MULTIMEDIA TECHNOLOGY SMM 3001 MEDIA - IMAGES

Processing digital Images digital images are often processed using “digital filters” digital images are often processed using “digital filters” digital filters are based on mathematical functions that operate on the pixels of the image digital filters are based on mathematical functions that operate on the pixels of the image

Processing digital Images there are two classes of digital filters: global and local there are two classes of digital filters: global and local global filters transform each pixel uniformly according to the function regardless of its location in the image global filters transform each pixel uniformly according to the function regardless of its location in the image Eg. Adjusting the overall tonal qualities, lightness & darkness Eg. Adjusting the overall tonal qualities, lightness & darkness local filters transform a pixel depending upon its relation to surrounding ones local filters transform a pixel depending upon its relation to surrounding ones Eg. Sharpening the edges Eg. Sharpening the edges

Global Filters Brightness and Contrast control Brightness and Contrast control Brightness refers to the overall intensity of the pixels in the image Brightness refers to the overall intensity of the pixels in the image Image can be improved by lightening/darkening Image can be improved by lightening/darkening Grayscale or black & white image – by adding intensity values from each pixel Grayscale or black & white image – by adding intensity values from each pixel Contrast – relative difference between distributions of lighter & darker pixels in an image Contrast – relative difference between distributions of lighter & darker pixels in an image Histogram thesholding Histogram thesholding Histogram stretching or equalization Histogram stretching or equalization Color corrections Color corrections Hue-shifting and colorizing Hue-shifting and colorizing Inversions Inversions

Global Filters a histogram is a graph depicting the frequency distribution of pixel values in the image a histogram is a graph depicting the frequency distribution of pixel values in the image thresholding creates a binary image by converting pixels according to a threshold value thresholding creates a binary image by converting pixels according to a threshold value The threshold operation chooses an intensity value to serve as cutoff point for redistributing the pixel values in the image The threshold operation chooses an intensity value to serve as cutoff point for redistributing the pixel values in the image

Global Filters

Histogram stretching redistributes pixel values in the image that has poor contrast Histogram stretching redistributes pixel values in the image that has poor contrast Sometimes the pixel values may be clustered toward the middle of the range Sometimes the pixel values may be clustered toward the middle of the range Equalization improves images with poor contrast Equalization improves images with poor contrast

Global Filters Histogram stretching redistributes the intensity of colour values of the pixels in Image. The darkest pixels in the image are mapped to some minimum value (Min) While the lightest pixels are made the maximum brightest value (Max).

Global Filters Hue-shifting is used to modify the color makeup of an image Hue-shifting is used to modify the color makeup of an image Usually this is done only for selected areas for colour corrections, balancing, or special effects Usually this is done only for selected areas for colour corrections, balancing, or special effects Pseudo-coloring assigns hues to intensity ranges for better rendering of details Pseudo-coloring assigns hues to intensity ranges for better rendering of details Colorized image of Mississippi at Vicksburg

Local Filters The filter/mask serves as a template defining how the pixel will be transformed in relation to its neighbours The filter/mask serves as a template defining how the pixel will be transformed in relation to its neighbours Sharpening Sharpening Blurring Blurring Unsharp Masking Unsharp Masking Edge and line detection Edge and line detection Noise filters Noise filters

Local Filters Edge and line detection filters subtract all parts of the image except edges or boundaries between two different regions Edge and line detection filters subtract all parts of the image except edges or boundaries between two different regions edge detection is often used to recognized objects of interest in the image edge detection is often used to recognized objects of interest in the image

Local Filters edges and lines detected in an image of toy blocks