Showing papers on "Grayscale published in 1979"

A Note on the Use of (Gray Level, Local Average Gray Level) Space as an Aid in Threshold Selection.

Abstract: : Various methods have been proposed for improving the gray level histogram of an image so as to make it easier to select thresholds for segmenting the image. This note describes how (gray level, local average gray level) feature space can be used to define improved image histograms. The approach is analogous to that in an earlier note which made use of second-order gray level histograms('cooccurrence matrices') for similar purposes. (Author)

Electronic rescreen technique for halftone pictures

Abstract: A method for rescreening a halftone image to produce an edge-enhanced halftone copy from a halftone original. The halftone original is scanned by a raster input scanner and the resultant analog voltage is compared to a reference voltage to produce a one bit per pixel bit stream, where a pixel is defined as the smallest image (picture) element discernable by the system. For example, in a raster input scanner using a CCD array, the smallest picture element, pixel, is the analog voltage output of one CCD cell. This voltage subsequently can be converted to a digital gray scale representation requiring a plurality of bits per pixel, or either analog or digital representation can be compared to an analog or digital reference voltage to produce a one bit pixel. A six bit per pixel gray scale output is produced therefrom by adding an integrated value and an edge enhancement value for each input pixel received. The integrated value is calculated by summing the number of one bits in the seven by nine bit section surrounding each pixel. The edge enhancement value is calculated by determining the difference between the number of one bits in the right and left halves, and upper and lower halves, of the six by seven bit section surrounding each pixel. A set of equations is used to process these differences to produce an edge enhancement value which is added to the integrated value. From this six bit per pixel gray scale output the six bit output can be preserved, or a halftone copy can be produced by any well-known process. A simple and inexpensive circuit to perform the above functions at high data rates is also disclosed.

Region Representation: Raster-to-Quadtree Conversion

Abstract: : An algorithm is presented for constructing a quadtree for a binary image given its row-by-row description. The algorithm processes the image one row at a time and merges identically colored sons as soon as possible so that a minimal size quadtree exists after processing each pixel. This method is spacewise superior to one which reads in an entire array and then attempts to build the quadtree. Analysis of the algorithm reveals that its execution time is proportonal to the number of pixels comprising the image.