Photography
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                    Pixels and Digital Cameras
                                                                                                 by Wayne Rockwell

Most digital cameras today boast of greater resolution and picture quality.  What does that mean to the amateur or occasional photographer?  
You hear of cameras with
3 megapixals up to 6 or 7 megapixals.  What is that?  The book that comes with the camera explains all the buttons,
bells and whistles, but does not explain megapixels.  Most people do not like to work with numbers much, but it is necessary to understand
pixels.  So here's my attempt to explain pixels.  I'll try not to involve too many numbers.

To understand pixels, one must first remember the good old days when you took pictures on film and let the
development labs worry about pixels.  But, they didn't really have to, because the exposed negative just captured
the image that was reflected through the lens.  It was all there and the only thing that affected quality was the
size of the negative.  The bigger the negative was, the larger the picture that could be produced.  

When the world went digital, the pixel was invented.

So what is a pixel?
 If you divided a picture in hundreds of horizontal and vertical lines, you would actually have
a large number of little squares that when put together, created the picture.  Each square is a
pixel.  So, when
a digital camera says it has 1-megapixel capabilities, it means that the total number of horizontal and vertical
squares produced when a picture is taken equals 1 megapixel (1,000,000 pixels).

A 3 megapixel camera produces a picture that has 3 million pixels in its makeup.  If all the pictures were the
same size in each camera, it would be easy to understand why a camera that produces more pixels would be a
better quality camera.  Here is where the camera makers are not forthcoming with information.  What they don't
tell you is that as far as I can tell,
every digital camera produces pictures that have 72 pixels per inch per picture
both horizontal and vertical
.  The only difference is that a 3 megapixel camera produces a larger picture than a 1 me-
gapixel camera and a 5 megapixel camera produces an even larger picture yet.  The reason I say "as far as I can tell"
is that I have not tried all cameras or studied the information on all cameras.  There may be some out there different,
but they probably are not in the amateur photographer's price range.

Conclusion:  For video uses only, your camera purchase decision should be based on features other than the number of pixels.


Pixels, Digital Cameras and Printing 4x3 Inch Photos

Why is a 3 megapixel camera better than a 1 megapixel camera?  It really depends on how you intend to reproduce the picture.  The reason
cameras produce pictures at 72 pixels per inch is that this format is standard in video uses such as television and DVD.
 So there is no
noticeable difference in quality when viewing pictures on a TV or DVD.  The difference appears when you are cropping and/or printing these
pictures.  If you are not familiar with the term cropping, I will explain it later.  But first let's talk about printing.

Even the most inexpensive of printers these days are capable of printing at 300 dots per inch (dpi).  Most are capable of printing at 600 dpi and
you can buy relatively affordable printers that print at 1200 dpi and above.  You may have noticed that
with cameras it's called pixels per inch
and with printers it is call dots per inch.
 The terms are hardware specific, but relate to the same principal.  A printer prints a specific number of
dots of ink per inch on the paper whereas a TV displays a specific number of pixels per inch on the screen.  In either case, combining the dots or
pixels creates the picture.

So how does this affect quality?  If we're printing a picture that has 72 pixels per inch from a 1-megapixel camera on 4x3 printer paper we've got a
problem.  (Here is where I have to crunch some numbers, so please bear with me.)  Let's figure it out.  

                       Four inches times 72 pixels (dots) per inch equals 288 pixels (dots) on the vertical line.  
                       Three inches times 72 pixels (dots) equals 216 pixels (dots) on the horizontal line.  
                       The total picture would have 288 times 216 or 62,208 pixels.  That's way short of one million.

So where did the other pixels go?  If you're printing this picture at a store or camera shop that has conversion capabilities, the machine that you
are printing on actually crunches the picture down for you.  The size of the picture taken by a 1-megapixel camera is approximately 16 inches x12
inches.  

                       16 x 72 = 1152 pixels and 12 x 72 = 864 pixels and
                       864 x 1152 = 995,328 pixels

The machine makes this picture into a 4x3 by increasing the number of pixels per inch.  
The 4x3 picture is 1/4th the size of the 16x12 so there
has to be four times as many pixels per inch to reduce this picture to 4x3.  Four times seventy two equals two hundred eighty eight pixels
(dots) per inch.  With more pixels or dots per inch, the picture can be reproduced at a higher quality level making details sharper and more
distinct.  So a 1-megapixel camera can produce a reasonably good quality 4x3 inch picture on a 300 dpi printer.
 That's what most amateur
photographers get with their snapshot cameras.  If you try to get larger pictures, then the picture quality begins to deteriorate.   

Conclusion: If you have a printer with more than 300 dpi capabilities and all you want is 4x3 inch prints, then you are not using all your printer's
abilities.  If you want prints larger than 4x3 inch, then you need a camera with a higher quality output capability.  If all you want is 4x3 inch prints
and video reproduction without cropping much, then a 1-megapixel camera and 300 dpi printer should serve you fine.


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About the Author:

Wayne Rockwell
Wayne Rockwell is a professional videographer at Legacy Pictures to Video (
http://www.picstovid.com) and specializes in Photo Video Montage
creation and Photo Retouching.
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This example shows an image with a portion greatly enlarged, in  
                  which the individual pixels are rendered as little
                  squares and can easily be seen.
                  Source:
Wikipedia
More About Pixels and Color

In a color image, each pixel can be described using its hue, saturation, and value (HSV), but is usually represented instead  
as the red, green, and blue intensities (in its RGB color space).

The number of distinct colors that can be represented by a pixel depends on the number of bits per pixel (bpp). The  
maximum number of colors a pixel can take can be found by taking two to the power of the color depth. For example,
common values are
          8 bpp, 28 = 256 colors
          16 bpp, 216 = 65536 colors; known as Highcolor or Thousands
          24 bpp, 224 = 16,777,216 colors; known as Truecolor or Millions
          48 bpp; for all practical purposes a continuous colorspace; used in many flatbed scanners and for                 
                         professional work.

Source: Wikipedia
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