA Color System' proposed and implemented by the FCC. Shadow masks were exactly what allowed a system to be (easily, cost effectively) built where the exact same TV signal could support both color televisions and black and white televisions.

Masks were not first implemented because if computer monitors. They (or grills) are integral to all current direct view (color) CRTs.

http://www.princetoninfo.com/200111/11114c01.html
http://www.novia.net/~ereitan/Color_Sys_RCA.html
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post #197 of 306 Old 11-22-2004, 09:05 AM
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Quote:
Originally posted by dt_dc
Yes ... your perfect world is something like this?
http://members.cox.net/dt_dc/TriadsPerfect.gif
And you're saying that when you run 1280x1024 ... the above is what it SHOULD look like ... however the beam is a little wider than pictured above ... so you're getting overlap? Is that correct so far?

I'm asking ... describe the path of the beam when you then run 1280x1024.
No.

You still dont have the lines correct as I understand them. They are interlaced. and in the area you have 2 lines are actually parts of three lines(one full line and two half lines.)

For arguments sake lets say all lines are composed of triads with red at the top(they are all composed of equally oriented triads I think, I just dont know which color is at the top and it doesnt really matter.) Again could you paint a one line on one line off based on all lines being composed of red dot topped triads as kdb described earlier?

ss
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post #198 of 306 Old 11-22-2004, 09:28 AM
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Quote:
Originally posted by dt_dc
A direct view CRT without a shadow mask is called ... a black and white TV or monochrome monitor.

There were a few prototypes of other systems back when they were first implementing color TV.

However, when the first color TVs arrived in stores from RCA ... they contained ... shadow masks. Shadow masks were part of the 'RCA Color System' proposed and implemented by the FCC. Shadow masks were exactly what allowed a system to be (easily, cost effectively) built where the exact same TV signal could support both color televisions and black and white televisions.

Masks were not first implemented because if computer monitors. They (or grills) are integral to all current direct view (color) CRTs.

http://www.princetoninfo.com/200111/11114c01.html
http://www.novia.net/~ereitan/Color_Sys_RCA.html
Both great reads. Here the quote I was basing my info on:

Quote:
Masks - Refining the Electron Beams

Televisions have the same type of faceplate as monitors do - with a an inner coating of color phosphor. A problem occurren when they tried to use TV screen for computer monitors - the text was blurry. It seemed the CRT could not define crisp, clear edges. This is fine for television, since the text that is used is just credits at the end of a show, and usually it is quite large. Monitors require much tighter control.

The electron beams, upon leaving their respective Red Green and Blue guns, disperse slightly, and lose their sharp edges. It was found that if a sheet of metal was placed in front of the phosphor with tiny holes drilled into it - it "chopped off" the blurry edges of the circular beam and directed an exact, tight circle of energy onto the phosphor. This was known as a "shadow mask"

Today, manufacturers now place an ultra-thin metal covering behind the phosphor in all monitors, that directs and refines the electron beams. There are two types - shadow mask, and aperture grill. The shadow mask has been around a long time, and is simply a sheet of metal perforated with holes. The other type, introduced by Sony with their Trinitron Monitors, and now very common - is called the "Aperture Grill". As the name implies, a "grill" with vertical slats is laid down behind the phosphor. The metal strips allow the beams to penetrate as vertical slats that run up and down the screen.
I stand corrected, I still dont believe that the mask is a necessity however. I think it improves the image but is not a requirement in producing the signal. Sony's apearture grille is minimalistic - no break vertically and little horizontally.

ss
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post #199 of 306 Old 11-22-2004, 09:53 AM
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The tech at KDS said beam spot size does not change and is similar to but slightly larger than pitch
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I for one have been using beam spot size inappropriately. A better term would be beams strike area. The beam spot size on a direct view CRT is close to the opening size in the dot mask. The strike area is quite a bit larger than this and similar to pitch due to the spread caused by the locations of the guns to each other in space and being converged at the mask.
Well then, at what point is 'beam spot size' ... or 'strike area' 'similar to but slightly larger than pitch'? The picture above shows a beam spot (with your terms) size equal to pitch ... and the 'strike area' limited only by the functionlity of the mask.
http://members.cox.net/dt_dc/TriadsPerfect.gif
Now you say ... no ... 'beam spot size' is actually about equal to actual holes in the mask and 'strike area' is equal to the pitch? Hole diameter is about 1/3 of pitch ... so somehow ... the 'strike area' is 3 times the size of the mask holes ... about 3 times (a tad smaller) the 'beam spot' in your terms? The beam is getting 3 times as large in the tiny amount of space between the mask and the phosphors ... yet the beam is remaining the same size BEHIND the mask? Well ... that's impossible. If the beam is expanding ... it's expanding ... at the same rate behind and in front of the mask. The gun would have to be just about the same distance from the mask as the mask is from the phosphors.

