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. It can be helpful if you are thinking about ordering
enlarged prints or canvas prints of your pictures from an online printer like Shutterfly.com or Mixbook.
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 to
certain print 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
Digital SLR cameras like the Nikon D5300 have larger image sensors than a digital compact camera like the Canon
Powershot ELPH 130 HS or a camera phone like the Samsung Galaxy S5. The larger sensors found in Digital SLR
cameras produce larger pixels which leads to higher quality images. However, the image sensors found in the other
types of cameras produce great images for the average photographer.
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 that
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 number of pixels in an image, just multiply the number of pixels in the width of the image by the
number 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 number 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 or in your computer hard drive.
Also, images with smaller file sizes are easier to send and download when using email or social media. Taking
pictures at different file sizes will make more sense as you continue to read about image resolution and print sizes.
If the pictures you have already taken are large files, many photo editing programs have functions which allow you to
reduce the size of an image file. Adobe Photoshop Elements is the best known photo editing software from which you
can change file sizes as well as enhance and/or fix your images.
Image Resolution: In general terms, image resolution refers to the amount of digital information contained in an
image file. A picture file size of 4,000 x 3,000 pixels will have a higher image resolution than a file size of 2,000 x
1,500 pixels. Higher resolution pictures will be sharper, clearer, and more accurately reproduced when printed.
More specifically, image resolution refers to pixel density in terms of Pixels Per Inch (PPI) rather than the size of the
whole image file. PPI is the number of pixels contained in one square inch of an image file. Computer screens are
able to show clear and sharp images at low screen resolutions such as 72 PPI or 96 PPI.
If you will be taking pictures that are intended for on screen viewing only, you can set your camera to a low resolution
setting like 2 or 3 megapixels. The images will look fine on a computer screen. Taking your pictures at a higher
quality setting like 14 megapixels will not make the image look better on a 72 PPI computer screen.
On the other hand, it is absolutely necessary to set your camera to one of its highest quality settings if you are going
to make enlarged prints of your images on photo paper. A picture taken at a 2 megapixel setting will make a very
poor quality 11 X 14 size printed picture. If you have a 14 megapixel camera and know that you will be making
enlarged prints from your images, use the 14 megapixel setting to ensure that you will get the best quality prints.
high resolution prints up to size 8.5 X 11. If you don't want to make your own prints or need high quality prints up to
20 X 30 size, you can order them online from Shutterfly.
PPI. DPI refers to the number of dots of ink per inch used by a printing device to produce a picture on photo paper.
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 just 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 number of pixels in the width of the file by
the 200 DPI. (2,000/200=10). Next, divide the number 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.