Cross Polarisation Explained by Grzegorz Baran

#polarisation #pbr #crosspolarisation #polarization #crosspolarization #realitycapture
In this video I am trying to explain the polarisation and cross polarisation phenomenon
and present how it can be used as a tool for reality capture.
This is definitelly something worth to know 'good to know' when we deal with any shiny or reflective surface capture.
In details I present
- how polarisation and crosspolarisation works
- how to use polarisation filters
- the real color of stainless steel, gold and silver metals after we remove all reflections and glares from them
- difference between linear and circular polarisation filters
I hope someone finds this video useful.
If you like it and want me to create and share even more content like this one, please subscribe to my channel and leave the thumbs up.
Also I would appreciate if you share this video to anyone who might find it helpful as it really helps to grow this channel.
Big thanks for watching and for your support.
For those interested here is my Artstation profile:
www.artstation.com/gbaran
Cheers!
Grzegorz Baran
Btw.
big thanks to Roy Streicher who pointed me out that I wasn't correct regarding to metal surface color.
He helped me to understand that there are two different type of surfaces.. metals and non-metals (dielectrics and non-dielectrics)
Metals reflect polarised light while non-metals depolarise it. It is because metal atoms have pararel layered structure so they reflect the light under the same angle while non-dielectics(non metals) are more random and when the light hits the surface it enters it and bounces back in more chaotic manner (depolarised). So nondielectircs (nonmetals) depolarise reflected light.
So this is why we can cut the glare form non-dielectics but we can still see the surface color information as it is being transmited by depolarised light and filter doesnt cut it while when the polarised light hits the metal surface, it reflects back polarised so the color information with glare is cut by the polariser.
In my experiment I was able to see the silver as I saw the oxidised layer which is non-dielectric (isn't metal)
Maybe will cover it in a video about what colors are :)
Anyway I was wrong telling that with crosspolarisation we can distingush silver from stainless steel metal.. we can't .. my bad :(
----
Music for all music-right claimers:
I composed all the music for all my videos with this one included.
The music is composed with use of purchased and licensed for commercial use content (www.loopmasters.com)

[@nellomaxim]

I was looking this topic up in lots of videos but you have brought together a loy of the seperate slbits of info in to one place for a proper consolidated fundemental understanding

[@GrzegorzBaranArt]

Thanks, very appreciated. I think I coverd it even better in some of my further videos

[@mahmoudjassim8397]

First of all thank you for this great information. Second: When I saw this video, I said to myself, I do not think that this person is interested in ordinary photography only, he must be a specialist in the field of 3D software, after I saw the logo of Ubisoft on your T-shirt, I told myself that there is no doubt that he works in the Ubisoft company, and after I visited your account on ArtStation I said yes, he is a specialist in texturing. Thank you again.

[@GrzegorzBaranArt]

You are welcome :), doing my best :)

[@mahmoudjassim8397]

@@GrzegorzBaranArt 11:43 800 Lumens! Too strong to shoot the eye, it will hurt the eye. What is the suggested lumen value when photographing the eye?

[@GrzegorzBaranArt]

@@mahmoudjassim8397 I would simply use a flesh light to do it and problem solved. The flash is usually to quick to damage anything :).. can be also much stronger to 800lumens. Cheers!

[@rafograph854]

I bounced around the web and didn't found a specialized and detailed explanation like this. Thank you very much

[@GrzegorzBaranArt]

You are welcome :)

[@Tarbard]

Such a great video

[@GrzegorzBaranArt]

Thank you Darren, big thanks for watching :)

[@sequoia821]

This is so helpful. Thank you so much! And your dog is so lovely.

[@GrzegorzBaranArt]

Thank you so much from us both :)

[@jamesvella]

Excellent video Grzegorz! I have been watching your work for awhile and I think you explain things in a fantastic way. Thanks for sharing I would love to see and hear more from you, keep up the great work mate!

[@GrzegorzBaranArt]

Thanks James, appreciated

[@NicolaiBecker]

Awesome tutorial, thanks a lot!!

[@GrzegorzBaranArt]

Thank you. Glad you like it :)

[@peterallely5417]

Really appreciate your videos, friend. Please keep making them 🙏🏼

[@GrzegorzBaranArt]

Thank you Peter for your kind words :D, very appreciated. I didnt give up with new content yet, so stay tuned. It just takes some time to make it.

