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    Pixels, Image Resolution, and Print Sizes   

    The quality of a digital picture is largely dependent upon the number and size of the digital camera pixels contained in
    the image. The image resolution is simply the information about the pixel density of the image. Higher resolution images
    can be printed to larger sizes with less loss of image quality than low resolution images.

    For reference purposes, there is a photo enlargement chart further down on this page that will give you an idea of the
    best image resolution needed for various photo print sizes.

    However, it is probably a good idea to first read the following information on pixels, image file sizes, and image resolution.
    That way, you will have a better understanding as to why certain images should only be enlarged and printed to certain
    sizes.

    What are Pixels?  The word Pixel is a shortened and combined version of the words Picture and Element. Every digital
    camera contains a device called the image sensor which has  millions of light capturing cells. The light  captured at each
    cell location is called a digital camera pixel. For the record, there are one million pixels in a megapixel.

    Digital Single Lens Reflex cameras like the Nikon D5300 have larger image sensors than a digital compact camera like
    the Canon Powershot ELPH 130 HS. The larger sensors produce larger pixels which leads to higher quality images.

    The colors and light intensity for each of the millions of individual pixels appear to be blended together when we view
    them as a printed picture or on a computer screen. Picture 1A below is an ordinary picture taken with a compact digital
    camera. Picture 1B shows a portion of picture 1A  with the pixels greatly magnified and exaggerated so you can see how
    pixels form an image. However, there will be thousands or millions more pixels in an area equivalent to picture #1B  when
    you take your pictures.
















    Image File Size: The file size of an image is expressed by the total number of pixels in the width and height of an image.
    For instance a file size might be written as 3,456 X 2,304. That means there are 3,456 pixels in each row of pixels in the
    image from left to right, and 2,304 pixels in each column of pixels from top to bottom.

    To find the total # of pixels in an image, just multiply the # of pixels in the width of the image by the # of pixels in the
    height of the image. (3,456 X 2,304=7,962,624 ) Usually the total amount of pixels is rounded up or down  to the nearest
    megapixel. So in this case the image might be called an 8 Megapixel picture although it does not contain a full 8 million
    pixels.

    Although digital cameras are often marketed with emphasis on the total # of megapixels available for an image, they all
    have settings which allow the photographer to take pictures with smaller file sizes. That feature can save space on your
    cameras memory card or in your computer hard drive. Also, images with smaller file sizes are easier to send and
    download when using email. Taking pictures at different file sizes will make more sense as you continue to read about
    image resolution and print sizes.

    Image Resolution: In general terms, image resolution in digital photography refers to the amount of information
    contained in an image file. That information is the amount of pixels contained in any digital picture you take. A picture file
    size 4,000 x 3,000 will have a higher picture resolution than a file size 2,000 x 1,500. Higher resolution pictures will be
    sharper, clearer, and more accurately reproduced when printed, or when they are viewed on a computer screen.

    More specifically, image resolution refers to density in terms of Pixels Per Inch (PPI) or Dots Per Inch (DPI) rather than
    the size of the whole file. Sometimes the terms PPI and DPI are incorrectly used interchangeably. In this tutorial, PPI
    refers to the resolution of an image when viewed on a computer screen. DPI refers to the output of a machine such as an
    ink jet printer. In other words, DPI refers to the number of dots of ink per inch used to produce an image on paper.

    Image resolution is usually written as numbers such as 72 PPI, or 300 DPI. What those numbers mean is that a particular
    image file contains 72 pixels (PPI) or 300 dots (DPI) within a one square inch area of the file. That will be 72 PPI or 300
    DPI from left to right as well as from top to bottom for each inch of the file. That information is important when it comes to
    how your pictures will be displayed.

    Computer screens are able to show clear and sharp images at low screen resolutions such as 72 PPI or 96 PPI. If you
    take pictures that will be for on screen viewing only, you can set your camera to a low image quality setting such as one
    megapixel or less. Taking pictures at high quality settings like 14 megapixels will not make the image look better on a 72
    PPI screen. However, you will definitely need to set your camera to higher quality settings if your are going to make
    enlarged prints of the pictures you take.

    Calculating Maximum print sizes: As previously mentioned, to view pictures clearly on a computer monitor, the screen
    only needs an output resolution of 72 PPI or 96 PPI. However, in order for a printed image to be sharp and clear, the
    output resolution from the printer needs to be much higher. A printer output resolution from 140 DPI to 300 DPI is a good
    range for making prints from your image files. (that is with 300 DPI being professional grade printing)












                                                               
                                                           














                                                                   
    The photo enlargement chart shown above will gives the approximate maximum print sizes (in inches) to which you may
    enlarge your pictures and retain good quality. Take note that the maximum print sizes listed are guidelines and prints can
    be enlarged to sizes slightly larger than those listed. However, a 3MP image that is enlarged to 20 x 15.0 size will be a
    very poor quality print. Making prints smaller than the recommended maximum for the file size listed is not a problem. The
    prints will still be very high quality.

    The photo enlargement chart shows exact print sizes in inches. However, in reality those sizes are usually rounded off to
    match the standard printing paper sizes available. Some of the more common print sizes are 4X6, 5X7, 8X10, 10X13,
    11X14, and 16X20.

    It is actually pretty easy to determine the maximum print size you can make from your digital images. First you need to
    determine how many DPI (dots per inch)  will be used when the file is being printed. To keep it simple, lets say the printer
    output resolution will be 200 DPI. If your image file size is 2,000 X 1,600 you will be able to get a quality print size up to
    about 10 X 8.

    The math involved in coming up with that size print is to simply divide the # of pixels in the width of the file by the 200 DPI.
    (2,000/200=10). Next,  divide the # of pixels in the height of the file by 200. (1600/200=8). So there you have it. A file size
    of 2,000 pixels X 1600 pixels can be printed to make a good quality 10 X 8 photo when printed at 200 DPI.

    If you decide to make a print at 300DPI from the same image file, you will have a print with better resolution. However the
    maximum size for a quality print will be smaller. Lets do the math.... 2,000/300=6.6. Next, 1,600/300=5.3. So if you round
    the numbers out, the maximum standard size for that print will be about 5 X 7.

    Of course you won't have to do this type calculation every time you take a picture. Just keep in mind that when you are
    planning to take pictures that will be printed and enlarged, use one of your cameras' larger file size settings.
Picture 1A
Picture 1B, Example of pixels
    Photo Enlargement Chart
  File Size               
  
(Pixels)
Megapixels
Maximum Print Size
 @200 DPI
Maximum Print
Size @300 DP
I
    1,600 x 1,200
    2MP
      8.0 X 6.0
    5.3 X 4.0
    2,048 x 1536
    3MP
    10.2 X  7.6  
    6.8 X 5.1
    2,592 x 1944
    5MP
    12.9 X 9.7
    8.6 X 6.4
    3,072 x 2304
    7MP
    15.3 X 11.5
    10.2 X 7.6
    3,264 x 2,448
    8MP
    16.3 X 12.2
    10.8 X 8.1
    3,648 x 2,736
    10MP
    18.2 X 13.6
    12.1 X 9.1
    4,000 x 3,000
    12MP
    20.0 X 15.0
    13.3 X 10
    4,288 x 3,216
    14MP
    21.4 X 16.8
    14.2 X 10.7
Original picture of flower
Example of flower showing pixels (pixelated)
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