Greetings Google Researchers.   If anyone out there is watching the
various questions I ask, they will probably be saying --- that guy
should go to school!   They are correct, but it is easier to ask for
instant knowledge from the great Google Answers gang.    This time I
am asking for help understanding PIXELS.   Am I correct that a pixel
is a dot of light?   For example, if a manufacturer says "active
matrix screen supports a resolution of 1600 by 1024 pixels" how can I
translate that into size of the screen?   Is there a set number of
pixels per inch?   If not, what determines the number of pixels per
inch?   Please give me a primer on this so that I can understand how
pixels, resolution, and screen size all fit together to determine the
quality of picture one will see on their monitor.  Thank you.

Hi seattle-ga,
     Hmm..GA better than going to school? Looks to me that you just
want an excuse to bunk classes.  ;-)
     Anyways, its great to have you back. Lets see if we can satisfy
your curious mind this time.

     What is a PIXEL?
=====================
     The name Pixel stands for a PICture ELement. A pixel is a single
point in a graphic image. You can consider it the smallest piece of
information we store about an image. Graphics monitors display
pictures by dividing the display screen into thousands (or millions)
of pixels, arranged in rows and columns. The pixels are so close
together that they appear connected.

Image/Screen Resolution
========================
      When we talk of the resolution, we are referring to the number
of pixels that make up the image. Common screen resolutions are :
640x480, 800x600 etc. As you can see, the resolution is described as
(the number of pixels available horizontally) x (the number of pixels
available vertically).

How does Resolution affect quality?
===================================
       Simple! Higher resolution = better quality. If you have a
higher resolution image, that means you are using more pixels to make
up the image. More pixels = more information = better quality.

How Many Pixels in an inch?
===========================
       There is no answer to this question. A pixel has no predefined
size. Think of a pixel as a dot. You can draw a one inch dot or you
can draw a 1 mm dot.
    This is why you cannot determine screen size from the screen
resolution. A 14 inch monitor can display the screen at multiple
resolutions eg. 640x480 or 800x600. The size of a pixel displayed by
it at the 800x600 resolution is smaller than the size of the pixel it
uses at 640x480, but the overall screen size(14 inch) remains the
same. As you can see, the number of pixels per inch(ppi) determines
the screen resolution. Higher ppi = Higher resolution
    Another thing to note is that the number of ppi(and hence the
resolution) affects the size of the images and text being displayed.
An image of size, say, 100x100 pixels will appear larger at a lower
resolution of 640x480, than at a higher resolution of 800x600, due to
the lower ppi value at 640x480.

Colour Depth
============
     A very important component of image quality, is the Colour Depth.
Colour depth can be defined as the number of bits being used to store
colour information for a pixel. The larger the bit depth, the more
colours a pixel can take on. More colours = Better quality. The table
given below shows some of the common colour depths available, and the
number of colours they allow :
     Colour Depth    -   Number Of Colours
         1                      2
         8           -        256
        16           -      65535  
        24           -      millions of colours

Screen Size
============
      The monitor screen sizes are determined by the manufacturers,
and do not affect pixel size as such. However, small screened monitors
(such as 14/15 inch ones) are not capable of displaying high
resolution(say 1600 by 1024) images, because then the number of pixels
per inch(ppi) will be very large and hence, the size of a pixel too
small to be useful. This is why people prefer large screen (17 inch
and above) monitors.

Picture Quality
===============
      All the metrics defined above go into defining your picture
quality. A large screen size would mean that even at high resolutions,
the pixel size won't become too small, and this will result in a
clearer picture.
      Higher resolutions are obviously better, because higher
resolution = larger number of pixels making up the image = Better
quality.
      Larger colour depth allows your image to have more shades of
colour, thereby improving quality.
      So, for improved viewing pleasure, use a large monitor (17 inch
and above), set to a high resolution (1024x768 or higher) and high
colour depth(16 bit or more).

Some extra readings
====================
         
       - Computer Graphica : What Is a pixel ?
         ( http://www.computer-grafica.com/d16.asp )

       - PhotoELF - What is a Pixel
         ( http://www.photoelf.com/support/faq/pixel.shtml )

       - Understanding Monitors:Controlling Pixels, Resolution &
Screen Size
         ( http://www.smartcomputing.com/editorial/article.asp?article=articles%2Fpctoday%2Ftips%2F970134a%2Ehtml)

       - Screen Size and Resolution
         ( http://lowendpc.com/tech/resolution.shtml )

=========================================

Well, hope this helps.
If you need any clarifications, just ask!

Regards,
Theta-ga


==========================================
Google Search Terms Used :
       "What is a pixel"
       "what is dot pitch"

I now understand PIXELS!!!  Thank you theta!!!

heres some other junk you might find useful:

There are some standard pixel DPI's. 72 seems pretty common, I've seen
75, and some new systems are 96.

if you ever see 'dot pitch', that refers to the border space between
pixels. The lower, the better. '.28' used to be pretty common, '.25'
was better. I've seen '.29' on some crappy newer ones, and the Hitachi
Elite 19" professional monitor I bought the other day has a
surprisingly good '.22'.

Pixels are not necessarily square. Some unix systems have nonsquare
pixel monitors.