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Image segmentation in Digital Image Processing
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- 43. • Powerful cueused by humans to extract objects and regions. • Motion arises from – Objects moving in the scene. – Relative displacement between the sensing system and the scene (e.g. robotic applications, autonomous navigation). • We will consider motion – Spatially. – In the frequency domain. Use of Motion in Segmentaion
- 44. • Difference imageand comparison with respect to a threshold: ij 1 d (x, y) if f (x, y,ti ) f (x, y,tj ) T 0 otherwise • The images should be registered. • Illumination should be relatively constant within the bounds defined by T. Basic Spatial Motion Segmentation
- 45. • Comparison ofa reference image with every subsequent image in the sequence. • A counter is incremented every time a pixel in the current image is different from the reference image. • When the kth frame is being examined, the entry in a given pixel of the accumulative difference image (ADI) gives the number of times this pixel differs from its counterpart in the reference image. Accumulative Difference Image (ADI)
- 46. (x, y) otherwise •Absolute ADI: A (x, y) Ak1(x, y) 1 if R(x, y) f (x, y,tk ) T k A k1 • Positive ADI: if R(x, y) f (x, y,tk ) T otherwise(x, y) P (x, y) Pk1(x, y) 1 k P k1 • Negative ADI: if R(x, y) f (x, y,tk ) T otherwise(x, y) N (x, y) Nk 1(x, y) 1 k N k1
- 47. • ADIs fora rectangular object moving to southeast. Absolute Positive Negative • The nonzero area of the positive ADI gives the size of the object. • The location of the positive ADI gives the location of the object in the reference frame. • The direction and speed may be obtained fom the absolute and negative ADIs. • The absolute ADI contains both the positive and negativeADIs.
- 48. • To establisha reference image in a non stationary background. – Consider the first image as the reference image. – When a non stationary component has moved out of its position in the reference frame, the corresponding background in the current frame may be duplicated in the reference frame. This is determined by the positive ADI: • When the moving object is displaced completely with respect to the reference frame the positive ADI stops increasing.
- 49. • Subtraction ofthe car going from left to right to establish a reference image. • Repeating the task for all moving objects may result in a static reference image. • The method works well only in simple scenarios.