what are Pixels ? 
what are MegaPixels ? 
what is Resolution ?
what is bit depth ?

What are Pixels ?
  •  Pixel (or Pel ) is an an abbreviation for picture element , The pixel is the smallest portion of an image that a computer is capable of displaying or printing.
  • Too few pixels and an image appears “blocky” because there is not enough detail to work with.
  • the more pixels you have ( in the photo ), the more RAM you need (to process more information ) and extra disk space to store them
What Are Megapixels?
  • A megapixel ( MP or Mpx ) is simply a unit of storage, whether internal or on a removable card. A megapixel is one million pixels 
  • A megapixel  is a term commonly used to describe how much data a digital camera can capture (the actual quality of a photo it is capable of producing) 
  • For example, if a camera can capture pictures at 2048 × 1536 pixels, it is referred to as having 3.1 megapixels (2048 × 1536 = 3,145,728 MP).
  • Professional photographers usually needs  more pixels than a normal consumer  
Note : More megapixels does not guarantee a better picture. beside MegaPixel there are many elements that  determine the quality of photo like shutter speed – camera sensors – focus  …. etc      
What is Resolution ?
  • When talking about Resolution you must specify the unit , and to specify the unit you need 1st to specify the device that you are working with  (screen – printer – scanner ) 
  • The term resolution is often used for a pixel count in digital imaging 
  • Resolution = number of pixel columns ( width ) x number of pixel rows (height) . for example as 640 by 480 
  • Columns and rows  are so close together that they appear connected. 
  • An image that is 2048 pixels in width and 1536 pixels in height has a total of 2048×1536 = 3,145,728 pixels or 3.1 megapixels (we can refer to it as 2048 by 1536 or a 3.1-megapixel image )

How to describe image  Resolution ?
there are many ways to describe image Resolution these ways are :
1- Dots Per Inch (dpi)

  • The most common term used to describe image resolution
  • dpi uses with Printers
  • To determine dpi, it is necessary to count the number of dots that can fit in a 1 inch × 1 inch area.
  • A higher dpi can mean smoother photographs or better looking images
  • example : Consumer printers easily print at 600 dpi or even higher.

2-Pixels Per Inch (ppi)

  • ppi is used in Computer monitors (Windows OS uses 96 ppi  - The Mac OS uses 72 ppi .
  • As computer monitors support variable resolution settings. so the actual ppi for a screen can vary greatly depending on the physical size of the screen  and the resolution being used by the computer’s graphics card.
  •  the standard measurement of resolution in Photoshop (and most computer programs) is ppi.
3-Samples Per Inch (spi)
  • Scanners don’t use dots (dpi), they use samples. 
  • A sample is when a scanner captures part of an image. 
  • Samples per inch (spi) is a measurement of how many samples are captured in 1inch 
  •  an increase in sampling leads to a better image
  • Consumer-level scanners can capture optical resolution ranging between 300 to 4800 spi.
 What is bit Depth ? 
  • it is one of the factors that affect the picture quality 
  • bit depth means the way colors are processed (it measures how much color is available for display or printing of each pixel).
  • A higher bit depth means that each pixel contains more information for describing the color.
  • The most common bit depth is 8-bit mode, which has a possible value of 256 intensity levels per color channel.

Some samples to describe the different between high resolution pictures (more pixels ) and low resolution pictures

    High Resolution
    Medium Resolution

    Low Resolution