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Why does monitor size change depending on color?

Posted on 2004-04-06
Medium Priority
Last Modified: 2013-11-08
I'd like as technical an answer as possible, since this isn't really a problem more of a curiosity.  I've noticed that on most monitors and possible TVs, the size of the screen changes slightly depending on the colors on the screen.

For example, my desktop has a blue background, and this window is mostly white.  It I switch between a maxmized notepad and this window, the screen doesn't change, but if I minimize and go back to my desktop, my screen shrinks by about 1-2 pixels on each side (more on the sides, but a bit on the top and bottom) then streches part way back.  It is noticably smaller on the background.

It doesn't really bother me, but I'm curious as to why it does this.  If it matters, it's a 19" CRT running at 1152 x 864, 85Hz.
Question by:grantemsley
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Expert Comment

ID: 10771664
i think it depends on the brightness , resolution and refresh rate also

my old monitor has started this problem too.

as a  wild guess, i think some poorly designed or ir-regulated power suply or related ckt can cause this...

elexctrical experts here can shed some more light i guess


Expert Comment

ID: 10771872
My new Compaq 17" certainly doesn't do this.
I'd say its something to do with your monitor....How old is it????

Perhaps advances in technology have eliminated this problem?

Expert Comment

ID: 10772591
two things:
first of all - this is probably just a light/shades thing.you know, vision illusion.
as you switch to darker colors,the screen might appear smaller.it happens.
second - this realy could be a problem with your P.S. - maybe it just doesnt fit a large screen as you have and it cant "push" it hard enough to keep the size the same on all views.
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Expert Comment

ID: 10772966
My girlfriends new 17" Relisys monitor looks like it changes size slightly depending on the colour of the window open.
Mine doesn't do it (19" CTX monitor that I've had for 4 years now). I've tried switching between the same colours on both monitors and only hers does it.

I think my little test proves that it's not an optical illusion caused by the human eye, but don't take my word for it!

Monitors use an enormous amount of power, perhaps some colours require less colour to display than others on the phosphorous? This might mean that power going into the electron gun 'dips' and 'spikes', perhaps causing a minor change in the refresh rate (0.1hz?), and as we all know, changing the refresh rate changes the size of the screen.

This is all me guessing here, so I'd probably wait till a certified electrician comments! :o)

Assisted Solution

lombardp earned 120 total points
ID: 10775941
It is very difficult to say why it happens, but the last two answer are quite good.

An electron beam draws pixels on screen one row after the other, going from left to right. The beam goes from left to right thanks to the horizontal magnetic deflection (there is also a vertical magnetic deflection to change row). The problem is that when the screen is very bright, someway the horizontal magnetic deflection slightly changes. I don't know the exact answer, but I think that when screen is very bright, there are a lot of electrons in the beam and some of them could affect the horizontal magnetic deflection.

Author Comment

ID: 10778665
kiranghag and asmodeusnz:  Its a monitor I got second hand about 6-8 months ago, and it's definately not top of the line for what I paid for it.  I can't be certain how old it is, but I think it was manufactured around 97-98.

yabelson:  it is definately not an optical illusion.  I also don't understand what my power supply would have to do with it, unless you mean the one in the monitor, but I read it as the one in the computer, and if you meant the monitor, I assume they put in enough power to properly run the device.

Unless anyone has a more detailed explaination to add, I'll split the points between Nilknarf and lombardp, who's answers seem to make the most sense.

Expert Comment

ID: 10778840
I'd say if you can visually see a change when minimizing and maximizing then I would say your monitor is starting to play up. Simple as that.
The fact is that it shouldn't do that at all.
I have 5 computers at my house, 2 for me, 1 for the wife, 1 for my son and 1 for my daughter.
None of these monitors (2x 17", 2 x 15", 1 x 14") replicated the problem you are having.

1 more thing to try is to set the resolution to 1280 x 1024.
1152 x 864 "Doesn't match" normal monitor resolutions. Do you know what I mean??
ie (640 x 480 for 14" monitors, 800 x 600 for 15" monitors, 1024 x 768 for 17" monitors, 1280 x 1024 for 19" monitors)
1152 x 864 is "In-between" and your monitor is obviously having problems displaying it properly.
All the developers here at work have their 19" monitors set at 1280 x 1024 (I set it myself) and they aren't having any problems at all.

So try 1280 x 1024 and see how that goes, it will probably fix the problem.

Expert Comment

ID: 10779404
I use 1280 x 960 @ 85hz constantly, it's my preferred resolution for my 19" monitor, it may be an "in-between" resolution, but as I said earlier, I don't experience the 'screen resizing phenomenon', so I don't think that the resolution has anything to do with it.

Also, I just tried my Girlfriends monitor at different resolutions just to check, and it still does the resizing thing, she runs it at 1024X768 @ 85hz normally.

Hope this helps you out grantemsley :o)

Expert Comment

ID: 10779458
>I use 1280 x 960
no such resolution....

Expert Comment

ID: 10779500
Don't be daft! :o) How come I was able to take this screenshot then?! :


And I've used that resolution with a GeForce Ti 4200 and a Radeon 9600XT Card.