You're suggesting something like this:
http://members.cox.net/dt_dc/NotHappeningCRT.GIF
However, the guns on a CRT are MUCH further away than the mask is from the phosphors ... so that would require something like this:
http://members.cox.net/dt_dc/ImpossibleCRT.GIF
Well, this is impossible.

No ... the electron beams maintain a constant diameter from the time they leave the gun to the time they hit the mask. What passes through the mask maintains a contant diameter to the time it hits the phosphors. This is (as pointed out above) ... the whole point of the vacuum in a CRT.
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post #200 of 306 Old 11-22-2004, 09:58 AM
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Originally posted by gdg
Actually no. The wave behavior of subatomic particles is manifest at the level of of the particles wavelength. This is many magnitudes smaller than what you are describing here. I only brought up the fact that sub atomic particles display both particle and wave properties because I figured someone might erroneously make the wrong connection. For our purposes and at the level CRT's are engineered at, for all intents and purposes, an electron may be considered a particle. Particles travel in straight paths unless influenced by an outside force (Newton). The edges of an opening cannot deflect a particle as you have described. ( A very small number of particles could conceivably bounce off one edge and across to the other side. A few might even go beyond the edge of the beam at the other side, but the flux density would be utterly insignificant.
Then why does the electron beam disperse at all in the relatively extremely short distance between the gun and the screen that it would require the mask at all? If the beam acts as ideally as you are suggesting, why not just engineer the beam spot sizes accordingly and dismiss the mask/grille entirely?

And recall its not just a single beam in most cases converging on that point it is all three.

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post #201 of 306 Old 11-22-2004, 10:08 AM
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Originally posted by dt_dc
Well then, at what point is 'beam spot size' ... or 'strike area' 'similar to but slightly larger than pitch'? The picture above shows a beam spot (with your terms) size equal to pitch ... and the 'strike area' limited only by the functionlity of the mask.
http://members.cox.net/dt_dc/TriadsPerfect.gif
Now you say ... no ... 'beam spot size' is actually about equal to actual holes in the mask and 'strike area' is equal to the pitch? Hole diameter is about 1/3 of pitch ... so somehow ... the 'strike area' is 3 times the size of the mask holes ... about 3 times (a tad smaller) the 'beam spot' in your terms? The beam is getting 3 times as large in the tiny amount of space between the mask and the phosphors ... yet the beam is remaining the same size BEHIND the mask? Well ... that's impossible. If the beam is expanding ... it's expanding ... at the same rate behind and in front of the mask. The gun would have to be just about the same distance from the mask as the mask is from the phosphors.

You're suggesting something like this:
http://members.cox.net/dt_dc/NotHappeningCRT.GIF
However, the guns on a CRT are MUCH further away than the mask is from the phosphors ... so that would require something like this:
http://members.cox.net/dt_dc/ImpossibleCRT.GIF
Well, this is impossible.

No ... the electron beams maintain a constant diameter from the time they leave the gun to the time they hit the mask. What passes through the mask maintains a contant diameter to the time it hits the phosphors. This is (as pointed out above) ... the whole point of the vacuum in a CRT.
The strike area is caused by the divergence of the three beams after exiting the mask. Assuming the beam spot is similar in diameter to a SINGLE phosphor dot, the collective stike areas of the three beam spots are 3x the area of a single beam spot. The three beams converge and are trimmed by the shadow mask then diverge after exiting the shadow mask to strike a single phosphor triad - hopefully.

