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I understand that the resolution of a display is the number of pixels it can accommodate vertically and horizontally. So if my resolution is 1920 x 1200 it means there are 1920 horizontal pixels and 1200 pixels vertically.

So here are my questions

  1. Is the pixel size fixed across all display devices? I feel it is not, but please clarify. If the size is different, how are images taken with one device is displayed in some other display device? What is the mapping?
  2. My PC monitor and Laptop monitor both are 17" in size but the resolutions supported are different. Why is that?
  3. What happens in the background when I reduce the resolution of my monitor? Why the displayed text/image grows bigger when I decrease the resolution and why does it grow smaller when the resolution is increased?
  4. What happens when a high resolution image is displayed on a low resolution screen and vice versa
  5. Many times I notice that large images are displayed as a smaller image such that they fit the display? (Like 'view actual size', 'fit to screen', 'stretch to fit screen' etc) How is the mapping done?
  6. Does the operating system has anything to do with the resolution? Is there anything like, this operating systems supports only this much resolution?

Throw some light on my questions. I very much appreciate any help.

Thanks in advance.

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3 Answers 3

Yo have to understand, what is hardware pixel and what is software pixel. The resolution, that you are setting in display settings, is just a conversion parameter.

The monitor screen size (17" for example) has fixed number of hardware pixels, which equal the maximum resolution of this specific monitor. One pixel in harware is one dot, that can have any color. When technologies evolve, the number of pixels that can be put into one mesurment unit grows: smaller and smaller pixels, like bigger and bigger screen sizes, gives more pixels = bigger maximum resolution. As with more pixels you can see smaller details of an image on screen.

The monitor allows you maximum resolution, your OS detects that and gives you only those resolutions that are allowed by monitor. If you give smaller software resolution than your monitor can handle, the video card simplifies the image going to the monitor. For example, making 4 pixels (in square), show the same color that 1 pixel of your image contain. The lower the resolution, the more pixels will be "unused" - marked with same color.

The image [typically] contains a fixed number of pixels - the same as your monitor. The size of pixel depends on monitor. So, if you have 1600x1200 screen, but are running at 800x600 resolution, your 800x600 image will show twice as large as it would be if viewed on 1600x1200 resolution.

If you view an image, that is 1600x1200 on 800x600 screen, you will see only 1/4 of it on screen. If you zoom it out, to make it show fullscreen, you will see all of it, but it will be simplified - the pixels, depending on ratio (in this case 1/4), will have calculated an average color/brightness from 4 pixels of your image, giving you and average color, from each of 4 pixels (in square) into 1 pixel on screen.

There are chains on which maximum resolution depends on - monitor screen size, pixel density for that screen, graphics card output possibilities, operation system output possibilities. If any of latter fails to support your monitor maximum resolution, you will not be able to us it at its full potential.

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Is the pixel size fixed across all display devices? I feel it is not, but please clarify. If the size is different, how are images taken with one device is displayed in some other display device? What is the mapping?

Pixel sizes can be different for different display devices but the difference in most of the cases will not be noticeable with naked eye. This really depends on the hardware manufacturing methods.

My PC monitor and Laptop monitor both are 17" in size but the resolutions supported are different. Why is that?

Because both can have different width to height ratio. Normally laptops have wider screens than the PC monitors.

What happens in the background when I reduce the resolution of my monitor? Why the displayed text/image grows bigger when I decrease the resolution and why does it grow smaller when the resolution is increased?

When you decrease the resolution, this means that you are simply mapping more hardware pixels to one software pixel. For example, your hardware can support four pixels but software is providing only one pixel data. The data will simply be stretched accordingly i.e., 1 pixel of data will be stretched to 4 pixels of hardware.

What happens when a high resolution image is displayed on a low resolution screen and vice versa You cannot display a higher resolution than the maximum hardware capacity. However, it is quite possible that you have set your screen resolution to less than what the hardware (read 'monitor') is capable of. In that case, an image having higher resolution than this will be squeezed (opposite of stretched) to fit into this resolution.

Many times I notice that large images are displayed as a smaller image such that they fit the display? (Like 'view actual size', 'fit to screen', 'stretch to fit screen' etc) How is the mapping done? Mapping is simply based on ratio of input to output where input is the software pixels and output is the hardware pixels.

Does the operating system has anything to do with the resolution? Is there anything like, this operating systems supports only this much resolution? No, this mapping is done by the software however, Operating systems provide certain built-in methods (Known as APIs in programming world) to accomplish this.

