1. TOPIC 11 THE GREY LEVEL HISTOGRAM & POINT OPERATIONS

3. COM366 function BG = SetBackground(frame) %To use a particular frame as a the background filename = ['WhiteVan', int2str(frame), '.jpg'] I = imread(filename); GI = rgb2gray(I); imshow(GI); BG = double(GI)+1; %Extra line added to show the image histogram imhist(GI,255); Image Histogram in MATLAB

8. COM366 If a = 1 and b = 0 the image is simply copied If a>1 the contrast is increased and if a < 1 the contrast is decreased. If a = 1 and b is non zero then the output image has the grey levels moved up or down. Thus the entire image becomes darker or lighter. If a < 0 then light areas become dark and dark areas become light. In effect the image is complemented. Consequences of

9. COM366 Correcting sensor non linearity We can regard the sensor response as a function G which transforms the true pixel values to non linear values The sensor records G(D A ) a non linear distorted version of D A. Applying the inverse transform G -1 corrects for the distortion and restores the value D A.

11. COM366 Histogram equalisation N i is the number of pixels with brightness I T is the total number of pixels

13. COM366 function equalise %To show the effects of histogram equalisation J = imread('eyeball.jpg'); subplot(2,1,1);imshow(J); K = histeq(J); subplot(2,1,2);imshow(K); Histogram equalisation in MATLAB

14. Photometric calibration

16. COM366 Background subtraction (Background)(Scene)(Difference) |I 1 – I 2 |

17. COM366 function RoadSegment(frame,BG) % Takes an RGB image and segments out the vehicle content %This function assumes the background image BG is available filename = ['WhiteVan', int2str(frame), '.jpg'] I = imread(filename); GI = rgb2gray(I); A = double(GI)+1; C1 = A - BG; C = uint8(round(C1-1)); outfilename = ['SegVan', int2str(frame),'.JPG'] imwrite(C,outfilename,'jpg') imshow(C)

18. COM366 The principle of thresholding

19. COM366 function ThreshHold %To demonstrate thresholding an image J = imread('eyeball.jpg'); subplot(2,1,1);imshow(J); BW = im2bw(J,0.6); subplot(2,1,2);imshow(BW); Thresholding an image in MATLAB