Was the picture area of a CRT a parallelogram (instead of a true rectangle)?What was this Apple external CRT monitor that looked like an iMac G3?Adjusting focus for old CRT monitorsTimeline of progressive scan CRT resolutionsCRT Geometry AdjustmentWeird Brightness Problem On CRTHigh Voltage in Bell of CRT Tube?Can the wrong sync frequency really destroy a CRT monitor?Safely adjusting CRT while it's on?Fixing the horizontal size(width) of an old CRT monitor (Zenith ZCM 1390-E)CRT contrast issue: light grey on dark grey
Simple recursive Sudoku solver
Hostile work environment after whistle-blowing on coworker and our boss. What do I do?
Bob has never been a M before
I2C signal and power over long range (10meter cable)
Can I rely on these GitHub repository files?
What if somebody invests in my application?
In Star Trek IV, why did the Bounty go back to a time when whales were already rare?
Is a naturally all "male" species possible?
Indicating multiple different modes of speech (fantasy language or telepathy)
Why isn't KTEX's runway designation 10/28 instead of 9/27?
How do I repair my stair bannister?
Java - What do constructor type arguments mean when placed *before* the type?
What to do when my ideas aren't chosen, when I strongly disagree with the chosen solution?
Can a Bard use an arcane focus?
Should my PhD thesis be submitted under my legal name?
Who must act to prevent Brexit on March 29th?
Can I use my Chinese passport to enter China after I acquired another citizenship?
Why are on-board computers allowed to change controls without notifying the pilots?
Reply ‘no position’ while the job posting is still there (‘HiWi’ position in Germany)
How to deal with or prevent idle in the test team?
node command while defining a coordinate in TikZ
Science Fiction story where a man invents a machine that can help him watch history unfold
Is there a problem with hiding "forgot password" until it's needed?
For airliners, what prevents wing strikes on landing in bad weather?
Was the picture area of a CRT a parallelogram (instead of a true rectangle)?
What was this Apple external CRT monitor that looked like an iMac G3?Adjusting focus for old CRT monitorsTimeline of progressive scan CRT resolutionsCRT Geometry AdjustmentWeird Brightness Problem On CRTHigh Voltage in Bell of CRT Tube?Can the wrong sync frequency really destroy a CRT monitor?Safely adjusting CRT while it's on?Fixing the horizontal size(width) of an old CRT monitor (Zenith ZCM 1390-E)CRT contrast issue: light grey on dark grey
This may seem like an absurd question at first, but I've been giving it some thought and I'm genuinely curious about the design details of these devices.
I was reading an answer on an unrelated Stack Exchange site about the retrace/flyback details on old CRTs, and the image attached to that answer piqued my interest:
I understand that both the horizontal and vertical deflection of the electron beam is controlled by two sawtooth waves, the vertical running at the refresh rate and the horizontal running a few hundred times faster than that. I also understand that both sawtooths are constant sweeps, and not "stair stepped" to hold at any particular voltage to accommodate the viewable lines or retrace periods.
Here's the premise of my question: In the context of one single horizontal trace across the screen, the vertical position is also constantly increasing (towards the bottom) in preparation for the next scan line. It then follows that the scan line's vertical position at the left edge of the screen is slightly higher than the position at the right edge, and the whole screen is a parallelogram with left and right edges perfectly vertical, and top and bottom edges both slanted down towards the bottom right.
Assuming the premise is correct, was it common (or even feasible) for the designers of CRT computer displays to counteract this effect and make the screen and its contents perfectly square? Would such a compensation have even been worth the effort?
crt-monitor display
New contributor
add a comment |
This may seem like an absurd question at first, but I've been giving it some thought and I'm genuinely curious about the design details of these devices.
I was reading an answer on an unrelated Stack Exchange site about the retrace/flyback details on old CRTs, and the image attached to that answer piqued my interest:
I understand that both the horizontal and vertical deflection of the electron beam is controlled by two sawtooth waves, the vertical running at the refresh rate and the horizontal running a few hundred times faster than that. I also understand that both sawtooths are constant sweeps, and not "stair stepped" to hold at any particular voltage to accommodate the viewable lines or retrace periods.
Here's the premise of my question: In the context of one single horizontal trace across the screen, the vertical position is also constantly increasing (towards the bottom) in preparation for the next scan line. It then follows that the scan line's vertical position at the left edge of the screen is slightly higher than the position at the right edge, and the whole screen is a parallelogram with left and right edges perfectly vertical, and top and bottom edges both slanted down towards the bottom right.
Assuming the premise is correct, was it common (or even feasible) for the designers of CRT computer displays to counteract this effect and make the screen and its contents perfectly square? Would such a compensation have even been worth the effort?
crt-monitor display
New contributor
add a comment |
This may seem like an absurd question at first, but I've been giving it some thought and I'm genuinely curious about the design details of these devices.
I was reading an answer on an unrelated Stack Exchange site about the retrace/flyback details on old CRTs, and the image attached to that answer piqued my interest:
I understand that both the horizontal and vertical deflection of the electron beam is controlled by two sawtooth waves, the vertical running at the refresh rate and the horizontal running a few hundred times faster than that. I also understand that both sawtooths are constant sweeps, and not "stair stepped" to hold at any particular voltage to accommodate the viewable lines or retrace periods.
