Guidelines for Nighttime Visibility of Overhead Signs (2016) / Chapter Skim
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44 Assessment of Background Complexity Using Digital Images of Roadway Scenes by Image Processing This appendix contains information about assessing the complexity of a roadway scene based on images captured by mobile photometric equipment at night. The procedure that produced a complexity rating from a combination of parameters for each image was applied to generate a complexity rating for each sign in the open-road study described in Chapter 4.
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45 and consistency. This study aimed to design a system that automatically evaluates the background complexity of overhead traffic signs from digital images of nighttime roadway scenes by using image-processing techniques and multiple linear regression.
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46 linear combination of the six factors, and their weights were determined by the least-squares method. It was found that the structural factor of a color picture and the color variance could significantly affect the image complexity.
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47 objects, such as lighting sources, commercial billboards, and oncoming vehicles, all of which could strongly affect drivers' observations. Contrast Contrast is a measurement used to represent the degree of difference in the grayscales between a pixel and its neighbor over an image.
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48 Figure B-3. Example of image properties.
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49 of uncertainty associated with random variables, considered a statistical measure of complexity (11)
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50 The noise is usually assumed to follow a multivariate normal distribution. The ordinary least square (OLS)
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51 Images Group A Group B Overall Average Overall Std.
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52 Images Overall Average Overall Std.
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53 Parameters Ordinary Least Square Bootstrap for OLS Estimation Value Standard Error Estimation Value Standard Error Intercept −7.1612 1.7524 −6.1491 2.6007 Entropy 0.2422 0.3651 0.1907 0.4276 Contrast 0.0138 0.0049 0.0128 0.0088 Energy 0.3789 2.8844 0.0543 3.4869 Homogeneity 3.9557 1.361 2.7531 2.8927 No. of Saturation Pixels 0.4068 0.1691 0.4414 0.1888 Edge Ratio 92.9387 57.5493 102.1324 61.2105 No.
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54 Figure B-6. Results of validation by LOOCV.
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55 signs, and those ratings can be used to more accurately assess the visibility of the signs. Suggestions for future research include extending the work to measure other important characteristics of nighttime images, such as 2D spectrum information and relative localization of traffic signs.
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