Digital Data and Binary Numbers - web.pdx.edu

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Digital Data and Binary Numbers

1.Digital Data 2. Binary numbers 3. How digital data is displayed on the monitor 4. Color 5. Data formats

1

Digital Remote Sensing Data -Matrix of rows and columns -Each pixel has a value -corresponds to brightness range of the color in each array

2

Binary Numbers

101001

3

Binary numbers are ‘base two digits’

193= 100+90+3

Hundreds

Tens

Ones

1

9

3

102

101

100

1

9

3

193 is really {(1*10*10)+(9*10)+(3*1)} =100+90+3

Binary numbers are ‘base two digits’

22

21

20

4

Binary numbers are ‘base two digits’

7= 4+2+1 3=0+1+1

22

21

20

1

1

1

22

21

20

0

1

1

Binary number= 111 Binary number= 11

- Each column represents one “bit”

22

21

20

1

1

1

- “8-bit image” stores 8 bits for each pixel (from 00000000-11111111)

28 = 256 (grayscale)

5

“Additive color” -Red, Green, and Blue are primary colors, all others can be made from them -yellow is not yellow, it is a combination of red and green

True Color

-Adds Red, Green, Blue arrays (each are 8 bits) together - “24-bit image”

6

But data collected from sensors not in 0-255 values, so must be converted. Signed vs. Unsigned

Maximum Possible Value

Other Names, Abbreviations & Symbols in Use

Number Type Name

No. of Bits

Minimum Possible Value

Unsigned Byte

8

0

255

Byte

Signed Short Integer

16

-32,768

32,767

Short, I2, Integer*2

Signed Long Integer

32

-2,147,483,648

2,147,483,647

Long, I4, Integer*4

Single Precision Floating Point (SAR image)

32

-3.403*1038

3.403*1038

Single, R4, Real*4

7

2 ways to convert: 1. Linear Mapping Take numerical range of data for each of the three colors and create a linear map (equal class intervals)

255

0

Problem: if you have outliers, image will be really dark or really light.

2 ways to convert: 2. Equalization (equal class frequencies) Produces image with more contrast

8

3 types of images can be stored and seen on the computer:

1. Color images a) Natural color images: Red, green, blue bands represent these actual colors as we see them

b) False color images: assign three bands that do not represent actual green blue and red

c) Pseudocolor image: one band, values range from 0-265 and levels of values are assigned a color on a look up table.

3 types of images can be stored and seen on the computer:

2. Grayscale images -One single band -has all colors, but colors have same values (127, 127, 127)

9

3 types of images can be stored and seen on the computer:

3. Labeled/classified images -pixels’ value represents a tag that indicates a property -used for landcover, e.g.: 1=ag., 2=water, etc.

Data Formats

10

Data format Describes the way that data is written to storage Usually contain: 1. Metadata (description about the data: projection, scan lines, pixels per line)

2. Image Data -pixel values of each band, arranged band by band

a) Band Sequential (BSQ)

b) Band Interleaved by Line (BIL)

11

File compression Lossy vs. Lossless Lossless: preserve all data -can always obtain original data - file size may not be compressed that much Lossy: loses some information in compression (JPEG) -smaller file sizes, easy sharing -cannot obtain original data

8888883333 Lossless: 8[6]3[4] Lossy: 83

File compression quadtree: as a 2-D compression scheme -image must be square and length must be a power of 2.

If many homogeneous areas, file will be compressed If many non-homogeneous areas are there, file may be much larger

12

System Processing

*System Processing: need to take info collected from sensors and turn into usable format

-remove noise -correct for pixel misalignments from sensors (called geometric correction in Ch.4) -pixels relocated (projected) (Chapter 4) -image geometry corrected determined by orbital height, direction of motion

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Digital Data and Binary Numbers - web.pdx.edu

Digital Data and Binary Numbers 1.Digital Data 2. Binary numbers 3. How digital data is displayed on the monitor 4. Color 5. Data formats 1 Digita...

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