Expert Comment

ID: 10780064
Hmm, Well thats bizarre........never seen that before.
My Geforce 4 doesn't have that resolution.....nor do any of my other 5 computers.....

Author Comment

ID: 10780284
Okay, I tried a variety of resolutions, color depths and refresh rates, and all do the same thing.  The monitor works fine, color is still good and everything.  Not quite as bright as I'd like, but no monitor is when you have the glare off the window it's pointing at.

I also did a little test to try a few more colors (opened a couple paints and drew a huge rectangle).  I made the following colors:  green, red, blue, black, white, yellow.
black --> white -- screen streches horizontally, compresses vertically, very noticable.
black --> red, green -- same effect, but smaller
black --> yellow -- almost as bad as white.

switching between RBG the effect is almost unnoticable, but still there.
swtiching between RBG to yellow is worse, and to white is almost as bad as black.

Again it's only a small amount, a couple pixels at worst.

Any other ideas of what might cause it?  I'm leaning towards Nilknarf's idea of a slightly changing refresh rate, since it's similar to the type of resizing I get when I change refresh rates, but not nearly as bad.

Expert Comment

ID: 10781359
I think I might have another idea! :o)
I just remembered that all monitors and TVs have 3 electron guns, one for red, one for green and one for blue. Is it possible that the three guns are simply not 100% in line with each other? (Poniting at the same spot) This might also cause a slight shift of the image for different colours. Once again, this isn't a proven fact, just my idea! :o)

Oh yes, and asmodeusnz, about the monitor resolution thing. Maybe some resolutions available are monitor or driver dependent?
All the monitors that I have come into contact with support 'odd resolutions', but maybe I've just been lucky! :o)

I just had a quick look through the technical specs of several ATI cards and nVidia cards and they all support a wide range of odd resolutions, including the ones grantemsley and I use, so it's probably a monitor/driver specific thing. And if I remember right, the standard microsoft drivers for my card supported 1280 x 960 as well, so it's probably just a monitor thing.

Accepted Solution

Nilknarf earned 160 total points
ID: 10782031
According to a hardware book on my shelf, colour CRT monitors do indeed have three independent electron guns for red, green and blue.

On the screen there are three colours of phosphor which react with their respective electrons. At the back of the electron gun is a cathode, this is where the electrons 'boil' off and are subsequently accelerated towards the phosphor-coated surface. The electron beams are focused using electromagnets. The electron then pass through a shadow mask (or aperture grill in some monitors) which has lots of holes in, these holes ensure that electrons only hit triads of red-green-blue phosphorus. Each one of these spots is a pixel as we know it.

There are two main circuits in monitors, the ‘drive board’ and the ‘raster drive board’. It is the raster drive board that contain the high-voltage circuits that actually drive the CRT and direct electron beams around the screen. On the raster board there is something called a ‘vertical sweep oscillator’, this is the thing that refreshes the screen (60, 70, 75, 85hz etc..).

So, from what I’ve gathered about monitor design I can make a good guess as to why the screen changes size when looking at different colours.

Firstly, my last idea about the red, green and blue electron guns being slightly misaligned cannot be true. If the electron guns were out, even by a pixel, the whole image would be blurry, which is not the case (at least on my girlfriends monitor, which has a sharp and clear image).

So I can theorise that power ‘spikes’ and ‘dips’ caused by differing power consumption from the different electron guns are effecting the vertical sweep oscillator, thus altering the refresh rate of the monitor by a tiny amount.

(Alternatively, the electromagnets that direct the electrons are affected by the power changes).

Well, you said you’d “like as technical an answer as possible”! :o)

I hope this rambling helps you out!

Author Comment

ID: 10784807
I think you got it Nilknarf.  I'll wait a little while to see if anyone else has any good ideas though.

and asmodeusnz, there is a program called power strip that will allow you to use "non standard" resolutions if your video card drivers don't support them.  From what I've seen, it seems that typically the default microsoft drivers don't have this resolutions available, but the manufactuer supplied drivers do.

Expert Comment

ID: 10785287
Yeah, I think you're right about the "non standard" monitor resolutions being available in manufacturers drivers. The basic Microsoft ones only support VESA (Video Electronics Standards Association) standard resolutions (800 x 600,  1024 x 768,  1280 x 1024  and  1600 x 1200).

Most of the standards were introduced by IBM, VGA, SVGA, XGA etc...

I think most monitors today support something called 'UXGA' - Ultra Extended Graphics Array - (It'll probably be 'Super Duper Ultra Extended Graphics Array' one day!) , I think that's the standard that allows non-standard resolutions. It's obviously not VESA approved or something.

Expert Comment

ID: 10912211
I don't see it with my system 9700pro/Hitachi Superscan elite 19.

It may not be the monitor at all but the signal from the video card changing slightly.

1.  Weak power supply inside the monitor
2.  Weak power supply in computer which in turn may effect the video card.
3.  Just a quirk with certain video cards.

one of those.


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