Here's the premise of my question: In the context of one single horizontal trace across the screen, the vertical position is also constantly increasing (towards the bottom) in preparation for the next scan line. It then follows that the scan line's vertical position at the left edge of the screen is slightly higher than the position at the right edge, and the whole screen is a parallelogram with left and right edges perfectly vertical, and top and bottom edges both slanted down towards the bottom right.
Assuming the premise is correct, was it common (or even feasible) for the designers of CRT computer displays to counteract this effect and make the screen and its contents perfectly square? Would such a compensation have even been worth the effort?
crt-monitor display
New contributor
This may seem like an absurd question at first, but I've been giving it some thought and I'm genuinely curious about the design details of these devices.
I was reading an answer on an unrelated Stack Exchange site about the retrace/flyback details on old CRTs, and the image attached to that answer piqued my interest:
I understand that both the horizontal and vertical deflection of the electron beam is controlled by two sawtooth waves, the vertical running at the refresh rate and the horizontal running a few hundred times faster than that. I also understand that both sawtooths are constant sweeps, and not "stair stepped" to hold at any particular voltage to accommodate the viewable lines or retrace periods.
Here's the premise of my question: In the context of one single horizontal trace across the screen, the vertical position is also constantly increasing (towards the bottom) in preparation for the next scan line. It then follows that the scan line's vertical position at the left edge of the screen is slightly higher than the position at the right edge, and the whole screen is a parallelogram with left and right edges perfectly vertical, and top and bottom edges both slanted down towards the bottom right.
Assuming the premise is correct, was it common (or even feasible) for the designers of CRT computer displays to counteract this effect and make the screen and its contents perfectly square? Would such a compensation have even been worth the effort?
crt-monitor display
crt-monitor display
New contributor
New contributor
New contributor
asked 3 hours ago
smitellismitelli
1111
1111
New contributor
New contributor
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
IIRC, the electron gun was actually installed in a position where it was rotated slightly relative to the tube, to compensate for this effect, so the scan lines did end up being horizontal.
... which means that it is still a parallelogram, it's just the sides that aren't vertical rather than the top and bottom that aren't horizontal!
– Tommy
59 mins ago
add a comment |
To expand further, it actually wasn't especially feasible — there is no easy solution that doesn't eliminate the interlacing.
Interlacing works because the timing of the vertical retrace varies. On odd fields it is triggered so that scanning resumes at the beginning of a line. On even fields it is triggered so that scanning resumes in the middle. Because of the diagonal scan, that sets one field 0.5 lines higher than the other. If the scan weren't diagonal then the two fields would not enmesh in that manner — they would instead sit exactly on top of each other, just starting in different places.
On a classic TV it's undesirable to make the diagonal scan anything other than diagonal because the flying spot during the capture process was diagonal. So you wouldn't be unskewing the image, you'd be skewing it.
On a monitor life is slightly different, and true horizontals are likely accurately to reflect the image. But it's also generally the case that monitors have smaller scan lines in order to output a higher resolution, so the effect is less visible anyway — on a 14" 800x600 monitor you're already talking about the right hand side being less than 3mm lower than the left, but being almost 28.5cm to the right. With a multi-sync monitor, how far down the right is compared to the left is a variable function of the resolution.
add a comment |
Your Answer
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "648"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
noCode: true, onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
smitelli is a new contributor. Be nice, and check out our Code of Conduct.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fretrocomputing.stackexchange.com%2fquestions%2f9426%2fwas-the-picture-area-of-a-crt-a-parallelogram-instead-of-a-true-rectangle%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
IIRC, the electron gun was actually installed in a position where it was rotated slightly relative to the tube, to compensate for this effect, so the scan lines did end up being horizontal.
... which means that it is still a parallelogram, it's just the sides that aren't vertical rather than the top and bottom that aren't horizontal!
– Tommy
59 mins ago
add a comment |
IIRC, the electron gun was actually installed in a position where it was rotated slightly relative to the tube, to compensate for this effect, so the scan lines did end up being horizontal.
... which means that it is still a parallelogram, it's just the sides that aren't vertical rather than the top and bottom that aren't horizontal!
– Tommy
59 mins ago
add a comment |
IIRC, the electron gun was actually installed in a position where it was rotated slightly relative to the tube, to compensate for this effect, so the scan lines did end up being horizontal.
IIRC, the electron gun was actually installed in a position where it was rotated slightly relative to the tube, to compensate for this effect, so the scan lines did end up being horizontal.
answered 3 hours ago
rwallacerwallace
9,892450148
9,892450148
... which means that it is still a parallelogram, it's just the sides that aren't vertical rather than the top and bottom that aren't horizontal!
– Tommy
59 mins ago
add a comment |
... which means that it is still a parallelogram, it's just the sides that aren't vertical rather than the top and bottom that aren't horizontal!
– Tommy
59 mins ago
... which means that it is still a parallelogram, it's just the sides that aren't vertical rather than the top and bottom that aren't horizontal!
