Using image analysis to develop reference standards for the video trashmeter

Using image analysis to develop reference standards for the video trashmeterDevron P. Thibodeaux and Janice P. EvansUSDA, ARS, Southern Regional Research CenterNew Orleans, Louisiana 70124ABSTRACTResults ofresearch to develop a reference method for calibrating standard dot image tiles and cotton trash boxes arereported. The tiles and trash boxes are produced by the Agricultural Marketing Service for use in standardizing HVJ VideoTrashmeters. The reference method involves use ofa highly sensitive image analysis system (the Quantimet 970) to measure thenumber and percent area fraction ofparticle images produced on the replica tiles or ofreal trash particles placed on the surface ofcotton incased in plastic boxes. Calibration data for a set oftiles and boxes is presented. The effects of magnification (systemresolution) and detection threshold are investigated as related to measurement accuracy.Keywords: video trashmeter, cotton, image analysis, image tiles, detection threshold, image resolution1. INTRODUCTIONThe USDA, Agricultural Marketing Service (AMS), Cotton Division, utilizes High Volume Instrument (HVI) systems toclassif' the U.S. cotton crop each year. Classification is based on fiber length, strength, Micronaire, color, and trash. One of thebiggest problems is the standardization and calibration oftrashmeters. The cotton video trashmeter was first described by Taylorwho discussed two new methods for estimating the trash content ofcotton. Results from the two methods were consistent and thevideo trashmeter was recommended because ofits speed and ease ofoperation.' The video trashmeter measures the Number and% Area ofvisible trash particles on the surface ofa cotton batt compressed against a viewing window. It consists of a samplewindow (approximately nine square inches), fiber compression device, illumination system, video camera, digital image capturemodule, and computer.2 Duiing the ensuing peiiod considerable effort was put into improving and maintaining the quality andconsistency ofthe trashmeter measurement.3 This consisted ofinstallation ofvideo trashmeters in 14 AMS HVI systems in 1987with results that they give fairly accurate readings oftrash in cotton samples giving reasonable agreement with classer trashgrades. These tests were conducted at 20 classing offices and comparisons were made the Quality Control trashmeter inMemphis. In an effort to improve the accuracy ofthe trashmeters, Taylor has reported on modifications to the video system of theMotion Control Model 3000 video trashmeter by addition of a small solid state TV camera that allowed digitization ofthe imageofthe trash particles to measure the area ofthe trash particles present in cottons obtained from the AMS.4 Utilization oftrash dataobtained from the particle size information improved trashmeter agreement with non-lint content as measured by the ShirleyAnalyzer and processed yarn quality.In a further effort to improve the trashmeter, efforts were undertaken to develop calibration Stand&dS. One problem withtrashmeter standardization was the fact that there are two different manufacturers marketing HVJ systems (Motion Control, Inc.and Zeliweger Uster, Inc.) and each supplied its own standard image tile with different patterns ofcolored dots.6 Anotherproblem was that, when AMS attempted to produce cotton batts with different amounts oftrash to be used as Standards, some ofthe surface trash particles would be lost during repeated handling. This led to inconsistent readings resulting in questions of thequality ofdata. AMS has addressed these problems by constructing standard image tiles and enclosed cotton trash boxes forcalibration and evaluation ofvideo trashmeters.7 A "universal" calibration tile was designed and constructed using repeatingpatterns ofdots plotted on paper and mounted under optical quality glass for presentation to the trashmeter optics. Samplecottons representing a wide range of color grades and leaf contents were also prepared in special plastic boxes and compressedunder the optical glass. The image tiles have various dot patterns and shadings generated by a CAD program and printed with acolor plotter on paper with different shadings (Neutral, White, Yellow, or Gray). The tiles consist of the printed image papersmounted with a plastic backing and covered on top with optical quality glass. There are a total of nineteen of these tiles withdifferent patterns and background colors. The cotton trash boxes are constructed of plastic into which either white or spottedcotton is placed and trash particles of given size and number are located on the surface by hand. This report describes the work ofthe authors in supporting the AMS by image analysis of these reference materials to establish values for the number and areafraction of dot images of trash particles on the surfaces of the reference standards.