Bit

• A single binary digit
• Bits are always combined in units of 8

Byte - 8 bits

• 1 B = the storage required for a single character of text
• 10 B = the storage required for several words of text such as, "my computer"
• 100 B = the storage required for 12 words of text
• 500 B = the storage required for a paragraph of text

Kilobyte - Kb (Thousands) - 1,024 bytes

• 1 Kb = an 8 ½ x 11 double-spaced sheet of text
• 10 Kb = an 8 ½ x 11 single-spaced sheet of text
• 100 Kb = a low resolution (JPEG) 3 x 5 image
• 500 Kb = an 8 ½ x 11 sheet of text with 2 low resolution (JPEG) images or a 3.5" low density floppy

Megabyte - Mb (Millions) - 1,048,576 bytes

• 1 megabyte = one 8 ½ x 11 sheet of text with 7 low resolution (JPEG) images or a 3.5" high density floppy
• 2 Mb = 3,000 - 8 ½ x 11 sheets of single spaced text
• 5 Mb = an 8 Bit RGB Photoshop file 1050 x 1500 dpi (3 ½" x 5") 300 ppi
• 10 Mb = an 8 ½ x 11 sheet of text with 10 high resolution (TIFF) images
• 50 Mb = a Web site with 7,000 files with 3,000 screen pages - low resolution graphics (JPEG)
• 100 Mb = the storage capacity of a ZIP disk or 15 pages of high resolution graphics (TIFF) and text
• 250 Mb = Windows 98 operating system installation
• 500 Mb = the storage capacity of a CD ROM disk

Gigabyte - GB (Billions) - 1,073,741,824 bytes

• 1 Gb = 3 hours of a video with medium quality resolution
• 2 Gb = 4 medical x-ray images
• 5 Gb = the storage capacity of a DVD disk
• 100 Gb = the storage required for 20,000 pages of text with high resolution images

Terabyte - TB (Trillions) - 1,099,511,627,776 bytes

• 1 Tb = the storage required for the insurance records of 50,000 clients
• 2 Tb = the storage required for the medical imaging records of a regional medical center
• 5 Tb = the storage required for all of the medical records in the largest medical center
• 10 Tb = the storage required for every book published up to year 2000

The next level of storage is a quadrillion bytes (Petabytes) and continues to increase accordingly. The levels above Terabytes are as follows:

Petabytes - Pb 1,125,899,906,842,624 bytes

Exabytes - Eb 1,152,921,504,606,846,976 bytes

Zettabytes - Zb 1,180,591,620,717,411,303,424 bytes

Yottabytes - Yb 1,208,925,819,614,629,174,706,176 bytes

File Size Calculation

Scanned images, digital camera images, or edited images are all raster images. Thus, our calculations for file sizes will refer to the file sizes of raster images. As the image resolution changes or the image dimensions change, the size of the file required to store the image will also change. Factors such as sharper detail requiring more dpi's for print, will require larger files sizes, which slow down accessing, editing, output, and image transfer processes. Further, some output devices, video screens, and authoring software have limitations on the number of ppi they can support, so it becomes important to understand the limitations and work within the boundaries allowable.

Computers can display and manipulate image color by selecting and working within the various color modes. Page layout software provides different color modes for use in a variety of color tasks, such as capture and output. Some modes are best suited for specific types of images, while others may only serve to create large digital files, which are cumbersome to access or output. There are four modes currently used for imaging: bitmap, greyscale, RGB, and CYMK. Color modes are separated into single channels or color spaces each containing 8 bits of pixel depth or 8 bits of information that is captured and displayed uniformly. Color channels play a role in the calculations for determining file sizes so it becomes important to not only understand how to account for the channels but also to grasp the value of using different color modes to develop, produce, and manage images more effectively.

Proper management of digital images not only involves software tools, but also mathematical tools. The following calculations will be of value to gain an understanding in managing image files:

1. File resolution calculations to be used with a specific line screen
2. Pixel calculation to determine if the resolution is within allowable ranges for output
3. File size calculation for storage, output, or distribution of files
4. Color channel calculation to determine the total size of the file being created