[@benarandano]

the most clever explanation!!!! Thank you

[@GrzegorzBaranArt]

Glad it was helpful!

[@Smoluck]

Nice instructive video. Thanks for sharing.

[@GrzegorzBaranArt]

Thanks, please read the 'description' section as I was wrong about a few things and I explained them there. Cheers!

[@rameshkumarthakur8565]

This was the best explanation on the topic of cross polarisation technique ,really helpful .🎉

[@GrzegorzBaranArt]

Thank you, very appreciated

[@vrfxrealtime]

amazing again, thanks for this clear explanations and sharing!

[@GrzegorzBaranArt]

You are welcome again :)

[@skybone7]

Very informative. Thank you.

[@GrzegorzBaranArt]

Glad to know you found it useful :) Cheers!

[@georgigeeksky8349]

Thanks for the great explanation!

[@GrzegorzBaranArt]

You are welcome :)

[@442jetmech]

You are very well spoken and made those much easier to understand. Thanks for putting so much effort into the video!

[@GrzegorzBaranArt]

Thank you very much

[@rendermanpro]

Such a wonderful channel!

[@GrzegorzBaranArt]

Thank you renderman, very appreciared :)

[@pasindueranga121]

Very informative video!

[@GrzegorzBaranArt]

Thank you

[@ChrizLizt]

Very cool. thanks for explaining in depth and with testing. Looking forward to your Photometric stereo technique.

[@GrzegorzBaranArt]

Thanks, still on it but getting closer :D to the editing phase

[@ofiravphotographer]

Amazing explanation, thank you! goes deep but still made simple to be clear

[@GrzegorzBaranArt]

Thank you Ofir :)

[@mateolinares1634]

This is such a great video! Trying to get a budget lighting setup for indoor photogrammetry and this has helped a lot

[@GrzegorzBaranArt]

Glad to hear that, thanks Mateo

[@finnspencer9924]

what a great video, thank you

[@GrzegorzBaranArt]

Thanks Finn, super happy to hear that... just please read the description since I tell there that I was wrong regarding to metal vs silver part in this video and explaining why. I guess I will cover it deeper in the one about colors and how surface reflects the light :) in a future. Cheers! :)

[@vrguytokyo]

Excellent! ...and... Nice shirt agent!

[@GrzegorzBaranArt]

Cheers :)

[@UnrealVirtualUniversity]

Awesome, a quite complicated and interesting topic that isn't well covered in yt. And the stereo photogrammetry? I can't wait for it, clicking bell now. Thanks for sharing.

[@GrzegorzBaranArt]

Thanks a lot, appreciated :D ... it's a photometric stereo I am planning to cover next though.. if nothing changes this is the plan for the next video. But since crosspolarisation is a tool useful for both, photogrammetry and photometric stereo techniques I decided to cover it as a seaparate video.

[@UnrealVirtualUniversity]

@@GrzegorzBaranArt Really useful and well thought. All this topics seem like tricks magician don't dare to tell and you are pouring buckets of pure knowledge about it. For sure is going to help many to start in CGI.

[@Gringottone]

I really love your channel mate.

[@GrzegorzBaranArt]

Thanks Michal, I am really glad to hear that

[@mr_vky]

Thank you

[@GrzegorzBaranArt]

You are welcome :)

[@anadetoledo1]

Thank you! ;-)

[@GrzegorzBaranArt]

You are welcome ;P

[@michaeltyers7336]

I'm going to try 3D printing filter holders for my speedlights.

[@GrzegorzBaranArt]

Good luck Michael, feel free to share if it worked well or what problems did you encounter :) Cheers!

[@iskrenmarinov9737]

Thanks man !

[@GrzegorzBaranArt]

Anytime :)

[@tomaspuskas950]

Here because of William Faucher. thanks

[@samcraftYT]

Great explanation Grzegorz. Are you at Montreal? That reflection floor and surround look like the Forum

[@GrzegorzBaranArt]

Thanks, nah, it was Metro Centre in Newcastle (UK) :D

[@Barnyz]

i had no idea about using 2 polarisers! Cool and interesting video, i hope the silver cats were not a present from you 😁😁😁

[@GrzegorzBaranArt]

Thanks, nah, they were not ;P

[@JamesKellyWickerman123]

Cross polarisation is something I was aware of and understood the basic concepts of but this video really helped to make the technique really clear! Thank you for such an in-depth video. My only question is have you experimented with using a diffuser on top of a polarised light source? Would it re-scatter the light passing through therefor returning it to a non-polarised state or would the light stay polarised after passing through the diffuser?

