15 bits and processing

Contrast

- determines the range of brilliancies that are displayed. Are the whites white? Are the blacks black? Bistable images are high contrast.

BISTABLE

2 choices - black or white on or off high contrast narrow dynamic range poor contrast resolution

How many bits are needed to represent 10 shades of gray? How many bits are needed to represent 11 shades of gray? . How many bits are needed represent 15 shades ot gray?

4 bits

Byte

A group of 8 bits is byte v, 2 bytes (16 bits) is a word. Example: Byte: 10011000 Word: 10011111 1011100o1

Note Binary

Binary numbers are based on 2, Decimal numbers are based on 10. v

Binary Digit,

Bit Binary Digit, the smallest amount of digital storage. A bit is bistable; having a value of either zero or one.

Brightness

Brightness - related to the brilliance of the image How 'lit up' is the image?

Bistable vs. Gray Scale Controls

Brightness Contrast

Scan converters

Changes the data format from penetrations (spokes) to horizontal lines of a display. Made gray scale displays possible.

Digital

Computer world: a variable attains only discrete values. » Measuring weight on a digital scale

Analog-to-Digital Conversion

Electrical signals created by the PZT are analog. However, a digital scan converter can only process computer information. So, the analog signal must be converted, or translated, into digital form for input into the scan converter. This is done by the Analog-to-Digital (A-to-D) Converter. A computer mouse is an a-to-d converter, taking hand motions and converting them to computer signals.

Digital-to-Analog Conversion

Information in the scan converter is digital. However, some displays are analog. When this is the case, the image data must be re-converted to analog form prior to display. Performed by the Digital-to-Analog (D-to-A) Converter. An IPOD is a d-to-a converter, taking computer files and converting them into sound waves in the form of music.

Postprocessing

Manipulating the data after it has been stored in the scan converter memory but prior to display. Increases versatility of the display process. This can be undone. Postprocessing is performed on frozen images.

Preprocessing

Manipulating the data before storage in the scan converter. Once pre-processing occurs, the data is altered forever. Preprocessing cannot be reversed or "undone".

Analog

Real world: a variable attains a continuum of values. v >> Actual weight of an individual True length of a piece of string

Analog

Real world: a variable attains a continuum of values. v >> Actual weight of an individual True length of a piece of string Digital

Dynamic Range or Log Compression

Related to ability of humans to see the gray scale differences in anatomic structures. Log compression lowers the high level echoes and boosts the low level echoes. The image data's dynamic range is reduced. Controlled by the sonographer.

Preprocessing

TGC dynamic range write magnification fill-in interpolation persistence (frame averaging) spatial compounding

Analog

The everyday, real world that we live in is analog.

Pixel Density

The more pixels per inch (called pixel density), the more detail in the image, spatial or detail resolution. v.

Pixel

The smallest element of a digital picture. If we divide the picture into a grid (checkerboard), each square is a pixel.

Digital

The world of computers is digital.

Binary number

a group of bits a series of zeroes and ones. Example: O010011001001 or 101 Digital (computer-based) means binary.

How to calculate the number of gray shades that a collection of bits can represent:

a word. 10011111 1011100o1 1. Find out how many bits are assigned to each pixel. 2. Multiply the number 2 by itself the same number of times as there are bits. That's the answer. • The number of gray shades displayed by 'n' bits is 2" What number of shades that can be represented by 10 bits? 210! 1024. v

Scan converters The image

can be manipulated in between the "storing" and the "displaying" of the data. For example, a black-on- white image can be inverted and turned into a white-on- black image.

Digital-to-Analog (D-to-A) conversion is less

common since many devices, such as printers and storage devices, are digital. Thus there is no longer a need to convert signals back to analog form.

Bistable vs. Gray Scale

high contrast low contrast

v Spatial resolution

is also related to the number of lines per frame.

A group of "bits"

is assigned to each pixel to store the gray scale color assigned to that pixel. The more bits per pixel, the more shades of gray, and the better is the contrast resolution.

• Spatial resolution on a digital display

is determined D the pixel density (the number of pixels per inch).

GRAY SCALE

many shades of gray multiple levels low contrast wide dynamic range good contrast resolution

Digital Scan Converter

microprocessor digitizes images. This converts the imane into a string of zeroes and ones which are stored in memory. The numbers (digital image data♥) can be processed and then re-converted for display as an image.

Computer memory is called

random access memory or RAM.

Postprocessing

read magnification 3-D rendering

Processing is "pre" or "post" based on

whether date stored in the scan converter. Ask the question, "Do I have the information in image form?" If "yes", then postprocessing.