resolution and dot pitch

[mevans]

I'm hoping someone can help me understand the connection between the dot pitch of a shadow mask and screen resolution. The dot pitch is fixed, yet you can change the screen resolution (for example 800x600 or 1024x768) which changes the pixels per inch displayed on the monitor. To increase the pixels per inch displayed on the monitor, the pixels have to be brought closer together. But how can this happen when the dot pitch of the shadow mask is fixed? Thanks. Yours, Mr. Confused.

 

[GoSharks]

In terms of a monitor there really is no concept of a pixel. Monochrome monitors did not have a mask structure. They used a single beam and no mask structure. The entire inside face of the CRT was coated in phosphor. From the monitors point of view the pixel was defined for the most part as the size of the electron beam. Same concept in a color monitor, only you have three beams and a mask to ensure the correct beam hits the correct color phosphor. For all the monitor cares, the video card could be building each line out of millions of active logical pixels. I like to think of a logical pixel as the speed the video card modulate the beam, this determines beam size.

The number of the holes in the mask and stripes in the aperture grill technically set the maximum resolution of the monitor. At lower resolutions the logical pixels simply cover more than one hole or slot. The logical pixels do not need to line up with the physical holes or slots nor is there any mechanism to do so.

At resolutions that exceed the number of holes or slots across the screen, logical pixels (electron beam size) no longer hit the phosphors accurately enough to guarantee constant colors or luminance. Some of the beam is intercepted by the mask structure. On monitors with lower horizontal dot / aperture pitch, more of the beam is intercepted by the mask. However an image will still be displayed and in practice will look OK.

I find it is best to run at a minimum of 85Hz-refresh rate and resolutions just below the maximum number of holes or slots in the mask to keep accurate colors and luminance. This is why I post 1600 x 1200 at 85Hz at the maximum resolution. You will note I do this to even the playing field for all products on my web site.

For example: A 19" monitor typically has a horizontal viewable area of 360mm. Let's assume it has a 0.22mm horizontal dot pitch. 360 / 0.22 = 1636 dots across the screen. A monitor with the same viewable area and a 0.24mm horizontal dot / aperture pitch has 1500. This is one reason 1600 horizontal resolution is so popular.

Vertically is not so much a problem. A typical 19" monitor has a vertical viewable area of 270mm. Aperture grill monitors have a 0.00mm vertical aperture pitch. Vertical resolution capability is virtually unlimited. As with every technology the trade off is more beam current hitting the phosphor making them more susceptible to screen burn. Use a screen saver!

Most shadow mask monitors have a 0.14mm vertical dot pitch. 270 / 0.14 = 1928 lines far more than any video card can produce at any decent refresh rate.

Jim Witkowski
Chief Hardware Engineer
Cornerstone / Monitorsdirect.com

<A HREF="http://www.monitorsdirect.com" target="_new">MonitorsDirect.com</A>

 

[mevans]

Thanks for your fast and detailed reply, Jim!

I see how you can consider a logical pixel as the speed at which the video card can modulate the beam for a monochrome monitor. With color though, there isn't a continuous phosphor screen. I'm wondering if you could also think of a pixel as a logical grouping of phosphor triads -- so depending on the resolution of the graphic you're displaying, a pixel could be represented by 1 triad or 9 triads, for example.

I think to really grasp all this, I need to learn more about monitor design and function. Do you know of any books or other references that cover this well? I'm a technical writer and I want to write a magazine article for tech writers that covers what's meant by the word resolution, from the perspective of the the graphic, the monitor, and the printer.

Thanks again,

Mark Evans

 

[GoSharks]

A triad is simply one red,green and blue phosphor. However like I said in my first post, this has nothing to due with a "Pixel".

There are many definitions of resolution when it comes to monitors. LCD monitors for example, use a matrix of cells, one red,green and blue (sub-pixels). Since LCD monitors use a matrix of cells, you can say that three sub pixels equals one pixel. This matrix of cells define the "Native" resolution of the monitor.

