Jump to content
weiwei

The size of dome

Recommended Posts

Hello !I have a question.I hope you will help me .

 I wonder know why the radius of the dome is three times the diameter of the target?Is there any theoretical basis?

Share this post


Link to post
Share on other sites

The recommended standoff of the lights for RTI is 2 -4 times the diagonal size of the subject.  This is described in the Guide to Highlight Image Capture on page 23 (see below)

If you use less than 2 times the size of the subject, you will not get accurate surface normals for the area outside the center of the subject that doesn't meet the light standoff requirement.  I'm asking one of the computer graphics folks to reply as to the technical reasons for this. I know from experience and testing that this is true.

 

Quote

 

Setting up light-to-subject distance

Set the light distance at 2 to 4 times the diagonal size of the target object (or portion of the object being shot). If it is impossible to set the object at this distance, try to set it as far away from the light as possible. The minimum distance is twice the diagonal size of the object.

 

Carla

PS: I removed this identical question which you added to the end of another unrelated topic in the photogrammetry forum.  This is appropriately a separate topic, and the discussion should take place here.  As a reminder to folks - it is not helpful to post the same question in more than one place on the forums.  Please find the most appropriate forum, and either add to an existing topic (if your question is part of that topic) or start a new topic.  Thanks!

Share this post


Link to post
Share on other sites

I am so sorry post the same question in more than one place on the forums.This is my first to post the question,so I will find the most appropriate forum.

Thank you for your replay.It is very helpful for me .

Share this post


Link to post
Share on other sites

Dear weiwei - do not worry.  You set up a new topic, which was appropriate, and there is some information here that hopefully is useful.  Also others should be able to find this, and I deleted the duplicate.  Sometimes it is helpful for me to remind people, since this does happen from time to time.

Welcome to the forums!

Carla

Share this post


Link to post
Share on other sites

This is a useful rule-of-thumb, but I've found that you can sometimes stretch this a bit. I just did RTI on a 7" long Mayan lithic blade inside a dome with a 9" light to object distance, and got a more than acceptable photo out of it (with a bit of work in Photoshop).

Share this post


Link to post
Share on other sites

Well, you can get decent visualizations if you violate this rule, but you won't have good normals, as you move farther away from the center of the subject.  If you use normals visualization or specular enhancement with no color (both rely heavily on the normals data) you will see problems around the edges.  So, it's all about "fit for purpose".  If you want good normals for the whole subject, then you need the standoff.  If you just want some relighting to get a decent screen shot, you might get away with less.

 

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×