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Engineering education for today’s classroom Outline • How Can We Use Digital Images? • A Digital Image is a Matrix • Manipulating Images • Improving Images for Robot Eyes 2 infinity-project.org Engineering education for today’s classroom 4.1 How Can We Use Digital Images? 3 infinity-project.org Engineering education for today’s classroom The Power of Digital Images • It is easier and easier to acquire or make digital images Digital cameras and scanners • Chief advantage over analog (e.g. film) images: Easy to change • How might we change images? 4 infinity-project.org Engineering education for today’s classroom Image Softening and Blurring 5 infinity-project.org Engineering education for today’s classroom Image Sharpening 6 infinity-project.org Engineering education for today’s classroom Finding Edges in Images • Edges in images • usually define solid objects in our 3D world Finding edges is a first step to navigation and manipulation 7 infinity-project.org Engineering education for today’s classroom Subtracting Images •Image subtraction is a simple way to find differences between two images •Useful for security, recognition, and navigation applications 8 infinity-project.org Engineering education for today’s classroom Image Segmentation • • Segmentation: Dividing images into regions Applications Identifying foreground vs. background Finding objects using only one image 9 infinity-project.org Engineering education for today’s classroom 4.2 A Digital Image Is a Matrix 10 infinity-project.org Engineering education for today’s classroom Digital Images are Matrices • Matrix: A = An array of numbers 14 12 5 7 0 1 6 5 4 3 11 10 3 rows and 4 columns • Elements: A(i,j) , i and j are integers Examples: A(2,3) = 6, A(1,4) = 7, A(3,4) = 10 11 infinity-project.org Engineering education for today’s classroom Classes of Image Manipulation 1. 2. Mapping: Pixel-by-pixel operations Arithmetic Combination of Two Images: e.g. addition, multiplication 3. Filtering: Operations on groups of pixels in an image (neighborhood operation) Fact: Almost all applications are made up of simple combinations of these manipulations 12 infinity-project.org Engineering education for today’s classroom Image Mapping • All of the form B(i,j) = {function of A(i,j)} where B(i,j) is the output image • Many familiar effects: Brightness, Contrast, Negative, Thresholding, Gamma Correction 13 infinity-project.org Engineering education for today’s classroom Brightness Mapping k = 50 k = -50 B(i,j) = A(i,j) + k k = constant (expressed as a table) 14 infinity-project.org Engineering education for today’s classroom Example: Brightness Mapping Original 24-bit image Each color increased by 60 Each color decreased by 60 Green and blue +60, red -60 15 infinity-project.org Engineering education for today’s classroom Contrast Mapping • Formula: B(i,j) = s • A(i,j) If s > 1, contrast is increased If s < 1, contrast is decreased • Need to quantize after multiplying, as • s • A(i,j) may not be an integer Aside: This setting is found on most TV sets 16 infinity-project.org Engineering education for today’s classroom Contrast Mapping (cont.) s>1 s<1 s > 1 and k < 0 s < 1 and k > 0 17 infinity-project.org Engineering education for today’s classroom Example: Contrast and Brightness Higher contrast with lower brightness Higher contrast • Formula: B(i,j) = s • A(i,j) + k • This is easy to do! 18 infinity-project.org Engineering education for today’s classroom Example: Contrast and Brightness • Given the 4-bit grayscale image A= 14 12 5 7 0 1 6 5 4 3 11 10 • Compute the image with a contrast of 1.5 and a brightness of 2 19 infinity-project.org Engineering education for today’s classroom Solution: Contrast and Brightness • Answer: B(i,j) = 1.5•A(i,j) + 2 15 15 10 13 B= 2 4 11 10 8 7 15 15 Quantization causes values such as 9.5 and 3.5 to be rounded up Image is clipped at 15 (Why?) 20 infinity-project.org Engineering education for today’s classroom Infinity Project Experiment – 4.1 21 infinity-project.org Engineering education for today’s classroom Brightness and Contrast Grayscale 22 infinity-project.org Engineering education for today’s classroom Brightness and Contrast Color Image 23 infinity-project.org Engineering education for today’s classroom Brightness and Contrast Color Camera 24 infinity-project.org Engineering education for today’s classroom Brightness and Contrast Cascade 25 infinity-project.org