Deinking Evaluation Using Near Infrared Digital Image Analysis, 2014 PEERS Conference

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This study is a follow-up to the paper “Deinking Evaluation Using Near Infrared Narrow Band Digital Image Analysis,” which has been presented at 10th Research Forum on Recycling (Green Bay, WI). Near infrared (NIR) image method can obtain high contrast ink speck images by reducing the influence of paper surface unevenness. The mechanism is the same as TAPPI T 567 method. By using narrow NIR band light and a high-resolution digital camera, reliable and uniform results are obtained compared with those from visible light image method. It doesn’t have the two-sidedness problem found in visible light image analysis. The NIR image method has good correlations with handsheet paper brightness and luminosity. However, the results (equivalent black area, or EBA) from NIR image method were lower than those from visible image method. One argument suggested some ink specks might have been missed because the narrow band-pass filter only allows limited light to pass through. A cut-off IR filter is applied in this study to increase the incident light intensity and produce more signals on the image sensor. However, there is no significant difference between cut-off filter and band-pass filter. The argument of missing ink specks because of low NIR light is unlikely true. In contrast, the visible light image method may count more false ink specks than we expect. In addition, NIR camera with cut-off filter significantly improves the measurement efficiency due to the increased light intensity. Ink elimination rate via image analysis method is discussed, which demonstrates good correlation with paper optical properties.