Issues with RTI output quality

[Aaron Graham]

We are new to using the ReLight process to create RTI files from sets we've taken with our PTM Dome (WSRP / 2008):
I followed the process and shared the RTI files of some angles of cuneiform clay tablets with the scholar, and the following was their feedback:

"The dual lights barely provide readable images, and the specular mode is useless on them."

"The dual lights are too bright, so that n place can get the lights dark enough for good shadows.  But the specular is way too dark, and when it brightens at a few spots, it immediately looks overexposed!"

We have been using a standalone PTM Viewer that we've historically used to view RTI/PTMs in the past -- does anyone have any thoughts on what I can do to rectify and correct our processing?

Should I go with a different output than RTI? Are there settings I should aim at either in the Raw processing (CR2 / Adobe Bridge) or the JPEGs that I am missing?

[cdschroer]

It's really impossible to tell what is going on without seeing a couple of example input images (for example, a low angle and a high angle image) and also a screen shot or two from the RTI to know what is being experienced.  Are you creating PTMs or HSH based RTI files?  Also, are adjustments being made in the RTIViewer in specular mode - such as turning down the specularity?

Frequently when the specular mode is too dark, it's an indication that there isn't enough even illumination across the surface of the subject.  Also, there might not be enough stand-off of the lights.  How big is the dome?  (I mean the radius from the center of the subject to a light?). How big is the subject?  You need an absolute minimum of 2 times the diameter of the subject in light stand off.  And 3 or more times is better.  Also underpowered domes with very small lights can cause issues.  If you are turning up the iso on the camera due to under powered lights, that can introduce noise.  So can a long exposure.  The impact of these things is very dependent on the camera sensor and the noisiness for various scenarios.

You can certainly try a different algorithm, but if you have problematic images (which you may not - I can't tell from this description) then a different algorithm won't fix it. It is possible there is an error in the fitting being done in RelightLab - if you can try rebuilding an image set that you built in RTiBuilder with Relight Lab and compare results (using the same algorithm to reduce variation - i.e. HSH or LPTM) then that would be useful info for where the issue might lie.

 

Carla

[Aaron Graham]

Thank you, Carla: I appreciate this.1913_14_0370_Obv_TEST3_700.ptm1913_14_0370_Obv_TEST2_700.ptm1913_14_0370_Obv_500.ptm

I've attached 3 different PTM files: The first 2 were created using ReLight, and the 3rd one is via our old process that used a .jsx script in Photoshop.

I will have to look into the specifics you advised me to be aware of (size of subject vs. size of dome).

[cdschroer]

Somehow when I read this the first time, I missed that you were using the WSRP viewer which is the only RTI viewer (that I know of) that supports two lights.  It was done as proprietary software many years ago, so we (and others working in this space) have no way of knowing how that feature was implemented - and therefore can't support it in any way.  If you use the more standard RTIViewer with PTM or RTI files - which is how I looked at these - I couldn't tell any difference.  Also, I don't know what your photoshop .jsx script approach was.  The only software we've ever supported is RTIBuilder - and now Relight.  We have done some batch processing using the PTMfitter in a command line way - so maybe that's what your script was doing? 

[Aaron Graham]

Thank you, Carla: I sent you a DM with a link to a shared folder I created that has the .jsx scripts, both for the Domed processing which still works when all 32 lights operate, and our older Javascript process for domeless/reflectance RTI processing, which has not worked for some time on modern OS.