Number 284 - January 2007
What's in a Megapixel?
by Hu Filleul, BB&C, Victoria, BC
   I have a neat little Panasonic Lumix digital camera that hangs around my neck and fits nicely into my shirt pocket. People see it and are impressed by its small size and "big" screen. Invariably, the first thing they ask is "How many megapixels does it have?" I feel like saying "What bloody difference does that make?" It is however more BB&C-friendly to just say, "five", and leave it at that. The whole sales myth about the more megapixels the better the camera has been out of hand since digital cameras were invented.

   Before I get to the subject of Megapixels, I will remind the reader that we have a bank of newsletter articles on the subject of digital cameras. Just go to our website at www.bbc.org, select Newsletter then:

   Click on Newsletter to bring up the following links:
   
  • Issue
    •    
  • Author
    •    
  • Vendor
    •    
  • Category
    •    
  • Topic


    •    Select Topic and then Cameras. The following informative articles plus more are there for anyone to read. Even though they are several years old, the basics still apply, just like with arithmetic.

       October 2001 Choosing a Digital Camera by Grant Fuller
    www.bbc.org/newsletter/oct01nl/camera.html

       December 2002 Gone Digital by Arlene Bolokoski
    www.bbc.org/newsletter/dec02nl/digital.html

       April 2003 Choosing a Digital Still Camera by Ira Wilsker
    www.bbc.org/newsletter/apr03nl/camera.html

       February 2004 Digital Photography Pocket Guide by Derrick Story reviewed by Les Benson
    www.bbc.org/newsletter/feb04nl/digitalguide.html

       September 2004 Digital Photography Hacks 100 Industrial-Strength Tips & Tools by Derrick Story reviewed by Ken Beattie.
    www.bbc.org/newsletter/sep04nl/digitalphotohacks.html

       On with the subject

    What is a pixel?
       Here (slightly edited for readability) is what the Wikipedia free encyclopedia has to say about a pixel. "A 'pixel' (short for 'pic' ture 'el' ement, using the common abbreviation "pix" for "picture") is one of the many tiny "dots" that make up the representation of a picture in a computer's memory. Each such information element is not really a dot, nor a square, but an abstract sample (signal)|sample. With care, pixels in an image can be reproduced at any size without the appearance of visible dots or squares; but in many contexts, they are reproduced as dots or squares and can be visibly distinct when not fine enough. The Intensity (physics)|intensity of each pixel is variable; in color systems, each pixel has typically three or four dimensions of variability such as RGB color model, red, green and blue, or CMYK color model, cyan, magenta, yellow and black".

       That is just the first paragraph. There is another 16Kb of information

    What is a Megapixel?
       Wikipedia: http://en.wikipedia.org/wiki/Megapixel "A megapixel is 1 million pixels, and is used not only for the number of pixels in an image, but also often to express the number of sensor elements of digital cameras or the number of display elements of computer display | digital displays. For example, a camera with an array of 2048W1536 sensor elements is commonly said to have "3.1 megapixels" (2048 x 1536 = 3,145,728)."

    What are Photo Sensitive Electronics?
       Wikipedia: "Digital cameras use photosensitive electronics, either Charge-coupled device (CCD) or CMOS image sensors, consisting of a large number of single sensor elements, each of which records a measured intensity level. In most digital cameras, the sensor array is covered with a patterned color filter mosaic having red, green, and blue regions in the Bayer filter arrangement, so that each sensor element can record the intensity of a single primary color of light. The camera interpolates the color information of neighboring sensor elements, through a
    process called de-mosaicing, to create the final image. These sensor elements are often called "pixels", even though they only record 1 channel (only red, or green, or blue) of the final color image. Thus, a so-called "N-megapixel" camera that produces an N-megapixel image provides only one-third of the information that an image of the same size could get from a scanner. Thus, certain color contrasts may look fuzzier than others, depending on the allocation of the primary colors (green has twice as many elements as red or blue in the Bayer arrangement).

       In contrast to conventional image sensors, the Foveon X3 sensor uses three layers of sensor elements, so that it detects red, green, and blue intensity at each array location. This structure eliminates the need for de-mosaicing and eliminates the associated image artifacts, such as color blurring around sharp edges. Citing the precedent established by mosaic sensors, Foveon counts each single-color sensor element as a pixel, even though the native output file size has only one pixel per three camera pixels. www.x3f.info/technotes/x3pixel/pixelpage.html Foveon X3 Pixel Page. With this method of counting, an N-megapixel Foveon X3 sensor therefore captures the same amount of information as an N-megapixel Bayer-mosaic sensor, though it packs the information into fewer image pixels, without any interpolation."

       So What?

       I chose to quote from Wikipedia's online encyclopedia because so much of the other information on the internet was protected by copyright. If you want to get at this information just Google the word 'megapixel'. I will quote one line about the myth of megapixel importance from a copyright article at kenrockwell.com http://kenrockwell.com. "The megapixel myth is also prevalent because men always want a single number by which something's goodness can be judged."

       There are many factors besides the Megapixel number to consider when buying a digital camera including the buyer's attitude towards photography and the depth of his or her pockets.



    The happy brother in the photo is holding a big lens old Olympus 1.4 megapixel camera while the grump has just been asked again how many mega-pixels he owns in his Panasonic mini.





    For good advice on digital photography, join the BB&C Digital Camera SIG.

       Copyright (C) 1990-2006 by Big Blue and Cousins: The Greater Victoria Personal Computer Users' Association. www.bbc.org
      Number 284 - January 2007