Browse Prior Art Database

MULTIPLE FIXED-LEVEL ADAPTIVE THRESHOLDING

IP.com Disclosure Number: IPCOM000024606D
Original Publication Date: 1981-Apr-30
Included in the Prior Art Database: 2004-Apr-02
Document File: 2 page(s) / 96K

Publishing Venue

Xerox Disclosure Journal

Abstract

Where the goal is to simply convert grayscale input image data into binary output data, a fixed thresholding circuit may be used to accomplish this function. However, in some cases a more robust function is needed to permit copying with high background densities or with low density input line copy, or for the detection of fine lines.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 57% of the total text.

Page 1 of 2

MULTIPLE FIXED-LEVEL ADAPTIVE THRESHOLDING
James C. Stoffel

Proposed Classification US. Cl. 358/283
Int. Cl. H04n 1/40

>- 1.. I 0 0 I I 4p&m..o

(BLACK>

+I*

(WHITE)

~ '0'

-..o 0 I 0 0 I

hL..o 0 0 0 0 0

JT

FIG. 2

Where the goal is to simply convert grayscale input image data into binary output data, a fixed thresholding circuit may be used to accomplish this function. However, in some cases a more robust function is needed to permit copying with high background densities or with low density input line copy, or for the detection of fine lines.

The following describes an adaptive thresholder wherein the input is subjected to a number of fixed thresholds and the resulting binary data streams are used to compute the 'kolorI1 of the output (Coarse Quantization). While a two-dimensional context is utilized in general to compute the output color, a one-dimensional version of the algorithm will also work well.

[This page contains 1 picture or other non-text object]

Page 2 of 2

MULTIPLE FIXED LEVEL ADAPTIVE THRESHOLDING (Cont'd)

To understand the adaptive thresholder , a simple one-dimensional version is examined. Referring to Figures 1 and 2, an analog waveform 5 representing the video input is thresholded by comparators 6, 7, and the binary output is utilized for table look-up computation of the color of the input via threshold logic 8.

The higher threshold T2 voltage (for example, 0.3 density) will determine the output color for the cases when the background is below TI and the line copy is above T For the cases when the background is high, i.e., between TI and T2, the thresholg T2 output will represent the desired output. Furtherm...