5 Common Mistakes when Photographing for Photogrammetry | CLICK 3D EP 1 | 3D Forensics CSI

so   hey everybody welcome to click 3d this is  the program we're going to be talking about   photogrammetry and how you can use nothing  more than just a simple digital camera and   some software to create some really really nice 3d  models my name is eugene lisho i'm a 3d forensic   analyst and i've been using photogrammetry for  years now i've been teaching it i've been using   it in my case work and i really believe that  photogrammetry is an amazing technology because   it allows you to do so much with very very little  and so i've been trying to promote photogrammetry   along the way and teach it to people and give  them a lot of tips and advice and that's what this   program is really going to be about so this is the  first episode and today i'm going to be covering   a few things uh but i am going to be covering  five common mistakes when photographing for   photogrammetry and these are things that i have  seen people do in my training courses or just on   their own when they're new to photogrammetry maybe  people that are not all that comfortable with   a camera and so what i want to do is  just highlight some of these things   this is not a full complete list these are just  five common things and um there are other things   that you can consider as well when you're creating  a a photogrammetry model so i've got some graphics   that i'm going to show you and we're going to get  in and we're going to get right to this for sure   so the first one mistake number one not getting  in close enough and i'm not sure what it is   but uh when people are new to photogrammetry a  lot of them take when they take their photographs   they feel like they have to get the the object  or the subject that's of importance plus a lot   of the background and so as a result the image  or the subject is taking up a very very small   portion of the uh of the view and that's  not really what we want to do so for example   if you look at these images that i have  here uh let me zoom in on that a bit more   the image on the left is you know we have a knife  on the ground there and we get a lot of background   right so we have a lot of this background stuff if  i was just interested in the knife though i want   to get in close just like the image on the left  so like i said i'm not sure why of course you   can do both you can get in all around and get  the background and then you can also bring in   the close images so there's nothing wrong with  doing both sets in fact i would recommend that   you do both but oftentimes people just forget  about getting in close okay so that's a very very   simple tip when taking your photographs especially  if you want to reconstruct a a particular model   um don't be far away and it really comes down to  the number of pixels that that subject is taking   up if you're far away in the image it only takes  up you know 100 or 200 pixels well it's not going   to be all that helpful and this is also really  common where with people who are flying drones   so you're flying from very high up you know  you're flying over a roadway or something   like that you're taking a lot of photographs but  if let's say this was a crash scene or something   like that and there's evidence on the ground you  got to get in close to the evidence if you want   to see it in great detail don't rely on you know a  drone that's you know 400 feet in the air um even   though it's a high resolution camera to get you a  really great result you got to get close and now   when i talk about getting in close i also don't  mean just zooming in with your lens try to get   physically close to the object okay so that's an  important point if you get physically close it's   not the same as being far away and then you know  using a telephoto lens so this is uh the first uh   example here and uh keep that in mind okay so uh  number one getting close let's go to the next one   oh yeah i forgot about that i was gonna talk  about this as well and that has to do with   breaking things into thirds so this was just a  tip so we're not moving into the next one just yet   one little tip that i give people is if you  have a subject and you want to get in close   break it into three pieces in your head so kind  of break it up into thirds and here you'll see   that i've just kind of drawn two lines to say you  know there's the bottom of the shoe the middle   and then you know the front end of the shoe  and when taking the photographs for this   uh you know it would look something like this  so you'll see that the front half of the shoe   or the first third takes up uh most of the view  in fact you can even cut off part of it don't   be afraid to get in even closer but this would  work okay um you know 70 you know 70 80 percent   of the image is taken up really close and as  you overlap you'll see that and you've got the   different images there there's enough that it can  reconstruct this particular model so breaking it   into thirds is really really helpful okay now  we're on to mistake number two and that is uh   and i sort of given a hint i talked about overlap  and not having enough overlap so overlap is really   important because a photogrammetry software can  only reconstruct what is common in multiple images   so if you have a photograph but there isn't any  overlap of that particular item in other images   or can't see it enough in the other images it  doesn't get reconstructed and so let me give you   an example of that in a a little video here so i'm  going to play this is something that i was at a a   yard where i was doing an inspection on a vehicle  and i had this interesting truck that was here   with some damage so i just took my phone took some  pictures very quickly maybe a dozen photos or so   and reconstructed the model so it looks pretty  cool but what you'll notice is that there's some   missing things here so up on the top uh over  here you know i had some missing data uh over   here you'll see there's some little patches that  are missing little holes and that sort of thing   and that has to do with not taking enough photos  and not having