Q: Dot Pitch Vs. Resolution

Archived from groups: alt.tv.tech.hdtv (More info?)

I'm confused by the distinction between the number of "dots" on a TV
screen or monitor, and the "resolution" the picture is displayed at.

Is there an arbitrary relationship, so that the pixels get displayed by
the "dots" (assuming there are sufficient numbers of dots) with the
pixels projected onto one or more dots? Is this what accounts for the
moire patterns one sees occasionally?

And why is it that computer monitors routinely specify the dot pitch,
while TVs seem to ignore this specification?

If different brands of TV have different size dots, why don't some
manyufacturers brag about it? Is it because TV is so low-res that all of
them have enough dots so it makes no practical difference?

--
....I'm an air-conditioned gypsy...

- The Who
13 answers Last reply
More about pitch resolution
  1. Archived from groups: alt.tv.tech.hdtv (More info?)

    ANd - to expand on Russ's elegant explanation - conventional tube type tv's
    that use 3 gun technology also must use a shadow mask which keeps the 3
    colored dots separate. As you can imagine, there is a limit to the number
    of "holes" that can be punched in that shadow mask. The smaller the screen,
    the fewer holes and the lower the resolution possible. Dot pitch describes
    the size of the hole.


    when<EskWIRED@spamblock.panix.com> wrote in message
    news:cm8a06$k7q$2@reader1.panix.com...
    > I'm confused by the distinction between the number of "dots" on a TV
    > screen or monitor, and the "resolution" the picture is displayed at.
    >
    > Is there an arbitrary relationship, so that the pixels get displayed by
    > the "dots" (assuming there are sufficient numbers of dots) with the
    > pixels projected onto one or more dots? Is this what accounts for the
    > moire patterns one sees occasionally?
    >
    > And why is it that computer monitors routinely specify the dot pitch,
    > while TVs seem to ignore this specification?
    >
    > If different brands of TV have different size dots, why don't some
    > manyufacturers brag about it? Is it because TV is so low-res that all of
    > them have enough dots so it makes no practical difference?
    >
    > --
    > ...I'm an air-conditioned gypsy...
    >
    > - The Who
  2. Archived from groups: alt.tv.tech.hdtv (More info?)

    dot pitch say .28 is the size of the pixel... the smaller the better as more
    dots (pixels) can be placed in the screen, therefore greater resolution.

    Hope that helps
    Russ


    <EskWIRED@spamblock.panix.com> wrote in message
    news:cm8a06$k7q$2@reader1.panix.com...
    > I'm confused by the distinction between the number of "dots" on a TV
    > screen or monitor, and the "resolution" the picture is displayed at.
    >
    > Is there an arbitrary relationship, so that the pixels get displayed by
    > the "dots" (assuming there are sufficient numbers of dots) with the
    > pixels projected onto one or more dots? Is this what accounts for the
    > moire patterns one sees occasionally?
    >
    > And why is it that computer monitors routinely specify the dot pitch,
    > while TVs seem to ignore this specification?
    >
    > If different brands of TV have different size dots, why don't some
    > manyufacturers brag about it? Is it because TV is so low-res that all of
    > them have enough dots so it makes no practical difference?
    >
    > --
    > ...I'm an air-conditioned gypsy...
    >
    > - The Who
    >
  3. Archived from groups: alt.tv.tech.hdtv (More info?)

    In alt.tv.tech.hdtv, kw5kw <qwerty.kw5kw@swbell.net.qwerty> wrote:
    > dot pitch say .28 is the size of the pixel... the smaller the better as more
    > dots (pixels) can be placed in the screen, therefore greater resolution.

    Yes, that I know.

    But is there any necessary relationship between the actual number of
    dots, and the actual number of pixels? Or are there lots and lots more
    dots (on a monitor) than pixels, so the mathematical relationship is
    arbitrary?

    And why don't TV manufacturers give a spec for dot pitch, like computer
    monitor manufacturers do?


    --
    ....I'm an air-conditioned gypsy...

    - The Who
  4. Archived from groups: alt.tv.tech.hdtv (More info?)