– Tommy
59 mins ago
... which means that it is still a parallelogram, it's just the sides that aren't vertical rather than the top and bottom that aren't horizontal!
– Tommy
59 mins ago
add a comment |
To expand further, it actually wasn't especially feasible — there is no easy solution that doesn't eliminate the interlacing.
Interlacing works because the timing of the vertical retrace varies. On odd fields it is triggered so that scanning resumes at the beginning of a line. On even fields it is triggered so that scanning resumes in the middle. Because of the diagonal scan, that sets one field 0.5 lines higher than the other. If the scan weren't diagonal then the two fields would not enmesh in that manner — they would instead sit exactly on top of each other, just starting in different places.
On a classic TV it's undesirable to make the diagonal scan anything other than diagonal because the flying spot during the capture process was diagonal. So you wouldn't be unskewing the image, you'd be skewing it.
On a monitor life is slightly different, and true horizontals are likely accurately to reflect the image. But it's also generally the case that monitors have smaller scan lines in order to output a higher resolution, so the effect is less visible anyway — on a 14" 800x600 monitor you're already talking about the right hand side being less than 3mm lower than the left, but being almost 28.5cm to the right. With a multi-sync monitor, how far down the right is compared to the left is a variable function of the resolution.
add a comment |
To expand further, it actually wasn't especially feasible — there is no easy solution that doesn't eliminate the interlacing.
Interlacing works because the timing of the vertical retrace varies. On odd fields it is triggered so that scanning resumes at the beginning of a line. On even fields it is triggered so that scanning resumes in the middle. Because of the diagonal scan, that sets one field 0.5 lines higher than the other. If the scan weren't diagonal then the two fields would not enmesh in that manner — they would instead sit exactly on top of each other, just starting in different places.
On a classic TV it's undesirable to make the diagonal scan anything other than diagonal because the flying spot during the capture process was diagonal. So you wouldn't be unskewing the image, you'd be skewing it.
On a monitor life is slightly different, and true horizontals are likely accurately to reflect the image. But it's also generally the case that monitors have smaller scan lines in order to output a higher resolution, so the effect is less visible anyway — on a 14" 800x600 monitor you're already talking about the right hand side being less than 3mm lower than the left, but being almost 28.5cm to the right. With a multi-sync monitor, how far down the right is compared to the left is a variable function of the resolution.
add a comment |
To expand further, it actually wasn't especially feasible — there is no easy solution that doesn't eliminate the interlacing.
Interlacing works because the timing of the vertical retrace varies. On odd fields it is triggered so that scanning resumes at the beginning of a line. On even fields it is triggered so that scanning resumes in the middle. Because of the diagonal scan, that sets one field 0.5 lines higher than the other. If the scan weren't diagonal then the two fields would not enmesh in that manner — they would instead sit exactly on top of each other, just starting in different places.
On a classic TV it's undesirable to make the diagonal scan anything other than diagonal because the flying spot during the capture process was diagonal. So you wouldn't be unskewing the image, you'd be skewing it.
On a monitor life is slightly different, and true horizontals are likely accurately to reflect the image. But it's also generally the case that monitors have smaller scan lines in order to output a higher resolution, so the effect is less visible anyway — on a 14" 800x600 monitor you're already talking about the right hand side being less than 3mm lower than the left, but being almost 28.5cm to the right. With a multi-sync monitor, how far down the right is compared to the left is a variable function of the resolution.
To expand further, it actually wasn't especially feasible — there is no easy solution that doesn't eliminate the interlacing.
Interlacing works because the timing of the vertical retrace varies. On odd fields it is triggered so that scanning resumes at the beginning of a line. On even fields it is triggered so that scanning resumes in the middle. Because of the diagonal scan, that sets one field 0.5 lines higher than the other. If the scan weren't diagonal then the two fields would not enmesh in that manner — they would instead sit exactly on top of each other, just starting in different places.
On a classic TV it's undesirable to make the diagonal scan anything other than diagonal because the flying spot during the capture process was diagonal. So you wouldn't be unskewing the image, you'd be skewing it.
On a monitor life is slightly different, and true horizontals are likely accurately to reflect the image. But it's also generally the case that monitors have smaller scan lines in order to output a higher resolution, so the effect is less visible anyway — on a 14" 800x600 monitor you're already talking about the right hand side being less than 3mm lower than the left, but being almost 28.5cm to the right. With a multi-sync monitor, how far down the right is compared to the left is a variable function of the resolution.
answered 47 mins ago
TommyTommy
15.5k14376
15.5k14376
add a comment |
add a comment |
smitelli is a new contributor. Be nice, and check out our Code of Conduct.
smitelli is a new contributor. Be nice, and check out our Code of Conduct.
smitelli is a new contributor. Be nice, and check out our Code of Conduct.
smitelli is a new contributor. Be nice, and check out our Code of Conduct.
Thanks for contributing an answer to Retrocomputing Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fretrocomputing.stackexchange.com%2fquestions%2f9426%2fwas-the-picture-area-of-a-crt-a-parallelogram-instead-of-a-true-rectangle%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown