Introduction to Pixels
Find a newspaper and look at the picture using a magnifying glass or low-power microscope. What do you see?
Unaided Eye
Magnifying Glass
Microscope (30x)

When looking at the paper with the unaided eye, it is easy to interpret what the image is. When the image is magnified, we find that the print is created using a series of dots. We can think of each of these dots as information, having a specific color and brightness.

The image in the center is magnified by a hand held magnifying glass. The image on the left is the end of the spider's leg as viewed by a 30x microscope.

As with printed information, digital cameras store images into points, or pixels. Each pixel has color information and brightness associated with it. The more pixels in the picture, the more detailed the image can be.

The movie below illustrates the importance of using the proper resolution so people can interpret the images. The first image represents a resolution of 10 pixels by 7.5 pixels. This means that there are 10 pixels across and 7.5 pixels down. Count the pixels to verify this. Each pixel has its own information, color and brightness.

What is the image?

Begin the movie by clicking on the arrow at the left hand lower corner. You can also move stepwise through the movie by moving the slider a frame at a time.

At what point can you figure out what the image represents?

Notice that the more pixels in the image, the more detailed the image is, to a certain extent. When you have more pixels within the set area than what your computer display is able to display, the image does not improve. Is there much of a difference between 320 x 240 pixels, and 640 x 480 pixels in this case?

Computer Displays and Image Resolution

Even the most inexpensive digital cameras have a resolution of at least 640 x 480 pixels. The viewing size of these images are determined by the resolution of the computer monitor you are using to view the images. Older computer monitors have a full screen resolution of 640 pixels x 480 pixels. If you viewed a 640 x 480 pixel image on a computer monitor with a full screen resolution of 640 x 480, the image would cover the entire screen of the monitor.

Newer computer monitors can have several different possible full screen resolutions, The size of the 640 x 480 picture could look quite small using a hi-resolution monitor. View the images below. These are views of the same 640 x 480 image of Niagara Falls on three different monitor resolutions: 1024 x 768, 800 x 600, and 640 x 480. Which view is the image shown on the 1024 x 768 monitor?

View A
View B
View C
When working on an image for display on the computer monitor, you need to consider the number of pixels across and down in the image for an image size for a given monitor resolution. You do not have to be concerned with the number of pixels PER INCH or pixels PER CENTIMETER. That will be determined by the type of monitor on which the image is viewed.
Printing and Image Resolution

If you are printing your image, you need to be concerned about two things: The number of pixels across and down in your image; AND the number of PIXELS PER INCH in your image. Ink-jet printers are popular, and can print good images using glossy photo paper. The printers have a maximum resolution, or dots per unit length, such as 300 dots per inch, or 300 dpi. Remember the newspaper print?

Some images are quite large, such as the NASA EarthKam images which can be downloaded to your computer. These images can be viewed on your monitors by scrolling from place to place on the image. You are not limited by your monitor size. However if you would try to print the 3060 by 2036 image on your 300 dpi ink-jet printer, you would almost completely cover your 8.5 x 11 inch sheet of paper. Suppose you wanted to print one of these images on a 4.5 by 3 inch area on a handout. What is the maximum number of pixels the printer could print across that rectangle (4.5 inches x 300 dots per inch)? Would the entire picture fit in that area without image modification?

Of course, some software packages allow you to insert an image in the document inside a given sized window, or you could change the print size of the image within the document, but you would not change the size of the file which would be added to your document. It would be most efficient if you could modify the image before inserting it into the document.

So would it fit? 1350 printed pixels across and 900 pixels down. You should reduce the size of your image to match your printer using the image software package which came with your computer.

Pixel Density of Selected Cameras

Listed below is a sample of the number of pixels per image which can be stored in a given camera. The pixel density usually influences the price of the digital cameras: the more pixels the higher price the camera. Note that you can find out the total number of pixels in the image by multiplying the number of pixels across by the number of pixels down.

Also note that the the camera needs to store color and intensity information of each pixel. Three of the cameras listed below are considered "megapixel" cameras. The Sony DSC-S30 is considered a 1.6 megapixel camera. What is the Olympus D-460 considered? Is the length to width proportion the same for all the cameras?

Model
Pixels Across (landscape)
Pixels Down (landscape)
Total Number of Pixels
Apple QuickTake
640
480
307,200
Sony Mavica FD7
640
480
307,200
Kodak DC260
768
512
393,216
"
1152
768
884,736
"
1536
1024
1,572,864
Olympus D-460
640
480
307,200
"
1280
960
1,228,800
Sony Cybershop DSC-S30
640
480
307,200
"
1024
768
786,432
"
1280
853 (3:2)
1,091,840
"
1280
960
1,,228.800
"
1472
1104
1,625,088

Image Compression

The Sony Mavica FD7 stores information for 307,200 pixels on the storage medium it uses. This includes information about location of the pixel, color, and intensity. The camera stores around 20 to 30 images on the diskette, depending on the types of shots being taken and the and the quality setting on the camera. This means for 30 images, there information stored on the diskette for up to 9.2 megapixels (30 shots x 307,200 pixels per shot). But the diskette stores only 1.4 Mb of information. How can the diskette store more information than the space available?

The camera uses a compression algorithm which takes the image information and compresses each file into a smaller file. Many cameras use a jpg compression, others use pict, and some give the option for no compression at all. Therefore, in order for a computer to understand the information about the image, it has to be able to decompress the files. Software is necessary in order for the computer to display the image. Most graphics software use standard compression/decompression techniques. Many computers include a picture viewing software package as standard on the hard drives, which means all you have to do is to select an image file, and the computer opens an appropriate graphics package to decompress the file for viewing.


©2000-2002 Dr.John Park for Science Junction, NC State University.
All rights reserved.
URL: http://www.ncsu.edu/sciencejunction/route/usetech/digitalcamera/res/resolution.html
Last updated 04/15/02

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