weiwei Posted August 27, 2018 Report Share Posted August 27, 2018 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? Link to comment Share on other sites More sharing options...
cdschroer Posted August 27, 2018 Report Share Posted August 27, 2018 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! Link to comment Share on other sites More sharing options...
weiwei Posted August 28, 2018 Author Report Share Posted August 28, 2018 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 . Link to comment Share on other sites More sharing options...
cdschroer Posted August 29, 2018 Report Share Posted August 29, 2018 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 Link to comment Share on other sites More sharing options...
leszekp Posted August 31, 2018 Report Share Posted August 31, 2018 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). Link to comment Share on other sites More sharing options...
cdschroer Posted September 20, 2018 Report Share Posted September 20, 2018 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. Link to comment Share on other sites More sharing options...
leszekp Posted October 5, 2018 Report Share Posted October 5, 2018 For lithics, I use the normals mode, then manipulate the RGB channels individually for maximum contrast. Convert to grayscale, do some more advanced contrast work (clarity/CLAHE), sharpen it up, and you get a fantastic image of the flake scars on the stone tool, better than any hand drawing. Link to comment Share on other sites More sharing options...
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