    EskWIRED@spamblock.panix.com wrote:

    > In alt.tv.tech.hdtv, kw5kw <qwerty.kw5kw@swbell.net.qwerty> wrote:
    >
    >>dot pitch say .28 is the size of the pixel... the smaller the better as more
    >>dots (pixels) can be placed in the screen, therefore greater resolution.
    >
    >
    > Yes, that I know.
    >
    > But is there any necessary relationship between the actual number of
    > dots, and the actual number of pixels? Or are there lots and lots more
    > dots (on a monitor) than pixels, so the mathematical relationship is
    > arbitrary?

    The dot pitch is a way of stating image density without reference to
    monitor size. If you have a monitor with a dot pitch of .254mm then you
    have 100 dots per inch. If your monitor is 19.2 inches wide, then you
    would have 1920 pixels on each line and that would be your maximum
    resolution.

    Lower horizontal resolutions are supported by using more than one dot
    per pixel. This works better on a CRT than fixed pixel displays as the
    analog nature of the electron beam does some dithering for free. Fixed
    pixel displays have to use scalars to dither and the scalars are of
    differing quality.

    > And why don't TV manufacturers give a spec for dot pitch, like computer
    > monitor manufacturers do?

    Because that only tells part of the story for TV. You can have 1920
    holes in the shadow mask of a direct view CRT and not have the
    electronics to back that up. If the TVs video bandwidth is lower than
    that required for full resolution, the image will be less than the dot
    pitch. Direct view TVs have other problems caused by wide electron beam
    deflection angles. Computer monitors usually have longer CRTs than TVs
    of the same size which reduces the deflection angles.

    Contrary wise, you can have no shadow mask (by using three CRTs) and
    have no dot pitch at all. The resolution limitations of CRT based RPTVs
    are in the electronics and display characteristics of the guns because
    they have no shadow mask.

    Matthew
  5. Archived from groups: alt.tv.tech.hdtv (More info?)

    EskWIRED@spamblock.panix.com wrote:

    > But is there any necessary relationship between the actual number of
    > dots, and the actual number of pixels?

    No. The relationship between dot pitch and pixel count on a CRT is not
    one-to-one. You can easily verify this by examining a working computer
    CRT monitor with a magnifying glass.

    You can think of dot pitch as the "native resolution" of the CRT (even
    though this is misleading, since CRT resolution also depends on other
    factors like beam focus). The resampling from signal to screen dots is
    entirely analog. The electron gun is fired in the pattern determined by
    the source pixels, and the electrons fall into whatever array of buckets
    (screen dots) is available.

    With fixed-pixel displays, e.g. LCD and plasma, the pixel pattern of the
    source is modified digitally to match the native resolution before being
    sent to the display hardware. The resampling uses a mathematical model
    of what happens "naturally" in a CRT.

    > Or are there lots and lots more dots (on a monitor) than pixels, so
    > the mathematical relationship is arbitrary?

    Generally there are only slightly more dots than pixels. This is also
    easy to verify. A 17-inch 4:3 monitor might have (optimistically) a
    viewable area that's 16 inches diagonally, for a width of 12.8 inches,
    or 325 mm. If its dot pitch is a typical 0.28 mm, the viewable area is
    about 1160 dots across, comparable to the 1024 or 1152 pixels across
    that would normally be displayed on a monitor of this size.

    (Dot pitch, BTW, is the distance between the centers of adjacent dots,
    not the "size" of the dot.)

    > And why don't TV manufacturers give a spec for dot pitch, like
    > computer monitor manufacturers do?

    Probably because TV resolution has historically been limited by factors
    other than the dot pitch, and because sharpness is a smaller component
    of perceived quality in TVs than it is in computer monitors, and because
    it would make TVs look bad compared to monitors, probably unfairly.

    Consider the different purposes of scale between the two applications.
    Computer monitors these days tend to have very similar dot pitches,
    regardless of their size. You buy a bigger computer monitor in order to
    fit more pixels onto the screen, *not* so that you can view a given
    resolution comfortably from a greater distance. No matter how big your
    computer monitor is, its resolution is roughly 100 DPI.

    The source resolution of a TV signal isn't something you or the TV can
    control. For this reason, and unlike computer displays, larger TVs have
    larger dot pitches. You can't compare absolute dot pitch across TVs of
    different sizes. The number you can compare across sizes is resolution,
    which has the added benefits of accounting for other factors and being
    roughly comparable to technologies other than CRT.

