A lot of new digital camera buffs wonder why they can view their entire digital pictures on their computer screen but when they try to email that same photo, it comes out huge and unwieldy on the recipient's end.

Welcome to the world of pixels and file management.  Understanding pixels and file management is paramount for enjoying your own digital photos and for sharing them with your friends.

Remember how much fun it was to bring out the photo albums of your last trip to Bangladesh?  Digital photography has retained that ability and expanded on it in ways you can only imagine and only limited by the photo processing applications installed on your computer.

Film Versus Digital
In regular film photography, the image was stored as a (analog) chemical change on the film medium you selected and then developed into a negative and then that image was transferred onto a piece of photography paper for direct viewing.  The original film image was immutable for all practical purposes.  It was truly a "What You See Is What You Get" (WYSIWYG) photo environment.

Digital photography has liberated that immutable film medium.  Anything in a digital photo is subject to change at the whim of the person at the controls.  This change can be artistic, malicious, or faithful, dependent on the person at the controls and the desired end result of the photo image.

Artistic or Malicious?
To understand this digital photo manipulation process, you should know some details about digital photos and what information a digital photo file contains.

For starters, a digital photo is represented in a computer by a single file.  A file in a computer is simply a single named collection of digital data in a digital computer format.  The conventional computer format is bytes.  A byte is 8 bits of data, a bit is either a "1" or a "0."  A computer has no interest in what information the 8 bit byte contains, the computers job is simply to shuffle those 8 bit bytes in your photo file around, according to your whim and desire.  Processing any digital photo file can enhance it's contrast, brightness, or any other attribute you care to change, including putting a mustache on your pet cat.

Photo Files
If you inspected a photo file and it's characteristics, there are a few common things you will notice.  For starters, most photo files are labeled "name.jpg."  The .jpg refers to the type of photo file compression used. There are other photo file formats such as "raw" where there is no file compression used. Your camera may have the option of storing in this format as well.  However, .jpg is the most common compression technique and the most widely used, especially in the arena of handheld digital cameras.  

A dot JPG compression allows the camera to store a photo with a minimum of file data resulting in a smaller and more manageable data file.  Translation, there are significantly fewer bytes per file with the dot jpg format then the original "raw" uncompressed format would produce. 
Most fixed lens digital cameras produce files in the "dot jpg" format with a varying selection of two or three compression formats.  In general, the higher compression formats generate smaller dot jpg files at a cost of loss in photo detail.  Vice versa, the lower compression ratios generate bigger dot jpg files and more photo detail.  A purist or professional would indeed prefer the raw format photo file which allows the most flexibility in capturing the exact nature of the image the camera stored.

The Digital Image File
In film we know for instance, that there is an analog type process of storing an image using various photo sensitive chemicals exposed to light producing an image of what ever the camera was pointed at, when the shutter was opened for a split second.

In digital photography, there is a photo sensitive silicon chip in place of the film media, that is capable of looking at a single small piece of a photograph, storing its characteristics in a digital form and then moving on to record the next single small piece of the photo, ad infinitum until it has reproduced the entire image in a digital format limited only by the capabilities and size of the recording silicon photo processing chip, itself.

In addition to the photo sensitive chip in your camera there are other silicon devices called embedded computer chips with enough computer processing power to control every aspect of your photo shooting effort and internal file management.  No fooling, that digital camera with the photo sensitive silicon you are carrying, is actually a very small and compact version of a real personal computer. 

The digital camera can be made small because it is singularly purposely minded to process and produce a single photo file per image, only.  It is only reliant on you to specify and setup the file formats, exposure times, flash or not etc. and then to actually take a picture.  The result of that photo is stored on the cameras removable memory chip.

That specific photo file stored on the cameras memory can then be transferred to a personal computer for photo processing of the photo files, or directly for viewing on a TV or for making printed copies by taking to any local store that has a photo processing center.

The point of this is, there is an inordinate amount of technology embedded in any digital camera: optics, mechanics, and electronics.

The PIXEL Defined
Back to the pixel.  First, the definition of a pixel.  A pixel is the smallest digital element of a photo, when the term is applied to cameras.  Pixel (pix-el) is an acronym for a single "picture element."  In a digital photo, a pixel is a single picture element stored in a digital .jpg photo file. 

If your camera is rated at 1.2 mega pixels for instance, that is how many digital pixel elements (1,200,000) of a picture which are stored in the photo file; that make up and compose your .jpg digital photo file.   The rendered photo is then stored as a compressed dot jpg file on your camera memory chip, ready for you to transfer (download) to your computer for photo processing and viewing.

A 1.2 mega pixels photo does not translate to a 1.2 mega byte file size. The fact of the matter is, it may take several bytes of information to specify one pixel due to its color and brightness, etc.  If you looked at a raw format file, that file size is how many bytes are required to define a photo in raw format.  In .jpg format, compression is used and overall file size will vary dependent on the nature of the photo while the number of pixels remains constant.  In another words, .jpg file compression does not compress the number of pixels your camera takes, it just compresses the information that is used to describe a pixel.

Visualize a PIXEL
To imagine what a physical pixel is, take an eight by ten photo and draw 800 evenly spaced vertical lines and 1000 horizontal lines on it, creating little squares that are 0.010" on a side.  If you look at one single tiny square in this matrix, that is a pixel. Now imagine digitally storing the photo information for exactly one pixel image.  That single pixel can have several shades and colors in it but no matter how many shades and colors are represented, your camera has to select the closest shade and color representing that whole pixel and then store it digitally, progressing to the next pixel and then the next, until all 800,000 pixels and their image characteristics, have been digitally stored.