[@GrzegorzBaranArt]

Thanks James, I am really happy to hear that as that was the main purpose of this video. I made it since while ago I struggled to understand polarisation by myself and had to spend some time before it all made sense for me. I didn't use diffuser but in theory .. when the polarised light bounces from any reflective surface it doesnt depolarise itself but changes angle of polarisation. So if you run polarised light through diffuser without changing light direction it shouldnt affect polarisation at all. If you use the diffuser which bounces light in many directions in worst case scenario this one might affect the angle of polarised light and turn it into randomly polarised one depending on how many different angles were there to bounce. I mean that it will be still polarised but under different angle. As the standard polarisation filter can block under certain angle at the same moment, you select this angle by rotating it. When polarised light bounces from any other reflective surface it changes its polarisation angle. So if the subject is illuminated by polarised source of light under angle X .. but also by mirrored part of it under angle Y.. by rotating the polarisation filter you have to chose do you remove part of reflection under angle X or Y, you cant block both at the same time. So the answer depends on what type diffuser you had in mind. So to find an answer try to think how the light bounces after it was polarised before it hits the subject. As far as I know depolarisation is a way more complex process to polarisation and has to be done by more complex devices to polarisation filters .. and even thou it is very hard to fully depolarise the light :)

[@Outdoorshuntingshooting]

@@GrzegorzBaranArt Oh, that's really useful info, I wondered the same, but also, to save making or buying a holder I have placed my filter behind the clear plastic cover and no difuser as it reduces light output. I Might have to rethink that. although my results have worked so far.

[@ohmss006]

Excellent video and very informative, so thank you very much for this! But I was wondering, might you know the difference between a 45 degree and 90 degree polarisation sheet? There are many that are advertised with different angles with little-to-no explanation, might you know what these different angled degrees mean by any chance??

[@GrzegorzBaranArt]

Thanks. You change the polarisation angle by rotating the filter. There are two types of polarisation filters.. circular and linear ones. Linear filters works both ways (double sided) while circular only one way (one sided). The polarisation angle depends on orientation of crystals the polarisation filter was made of - its fixed. I guess polarisation filter might be cut into sheet with them being aligned verticaly: up - down.. or horizontally: left-right .. or from one corner to another - 45 degree. The thing is that orientation of them depends on filter rotation. Cross-polarisation angle, depends on angle between two sheets in relation to eachother. So depending on what you want to do, if you want to automate production of LCD sceens, you wont align all filters manually but you will use huge roll of polarisation filter - in this case you need to know how it is oriented. If you plan to rotate it manuyally per case, like I do, orientation of polarisation crystals within this sheet doesnt really matter. At least this is the only reason for polarisation angle being defined by producers which comes to my mind. So if you purchase a rectangular polarisation filter as you want to build your own LCD screen, it has to be oriented in an exact direction. And you need another one which is oriented 90 degree to the first one. If your screen is 1x2 meters.. you will need one sheet which is 1x2m polarised vertically and one 1x2, which is polarised horizontally. If you purchase 2x2 and cut it in half you wont be able to make it.. dunno. This is the only thing which comes to my mind which would explain why someone tells you the direction/orientation of crystals.. to save your money so you use the sheet you purchased in the most efficient way instead of having leftovers :D

[@ohmss006]

@@GrzegorzBaranArtOnce again, thank you very much for that detailed and informative response, really grateful and I hope it is useful to others too! 🙂 In my case (where I would want to do Cross-Polarisation) I would want to place Polarisation sheets onto soft boxes (e.g. 30x30cm), working with a Circular Polarising Filter (CPL) mounted onto the camera lens (as you would). What degree or angle should I use to make the Cross-Polarisation effective to remove all, if not most of the Specular/Highlights? 🤔🙏

[@nervousorg]

Thank you Grzegorz. You are saying in the video: "If we capture two images with and without reflections, by subtracting them we can isolate the specular level." My question is if you have the routine to capture roughness map using a photogrammetry?