    - Ernie http://home.comcast.net/~erniew
  6. Archived from groups: alt.tv.tech.hdtv (More info?)

    In alt.tv.tech.hdtv, curmudgeon <curmudgeon@buzzoff.net> wrote:
    > ANd - to expand on Russ's elegant explanation - conventional tube type tv's
    > that use 3 gun technology also must use a shadow mask which keeps the 3
    > colored dots separate. As you can imagine, there is a limit to the number
    > of "holes" that can be punched in that shadow mask. The smaller the screen,
    > the fewer holes and the lower the resolution possible. Dot pitch describes
    > the size of the hole.

    I've got a 36 inch HDTV. The text it displays when used as a monitor is
    very fuzzy. It looks like a horribly cheap computer monitor. Is that
    because the dot pitch is much coarser than a typical computer monitor?

    I was expecting better than what I get.

    And when I use my ATI component video adapter with my computer, using the
    HDTV as a monitor, the picture is much crisper than when I use S-Video,
    even at the same resolutions. Why is that, given that the dot pitch and
    the number of pixels are the same?


    > when<EskWIRED@spamblock.panix.com> wrote in message
    > news:cm8a06$k7q$2@reader1.panix.com...
    > > I'm confused by the distinction between the number of "dots" on a TV
    > > screen or monitor, and the "resolution" the picture is displayed at.
    > >
    > > Is there an arbitrary relationship, so that the pixels get displayed by
    > > the "dots" (assuming there are sufficient numbers of dots) with the
    > > pixels projected onto one or more dots? Is this what accounts for the
    > > moire patterns one sees occasionally?
    > >
    > > And why is it that computer monitors routinely specify the dot pitch,
    > > while TVs seem to ignore this specification?
    > >
    > > If different brands of TV have different size dots, why don't some
    > > manyufacturers brag about it? Is it because TV is so low-res that all of
    > > them have enough dots so it makes no practical difference?
    > >
    > > --
    > > ...I'm an air-conditioned gypsy...
    > >
    > > - The Who


    --
    ....I'm an air-conditioned gypsy...

    - The Who
  7. Archived from groups: alt.tv.tech.hdtv (More info?)

    > I've got a 36 inch HDTV. The text it displays when used as a monitor is
    > very fuzzy. It looks like a horribly cheap computer monitor. Is that
    > because the dot pitch is much coarser than a typical computer monitor?

    Maybe this is a clue for you. Part of what I do for a living involves
    making TV commercials. When we use a still picture in an (SD) commercial,
    there is no point in shooting it at any higher resolution than 640 X 480.
    That is higher than the resolution of an SD picture on a TV screen. If you
    sit as close to your TV set as you do to your computer monitor, it will look
    worse than a 640 X 480 monitor resolution on your computer monitor.

    This assumes SD resolution on your TV, however. How your HDTV reacts to
    text when used as a monitor, I don't know.

    mack
    austin
  8. Archived from groups: alt.tv.tech.hdtv (More info?)

    pixel = dot or
    dot = pixel


    <EskWIRED@spamblock.panix.com> wrote in message
    news:cmaocr$glf$2@reader1.panix.com...
    > In alt.tv.tech.hdtv, kw5kw <qwerty.kw5kw@swbell.net.qwerty> wrote:
    > > dot pitch say .28 is the size of the pixel... the smaller the better as
    more
    > > dots (pixels) can be placed in the screen, therefore greater resolution.
    >
    > Yes, that I know.
    >
    > But is there any necessary relationship between the actual number of
    > dots, and the actual number of pixels? Or are there lots and lots more
    > dots (on a monitor) than pixels, so the mathematical relationship is
    > arbitrary?
    >
    > And why don't TV manufacturers give a spec for dot pitch, like computer
    > monitor manufacturers do?
    >
    >
    >
    > --
    > ...I'm an air-conditioned gypsy...
    >
    > - The Who
    >
  9. Archived from groups: alt.tv.tech.hdtv (More info?)

    In alt.tv.tech.hdtv, Matthew L. Martin <nothere@notnow.never> wrote:

    > The dot pitch is a way of stating image density without reference to
    > monitor size. If you have a monitor with a dot pitch of .254mm then you
    > have 100 dots per inch. If your monitor is 19.2 inches wide, then you
    > would have 1920 pixels on each line and that would be your maximum
    > resolution.