enough overlap in these areas   and as a result i'm missing some data so if i  had to go back and do this again probably what i   would do is take photos in a ring-like fashion so  i'll just pause it here but basically going around   above and below and then even on the inside like  if you're down at the center of this particular uh   rim here what you want to do is point the camera  upwards and get the underside here of the rim and   that's really what's happening i'm missing some  really really important data here uh so those are   the types of things that i want to make sure  that i that i get another thing is if you're   photographing a person's face it's very common  for people to sort of photograph horizontally   from left to right and capture all this you know  all these different perspectives which is great   but what everybody forgets is this part under here  just under the chin so a good way to capture that   is to photograph this way and then photograph  from the top and then come down so that you got   a few overlapping images underneath the chin and  the neck area and then you'll be able to fill   that and otherwise when you create the model and  you lift sort of turn it upwards you're going to   see just a hole or a patch here now sometimes the  photogrammetry software will try to you know they   have algorithms will try to fill that in but  you won't have any texture and you won't have   accurate geometry whenever you fill in a hole okay  so uh keep that in mind it's really important to   get enough overlap with all those  particular images okay mistake number three   blurred images and i get this often uh sometimes  in the classes people will say hey you know i   took photos and i'm reconstructing the model but  it's not working out like there's something going   on it's either really noisy the model  looks terrible or whatever it might be   so often uh when people take photos and they  just look at the lcd or they look at the you   know the little view it looks great when you have  a picture that is really really small you look at   it it's like wow looks crisp looks like a great  photo well if you zoom in on your lcd on your view   get in really really close and then start looking  at corners of objects and items like that at high   high detail or high zoom factor and then you'll  be able to tell whether or not something is   blurred or not and so the uh the thing here  is that if you have two objects one like this   on the left uh where it's nice and crisp you  have a nice image and you have fine details   the photogrammetry software is going to be  looking at multiple images and the two images   beside each other let's say it'll try to pick off  fine details in one or little features in one and   then try to match them to another image and so if  i have a nice crisp uh image like this one on the   left these little details where you know you get  these sutures or whatever you want to call them   on the skull well those are going to resolve or  reconstruct really really well it's going to be   really really great and you're going to get good  textures as well on the right here i think it's   pretty clear you have a mess so the textures and  the quality of the model here is not going to be   great you're going to have a few problems trying  to put this thing together so a lot of people   don't pay attention to their images in close  detail so make sure that you get in nice and   close and that will be really really helpful to  the reconstructing the models okay number four is   a fairly big one and that is that a lot of  people don't pay attention to three important   camera settings right the three most important  camera settings that are uh you know that you can   easily control and you know some people maybe you  know don't consider themselves photographers but   um you have to remember you're taking photographs  to reconstruct these models and so it's based on   the quality of your photographs so if you have  you know a good digital camera and even on a lot   of the just you know regular phones and things  like that there's little apps now that allow   you to control um things like the exposure and  and shutter speed and iso settings so you know   download an app play with it a bit and get to know  your camera it's really really important so the   first thing that uh the first setting that i think  is really important is going to be your shutter   speed and so if you have a very fast shutter  speed it's great because you're going to get a   an image that's uh with very little blurring  or very little shake so here in these series of   images you'll see that the one on the left is at  1 500 of a second and so it's a nice crisp image   of this woman jogging and it's sort of frozen uh  in time there you don't see much blurring at all   but of course if we reduce the shutter speed  to 1 15th of a second now we start getting   problems well obviously this would not be a  model that you could reconstruct very well   now of course we when you're reconstructing a  model a lot of times it's if it's of evidence   or something like that it's something that's still  it's typically not moving but the photographer is   so if you try to hold your camera steady and take  a photograph and you have a very slow shutter   speed you're going to run into problems you're  definitely going to have blurring so typically   if you're holding the camera once you get down  to about 1 60th of a second or 180th of a second   or lower you're going to want to use a  tripod because it's just not possible to   hold it really really really steady and try as  you may you're breathing you know just pressing   the trigger or the shutter is going to cause  some issues for you and this is also apparent   with drones so when you're flying a drone and  especially if you're not stopped at one one   particular position so some people will take video  and they'll use the video to reconstruct the model   but even you know if you're under windy conditions  and the drone is moving around you know the camera   might be gimballed so it helps to stabilize the  image but if there's any movement you may get a   little bit of blurring so you want to