The Camera Calibrator Tag
Posted: 12 September 2012 02:50 AM   [ Ignore ]  
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Hello!

This is a very useful tool!
I was just wondering how you would go about to using this with a lens distorted image?
And especially, how would you use it with f.ex after effects?
Do you need to undistort it (somehow?) > take it into C4d > add the 3d geometry > redistort everything in AE.
If that is the case, how do you do this?

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Posted: 12 September 2012 07:04 AM   [ Ignore ]   [ # 1 ]  
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Hi Racecar,

Typically any image (or footage) should be undistorted, before used in the Camera Calibrator. Of course the is an amount of distortion that will be OK. However this is a process that calculates the data of a camera based on the idea of Vanishing points, which means that any distortion might change that and lead to less precise results. In that way, your question is spot on.

In short:
The idea is normally, that any lens correction will alter the quality of the image. As each change of the position of a pixel, which is not based on full pixel movements will mix pixel values. But exactly this is typically the case while correcting any lens distortion. The idea is, if not requested (director) otherwise, that the original footage as well the final footage stays untouched, for quality reasons. This means that anything in the pipeline has to be changed back and fore.

As a consequence the CG footage would suffer by adapting the distortion to it, later on. For that the Physical camera has some options. The suffering by itself sounds not nice, but most of the time I found myself adding a little blur to the CG footage anyway, as it is mostly more crisp than practical footage. If that isn’t good enough, you need to render larger, if the Physical camera is not your first choise anyway.

How to do that back and fore distorting? I like to work with “Lens Grids”. These are poster like Checkerboards, that one photographs and applies then the lens correction on. From there you know what the lens does, and the values from that process can be applied positive or negative to gain the results your need.

There is one thing that needs to be clear. An work on CG footage in post that was not lens corrected, will alter the size of the material. In some cases you need to render larger with a wider field of view—if—the CG content inside of the frame touches that area (area means here if the process shrinks to a certain degree the image, and the footage isn’t covering the full frame anymore)

To test your round-trip, your initial test should be, if you can work with the checker board inside Ae, and apply first the distortion to it and in a second step, reverse that effect. Then compare the original checkerboard and the double adjusted one, are they the same (perhaps Blend mode Difference).

If you like to work with footage, keep in mind that lens distortion can be tricky, and is not as simple as some believe. E.g., a Fisheye for example is in most cases recognized as lens distortion in the “best way” but it draws the lines as it should be… however there is an option with cheap constructions that these lines are not “drawn” as they should be, then I would talk about lens distortion. (This might be seen differently by some people…and there are different FishEye definitions available, so—long story) What I like to say is, there are several “layers” what a lens can do to your footage, a reason why I suggest to know your lens and the needed process.

I have shortly discussed the quality for images in my Siggraph Presentation
http://www.cineversity.com/vidplaytut/siggraph_rewind_2012_dr._sassi 
As you might have the best quality, you might follow the list that I share there.

In short you need to know what you have as source footage or “background-footage” This will lead you pick one of the ways I have mentioned above.

All the best

Sassi

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Dr. Sassi V. Sassmannshausen Ph.D.

Photography For C4D Artists: 200 Free Tutorials: Texture, Panorama, HDRI, Camera Projection, etc.
https://www.youtube.com/user/DrSassiLA/playlists

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Posted: 11 April 2018 10:26 AM   [ Ignore ]   [ # 2 ]  
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Is it possible to have this camera projected texture to be able to react to light that may be placed upon it. So if I have a sun facing on the faces of the buildings as seen in the demo, is it possible for the faces in light to receive sunlight and the ones in shadow be in shadow?

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Posted: 11 April 2018 11:00 AM   [ Ignore ]   [ # 3 ]  
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Hi Fauntail,

The Camera Calibrator is just a tool to “re-engineer” the camera point of view, point of interest (Directional) and the field of view.

The image used to do that is like any photo a result of merging the 4D world (3D plus time) into a 2D representation of it. In other words, the light is backed in. To have a new light source have any “natural” influence on the illumination, the photo would have the need to separate the colors, textures and shadow/light in passes. To my knowledge there was only a short time an app that was able to separate light and color, but not texture (Patterns etc.)

If not separated, the “compositing” of a new light would be just wrong. However, if the light was just diffuse, one can do a a little (not a lot) in camera mapping. I have discussed such thing in my JET series here or if you go with the link in my “signature”, there is a Music Video making of (Los Angeles) where I explain such technique.

The Camera Calibrator by itself, just to be clear has zero “add light” functionality in this regard.

Camera Projection is normally aimed to get away with as little geometry as possible, to have an advantage over building it. Which in return, doesn’t allow for a good shadow, light simulation at all. So, typically not, and is not advised, but well, with lots of time …

All the best

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Dr. Sassi V. Sassmannshausen Ph.D.

Photography For C4D Artists: 200 Free Tutorials: Texture, Panorama, HDRI, Camera Projection, etc.
https://www.youtube.com/user/DrSassiLA/playlists

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Posted: 11 April 2018 11:58 AM   [ Ignore ]   [ # 4 ]  
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Thanks so much for this awesome reply. Very thorough and something I really feel very confident in its answer. So thank you Dr. Sassi.

4D(3D plus time)? Holy moly! I’m going to be thinking about that along with inter dimensional travel, the space time continuum as features in back to the future, and stargates! I’m kidding about these last few sentences. Just a silly way to show my appreciation for your sharing of knowledge.

Cheers,

Fauntail

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Posted: 11 April 2018 12:21 PM   [ Ignore ]   [ # 5 ]  
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Thanks a lot, Fauntail.

Yes, all these weird “4++D” themes are wonderful and I love them. Besides my current main script, I work on a short story with time travel. I really love mind-bending stuff.

4D: Cinema 4D.

ENJOY.

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Dr. Sassi V. Sassmannshausen Ph.D.

Photography For C4D Artists: 200 Free Tutorials: Texture, Panorama, HDRI, Camera Projection, etc.
https://www.youtube.com/user/DrSassiLA/playlists

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Posted: 21 July 2018 04:58 AM   [ Ignore ]   [ # 6 ]  
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Time travel is exactly what I thought of when I saw this for the first time. Fascinating ideas. Do you publish your stories somewhere, Dr. Sassi?

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Posted: 21 July 2018 08:41 AM   [ Ignore ]   [ # 7 ]  
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Thanks for your interest, WadeDan.

This short is currently in pre-production, we will see how far it gets. I just finished a re-rewrite last weekend. VFX of course with: Cinema 4D.

Publishing: Typically I go to festivals only. Since they mostly don’t like to have it published on a the web, I often don’t use YouTube nor Vimeo, etc. Perhaps one day in the future I put them all on a Blu-ray. wink [dreaming].

Cheers

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Dr. Sassi V. Sassmannshausen Ph.D.

Photography For C4D Artists: 200 Free Tutorials: Texture, Panorama, HDRI, Camera Projection, etc.
https://www.youtube.com/user/DrSassiLA/playlists

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