Use of an image-capture system to measure the opacity of coatings: a visual psychophysics approach (2020-2024)
Start: October 2020
Student: Alan Chi
Supervisors: Richard Leach, Lewis Newton
Hiding corresponds to the visual property of paint which is associated with the ability to occlude the colour or colour differences of the substrate. In the paint and coating industry, the measurement of hiding is traditionally performed in a standardised procedure with controlled lighting, using a drawdown bar to specifically apply a constant thickness of paint, and measuring the contrast ratio of this applied paint (ASTM D2805). Such methods rely on the unrealistic assumption that paint will be applied in a smooth, uniform manner outside of the laboratory. Applying paint generally results in uneven film thickness and surface texture, which greatly impacts hiding power. This project seeks to develop a new method to measure hiding of applied coatings, without the requirements for controlled lighting and that can allow for paint films of non-uniform thickness – resulting in a more accurate and realistic measure of hiding power.
The development of this new method for measuring hiding will rely on the use of image capture. Images of applied waterborne paints will be analysed to obtain a metric for hiding power. This project will approach this from a visual perception perspective, rather than measuring the physical properties of the paint. The hiding metric will take into account different visual properties of the paint (as captured in the image) such as: colour, gloss, wet/dry state, illumination and surface texture. Psychophysical experiments will be conducted to determine which aspects of the images are relevant and meaningful to the visual perception of paint hide. This project will lead to an image-capture system that can accurately determine and measure the hiding power of applied paints in a realistic setting, using visual psychophysical data and images, without the need for measuring the physical properties of the paint itself.
Figure 1 Hiding is traditionally measured via the application of paint using a drawdown bar, applying an unnaturally uniform and evenly distributed layer of paint. Source: BYK Gardner USA.