minimize  that as much as possible now the downside of   increasing the shutter speed or making it faster  is that you get less light okay so if you get less   light uh then the photo doesn't come out as well  so you have to kind of balance those things out   all right the next one that i want to talk  about is going to be the aperture okay or the   f number so the the f number is also important to  the amount of light that comes in so if you have   a low f-stop number or a low f number the opening  okay or the iris is open very very big excuse me   so if you have a high f number it's very very  small and so small means you get less light   now the effect of uh or another effect of the  f-stop number has to do with the depth of field   and so if you're photographing something which  is very small so here i've got a this is a   shotgun shell that i'm showing here but if you  look closely here on the left i'm using a low   f number so that means that i have a very  wide opening i'm letting a lot of light   in and it's great because i get more light  but the problem is i reduce my depth of field   so the foreground and the background of this  particular image appear blurred they're just out   of focus okay it's not because of movement that  has to do with the depth of field on the right or   the image on the right okay i've got a much much  better image i'm using a high f number like f 22   or higher increase the depth of field the problem  is it becomes closer to like a pinhole a very very   small opening and as a result well i get less  light so i may have to increase my my shutter   speed to compensate for the light if i have a long  shutter speed going back to the previous slide i   may need a tripod because there's no way i'm going  to be able to hold this open for several seconds   in order to get a nice stable image okay so those  those two things right off the bat a little bit of   a balancing act between shutter speed and then  between the f-stop number um but unfortunately   it's just the reality of what we're working with  that's uh those are the two things that most   people will mess around with on their camera now  there is something else and that has to do with   the iso number so that's the third setting through  an important setting on a camera so uh the iso   has to do with the sensitivity of your sensor to  light so if you're in a very dark environment if   you increase the iso up to a very high number you  can shoot in very very low light scenarios and you   know still gather pretty good images however if  you have good lighting there's no reason to shoot   at a high iso number in fact you want to turn it  down as low as possible now these two images here   don't look very different from one another okay  so the one on the left and the one on the right   look like they're taken from a tripod and um  you know they look pretty much the same but   what we're going to do is i'm going to bring up a  couple of images and we're going to get in really   really close let me drag these well here you got  them you should have them up on the screen here   so you're seeing them uh let me go like this  so this image here on the left this has a low   f uh a low iso number excuse me so this is about  iso 100 and this image on the right has an iso   of about 6 400. now right off the bat you can  tell that these uh pixels here don't look as   grainy okay they don't look as noisy as the ones  on the right and if you've got a lot of noise or   a different gray you know this graininess  or whatever again when the photogrammetry   software is trying to match one pixel uh versus  the other well it's going to run into a problem   and that is that it's going to look for a nice  crisp pixel in one image and then it goes to   the next image and it finds a bunch of noise  so you have to be very wary of the iso number   what i would say if you have good lighting start  with a low iso number first that'll get you the   best best image if you can use a tripod  that's also really really helpful and then   you know use a a long shutter speed a high f-stop  number your image is going to start really really   dark but work down from there so don't just go  and use i know it's so easy to grab the camera and   click the automatic button and and take your  photos and sometimes it's good enough i i   i can't i'm guilty of that too but when you really  need to get into a high quality model and really   uh you know you really want to pay attention  to the details you have to consider those   um these three things on your camera okay so start  with a low iso number high f number high f stop   number and also start with a little bit higher uh  shutter speed uh use a tripod and then work down   from there if you can okay great so uh those are  four things that we've covered already are four   common mistakes uh and what i'm gonna do is i'm  gonna switch into the uh last one here okay so   this is the uh the fifth one that's very common so  that is choosing a bad subject for photogrammetry   now uh sometimes uh you're just stuck try as  you might and believe me i've experimented with   a whole bunch of things that gets me super  frustrated because i'm hoping that you know i'm   going to get a really great model out of something  and unfortunately it just doesn't work out the way   you want okay so some things are just not meant  to be used with photogrammetry just like a laser   scanner or other technologies they all have their  limitations okay so we have to keep that in mind   let me give you a very simple example here  so here i have just a a photograph of a of a   certificate on a wall here and there's a couple  of things going on here that are going to cause   problems first is let's talk about  the background okay so not the actual   frame and certificate itself but the  background a very plain background so   when you're taking photographs of just  plain walls or very flat textured items   they are not good subjects for photogrammetry  they're going to cause you some problems so if   you run this through any photogrammetry software  typically what's going to happen is where you get   high contrast so for example on the right side  where