1. 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

2. 2 Lecture 24. Digital image & image processing

3. 3 Digital image & image processing Digital Image

4. 4 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.

5. 5 Digital image & image processing Digital Image Sufficient pixels make image look continuous

6. 6 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.

7. 7 Digital image & image processing Digital Image Physical & logical pixels

8. 8 Digital image & image processing Digital Image Digital PIV image sample displayed on a PC screen presented as a 2D-function G(x,y)

9. 9 Digital image & image processing Digital Image 2D & 3D digital images

10. 10 Digital image & image processing Digital Image Histogram (PDF) of digital image PDF – Probability density function

11. 11 Digital image & image processing Digital Image Processing Pixel operation Filter operation Many others - Changing gray value of single pixel without considering the neighborhood - Changing gray value of single pixel considering the neighborhood of (2r+1)  (2r+1) pixels

12. 12 Digital image & image processing Pixel Operation Linear transformation

13. 13 Digital image & image processing Pixel Operation Binary operation

14. 14 Digital image & image processing Pixel Operation Threshold

15. 15 Digital image & image processing Pixel Operation Invert Square Root

16. 16 Digital image & image processing Digital Filter Smooth filter

17. 17 Digital image & image processing Digital Filter Gradient filter

18. 18 Digital image & image processing Digital Filter Laplace filter

19. 19 Digital image & image processing Digital Filter Regional normalization

20. 20 Digital image & image processing Digital Filter (Removing) unsharp mask

21. 21 Digital image & image processing Digital Filter Median Expansion Erosion

22. 22 Digital image & image processing Digital image files Device independent image files Device dependent image files - Microsoft Windows Bitmap “*.bmp” - Tag Image File Format “*.tif” - Graphics Interchange Format “*.gif” - JPEG File Interchange Format “*.jpg” - Many others - Raw image formats (e.g. *.raww) - TSI image file Format “*.img” - DANTEC image file format “*.img” - LAVISION image file format “*.img” - Others Basic components of a digital image Information in a bitmap header - Header, Palette, Bitmap Data, Footer etc. –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

23. 23 Digital image & image processing Digital image files Microsoft Windows Bitmap –14-byte file header (Version 2.x +) Byte 1  2File type, always 4D42h (“BM”); Byte 3  6Size of the file in bytes; Byte 7  8Reserved 1, always 0; Byte 9  10Reserved 2, always 0; Byte 11  14Starting position of image data in bytes. –Bitmap header Byte 1  4Size of this header in bits; Byte 5  8Image width in pixels;(2 bytes for version 2.x) Byte 9  12Image height in pixels; (2 bytes for version 2.x) Byte 13  14Number of color planes; Byte 15  16Number of bits per pixel; (end of version 2.x) Byte 17  20Compression methods used; Byte 21  24Size of bitmap in Bytes; Byte 25  28Horizontal resolution in pixels per meter; Byte 29  32Vertical resolution in pixels per meter; Byte 33  36Number of colors in the image; Byte 37  40Minimum number of important colors. (end of version 3.x) Up to 108 bytes for Version 4.x –Color Palette One-, 4-, and 8-bit BMP files always contain a color palette 24-bit BMP files never contain color palettes

24. 24 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 file File header:14 bytes Bitmap header:40 bytes Color palette:1024 bytes Bitmap data:15376 bytes Total size:16454bytes –Simplest Matlab program A=imread('image01.bmp'); A(1,1) A(1,124) A(124,1) A(124,124) A(62,62) imshow(A);