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I don't like this answer, as it has too many small inaccuracies (maybe I'm just pedantic). For #2, two screens can certainly be the same size and support different resolutions if they have different native ("hardware") resolutions - this also answers #1 that, no, pixels can be different sizes on different monitors because the one with higher resolution needs smaller pixels to fit a larger amount into the same area (which is certainly noticable to the naked eye). Also, scaling of images is typically done by the graphics card, not the software. –  BlueRaja Mar 31 '11 at 18:01
    
Also, to be a real nitpick, it is possible to disply a resolution higher than the monitor supports if your graphics card supports panning mode. –  BlueRaja Mar 31 '11 at 18:02
    
@aAamir: While it is common nowadays for laptops to have wide screens, it is also more common today that LCD monitors for desktops are wide screens as well. @BlueRaja: While the GPU may provide the processing necessary to scale images, would it not be accurate to say that software commands may dictate when and how scaling occurs? Also, with most scaling nowadays being based on algorithms, software can adapt to new algorithms and make them available to the users much more easily than hardware can. –  music2myear Mar 31 '11 at 18:32
    
@BlueRaja: Point taken for #2. For #1, I already said that pixel sizes can be different and I said that in 'most of the cases' those will not be visible to the naked eye. So, I thought you are over-pedantic here. For Scaling of images, well although graphics card provides these abilities but these have to be used by some software to take advantage of these abilities(or in other words, those APIs have to be used by some software). Furthermore, OP was asking whether it is done by OS so, the answer is that no, it is not done by OS. –  Aamir Apr 1 '11 at 4:36
    
@BlueRaja: Graphics card supporting Panning mode doesn't mean that monitor can display more than what its hardware allows at a given time. Only that Graphics card makes you believe that it is displaying more. –  Aamir Apr 1 '11 at 4:38
  1. The pixel size is not fixed. On LCD (flatscreen) monitors there is something called "Native Resolution", which is usually the maximum resolution, and corresponds 1 pixel sent from the graphics system correlating to one physical pixel on the LCD panel each of which contain a red, a green, and a blue ...something that are enabled in varying amounts to produce the desired color for that pixel. This is the resolution where images and text look their sharpest and clearest. On an old CRT (Ray Gun) tube, there is no native resolution because the monitor is shooting a nearly continuous but real-time modified stream of light at the screen which can be adjusted to work at whatever rate the video card is sending it information. On LCD monitors there is something called "Dot Pitch" which corresponds to the size of the individual pixels (I think). A smaller physical pixel allows a greater number of pixels to be squeezed on the screen.

  2. This shows the physical pixels are different sizes. You can look for settings related to DPI (Dots Per Inch) which in an image will correlate to how many pixels of that image will fit in an inch, similar to printers, but not in an "X by Y" notation like resolution, but in a "total number that fit in an inch" notation such as 75DPI or 90DPI (common for normal digital images and web graphics), 300DPI or 600DPI (common for basic laser printers and inkjets and high resolution pictures) or 1500DPI or 2400DPI (used in photo quality printing or extremely high resolution images for publication).

  3. This leads us to your third question. When you change the number of pixels that are fit onto your screen, this figure, correlated to the DPI of the image you've placed as your background, will essentially make the "inches" of the image match a larger or smaller section of your actual screen space. Windows offers several options for your desktop background image such as stretching or centering to allow the image to "fit" on your screen in the way you want. It does this by sampling the image differently, averaging the the pixels and showing only those that will correspond to pixels you've set as your desired resolution. When you lower the resolution that means there are less pixels sent to your screen, fewer pixels spanning across the display, and therefore few pixels of the image are necessary to fill the screen, resulting in the image (and all other visual elements on your screen) appearing larger. Raise the resolution and the opposite occurs. More pixels fit in a given area of your screen and therefore elements and pictures appear smaller and usually a little sharper.

  4. High resolution images will appear much less sharp than "normal" on a low resolution monitor. Most image viewing programs and operating systems automatically redraw or resize the image to fit on your screen or in the allowed space in the viewer program. And they usually do a very good job. If everything else looks sharp on your screen, regardless of the resolution, a super large image for which your operating system or viewer program is only showing a quarter or less of the pixels will still look as sharp as anything else.

  5. It's usually called sampling and it's the same thing that happens if you use your image manipulation program (like IrfanView or even Paint) to change the resolution of an image so you can send it as an email or post it to a webpage. The programs averages the pixels over a given area and then remove the ones that no longer fit in the desired output image. There are mathematical formulas that are very good at this and unless you're looking at an extremely poor example or an extremely zoomed in image, you'll hardly be able to tell the image was resized.

  6. Operating systems don't really care what resolution it is for the most part. Nowadays they are usually designed for resolutions higher than 800x600, while 20 years ago it was 640x480. At lower resolutions the OS UI elements can become so large the take up an inordinate amount of screen space. Windows or Mac OS would look pretty bad on a cell phone screen, which is one reason there are specialized OSes built for different size devices. But for the most part, it is the video card and monitor that determine the resolutions your system is capable of and the ones that look best.

Generally speaking, unless you have problems seeing smaller elements, I'd keep the screen resolution as high as the screen will allow. It will look sharpest and cleanest that way.

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1  
I think the "something" you're looking for in point 1 is "subpixel". –  Shinrai Mar 31 '11 at 14:18
    
You're probably right. I probably should've consulted Wikipedia for the more precise terminology. –  music2myear Mar 31 '11 at 15:18

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