The problem with your pic is as I posted above. Your are demonstrating lighting triads of three seperate lines with a single line pass. It cant be done the way you have it posted because of the angular problem and the fact that there arent holes in the shadow mask behind all the triads of that line at that level. The locations of the three phosphor dots relative to each other doesnt change we now know, meaning the colrs of each lit triad in identical in location. The key is understanding the seperate triad lines is that they are half-interlaced and all oriented identically as kdb explained earlier. I am thinking you dont understand this.

When you post a field of one line on - one line off it will become clear.

And I have absolutely no idea what your last two images depict, so I dont know that I am suggesting it either.

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post #202 of 306 Old 11-22-2004, 10:43 AM
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Televisions have the same type of faceplate as monitors do - with a an inner coating of color phosphor. A problem occurren when they tried to use TV screen for computer monitors - the text was blurry. It seemed the CRT could not define crisp, clear edges. This is fine for television, since the text that is used is just credits at the end of a show, and usually it is quite large. Monitors require much tighter control.
This is all true. However, the conclusions the author draws are horribly innacurate.
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The electron beams, upon leaving their respective Red Green and Blue guns, disperse slightly, and lose their sharp edges. It was found that if a sheet of metal was placed in front of the phosphor with tiny holes drilled into it - it "chopped off" the blurry edges of the circular beam and directed an exact, tight circle of energy onto the phosphor. This was known as a "shadow mask".
1) Shadow masks have been around since color TV was invented. They aren't 'new' or 'only required' with PC monitors.
2) All direct-view CRT sets sold from the introduction of color TV to the time the PC monitor was introduced contained shadow masks.
3) So all TVs were capable of "chopping off" the blurry edges of the circular beam and direct an exact, tight circle of energy onto the phosphor (as the author would put it). According to the author, this is adequate for presenting sharp text (yet they weren't).
4) Therefore, the shadow mask must NOT have been invented merely to make text sharp on PC monitors.
5) The author's conclusions are false.

I wouldn't put too much stock in this quote ... the author doesn't seem to know what they are talking about.

However, yes, the shadow masks they used for televisions were not sufficient for PC monitors. Text did appear blurry when displayed on standard televisions. The reason for this is that the shadow masks were too course. Sharp text requires finer shadow masks ... smaller dots ... more of them.
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post #203 of 306 Old 11-22-2004, 11:02 AM
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Sorry if I'm stating the obvious here but I want to make sure I have this clear:


1. Beam Angle (to the mask): determines color selection and purity

2. Beam Angle (to other beams): This is called convergence or focus, all three beams must land on a Single hole on the mask. Better convergence means better color purity

3. Beam width : is irrelevant unless the beam width exceeds the distance between successive holes on the mask


Cheers

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post #204 of 306 Old 11-22-2004, 11:15 AM
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Originally posted by dt_dc
This is all true. However, the conclusions the author draws are horribly innacurate.1) Shadow masks have been around since color TV was invented. They aren't 'new' or 'only required' with PC monitors.
2) All direct-view CRT sets sold from the introduction of color TV to the time the PC monitor was introduced contained shadow masks.
3) So all TVs were capable of "chopping off" the blurry edges of the circular beam and direct an exact, tight circle of energy onto the phosphor (as the author would put it). According to the author, this is adequate for presenting sharp text (yet they weren't).
4) Therefore, the shadow mask must NOT have been invented merely to make text sharp on PC monitors.
5) The author's conclusions are false.

I wouldn't put too much stock in this quote ... the author doesn't seem to know what they are talking about.

However, yes, the shadow masks they used for televisions were not sufficient for PC monitors. Text did appear blurry when displayed on standard televisions. The reason for this is that the shadow masks were too course. Sharp text requires finer shadow masks ... smaller dots ... more of them.
In the grand scheme of things its a minor issue. The shadow mask is a refining tool only. The fact that Sony builds sets with a negligible mask is evidence of that.

Larger issues abound.

-Does beam spot resize for multiples rates or does beam spot stay consistant regardless of scan rate. You have said it changes but again I have searched and found nothing supporting this. Have you found something supporting this? This is a huge issue in CRT function.

-Do you understand what a scan line comprises on a dot mask set? You have posted several graphics which show a scan line lighting all of one line and parts of two others. Do you understand what triads are affected on an individual scan line?

