Post on 28-Dec-2015
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
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
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
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.