TAILIEUCHUNG - Lecture Digital image processing - Lecture 17: Image Enhancement

This chapter presents the following content: Sharpening, 1st and 2nd order derivatives, laplacian filter, unsharp masking and high-boost filtering, First order derivatives using the gradient operator, shobel operator using first order derivatives, what are edges in image? modeling intensity changes, steps of edge detection. | Digital Image Processing CSC331 Image Enhancement 1 Summery of previous lecture Sharpening 1st and 2nd order derivatives Laplacian filter Unsharp masking and high-boost filtering 2 Todays lecture First order derivatives using the gradient operator Shobel operator using first order derivatives What are Edges in image? Modeling intensity changes steps of edge detection 3 Sharpening The term sharpening is referred to the techniques suited for enhancing the intensity transitions. In images, the borders between objects are perceived because of the intensity change: more crisp the intensity transitions, more sharp the image. The intensity transitions between adjacent pixels are related to the derivatives of the image. Hence, operators (possibly expressed as linear filters) able to compute the derivatives of a digital image are very interesting 4 Sharpening spatial filter By averaging over an image, then the image becomes blurred or the details in the image are removed. Now, this averaging operation is equivalent to integration operation. The opposite differentiation operation or derivative operations will make the image sharp. We need derivative operations First derivative Second derivative 5 Laplacian operator Usually the sharpening filters make use of the second order operators. 6 Laplacian filter 7 8 (a) and (c): Isotropic results for increments of 90o (b) and (d): Isotropic results for increments of 45o 9 10 11 12 13 Unsharp masking and high-boost filtering The technique known as unsharp masking is a method of common use in graphics for making the images sharper. It consists of: 1. defocusing the original image; 2. obtaining the mask as the difference between the original image and its defocused copy; 3. adding the mask to the original image. 14 15 Mask of High Boost 16 17 18 19 First order derivatives using the gradient operator 20 21 Properties of the gradient The magnitude of gradient provides information about the strength of the edge. The direction of gradient

• Đồ họa - Thiết kế - Flash
• Digital image processing
• Lecture Digital image processing
• Digital images
• Digital computers
• Image processing
• Gradient operator
• Sharpening spatial filter
• Image segmentation
• Local processing
• Global processing
• Morphological image processing
• Autonomous machine applications
• Region growing
• Image digitization
• Theory of sampling
• Image transformation
• Image enhancement
• Image restoration
• Image transform
• Image compression
• Dark image