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Measurements in Fluid Mechanics 058:180:001 (ME:5180:0001) Time & Location: 2:30P - 3:20P MWF 218 MLH Office Hours: 4:00P – 5:00P MWF 223B-5 HL. Instructor: Lichuan Gui lichuan-gui@uiowa.edu http:// lcgui.net. Lecture 24 . Digital image & image processing.

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instructor lichuan gui lichuan gui@uiowa edu http lcgui net

Measurements in Fluid Mechanics058:180:001 (ME:5180:0001)Time & Location: 2:30P - 3:20P MWF 218 MLHOffice Hours: 4:00P – 5:00P MWF 223B-5 HL

Instructor: Lichuan Gui

lichuan-gui@uiowa.edu

http://lcgui.net

slide4

Digital image & image processing

Digital Image

  • Images constitute a continuous spatial distribution of the irradiance at a plane.
  • Digital images consist of pixels. Each pixel represents a square region of the image on a square grid.
  • Pixel value (gray value) represents intensity of the irradiance
    • 1-bit: 0  1
    • 8-bit: 0  255
    • 10-bit: 0  1,023
    • 12-bit: 0  4,095
    • 24-bit: 0  16,777,215
  • Bitmap data in file.
slide5

Digital image & image processing

Digital Image

  • Sufficient pixels make image look continuous
slide6

Digital image & image processing

Digital Image

  • Color models
  • True color model: (Red,Green,Blue)=(0255, 0255, 0255)
  • Others: Palettes/look-up table (LUT)/color map/index map/etc.
slide7

Digital image & image processing

Digital Image

  • Physical & logical pixels
slide8

Digital image & image processing

Digital Image

  • Digital PIV image sample

presented as a 2D-function G(x,y)

displayed on a PC screen

slide9

Digital image & image processing

Digital Image

  • 2D & 3D digital images
slide10

Digital image & image processing

Digital Image

  • Histogram (PDF) of digital image

PDF – Probability density function

slide11

Digital image & image processing

Digital Image Processing

  • Pixel operation

- Changing gray value of single pixel without considering the neighborhood

  • Filter operation

- Changing gray value of single pixel considering the neighborhood of (2r+1)(2r+1) pixels

  • Many others
slide12

Digital image & image processing

Pixel Operation

  • Linear transformation
slide13

Digital image & image processing

Pixel Operation

  • Binary operation

- gray value threshold

slide14

Digital image & image processing

Pixel Operation

  • Threshold

- gray value threshold

slide15

Digital image & image processing

Pixel Operation

  • Invert
  • Square
  • Root
slide16

Digital image & image processing

Digital Filter

  • Smooth filter
slide17

Digital image & image processing

Digital Filter

  • Gradient filter
slide18

Digital image & image processing

Digital Filter

  • Laplace filter
slide19

Digital image & image processing

Digital Filter

  • Regional normalization
slide20

Digital image & image processing

Digital Filter

  • (Removing) unsharp mask
slide21

Digital image & image processing

Digital Filter

  • Median
  • Expansion
  • Erosion
slide22

Digital image & image processing

Digital image files

  • Device independent image files
  • Device independent image files
  • Basic components of a digital image

- Microsoft Windows Bitmap “*.bmp”

- Tag Image File Format “*.tif”

- Graphics Interchange Format “*.gif”

- JPEG File Interchange Format “*.jpg”

- Many others

- Header, Palette, Bitmap Data, Footer etc.

  • Information in a bitmap header
  • File Identifier
  • File Version
  • Number of Lines per Image
  • Number of Pixels per Line
  • Number of Bits per Pixel
  • Number of Color Planes
  • Compression Type
  • X & Y Origin of Image
  • Text Description
  • Others
  • Unused Space
  • Device dependent image files

- Raw image formats (e.g. *.raww)

- TSI image file Format “*.img”

- DANTEC image file format “*.img”

- LAVISION image file format “*.img”

- Others

slide23

Digital image & image processing

Digital image files

  • Microsoft Windows Bitmap
  • 14-byte file header (Version 2.x +)Byte 12 File type, always 4D42h (“BM”);Byte 36 Size of the file in bytes;Byte 78 Reserved 1, always 0; Byte 910 Reserved 2, always 0; Byte 1114 Starting position of image data in bytes.
  • Bitmap headerByte 14 Size of this header in bits; Byte 58 Image width in pixels; (2 bytes for version 2.x) Byte 912 Image height in pixels; (2 bytes for version 2.x) Byte 1314 Number of color planes;Byte 1516 Number of bits per pixel; (end of version 2.x)Byte 1720 Compression methods used; Byte 2124 Size of bitmap in Bytes; Byte 2528 Horizontal resolution in pixels per meter; Byte 2932 Vertical resolution in pixels per meter; Byte 3336 Number of colors in the image; Byte 3740 Minimum number of important colors. (end of version 3.x)Up to 108 bytes forVersion 4.x
  • Color PaletteOne-, 4-, and 8-bit BMP files always contain a color palette24-bit BMP files never contain color palettes
slide24

Digital image & image processing

Project warm-up

  • Write a Matlab program to read gray values at the center and 4 corners of image: http://lcgui.net/lectures/lecture02/image01.bmp
  • Try to use pixel or filter operations to process the digital image
  • A 124×124-pixel uncompressed 8-bit gray-scale BMP fileFileheader: 14 bytesBitmap header: 40 bytes Color palette: 1024 bytesBitmap data: 15376 bytesTotal size: 16454 bytes
  • Simplest Matlab programA=imread('image01.bmp');A(1,1)A(1,124)A(124,1)A(124,124)A(62,62)imshow(A);