    Ah. That makes sense.

    > Lower horizontal resolutions are supported by using more than one dot
    > per pixel. This works better on a CRT than fixed pixel displays as the
    > analog nature of the electron beam does some dithering for free. Fixed
    > pixel displays have to use scalars to dither and the scalars are of
    > differing quality.

    Ah. That explains some things to me too.

    > > And why don't TV manufacturers give a spec for dot pitch, like computer
    > > monitor manufacturers do?

    > Because that only tells part of the story for TV. You can have 1920
    > holes in the shadow mask of a direct view CRT and not have the
    > electronics to back that up. If the TVs video bandwidth is lower than
    > that required for full resolution, the image will be less than the dot
    > pitch. Direct view TVs have other problems caused by wide electron beam
    > deflection angles.

    Aha! I thake it that that explains the "fuzzy" text I get when I use my
    HDTV as a monitor. There is no real relationship between the CRT dots
    and the pixels projected onto them. The electron beam is not focused on
    any particular dot on the screen, and it may project the pixel onto one
    dot, or between two dots, or otherwise randomly. I think I'm startig to
    understand.


    Computer monitors usually have longer CRTs than TVs
    > of the same size which reduces the deflection angles.

    > Contrary wise, you can have no shadow mask (by using three CRTs) and
    > have no dot pitch at all. The resolution limitations of CRT based RPTVs
    > are in the electronics and display characteristics of the guns because
    > they have no shadow mask.

    Also very interesting. Is it fair to assume that RPTVs work better as
    computer monitors than direct views?

    --
    ....I'm an air-conditioned gypsy...

    - The Who
  10. Archived from groups: alt.tv.tech.hdtv (More info?)

    EskWIRED@spamblock.panix.com wrote:

    >
    >
    >>Because that only tells part of the story for TV. You can have 1920
    >>holes in the shadow mask of a direct view CRT and not have the
    >>electronics to back that up. If the TVs video bandwidth is lower than
    >>that required for full resolution, the image will be less than the dot
    >>pitch. Direct view TVs have other problems caused by wide electron beam
    >>deflection angles.
    >
    >
    > Aha! I thake it that that explains the "fuzzy" text I get when I use my
    > HDTV as a monitor. There is no real relationship between the CRT dots
    > and the pixels projected onto them. The electron beam is not focused on
    > any particular dot on the screen, and it may project the pixel onto one
    > dot, or between two dots, or otherwise randomly. I think I'm startig to
    > understand.

    That's pretty much it. The electron beams are larger than the pixels.
    The electrons that hit the shadow mask are absorbed and the rest go
    through to hit the phosphors. What gets displayed is the value of the
    beams as they sweep across the openings for that dot. This can easily be
    an intermediate value as the video amplifiers' outputs change.

    > Computer monitors usually have longer CRTs than TVs
    >
    >>of the same size which reduces the deflection angles.
    >
    >
    >>Contrary wise, you can have no shadow mask (by using three CRTs) and
    >>have no dot pitch at all. The resolution limitations of CRT based RPTVs
    >>are in the electronics and display characteristics of the guns because
    >>they have no shadow mask.
    >
    >
    > Also very interesting. Is it fair to assume that RPTVs work better as
    > computer monitors than direct views?

    Not really. Since there are three guns and complex optics, CRT based
    RPTVs have to control the geometry and convergence of the display
    electronically.

    Geometry controls where the pixels are displayed on the screen. If the
    all of the scan lines are perfectly straight and parallel and all of the
    pixels in each line are vertically aligned with the same pixel in all of
    the other lines, then the geometry is perfect. This is, of course,
    impossible to get over the entire area of the screen.

    Convergence controls the resolution of each pixel. If all three electron
    guns illuminate the same pixel sized spot on the screen at the same time
    then convergence is perfect. This is, of course impossible to get for
    every pixel on the screen.

    That's the bad news. The good news is that it isn't all that hard to get
    (and keep) the geometry and convergence acceptable for video purposes.
    Utility as a computer monitor for text suffers to the extent that
    convergence is less than perfect.

    CRT RPTVs can't rely on a shadow mask or fixed pixel boundary to make a
    sharp edge. On a CRT based RPTV, the transition from a black background
    pixel to a white character pixel will be smeared over the space between
    the pixels. You would probably describe that as being fuzzy. That
    smearing is useful when viewing video, IMHO, because it provides a film
    like image.