you have the little bit of shadows and it's   dark and then you get to the light that part there  will probably reconstruct so around the frame and   such that might be okay probably a little bit of  noise but near there especially where the wall is   near here you get a piece of the wall that kind  of reconstructs but as you go outward anything   that reconstructs if it even reconstructs is going  to be super noisy okay it's not going to be a high   quality model it's going to give you some problems  there and unfortunately not much you can do there   except you can add texture there are like little  tricks and other little things that you can do   there um you can put up tape you can put up other  things that have high contrast and that will allow   the photogrammetry software some things to hold  on to now there's other things that are going   on in this particular image and that has to do  with uh the glare from the glass so anything   that's reflective will cause you some problems so  as i move the camera the reflections move as well   so if we're talking about trying to match things  from one image to another and they're moving   they're not in the same spot so they're going to  give us some problems this is very very common on   cars on vehicles um vehicles are very challenging  because they tend to be flat textured or very   evenly textured or painted surfaces so the color  doesn't change or you don't get a lot of fine   details they're also very shiny or specular and  so as you're taking a photograph you'll see a lot   of reflections and as you move those reflections  move so it's this moving object that can't stay   stationary from one image to the next image to  the next image and so it causes a lot of problems   for the photogrammetry software couple that  with the glass as well which you know it's   kind of transparent you get reflections  you get all kinds of things happening   cars or vehicles are very very difficult unless  they are rusted dirty they got dirt on them   they're not shiny at all then that tends to help  so there's things that you can do coatings adding   tape or breaking up the texture somehow i'm not  going to get into those kinds of details but   those are the types of things that you would try  to do to improve you know a model with just poor   background poor texture reflections and that type  of thing now a better example would be something   like this so the background is useful because it's  got a lot of different colors and a lot of little   features that it can match from one image to  the next so this is a better subject a much   better subject even the paint brush itself  you'll see it has some writing on there   here where the bristles are there's a lot of  different types of textures and this should   be reconstructed fairly well now even on this  brush there's still some things that could cause   you problems and so the metal surface here is a  little bit shiny so as you move you could get some   changes in color reflection and things like  that this area over here with respect to the   the handle it's still kind of flat textured so  it may not resolve or reconstruct all that well   and so that's something else that you might  need to consider when doing the reconstruction   you know things that reconstruct really  really well are things like dirt so if   you're photographing something on the ground they  work great when you're flying a drone and you're   taking images of the uh like a roadway or ground  or something like that those also reconstruct   really really well um they're not shiny they're  not specular they you know they're obviously still   but they have a lot of texture a lot of  different features that are very unique   and so from one image to the next image  the next image they can be reconstructed   uh really really well so to summarize uh the  five things that can get you in trouble uh one is   not getting in close enough okay so make sure  you get close uh mentally take that subject   or whatever it is that you're gonna photograph  you can break it into thirds and then photograph   each section uh nice and close so you pick up all  those nice little features uh the next one is the   overlap right so you need a lot of overlap in  order to photograph a subject and reconstruct   it properly but make sure you get all those hidden  areas right we want we want to get photographs if   you're photographing a person's face or something  make sure you get underneath you get all the way   around in case of the the rim for the tire right  you have to get underneath and make sure you take   photographs upwards that's really really important  the other one is blurring so don't forget about   blurred images you know make make sure you hold  your camera stable if you can use a tripod that's   even better for sure uh also the fourth thing  your camera settings okay a lot of people don't   mess with their camera too much they just hit  the automatic you know automatic mode and hit   the shutter and then kind of go from there uh  play with these little buttons experiment with   it give it a go um and you'll you'll start to  notice differences and improvement in your model   when you get really really crisp images finally  the fifth thing is there's some things that   just aren't worth it with photogrammetry every  technology has a limitation and unfortunately   photogrammetry does too so if you're dealing with  really shiny objects really flat textured objects   they're not the best subject there's some things  that you can do to help but sometimes it's just   not worth it and you're gonna have to try some  uh different technologies like a laser scanner   or a hand scanner or something like that so uh  those are the five most common things that can   often get you in trouble especially for people who  are new to photogrammetry thanks for watching and   watch the next episode and we'll  give you some more tips take care bye you

Channel: 3D Forensics

Views: 24,856

Keywords: forensics, forensic, forensic science, 3d models, photogrammetry, vr, csi, crime scene investigation, 3d modelling, photos

Id: SzobKDdghGo

Length: 25min 58sec (1558 seconds)

Published: Sun Dec 27 2020