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RTI Viewer: Resolution and Colour


Sigmund

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Hello,

 

I'm a RTI beginner so my first questions might be foolish.

 

My first RTI results are good but, comparing them with the video examples on the CHI homepage, two things are still disappointing:

 

1. I can't manage to take the colour out as in the videos. My objects are painted stones. I would like to take out all the colour so that the painted parts disappear. However I try to change the setting with Specular Enhancement - there are always gleams of the original colour left.

 

2. In the videos the RTI viewer can zoom in very much. This is not the case with my RTIs. Is this a camera problem?

 

Another question I have on my mind is: Has the PTM viewer any advantages over the RTI viewer and where can I download it?

 

Sorry for asking foolish questions and thank you!

 

Sigmund

 

 

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1. To remove the color in specular enhancement mode, move the top slider "kd" all the way to the left.

 

2.  How far you can zoom in is a function of the resolution of your camera, and also how close in you were to the object when you took the images.  This is the same as regular photography, a function of how many pixels you have on the surface of the object or area you care about.

 

3.  The ptmviewer does have some features not found int he RTIViewer, however it is a research viewer and the interface is more difficult to work with.  It also only supports the ptm format, and not the .rti files.  You can get it from the HP website http://www.hpl.hp.com/research/ptm/downloads/agreement.html   There are only very limited instructions.  Also note that it will not work on the latest Mac OS releases 10.7 and above.

 

Carla

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Dear Carla,

 

thank you for your reply!

 

1. I already used the slider kd but there is still some colour left. Is that normal and what does it depend on?

 

2. In a RTI manual (West Semitic Research 2011) I found this: "Place your camera approximately as far away from the object as your string". However, this is too much, isn't it?

 

Thank you!

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1.  I am guessing that you mean there are still some light and dark areas, and not actually any color?  Maybe you can post a picture with what you are seeing?  (it's easy to add a photo - just use the "attach files" option.)

 

2. The length of the string and the distance of the light are unrelated.  The distance of the light (which you use the string to measure) is a function of the size of the object or portion of an object that you are imaging. The absolute minimum is 2 times the diagonal measurement of the object, and we recommend 3 times if it is possible within the space and with the light you are using.  The distance of the camera is a function of the optics (i.e. lens choice) and also the camera itself  (for example a full frame sensor camera vs a smaller sensor camera, which affects the optics)  You should choose appropriate optics to get your subject in focus.  We recommend using prime lenses such as a 50mm macro or a 100 mm macro.

 

If you have more questions about the camera position and string length, please post them in the capturing Data: Highlight Method forum.

 

I am not familiar with the manual you mention.  I will suggest to you the Guide to Highlight image capture on the CHI website:

http://culturalheritageimaging.org/What_We_Offer/Downloads/Capture/index.html

 

I'll note that the one currently on the website is a couple of years old and we are working on a major update to this guide, based on feedback from recent RTI training sessions. We are fortunate to have an advisory team on a grant we are finishing up, that have also provided really useful reviews and suggestions.  The updated guide should be out in April, and we will announce it on this forum site as well as to our email newsletter list and on our website, and facebook page.

 

We actually have a number of updates coming out in April and May, including user guide updates and software updates to both the RTIBuilder software and the RTIViewer software, thanks to some funding in our Institute of Museum and Library Services (IMLS) grant project: 

http://culturalheritageimaging.org/What_We_Do/Projects/imls/index.html  (this page will be updated as well.)

 

Carla

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  • 3 weeks later...

Dear Carla,

 

the stones I deal with were partly coloured with black colour in recent times. On my RTIs there are always some very dark areas left and I can't change that with the slider "kd". Is this normal? Is the colour hard to fade out?

 

Thank you

 

Sigmund

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Dear Sigmund (and others),

 

The advice you were given, "Place your camera approximately as far away from the object as your string" is completely *Incorrect*, and seems somewhat novice.

 

If you follow that rule you will NOT be taking full advantage of your camera sensor and full pixel coverage that it can offer.

 

The basic idea is to fill the camera frame with your 'area of interest'. Maximize those pixels, and make everyone of them count towards careful documentation — don't just point the camera at the subject. But rather, carefully compose your composition. Lens choice can make a big difference in this step.

 

Don't forget to include both spheres — place them carefully, as so they don't shadow your subject when you light from different positions.

 

Thanks for posting. Great to Clarify this matter.

 

marlin.

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Sigmund,

 

If you built a PTM, you can try looking at it in the ptmviewer from HP.  I don't think there is a problem in your capture set (the original photos you captured)  I have noticed that with some objects that have contrasting black and white area, that in RTiViewer there is still a bit of contrast, even with no color (i.e. kd slid all the way to the left)  The ptmviewer does a better job with this.

 

A couple of notes about the ptmviewer.  It was written by folks at HP Labs many years ago and is not actively being worked on. We consider it a "research" viewer due to it's limited documentation and interface and some other niceties that are missing.  That said, it performs very well, and is quite robust.  I'll note that for users on the mac it will not run on Mac OS 10.7 and higher.  

 

You can pick it up here: http://www.hpl.hp.com/research/ptm/index.html

Scroll down to the list of links at the bottom of the page, and you will see a link for  Downloads of PTMviewer, PTMfitter, Sample PTMs, etc. - that will take you to a page to agree to the license and download the software.

 

And finally - I will note that the RTiViewer which is open source was not based on any of the code in the ptmviewer which is not an open source project.  In other words, RTIViewer is a completely independent implementation. So the fact that there are some differences in how things are implemented is to be expected. 

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Actually, it does!  When you have everything set the way you want, you press the letter "t"  The ptmviewer will make a targa file (an older format that is uncompressed and used to be used a lot in game development)  This file will be placed on your hard drive in the same folder as the ptm file you opened.  It will be named screenshot001.tga.  If you make more they will be screenshot002, etc.  The tga file can be opened in photoshop (or other image processing tools) and converted to something else more standard.  The viewer will give you no feedback when it makes the file, but it will be there.  We used the ptmviewer exclusively for years before the RTIViewer was created.  There are a number of features that use the keyboard to enable.  There isn't a true user manual for it, bu there is a basic help file with some information. 

 

Carla

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