    Perfect geometry, convergence and hard interpixel boundaries give the
    advantage to fixed pixel HD displays for computer monitors.

    Matthew
  11. Archived from groups: alt.tv.tech.hdtv (More info?)

    This was a really good discussion and a good explanation.
    Thanks
    Russ

    "Ernie Wright" <erniew@comcast.net> wrote in message
    news:xaadnXZwrZMmmBTcRVn-vA@comcast.com...
    > EskWIRED@spamblock.panix.com wrote:
    >
    > > But is there any necessary relationship between the actual number of
    > > dots, and the actual number of pixels?
    >
    > No. The relationship between dot pitch and pixel count on a CRT is not
    > one-to-one. You can easily verify this by examining a working computer
    > CRT monitor with a magnifying glass.
    >
    > You can think of dot pitch as the "native resolution" of the CRT (even
    > though this is misleading, since CRT resolution also depends on other
    > factors like beam focus). The resampling from signal to screen dots is
    > entirely analog. The electron gun is fired in the pattern determined by
    > the source pixels, and the electrons fall into whatever array of buckets
    > (screen dots) is available.
    >
    > With fixed-pixel displays, e.g. LCD and plasma, the pixel pattern of the
    > source is modified digitally to match the native resolution before being
    > sent to the display hardware. The resampling uses a mathematical model
    > of what happens "naturally" in a CRT.
    >
    > > Or are there lots and lots more dots (on a monitor) than pixels, so
    > > the mathematical relationship is arbitrary?
    >
    > Generally there are only slightly more dots than pixels. This is also
    > easy to verify. A 17-inch 4:3 monitor might have (optimistically) a
    > viewable area that's 16 inches diagonally, for a width of 12.8 inches,
    > or 325 mm. If its dot pitch is a typical 0.28 mm, the viewable area is
    > about 1160 dots across, comparable to the 1024 or 1152 pixels across
    > that would normally be displayed on a monitor of this size.
    >
    > (Dot pitch, BTW, is the distance between the centers of adjacent dots,
    > not the "size" of the dot.)
    >
    > > And why don't TV manufacturers give a spec for dot pitch, like
    > > computer monitor manufacturers do?
    >
    > Probably because TV resolution has historically been limited by factors
    > other than the dot pitch, and because sharpness is a smaller component
    > of perceived quality in TVs than it is in computer monitors, and because
    > it would make TVs look bad compared to monitors, probably unfairly.
    >
    > Consider the different purposes of scale between the two applications.
    > Computer monitors these days tend to have very similar dot pitches,
    > regardless of their size. You buy a bigger computer monitor in order to
    > fit more pixels onto the screen, *not* so that you can view a given
    > resolution comfortably from a greater distance. No matter how big your
    > computer monitor is, its resolution is roughly 100 DPI.
    >
    > The source resolution of a TV signal isn't something you or the TV can
    > control. For this reason, and unlike computer displays, larger TVs have
    > larger dot pitches. You can't compare absolute dot pitch across TVs of
    > different sizes. The number you can compare across sizes is resolution,
    > which has the added benefits of accounting for other factors and being
    > roughly comparable to technologies other than CRT.
    >
    > - Ernie http://home.comcast.net/~erniew
    >
    >
  12. Archived from groups: alt.tv.tech.hdtv (More info?)

    In alt.tv.tech.hdtv, Matthew L. Martin <nothere@notnow.never> wrote:
    > EskWIRED@spamblock.panix.com wrote:

    > Perfect geometry, convergence and hard interpixel boundaries give the
    > advantage to fixed pixel HD displays for computer monitors.

    Thanks, Matt.

    --
    ....I'm an air-conditioned gypsy...

    - The Who
  13. Archived from groups: alt.tv.tech.hdtv (More info?)

    In alt.tv.tech.hdtv, kw5kw <qwerty.kw5kw@swbell.net.qwerty> wrote:
    > This was a really good discussion and a good explanation.

    Agreed. I learned a huge amount, and have a conceptual framework that I
    didn't have before. Thanks all who answered my badly-asked questions.


    --
    ....I'm an air-conditioned gypsy...

    - The Who
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