For more information see "Jims Corner" at Monitorsdirect.com

Jim Witkowski
Chief Hardware Engineer
Cornerstone / Monitorsdirect.com

<A HREF="http://www.monitorsdirect.com" target="_new">MonitorsDirect.com</A>

 

[compuhan]

In theory a pixel could be 1 triad if the electron beam was narrow enough. A pixel, in the most general form, is simply the smallest AREA of colored light that can be drawn by a computer onto a monitor screen. In short it's the smallest dot of colored light able to be produced by a monitor. In practical terms, the smallest area of screen able to give off a variably colored dot of light, at the current state of technology, is composed of a triad of phosphors (shadow mask); trio of filament rectangles (ap grille);trio of tiny lcd elements (lcd). However, 1 triad is rarely if ever possible since it is limited by the size of the electron beam.

Assuming you had all the technology down, the pixel then becomes smallest colored dot detectable by the human eye. Further assuming that we techonologically increases our acuity, it would then be limited to the physical ability of light to focus at the atomic level!

Higher resolutions are simply narrower beams of electrons sweeping across the monitor which result in smaller pixel size.

Resolution is simply the smallest defineable unit of something perceivable. In color monitor, it is a dot of colored light (pixel). In an printer it is a dot of ink or toner (dpi). Resolution is achieved to finer and finer levels by better and better instruments until physical properties prevent further reductionism.

Check out A+ certification exam guide by Michel Myers.

Quality is better than name brand, even regarding beloved AMD.

 

[GoSharks]

Spot size varies with resolution. Spot shape also varies depending on where the beam is landing on the screen. Since the beam is at right angles to the screen the shape is more circular, as the beam sweeps to the corners it becomes slightly oblong. This contributes to focus and convergence problems. This is typically why most monitors look good in the center and tend to fall of in focus as you get into the corners.


A 19” monitor for example typically has a horizontal viewable area of 360mm. Let’s assume it has a 0.22mm horizontal dot pitch. 360 / 0.22 = 1636 dots across the screen. A monitor with the same viewable area and a 0.24mm horizontal dot / aperture pitch has 1500. This is one reason 1600 horizontal resolution is so popular.

The people who who the A+ test need an education on how monitors really work.




<A HREF="http://www.monitorsdirect.com" target="_new">MonitorsDirect.com</A>

 

[compuhan]

The A+ certification is a very broad and basic test of computer hardware "mechanics". It not a rigorous exam covering expert monitor knowldege or even computer technology knowledge. A+ cert texts do provide any interested persons in understandign basic terminology like pixels.

Anyways, I don't think anyone was talking about the reasons behind the lack of focus caused by changing pixel size as an electron beam scans in an arc. I think electron beam size changing with resolutions was already mentioned in the last reply. I think your reply about pixel being a modulation of the electron beam (or something like that) was too technical and obfuscating to explain the simple concept of what pixel is.

Did you know that displaymate technology removed the cornerstone as being one of the best crts? I wonder why?

Quality is better than name brand, even regarding beloved AMD.

 

[GoSharks]

And like I said earlier, there is no concept of a “Pixel” on a CRT monitor. Thus the technical explanation of what really happens.

Displaymate removed the p1700 from their list of “Best Monitors” simply because we told them that the p1700 was discontinued almost one year ago. I was discontinued because Hitachi stopped making the CRT’s that where used in the p1700.

Jim Witkowski
Chief Hardware Engineer
Cornerstone / Monitorsdirect.com

<A HREF="http://www.monitorsdirect.com" target="_new">MonitorsDirect.com</A>

 

[compuhan]

What do you mean by "no concept of pixel on a crt monitor"? I think you are trying to say that a pixel is not an actual "thing". Remember, concepts don't have to be concrete things, concepts are abstract ideas and relationships of things or ideas. A pixel is definitely an abstract idea.

Quality is better than name brand, even regarding beloved AMD.