The fifty Cent Version of Digital Imaging

BitsBytesPixelsMatrixDynamic rangeMachine languageProcessors (8,10,12 bits etc.)Base 10 numberingBinary numbering systemHounsfield units (CT numbers)

OFF

The Basics of Digital Imaging

In this analogy the light bulb is apixel 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 upthe bulb (pixel)

Row and columns of pixelsform the matrix

Dynamic range of 2 (21)

How is contrast added to an image?

Magic switches. The more of them In the ON position, the brighter the light

ONOFF

ON ON

Dynamic range of 256 (28)

OFF OFF OFF

ON ON ON

OFFON

OFF

ONOFF OFF

ON ONOFF

OFFON ON

ONOFF

ON

1 2 3

0

2

1

3

4

5

6

More bits, in various configurations,create a greater dynamic range (analogous to the radiographic scaleof contrast)

ON ON ONOFF OFF OFF OFF OFF

An 8 bit processor can display a dynamic range of 256 (28)

8 bits = 1 byte

ON ON ON ON ON ON ON ON

In computer circuitry 8 bits are grouped together

8 bits = 1 byte

10011011111010010001011101011001

This is a machine language computer code

OFF OFFON ON

OFFON ON

0 0 1 1 0 1 1 1

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

0123410 10 10 10 10

ones

hund

reds

thou

sand

s

tensten

thou

sand

s

Ten is raised to every powerof itself to create columnsof higher orders

Binary numbering

20

21

22

23

24

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

1248163264128256

20

21

22

23

24

= 140 0 0 0 0 1 1 1 0= 421 0 1 0 1 0

1 1 1 1 1 1 1

= 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:

1248163264128256

28

= one byte = 256 shades of gray

An 8 bit processor displays a dynamic range of 256

1 1 1 1 1 1 1 1 = 255

0 0 0 0 0 0 0 0 = 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.

255 + 1 = 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?

512 102411 bits 2048 409613 bits 819214 1638415 bits 22768 44536

What effect does increasing the dynamic range have?

It increases the memory requirements dramatically!

10011011111010010001011101011001

OFF OFFON ON

OFFON ON

0 0 1 1 0 1 1 0

ON

1241632

= 55

What does this byte of computermemory do in this midsagittal MRI of the head?

It defines how brightly one pixel, inthe matrix of pixels, will be illuminated.In this case the decimal equivalent of the binary 00110111 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 pixelin X axis 250, Y axis 217.

Image data like this may be printed out by servicetechnicians for QA,calibration, and repair.

The computer’s binarycode is represented in decimal for the convenienceof us

The numbers in this area are fairly homogeneousand could represent thecerebrospinal fluid in thebody of the lateral ventriclesince 39-55 is relatively close to zero, which is the value of water on the Hounsfield scale.

Bone = + 1000

CT Numbers (Hounsfield Units)

Based on Water = 0

Air = - 1000 CT numbers (HU), express attenuation values relative to water

The Hounsfield scale, or units, commonly called CT numbers, is thescale on which the brightness of pixels is based in digital systems.