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Dear All,


I'm hoping you can help me with a query. I am currently involved in a project creating .ptm files of seal stones. Quite a number of these seals are made from carnelian and other semi-translucent minerals. We have noticed that red-orange, translucent stones result in a green tinge or green patches and decreased translucency once we build the RTI file. The green tinges are not present in the stone or in the original image captures, and in the original images the stones appear quite translucent. I've attached here an RTI screen-shot and an original capture to illustrate.


While the green tinge does not prevent us from studying the engraving, it does make the stone look very different to the original, which we would like to avoid.


Do you know whether any other researchers have experienced a similar problem, and if so, how they resolved it?


Many thanks, Erin



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Hi Erin,


We have seen areas turn green with highly specular material and when processed using LRGB PTMs. This is particularly true of gold objects. You might try creating an rgb PTM, or using HSH.  HSH will give more accurate surface normals, and handles shiny material better.  There is a more complete write up of PTM vs HSH here:




Note that RTIBuilder allows you to reprocess a data set without having to find the sphere and the highlights again.  It is pretty straightforward to load an existing project and just try building it different ways.  Instructions for this are in the RTIBuilder User Guide. 


Please update us after you have tried this, and let us know how it goes.



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Thank you for the quick reply Carla, I tried fitting using HSH and yes, it has removed the green and enhanced the shininess. The reduced rendering modes aren't such a problem for us at this stage but I will be interested to see whether diffuse gain and multilight modes can be introduced for .rti files in a future version of RTIViewer.

Keep up the great work!


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