[@GrzegorzBaranArt]

Unfortunately there is no simple answer to your question. There are many ways to create roughenss map and each has its own pros and cons. I plan to share some info on this subject at some point in the future. Regarding the routine you asked for: you would need to capture 2 images from each camera position - one fully cross polarised and one without cross-polarisation with glare on the subject. Next you need to reconstruct the subject from cross-polarised images and generate the texture from it. After replacing these images with these with glare you need to re-generate texture again. This way you should get one texture map with glare and one without.

[@nervousorg]

@@GrzegorzBaranArt Thank you again, will definitely have a look how it could be done. Just to take 2 images with and without cross polarization will ruin all my turntable automation...

[@epinician]

Dear Grzegorz. Thank you for such a beautiful explanation. It's people like you who that give me hope for humans. Unfortunately I did not fully succeed in implementing your ideas on cross polarization. Here is my setup: Macro lens with B+W Circular Polarizer and lighting with Twin flash with Linear Polarizer film stuck on with 1" doubled sided clear tape. I am unable to remove specular highlights completely in this setup even at f/29 (1/200s shutter speed and 100 ISO) to completely eliminate ambient light. Rotating the Circular Polarizer helps but the effect is not dramatic as yours. I wonder if the gel film on the flash is reversible or not. The circular polarizer of course can only go on the right way since it is threaded. But can the linear polarizer be on backwards? I cannot remove easily as I have limited supplies. Here are the items i used: Canon Rebel with 60mm EF-S Macro plus Yongnuo YN24EX Twin flash set to ETTL with +1/3 exposure compensation. The Kaeseman Circular Polarizer and Linear Polarizer film (0.3mm) are both high quality: B+W products. The sticky tape for the flash heads is 1 inch wide double sided clear tape. Is a twin flash too close to the subject to to remove specular highlights, I have seen professional products (Polar Eyes, Dentalize) that seem to succeed and want to use a homebrew to get the similar result so i can have more control over the process.

[@GrzegorzBaranArt]

Thank you for such kind words

[@epinician]

That does help; I will keep trying. Thank you very much for responding so quickly.

[@user-gu2ie7kv4c]

Hi,thanks for your video. I'm learn a lot,but here is a question, i use 4 light with the polarization sheet on different position and angle,and my camera also ues hte polarization filter,but the glare still here,so the light position angle should be same with the camera?

[@GrzegorzBaranArt]

Hey, not sure what is the question. Polarisation filter on the camera lens, can remove glare under one angle at the same time. You need to rotate the filter to align the polarisation filter with this angle. Its set when the flare is gone. If 4 light sources cause the glare under the same polarisation angle, the polarisation filter at the camera still can cut it, but the trick is to make sure all angles aligns, therefore you need to change te polarisation angle for each light the way, the angle of polarised glare light is the same and aligned with the polarisation angle of the filter mounted on the lens.

[@user-gu2ie7kv4c]

@@GrzegorzBaranArt ok,happy to see your reply！thank you so much

[@kevinbrouwers9381]

@@GrzegorzBaranArt So it is possible to use different polarized light sources but you have to align all the filters? I wonder if you could still move the camera around then or would you need to realign the filters every time the camera changes position? I also plan on using this for photogrammetry but with always on lights all around the subject

[@GrzegorzBaranArt]

@@kevinbrouwers9381 everytime camera angle changes in relation to the source of polarised light, the filters need to be adjusted to match the new angle. So, nah, I would not move the camera nor the light sources if set, I would just move/rotate the subject instead. To be honest, it should work in theory, but I havent tested such setup as I never needed it. I might tho to record a video to cover it. Please let me know if it work for you. Cheers!

[@michalserafin6972]

@Grzegorz Baran mam pytanie, czy najpierw robisz zestaw zdjęć z polaryzacją, a później bez? Czy najpierw od razu po dwa zdjęcia i przy każdym włączasz i wyłączasz polaryzację ?

