About Rank 5x5É drop-in for PhotoShop. This file should be placed in the same folder as your other PhotoShop drop-ins, and will then appear in the "Other" submenu under "Filters" This drop-in provides a number of rank operations for monochrome images. It ignores color images. The neigborhood is 5x5 pixels; by default, the four corner pixels are skipped to produce an octagonal (and hence more isotropic) result. Ranking of the 21 (or 25) pixel values is performed using a Shell sort. The dialog allows the user to select several modes: Median filter: a noise removal filter which saves the 11th (13th) brightest pixel in each neighborhood. Maximum: saves the brightest pixel in each neighborhood. Often useful for removing dark noise or creating a background to isolate dark features. Minimum: saves the darkest pixel in each neighborhood. Similar in use to the Maximum filter when the noise or features are bright. Range: saves the difference between the brightest and darkest pixels. Useful to create an image showing texture or in some cases edges. Top Hat (+): Performs two rank operations, one on the full 5x5 (square or octagonal) region and one on just the five central pixels forming a + in the center of the neighborhood, and saves the difference between the brightest pixels in each region. Isolates bright points and delineates edges. Top Hat (-): Similar to Top Hat (+) but saves the difference between the darkest pixels in the large and small regions. Isolates dark points and delineates edges. Note that for edges, the Top Hat (+) and (-) methods will mark the inside and outside of edges depending on the direction in which brightness varies across it. After the filter has been run by selection from the "Other" submenu, and the dialog selections made, repeating it by selecting Command-F will use the same dialog selections. To change these, you must again select Rank 5x5 from the submenu. These filters are described in J. C. Russ "The Image Processing Handbook" CRC Press, Boca Raton, FL (1992). The program is Copyright © 1992 by J. C. & J. C. Russ. It may be distributed at no charge provided the copyright notice accompanies the file. John C. & J. Christian Russ 213 Merwin Road Raleigh, NC 27606 fax: 919-851-8117 email: