Video Transcript
REtracker High Precision Calibrator Tutorial
Marwan Rassi · 1,274 views 22 Mar 2025 LOS ANGELES · Duration 14:26 · youtu.be/6cvvgIrkM2U
Allows you to calibrate your lens and calculate its distortion coefficients. In addition, its unique workflow allows you to measure the nodal offset relative to the lens with extreme precision. This video is courtesy of Tom Funk.
Auto-generated YouTube captions, grouped into ~45-second blocks. Product and technical terms may be misspelled. Timestamps link to the video.
okay so we're going to go through the retracker high Precision calibrator and to start main page you have some options if you have an existing lens file if you want to save your project for use later if you want to load a project you do it here otherwise we're going to go to input data and we'll start with the project frame rate my camera is coming in at 24 uh if you have your tracking delay you would put it here there are ways to get that uh figure it out we typically do it in onreal engine a symmetry has a tool to figure it out uh lens data I have a DZ 20 to 55 and then you're going to need to know
your sensor size this is just a description of course uh but your sensor size uh there are several places to get it online um manufacturer website etc for your specific camera uh I have a Blackmagic 12K it's 25.3 44 by 14.25 6 uh then your focus information now I only have um I don't have my Fizz connected at the moment but if I did I would be able to uh actually link into that and then based on having calibrated that already and when I turn the focus ring it would input this information into this system automatically but I'm going to do it manually here so mine is
currently set to 20 mm and um likewise for the sorry that was for Zoom obviously and then for Focus also going to put it in manually right now I'm set to this is in millimeters I'm set to about 1.6 M uh and then I'm at a 5.6 so that's the uh basic info coming in and then live link um first of all I would show you here so in the setup you're going to want to enable live link Bliss although you could use 3D uh secondly enable trag uh sorry tag tracking and that is of course for the April tag and um once that's done and you run your
bliss software uh you can see here my camera is actually already pointed at the April tag so it shows a one here but it's also shown up here uh in the software so it sees camera one which is what the the camera the live link or sorry the Bliss was set to and the uh camera 101 is actually looking at the um April tag uh but even though it sees it here we're going to need to come down and assign it so we're going to say camera 101 so it sees the two inputs but
it doesn't know what's what so here we're going to say that the camera is camera one and the April tag is 101 so that way the software knows which to use um next is media and you can see it pretty much automatically already saw my feed but uh I'm coming in at 1920 x 1080 uh I have an SDI source and it saw that my first one is the I have a Blackmagic um 8K capture card so it looked at this first one it was there but had I something else I could choose it here uh if I had HDMI coming in or an ndi or whatever uh this is where you would set that this is where you open it if you want to close the feed for some reason you do that
um once we have media we're going to go into the camera calibration so uh we don't start with this we're going to we're going to get to that we come down here first of all I'm going to do enable coverage map because that way I can see where I'm capturing the information um the first thing I do is actually this calibration board and you want to put in the number of rows and columns now remember that what we're looking at are the vertices here not the number of squares but the number of vertices so 1 2 3 4 5 6 78 columns and one two three four five
rows so 5 by8 and mine is on this one um 6.25 CM yours will be whatever yours is for your checkerboard once I have that I can start capturing so basically all I need to do is click here here and you can see this is the cover the coverage map and so the goal is to get these lines covering as much of this as possible now this is a little squeeze because the feed even though it's 169 is coming into this window which is not 16 by9 um so ignore that that is squeezed
like that so next step is basically going to be to move the camera around and or move the checker board and you're going to want to get it at different angles you're want to get it at different um distances uh basically uh you want to cover this with as many different variations as possible not going overboard like you know 12,000 separate hits but you'll see and you want to have some overlap that's probably a little more than necessary but and you can get it right up to the
edge but don't go over and sometimes it won't work uh for whatever reason maybe the lighting is a little off if there are reflections on the checker board sometimes it has problems seeing it if it's at too oblique an angle it might be a problem but uh you can see I can have part of this Square covered but as long as the vertex here is showing vertex is there you can um capture the data so just literally clicking on the screen here so that's the first pass and now
I'm going to actually move the checker board I'm going to put a little closer because it works a little better if you include some uh some close-ups I'm also going to change the angle a little bit [Applause] okay and that gives me a pretty good coverage um at that point we're going to
Simply do add to lens Distortion and we'll notice here when we click on that and it calculates there's my lens Distortion there's my um calcul field of view or focal length in my field of view and um that is pretty much how we do the Distortion now that we have the Distortion we can calculate the nodal offset we have to have the Distortion first so here uh we're going to well change what's on the screen
okay so there's my April tag um now it's possible uh a couple of things here first of all we're going to come down here to the information about the April tag and um the one that I'm using that we typically use is this April tag uh 36 h11 so make sure that's chosen but there are other possibilities but make sure of that also we're using tag ID number one there's a whole library of you know slightly different ones and uh you have to have your tag size correct so mine is [Music] 17 17.25 cm and and then if I click on
generate it's going to make it the correct size so what's happening here is that my Bliss is seeing it here uh this is generated based on what the Bliss is seeing but giving positional information and this is what obviously we're seeing optically and so comparing those at multiple different distances and angles is what allows the calculation of the nodal offset of the Bliss to the camera's nodal point the the lenses notal point and so similar to what we just did and just double checking that they look alike they're aligned right and uh we're basically similarly to what we did in the last step we're going to move the camera
around and or move the uh the tag around and the thing is you can move either it it's about its relative you know uh distance and and orientation uh rather than whether you should move one or the other uh so likewise we're going to click here and that's our first image and basically I'm just going to move it around and around the fact that this checker board by the way is here ignore that right as long as it's seeing this you don't have to have your image completely clear of other things because right now it's only looking for this and it's seeing it
okay now notice here that it says camera 101 it's yellow and that means it's not actually seeing the feed um it it's even though this is positioned it's uh this has to be green if it's not your whole calculation is going to be thrown off so on every single one you want to make sure it's getting a p [Music] Fe and sometimes that's literally just the way that the light reflects or it's something simple like that it might be that's a little too far but more typically it's you know it's the uh it's the lighting and just moving it around a little bit will help okay that should be plenty oh boy that
last one didn't work see I wasn't looking and it I noticed it turned yellow so I'm just actually going to get rid of that one and if you saw it before I clicked off of it there was a bit of a glare on it well there still is on the on the main screen here so yeah so I'm going to go back to that and click this one actually that should do that should be plenty let's see what happens so the next Set uh sorry step is we're going to click on add to nodal offset here and it snapped it right into position now to test it uh what we can do is move back and forth move
around now the fact that it's not there as I'm moving well again that's the tracking delay that's the amount of time it takes for the tracking information to get into the computer versus how long it takes for the video signal to get into the computer the video signal obviously takes a lot more time as it gets processed uh but we can see it it's good nodal um offset and you can use this transparency to see that it's in the same position I think compare lets you put a wipe across it so those are handy little things to have uh to make make sure this all works but um here's what my notal offset is and I know from experience that this is very approximately what it
always is um and again we had to have had this Distortion information before that works otherwise it'll just be wrong so now we're going to go back to settings we're going to go to export export and then here um I just put it in the root here but uh you can either saved as an Unreal Engine file uh lens lens file or an X symmetry lens file which would be an XML but I will save it as that and then I can also go back here and I can say save project and just give it a some name and I could load that later uh that's pretty much it so hopefully that
helps
Transcribed 19 blocks · Source: YouTube