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post #205 of 306 Old 11-22-2004, 11:20 AM
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Originally posted by xrox
Sorry if I'm stating the obvious here but I want to make sure I have this clear:


1. Beam Angle (to the mask): determines color selection and purity

2. Beam Angle (to other beams): This is called convergence or focus, all three beams must land on a Single spot on the mask. Better convergence means better color purity

3. Beam width : determines scan line width


Cheers
2. I would put hole where you said spot.

I agree with all those accept 3.

http://www.infocellar.com/hardware/m...mask-beams.gif

Each of the incoming beams is an inidivual beam spot, the strike area is comprised of three beam spots. I am used to using beam spot in reference to FPs which use 3-tube arrays which only have the single gun to each tube. Strike area and beam spot size are equal on single color tubes and B&w sets.

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post #206 of 306 Old 11-22-2004, 11:23 AM
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Originally posted by subysouth
The key is understanding the seperate triad lines is that they are half-interlaced and all oriented identically as kdb explained earlier. I am thinking you dont understand this.

When you post a field of one line on - one line off it will become clear.
I see what you and kdh are saying. It isn't right ... but it's going to take some time to go over this point by point so ...

I think the keys to showing this are going to be:
1) What happens when I switch scan rates on the display?
2) How can I get 'overlapping scan lines' in your example above at 1600x1200 ... a potential 'gap' between scan lines at 800x600 ...
3) What happens when I fine-tune some of the controls (Zoom/Overscan ... HPOS ... HSIZ ... VPOS ... VSIZ ... Rotation ... Pincusion ... etc.

Anyway, in the mean time ...
Quote:
http://www.arcadecontrols.com/files/Miscellaneous/crtfaq.htm
(From: Bob Myers (myers@fc.hp.com).)

Here is where some words of explanation are in order.

What many people fail to realize is that the phosphor triads of the screen *do not* correspond to pixels in the image; they are not kept in alignment with the image pixels/lines/whatever, nor is there are reason for them to be.
Unfortunately, I don't think the above link goes into the detail needed to show that point clearly ...

Be back soon ...
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post #207 of 306 Old 11-22-2004, 11:32 AM
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Originally posted by xrox
all three beams must land on a Single spot on the mask
This is very wrong. Beams can (and usually do) span multiple holes in the mask. On a typical PC monitor beams span 2 ... 3 ... often even more holes in the mask. This is very desireable. It improves the quality of the picture. When beam size starts to get smaller ... and approach the size of holes in the mask ... detail starts to get lost. Typical analog color TVs are set up so that beam size is only slightly larger than mask hole size (1.25x, 1.5x, etc). That's why text appears 'blurry' on them. Finer masks were needed for PC monitors ... allowing beam size 2x, 3x, etc. the size of holes in the mask were needed to get the 'sharp' detail of PC monitors.
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post #208 of 306 Old 11-22-2004, 11:32 AM
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Originally posted by subysouth
2. I would put hole where you said spot.

I agree with all those accept 3.

ss
3 would only be correct if the beam diameter was larger than the distance between successive mask holes. Below that diameter the width is determined by the combination of 1 and 2

I will edit my post

Thanks.

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post #209 of 306 Old 11-22-2004, 11:34 AM
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Originally posted by dt_dc
This is very wrong. Beams can (and usually do) span multiple holes in the mask. On a typical PC monitor beams span 2 ... 3 ... often even more holes in the mask. This is very desireable. It improves the quality of the picture. When beam size starts to get smaller ... and approach the size of holes in the mask ... detail starts to get lost. Typical analog color TVs are set up so that beam size is only slightly larger than mask hole size (1.25x, 1.5x, etc). That's why text appears 'blurry' on them. Finer masks were needed for PC monitors ... allowing beam size 2x, 3x, etc. the size of holes in the mask were needed to get the 'sharp' detail of PC monitors.
Sorry dt_dc I think you misunderstood me. I said on the mask, not on the phosphors.

The threee beams must converge onto the mask. they never do perfectly however!

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post #210 of 306 Old 11-22-2004, 11:37 AM
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Quote:
Originally posted by xrox
Sorry dt_dc I think you misunderstood me. I said on the mask, not on the phosphors.

The threee beams must converge onto the mask. they never do perfectly however!
No misunderstanding ... the beam spans multiple holes on the mask. This improves picture quality and is required for 'sharp text'.
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