What is the resolution of an image?

The resolution of a digital image relates to the number of pixels contained in the image file, or in a given part of it. For example, printer manufacturers rate their printers in dpi, or dots per inch. A printer that prints 300 dots per inch is not printing as high a resolution as a printer that prints 2400 dots per inch. The higher the dpi, the higher the resolution. Most digital devices, such as computer monitors, cameras, printers, and scanners, have resolutions reported in units of dots per inch (dpi). In general, if the size of an image remains the same, and the number of pixels in the image increases, the image becomes “smoother” and more pleasing to the eye. The resolution of an image is reported in units of pixels per inch (ppi). If the resolution of a device is low, then the smallest “tile” or pixel is quite large. This results in a “jagged” or pixelated image. Watches, VCRs, and the huge screens at stadiums often use large pixels to represent numbers. The numbers aren’t smooth, or very pleasing to look at, but they can be made with very few pixels.

What are some problems with resolution?

Sometimes viewing an image on different devices can cause confusion. For example, suppose we have an image of a stamp that is one inch wide and one inch high. The image is created for a printer that has a resolution of 300 dpi, and is composed of 300 pixels across and 300 pixels down. If we open that image on a display that has a resolution of 75dpi, the image will “look” like it is four inches wide and four inches high. An on-screen ruler might show us that the image is only one inch by one inch but it would look bigger. People are always surprised when they print out such an image and it looks very small. This is because they forget about the problems of scale caused by viewing an image in different resolutions.

What are bits?

The term bit is short for binary digit. A bit can take on one of two values, either "0" or "1". In black and white images, the number of bits per pixel specifies how many different shades of "gray" will be contained in each pixel. A one bit per pixel image only has two possible values, "0" which is black, and "1" which is white. A four bit per pixel image would have 16 possible shades of gray. As the number of bits per pixel increases, the possible number of shades of gray increases exponentially. For instance, an eight bit per pixel image would have 256 shades of gray, and would appear much smoother and more pleasing to the eye than a lower number of bits per pixel image.

What is compression?

The downside of using digital images is that they usually create large file sizes. Because they take up a great deal of space, methods were created to reduce the size of files through a process called compression. A digital image must store information about every single dot in the image. A black and white image of a baseball has many dots that make up the picture of the ball. In a given area, if 2000 individual white dots can be compressed to only a couple of pieces of information, the size of the digital images will be greatly reduced. A number of different compression techniques exist, some result in images that lose quality (called lossy) and some that do not lose any image quality (called lossless compression). JPEG is an example of a lossy compression technique, while GIF and TIFF are examples of lossless compression algorithms.

What is encryption?

Encryption is an encoding method that tries to hide information from others. For years, the military has relied on encryption to transmit secret messages from headquarters to soldiers in the field. The military needed to encrypt their messages so that the enemy would not know what information they were providing to their troops. In the modern world, on-line banking and other accounts rely on encryption to protect your information from others. Computer passwords, personal identification numbers (PINs), and credit card information can be encrypted for your protection. Encryption techniques rely on a key, which is a physical or virtual device that "unlocks" the code. For example, if a person's PIN number was 3434, and the encryption method's key was "add 4," the encrypted PIN that would be sent would be 7878. Only a person who had the key or who could figure out the key would know the "real" PIN value.

Communication Patterns and Learning

In order to understand each other, people must be able to communicate. Complex communication patterns have emerged in every culture, whether or not they use written communication (and many don't). Similarly, in order to understand issues within any discipline, scholars must be able to communicate. This often requires a vocabulary specific to the discipline. Sometimes, a word means two different things in two different areas of study. The word stress, for example, means one thing in building construction, and a different thing in psychology. Students should understand that communication between two individuals or groups requires a number of shared assumptions, and shared interpretation patterns.