1. Introduction to electrical and computer engineering Jan P. Allebach School of Electrical and Computer Engineering allebach@ecn.purdue.edu

2. Special thanks to l Dan Dickinson l Mu Qiao l Jennifer Talavage

3. Synopsis l What is electrical and computer engineering? l Digital photography l Image enhancement l Digital halftoning

4. What do electrical/computer engineers do? l Analyze and design systems l Develop algorithms l Write programs l Work with people –Team members –Customers –Management

5. What skills does an electrical/computer engineer need? l Desire to solve problems, and make things work l Willingness to work hard l Good math ability l Good communications skills l Ability to work with others

6. Technology areas l Materials and devices l Circuits and systems l Power systems l Computers l Communications and networking l Signal and image processing

7. Signal and image processing l CD and DVD technologies l High definition TV l Medical imaging systems –CAT scan –MRI l MP3 l Cell phones l Voice recognition and synthesis l Digital cameras l Inkjet and laser printers

8. Synopsis l What is electrical and computer engineering? l Digital photography l Image enhancement l Digital halftoning

9. Anatomy of a film-based camera

10. What’s different about a digital camera? Replace the film by –detector array –image processing module –digital storage

11. Detector array Note that we must demosiac the image to obtain 2048x1536 pixels for each of the R, G, and B frames.

12. Digitization of the pixel values Each pixel value is represented by three 8-bit binary numbers

13. A picture is worth a lot more than a thousand words! l Total no. pixels = 2048x1536 = 3,145,728 or 3.1 Megapixels. l With 3 bytes/pixel, we have 9.3 Megabytes/image. l With image compression, this image can be stored in about 1 Megabyte l A 512 Mbyte flashRAM card will then hold about 500 images.

14. Synopsis l What is electrical and computer engineering? l Digital photography l Image enhancement l Digital halftoning

15. Contrast modification l The image is mapped pixel-by-pixel through the transformation curve.

16. Alternate representation of the grayscale transformation

17. Contrast enhancement example Original Image Enhanced Image

18. Spatial filtering l Each output pixel is a weighted sum of input pixels in neighborhood of output pixel location.

19. Spatial filtering

26. l Filter responds only to edges – no response in constant areas.

27. Sharpening l To sharpen the image, we simply add to it a scaled component of the edge detection result.

28. Sharpening example Original Image Sharpened Image

29. Synopsis l What is electrical and computer engineering? l Digital photography l Image enhancement l Digital halftoning

30. Digital printing l Each pixel in a monochrome image is represented by a string of eight 0s and 1s. l A monochrome digital printer represents each pixel by a single 0 or 1: –“0” means no colorant at that pixel location –“1” means put a colorant dot at that pixel location l To create the impression of a continuous-tone image, we use a process known as halftoning.

31. Digital halftoning l The perception of levels of gray intermediate to black or white depends on a local average of the binary texture.

32. Digital halftoning l Detail is rendered by local modulation of this texture.

33. Screening is a thresholding process l Simple point-to-point transformation of each pixel in the continuous-tone image to a binary value. l Process requires no memory or neighborhood information. Threshold

34. Why not use a single threshold? l A single threshold yields only a silhouette representation of the image. l No gray levels intermediate to white or black are rendered. l To generate additional gray levels, the threshold must be dithered, i.e. perturbed about the constant value. Continuous-tone original image Result of applying a fixed threshold at midtone

35. Basic structure of screening algorithm The threshold matrix is periodically tiled over the entire continuous-tone image.

36. How tone is rendered l If we threshold the screen against a constant gray value, we obtain the binary texture used to represent that constant level of absorptance.

37. Dot profile function l The family of binary textures used to render each level of constant tone is called the dot profile function. l There is a one-to-one relationship between the dot profile and the screen.

38. That’s all! l Thanks for your attention l Now let’s try some of these ideas out!