Enhance Image Quality Using Histogram Equalization Technique
Learn how to improve image quality by applying histogram equalization for better contrast and visual appeal. Understand the process of mapping gray levels to enhance the overall image appearance through cumulative histograms. See examples and results of image enhancement using this technique.
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Presentation Transcript
Designing an Image Processing IP Vipin Kizheppatt
Problem This image looks washed out 2
Problem It is due to lack of contrast From the histogram, the range of gray levels are quite limited 3
Problem If we can enhance the contrast (distribute pixels to more gray levels), image might look better 4
Problem Now the histogram is more widely distributed One popular technique used for this purpose is histogram equalization 5
Histogram Equalization (HE) In HE, a mapping function is used to map a gray level in the input image to another gray level in the output image For this purpose, the cumulative histogram needs to developed first Cumulative histogram (CH) for a gray level is the cumulative sum of all the pixels in the image, whose gray level is less than or equal to the gray level that we are considering 6
Histogram Equalization (HE) Count 60 61 62 63 64 Value Count Value Count Value Count Value Count Value 52 1 4 6 9 10 14 64 65 66 67 68 69 19 22 24 25 30 33 72 73 75 76 77 78 40 42 43 44 45 46 85 87 88 90 94 104 51 52 53 54 55 57 113 Input Image 55 58 59 60 61 Histogram 122 126 144 154 62 15 70 37 79 48 106 58 63 17 71 39 83 49 109 59 7 Cumulative Histogram
Histogram Equalization (HE) Now use the mapping function ? ? ? (???) ??????????? ? (???)) ? 1 Lnew = round( For gray scale images using 1 byte/pixel representation, L-1 (total number of levels) will be 255 Value Lnew Value Lnew Value Lnew 239 243 247 251 255 Lnew Value Lnew Value 52 55 58 59 60 61 0 12 20 32 36 53 64 65 66 67 68 69 73 85 93 97 117 130 72 73 75 76 77 78 158 166 170 174 178 182 85 87 88 90 94 104 202 206 210 215 219 227 113 122 126 144 154 62 57 70 146 79 190 106 231 8 63 65 71 154 83 194 109 235
Hardware Design Cumulative Histogram Calculator Gray level Input pixel Input pixel valid Comparator Cumulative Histogram for input gray level Counter 10
Hardware Design Cumulative Histogram Calculator 0 Gray 0 CH 1 Gray 1 CH Input pixel Input pixel valid 2 Gray 2 CH 255 Gray 255 CH 11
Hardware Design Min Cumulative Histogram Calculator Min Gray level Input pixel Input pixel valid Comparator Min Cumulative Histogram Counter 12
Hardware Design New Level Calculator Image Size (total pixels) CH0 CH1 CH2 L0(new) L1(new) L2(new) Sequential New level (Lnew) Calculation CH255 L255(new) CHmin 13
Hardware Design Mapper L0(new) L1(new) L2(new) Mux Pixel Out L255(new) Pixel In 14
Hardware Design Min calculator AXI-M Read AXI-M Write Cumulative Histogram Calculator AXIS Image Reader New Level Calculator Image Writer AXIS Mapper AXI-Lite i/f Control logic Register File 15
Thank you any questions 16
