The fifty Cent Version of Digital Imaging Bits Bytes Pixels Matrix Dynamic range Machine language Processors (8,10,12 bits etc.) Base 10 numbering Binary numbering system Hounsfield units (CT numbers)

OFF The Basics of Digital Imaging In this analogy the light bulb is a pixel on a monitor The switch is a bit (binary digit) in the computer circuitry

ON The Basics of Digital Imaging Flip the switch (binary digit or bit) and light up the bulb (pixel)

Row and columns of pixels form the matrix

Dynamic range of 2 (2 1 ) How is contrast added to an image? Magic switches. The more of them In the ON position, the brighter the light

ON OFF

ON

Dynamic range of 256 (2 8 )

OFF ON OFF ON OFF ON OFF ON OFF ON OFF ON More bits, in various configurations, create a greater dynamic range (analogous to the radiographic scale of contrast)

ON OFF An 8 bit processor can display a dynamic range of 256 (2 8 ) 8 bits = 1 byte

ON In computer circuitry 8 bits are grouped together 8 bits = 1 byte

This is a machine language computer code OFF ON OFF ON ON The language computers speak is binary (two numbers) That’s because bits are either ON (1) or OFF (0)

Human beans count in decimals (base 10) because They have 10 fingers and 10 toes ones hundreds thousands tens ten thousands Ten is raised to every power of itself to create columns of higher orders

Binary numbering By definition: Any number raised to the power of 0 is 1 Any number raised to the power of 1 is the number itself * Count from right to left * Each column is twice the previous * Pick any column and it will be one more than the sum of all the previous columns

Binary numbering = = = 127 Binary numbering system (344): In the base 2 numbering system all values are represented by 0 or 1. Zero = OFF when representing an open switch. One = ON. Examples: Columns are derived from: Columns:

= one byte = 256 shades of gray An 8 bit processor displays a dynamic range of = = 0 When all the bits are ON a pixel is illuminated as brightly as it could get. There are 255 possibilities of a bit or bits being ON. When all the bits are OFF the pixel is black = 256: Ergo, 8 bits stores a dynamic range of 256 from dark to bright.

An 8 bit processor displays a dynamic range of 256 What will a 9 bit processor display? 10 bit? 12 bit? 16 bit? bits bits bits What effect does increasing the dynamic range have? It increases the memory requirements dramatically!

OFF ON OFF ON ON = 55 What does this byte of computer memory do in this midsagittal MRI of the head? It defines how brightly one pixel, in the matrix of pixels, will be illuminated. In this case the decimal equivalent of the binary is 55.

This print out of the data in each pixel of the image matrix shows that the decimal number 55 is the shade of gray for the pixel in X axis 250, Y axis 217.

Image data like this may be printed out by service technicians for QA, calibration, and repair. The computer’s binary code is represented in decimal for the convenience of us The numbers in this area are fairly homogeneous and could represent the cerebrospinal fluid in the body of the lateral ventricle since is relatively close to zero, which is the value of water on the Hounsfield scale.

Bone = CT Numbers (Hounsfield Units) Based on Water = 0 Air = CT numbers (HU), express attenuation values relative to water The Hounsfield scale, or units, commonly called CT numbers, is the scale on which the brightness of pixels is based in digital systems.