Opals go to top of class with new grading system

CSIRO's Leanne Bischof helped design the Gemmological Digital Analyser (GDA) and the mathematical algorithms behind the opal image analysis software.

The world’s first automated device to grade opals has been unveiled at the 2009 National Council of Jewellery Valuers forum in Sydney.

The Gemmological Digital Analyser (GDA), developed by the CSIRO and branded “Opallia”, uses image analysis technology to determine the colour characteristics unique to opals, which CSIRO image analyst Leanne Bischof says are the hardest gem for jewellers to appraise.

“Qualities such as ‘flash’, the way an opal reflects light and colour as it is rotated, can vary with human eyesight and lighting conditions,” she said.

“A person’s judgment of an opal’s colours, the brightness of those colours and the area each of them covers is a really difficult task, even for a skilled opal assessor. You really need objective image analysis and automation to assist with that.”

Using information sourced by opal mining professionals, the CSIRO designed a GDA prototype with Australian company Applied Robotics and then developed the mathematical algorithms to drive the image analysis system. A small camera inside the GDA takes 871 images of the stone as it rotates on a stage which moves 360 degrees horizontally and tilts 90 degrees vertically.

Computers linked to the devise analyse the images and quantify the opal’s gemmological characteristics, providing a classification grade based on colour, clarity, carat, cut and character, the data of which is summarised in a graph and stored in a database.

According to the Australian Bureau of Statistics, the value of the Australian opal industry is estimated to be worth around $50 million a year.

However, director of Opal Producers Australia and opal miner Peter Sutton says this figure is underestimated because valuations for a single stone can sometimes vary by thousands of dollars.

“We wanted to create an objective grading system that would improve the demand for and value of the Australian opal industry, giving miners a fair price and consumer’s confidence to trade with grade quality assurance,” he said.

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