[@GrzegorzBaranArt]

To zalezy od przypadku i tego co chcesz osiagnac. Robienie podwojnych zjec jest stosunkowo skomplikowane. Zdjecie polaryzowane i niepolaryzowane powinno byc wziete z dokladnie tej samej pozycji kamery. Mozna to obejsc poprzez automatyzacje lub podwojny skan w dwoch wersjach i reczny matching. W praktyce staram sie unikac takich przypadkow i uzywam full-crosspolaryzacji i jednej serii zdjec.

[@michalserafin6972]

@@GrzegorzBaranArt Bardzo dziekuje, za tak szybką odpowiedz. Robie skany kilku toreb skurzanych, set zdjec bez polaryzacji (zakladam ze, bede zdejmowal tylko jeden filtr z lampy, zrobilem luzny zaczep, ktory pozwoli mi nie ruszyc lampy, ani aparatu) bedzie mi potrzebny do zrobienia mapy roughness. Wydaje mi sie, ze to chyba jedyny sposob, bo matchowanie sie pozniej dwoch oddzielnych setow zdjec to jakis koszmar

[@peterallely5417]

I never knew that Ryan Gosling was a photogrammetry expert in his spare time.

[@GrzegorzBaranArt]

:D

[@swavecb]

Can this lamp, with polarization filter on, be put behind diffusor? Will it loose or weaken polarization?

[@GrzegorzBaranArt]

Polarisation filter polarises the light. When the light bounces from anything it changes the angle of polarisation. If the light is diffused, it basically gets bounced in many directions so in practice isnt polarised anymore. So no, if you put light diffuser after the polarisation filter you simply kind of depolarise it. Depolarisation will be as strong as diffuson is. I guess you want to diffuse the light to soften it, in this case you can diffuse/scatter light only before it passes through polarisation filter and gets polarised.

[@neotheek]

can we use linear polarising film in light source?

[@GrzegorzBaranArt]

Of course we can :). I do.

[@lipsach]

What would happen to a mirror, would it also turn black?

[@GrzegorzBaranArt]

WIth perfect cross polarisation and the light coming from a point light.. yes. Since mirror reflects almost 100% of the light, every single ray reflected would be cut. Same applies to metals. But only in theory, as in practice cross polarisation with these filters isnt 100% accurate and some of the light still leaks through the filter. It is caused also by the angle differences within the light surface as light rays cast from different points are cast under slightly different angle. So in practice, when you cross polarise the mirror you should cut most of the light. And even if you cut 99% you should still be able to see this leaked 1% which would appear probably as a dark. So you wont see the glare but you should still be able to see the position of the actual source of light reflected from the mirror. If you used a bright LED diode like the flash mobile has and cross polarise it, in the mirror you shuld be able still see it but as a dark, purple one. And last but no least, if you use the polarised light on the mirror, it reflects and lit the environment. Since all the environment will be lit by the different polarisation angle, it wont be cut during cross polarisation and will reflect in the mirror :). I believe that if you use a laser point light which cast a point light and use best polarisation filters and measure the result with 1px sensor camera you should be able to cut 100% of the light reflected by the mirror and see nothing.

[@DrewPlusPluss]

Are these linear or circular polarizers?

[@GrzegorzBaranArt]

These with the camera mount were circular while the square/sheet one was linear.

[@darty367]

Hello Greg, good video. I personally use cross polarisation for several months with some automatisation as you can see (sorry for the quality) photos.google.com/share/AF1QipMKruykwVwmw79ESTpTCIwhAwZpjgiukarxvLWLUPqXCbqhOaCttHETYJ-xQp0J6g?key=TnZQNHVLNVl3ZDZ3QWxQQW9aWnAtVkZseVZ5VmF3 In my knowledge, this is also the only way to extract a real value for roughness/specular map. Cross polarisation hated reflections, so use only a black mat surface as much as possible when you shoot and in controlled area.

[@GrzegorzBaranArt]

Thanks, makes sense. Unfortunatelly for photometric stereo I have found that white background gives me better results and significantly reduce the capture/exposure time. Also it is way easier to auto-mask out props for photometric stereo when the background is white. For photogrammetry capture black background it definitelly makes sense. I agree with the roughness/specular but its still a bit tricky and not sure is it worth to spend effort on it instead of generating it.

[@Aphobius]

What kind of idiot makes photography tutorial, but can't set focus manually?

[@GrzegorzBaranArt]

Any reason for being so rude and toxic Bogdan? Why assumption I dont know how to set focus manually?