Photographers - Does RTI work for coins?

Coinosaurus · May 18, 2016 1:02AM

Anyone out there familiar with RTI (Reflectance Transformation Imaging)? It's a 3-d imaging system that may provide more visual info than 2-d photography.

Here's a few examples-
http://culturalheritageimaging...Do/Fields/numismatics/

Has anyone tried this?

CoinZip · May 19, 2016 9:46AM

Has anyone tried this?

Dino-Lite has some newer models that do something similar.. Extended Depth of Field (EDOF) and Extended Dynamic Range (EDR)

messydesk · May 19, 2016 11:44AM

Interesting computational photography technique. The issue with showing someone a picture taken using this technique is that they need special viewing software to view it. The "image" that is being viewed has been stripped of all shadows and highlights. Each pixel represents the actual color of the coin as seen when the light is ideally placed to see that color. The viewing software is what provides a "virtual light" to view the coin. In order for the light to work, the coin now has to be a 3D surface, rather than a 2D image. In addition to the color, the elevation, surface normal, and reflectivity of that point of the coin must be known. All of these are derived from the initial set of photographs that are taken of the coin. A spot that varies from really bright to really dark is highly reflective, while a spot that doesn't vary no matter how it's lit could be fine corrosion. The surface color, reflectivity, normal, along with the size, shape, color, and position of the light (not demonstrated was how to diffuse or harden the light) determines how the coin is rendered for the viewer. Pretty cool.

The amount of data to transmit to someone for viewing, assuming they have the viewing software either installed on their device or available as a WebGL (or other similar technology) browser plugin would be more than for a normal image, but not by orders of magnitude. Each pixel needs, in addition to the RGB value, a z-coordinate, a 3D surface normal (x,y,z), and reflectiveness, which comes out to under 3x as much data as a plain old 2D image. It probably wouldn't be very tolerant to lossy compression, but it is still far less data than a video and gives the viewer much more flexibility.

So would taking the 24 pictures (the example in the article) slow the process down so much that it would make a TrueView cost $100 per coin? Nope. Much of the time spent taking the perfect coin shot is adjusting the lighting manually and interactively until it looks best. This is no longer necessary, as the privilege (burden?) of lighting is shifted to the viewer. The photographing step, including the RTI surface generation could be fully automated. The artistic work of the photographer would be limited to setting up an ideal representative traditional image by moving the virtual light(s) around and taking a virtual photo.

Will I be offering this service soon? Nope. Way too complicated for a low-volume one-man shop to set up at this point. Would I if I could? Damn straight!

Edit: After digging around the website a bit, it looks like the viewer and the RTI image builder software are free downloads. There are also samples to play with. The image capturing equipment is another story, however. For coins, you'd want the light to be on a robotic arm and controlled remotely along with the camera so that it's a repeatable process for all coins.

ricko · May 20, 2016 12:54AM

That is impressive.... would be great for viewing coins.... sure, expensive now, however, like all

new tecnology, it will come down in price.... Well worth it IMO...Cheers, RickO

mercurydimeguy · May 20, 2016 1:02AM

The problem with increasing capabilities of image processing is that the coin image begins to take away from the hobby as it makes it more about what you can see under 100x magnification versus what the coin actually looks like in hand, to a normal set of eyes.

Even the prettiest model on earth, if you take a close up of him or her at 50x, they look completely different. I for one think that coin imaging is where it needs to be, and any more, is distracting from the hobby.

I would want no more than what I have now to image raw coins. Slabs are a different beast! I wish slab imaging was easier somehow, because the slab is the problem in 99% of the instances...

messydesk · May 20, 2016 1:12AM

Originally posted by: mercurydimeguy

Even the prettiest model on earth, if you take a close up of him or her at 50x, they look completely different. I for one think that coin imaging is where it needs to be, and any more, is distracting from the hobby.

I would want no more than what I have now to image raw coins...

What this technology provides is not the ability to increase magnification, but the ability for any viewer to change the lighting while viewing the coin, just like you do when inspecting a coin in person. I downloaded and played with the viewer and the two samples. Unfortunately, neither of the samples is a coin, but the samples do give a good feel for what is possible.

Photographers - Does RTI work for coins?

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