1. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing Digital Image Processing Spatial Aliasing and Image Enhancement

2. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing Aliasing Spatial Aliasing : is insufficient sampling of data along the space axis, which occurs because of the insufficient spatial resolution of the acquired image. Critical Sampling Distance: is the Sampling Distance corresponding to the Nyquist Rate.

3. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing Aliasing Aliasing of a undersampled 1D sinusoidal signal Aliasing of a undersampled 2D image © 2002 R. C. Gonzalez & R. E. Woods

4. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing Anti-Aliasing © 2002 R. C. Gonzalez & R. E. Woods Aliasing problem of a downsampled image Aliasing problem avoided by using band limiting Low Pass Filter.

5. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing Moiré Pattern © 2002 R. C. Gonzalez & R. E. Woods

6. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing Image Enhancement Spatial Domain Methods: manipulates the pixel of a given image for enhancement. Frequency Domain Methods: manipulates the Fourier transform of a given image for enhancement.

7. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing f(x,y) : input g(x,y) : output T : transformation function g(x,y)=T[f(x,y)]

8. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing (x,y) 3x3 neighborhood (mask)

9. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing Image Enhancement in Spatial Domain Point Processing: enhancement at any point in an image depends only the gray-level at that point. Mask Processing/Filtering: where the values of the mask coefficients determine the nature of the process.

10. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing Contrast Stretching Contrast: is the difference in visual properties making an object/image distinguishable from other objects and the background.

11. Gholamreza Anbarjafari, PhD Video Lecturers on Digital Image Processing Summary  We have looked at:  What is aliasing?  What is anti-aliasing?  What is image enhancement?  Image enhancement in spatial domain  Next time we will talk about contrast stretching