Coating a printed surface with a smooth transparent layer can modify its color. This is due to light interreflections within the coating layer which produce a halo-shaped point spread function. The change of color is related to the coating thickness and the halftone screening used for printing. Thanks to an optical model able to predict the spectral reflectance of the coated print from the one of the non-coated print, we propose to study the impact of the halftone pattern (shape and profile) on the color change caused by the coating layer. It was found that line halftone patterns with a crenel profile induces the strongest changes of color. This is therefore the pattern that we use for an innovative application of this phenomenon: revealing a binary image by adding or removing a coating layer on the print that is originally uniform.
Farmers do not typically have ready access to sophisticated color measurement equipment. The idea that farmers could use their smartphones to determine when and if crops are ready for harvest was the driving force behind this project. If famers could use their smartphones to image their crops, in this case tomatoes, to determine their ripeness and readiness for harvest their farming practices could be simplified. Five smartphone devices were used to image tomatoes at different stages of ripeness. A relationship was found to exist between the hue angles taken from the smartphone images and as measured by a spectroradiometer. Additionally, a tomato color checker was created using the spectroradiometer measurements. It is intended to be made of a material that makes it easy to transport into the field. The chart is intended for use in camera calibration for future imaging. Different cloth materials were tested, with the eventual choice being a canvas material with black felt backing. Other possibilities are being investigated. The results from the smartphones and the charts will be used in further research on the application of color science in agriculture. Other possible future applications include monitoring progress relative to irrigation and fertilization programs and detection of pests and disease.
In this paper we present a set of multispectral images covering the visible and near-infrared spectral range (400 nm to 1050 nm). This dataset intends to provide spectral reflectance images containing daily life objects, usable for silicon image sensor simulations. All images were taken with our acquisition bench and a particular attention was brought to processings in order to provide calibrated reflectance data. ReDFISh (Reflectance Dataset For Image sensor Simulation) is available at: http://dx.doi.org/10.18709/perscido.2020.01.ds289.
Additive Manufacturing (AM) refers to a class of manufacturing processes which produces three dimensional objects directly from 3D model data. A range of AM processes, such as fused deposition modelling and laser sintering are deemed slow compared to injection moulding, as they depend on point-to-point consolidation. In order to progress into high speed manufacturing, a novel process called the High Speed Sintering (HSS) process is currently being developed at the University of Sheffield.HSS is a powder bed fusion process which employs an inkjet print head to print a cross sectional image of an <fig position="float" id="s37_f.1"> <label>Figure 1</label> <caption>Key components in the High Speed Sintering (HSS) process</caption> <graphic mime-subtype="tif" xlink:href="Images\s37_f01.tif" xmlns:xlink="http://www.w3.org/1999/xlink"/> </fig> object in radiation absorbing material (RAM) onto a powder build bed.[1] The build bed is subsequently exposed to infrared radiation to promote selective sintering of RAM coated powder, leaving the surrounding powder to act as a support. Consolidation is obtained by adding a new layer of powder in between printing successive images to form a 3D object. The HSS process uses Nylon-12 as its standard material, and is suitable to use with a range of polymer powder, especially thermoplastics. An overview of the HSS process with its key components is illustrated in Figure 1 below.Previous research on HSS has focused on assessing the effect of infrared lamp level,[2] the addition of flow agent[3] and the greyscale value on the mechanical properties of parts. Few studies have been performed on non-destructive characterisation of polymer parts, either by using Differential Scanning Calorimetry (DSC)[5] or NIR spectroscopy for laser sintered parts[6] and rubber parts[7]. This project aims to propose a non-destructive method to estimate the tensile properties of HSS Nylon-12 parts. Previous research based on the “greyscale level” suggested a correlation between the input ink dithering level during sintering process and the resultant parts tensile properties, however this method is not widely applicable across all inkjet print heads due to the difference in specifications. Spectroscopy method has never been used to assess parts made by the high speed sintering process and is advantageous as it quantifies an output grey level.In this contribution, an overview of the HSS processing of Nylon-12 powder will be provided. Reflectance spectroscopy will be performed on manufactured parts and the results compared with actual tensile tests. The correlation between HSS Nylon-12 parts reflectance values and their corresponding ultimate tensile strength values will be presented.