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Author Topic: First Face Scan, need tips  (Read 29632 times)

Mfranquelo

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First Face Scan, need tips
« on: September 16, 2013, 01:15:00 PM »
Hello  :)


I'd be really gratefull if anyone could answer these questions:
Taking account that im using one camera for tests purposes, and different views :

- Does it matter if the subject moves slightly from the first photo, till the last photo ? (this is important)

- Can photoscan take advantage of a pre-set photo-order ? for aligning purposes, more or like the ptgui templates or position xml's.
- How many photo's are needed to reduce the noise till its merely noticeable ? using a canon 600d 100 iso 50mm lens
- I?ve read that you need atleast 3 cameras pointing 45 degrees - 90 degrees for accurate point depth calculation, anyone had any experience with the minimum number of cameras needed to scan a face with quite reasonable accuracy and noise ratio ?

Thanks in advance.

Manuel.
« Last Edit: September 17, 2013, 10:38:20 AM by Mfranquelo »

Mfranquelo

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Re: Single camera, different views, drawbacks?
« Reply #1 on: September 17, 2013, 10:37:22 AM »
This is a first test i did using 1 camera with continuous light, no flash.
Geometry was pretty bad though, maybe because the subject moved during the process ?
« Last Edit: September 17, 2013, 12:40:24 PM by Mfranquelo »

Wishgranter

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Re: First Face Scan, need tips
« Reply #2 on: September 17, 2013, 12:30:47 PM »
can use the PRINT SCREEN button and put the resulting screengrab to JPG and share it ? not camera capture as you done it ? :-)
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Mfranquelo

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Re: First Face Scan, need tips
« Reply #3 on: September 17, 2013, 12:44:53 PM »
Hello Milos,
Sure, sorry for that. :)


Mfranquelo

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Re: First Face Scan, need tips
« Reply #4 on: September 17, 2013, 12:49:12 PM »
Im doing another test now with "proper" gear, two flashes (one of them is in-built camera flash) with diffusers and green chroma background.
Camera Canon 5D 50mm prime lens
Any tips for the test ?
Ill post results this afternoon.
« Last Edit: September 17, 2013, 01:59:08 PM by Mfranquelo »

meshmaster

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Re: First Face Scan, need tips
« Reply #5 on: September 17, 2013, 02:00:39 PM »
Hello  :)


I'd be really gratefull if anyone could answer these questions:
Taking account that im using one camera for tests purposes, and different views :

- Does it matter if the subject moves slightly from the first photo, till the last photo ? (this is important)




Yes, it matters.... it matters a lot.  Movement between photos is NOT desirable and will lead to errors, you want to avoid this at all costs.  This is why multiple cameras are really required for capturing human subjects.  Humans are always in motion... unless they are dead ;-)  So, if you aim to scan people and want the highest quality scans then you are going to need multiple cameras to do the job correctly.

Cheers,

Joe

Wishgranter

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Re: First Face Scan, need tips
« Reply #6 on: September 17, 2013, 03:57:34 PM »
1m distance and you work on approx 50micron precision/deviation per pixel ( 18Mpix image ) so even slightes movement is problematic as Meshmaster wrote even about the multicam setup.....
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meshmaster

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Re: First Face Scan, need tips
« Reply #7 on: September 17, 2013, 04:04:08 PM »
1m distance and you work on approx 50micron precision/deviation per pixel ( 18Mpix image ) so even slightes movement is problematic as Meshmaster wrote even about the multicam setup.....

Yes, I should have also said a multi camera setup using bright enough lights (either from strobe or continuous sources) to provide for reduced lens aperture and high enough shutter speed to eliminate movement from photos. Rock solid camera mounts and stands are also most helpful in reducing any wobble and shake :-)

Cheers,

Joe

Mfranquelo

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Re: First Face Scan, need tips
« Reply #8 on: September 17, 2013, 06:24:15 PM »
"1m distance and you work on approx 50micron precision/deviation per pixel ( 18Mpix image )"
How you did this calculation ? Interesting.

Ill try a set up with 6 cameras on my next test (i just did the one with flashes, ill post results)
How do you syncronize them ? Pocketwizard or camera axe ?
Im using two 580ex ii flash at the moment with diffusers. 1/125 speed.


- Objects on a turntable move relative to the camera, why theres no pixel deviation here? you mean that the error is on the movement of our facial muscles, so the geometry doesnt match ?

Thanks for your kind answers :)

xManuel.

meshmaster

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Re: First Face Scan, need tips
« Reply #9 on: September 17, 2013, 06:30:00 PM »

- Objects on a turntable move relative to the camera, why theres no pixel deviation here? you mean that the error is on the movement of our facial muscles, so the geometry doesnt match ?

Human beings are always moving... no matter how still you try to be there will always be movement, unless you are dead.  A turntable can be helpful, but will not solve the problem as a person simply can't stay totally still over a period of time... even a short period of time.  So yes, this will cause the geometry not to match exactly and this will cause errors.

Remember when you are talking about accuracy that is measured in microns... even the smallest movement might as well be a mile ;-)

Cheers,

Joe
« Last Edit: September 17, 2013, 06:32:06 PM by meshmaster »

Mfranquelo

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Re: First Face Scan, need tips
« Reply #10 on: September 17, 2013, 07:05:54 PM »
Okay i understand, im trying to reduce costs, maybe vertical 8 cameras mounted on a curved motorized rail. But if the error results to be to big i?ll consider on buying more cameras, (the motor would take maybe 20 secs from the start till the end.  I?d love to make a system balanced between accuracy and budget (i know its really hard :) )

What number of cameras do you suggest for a decent multicam face scan ? just the face, not the complete head / hair...

Thank you!

Wishgranter

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Re: First Face Scan, need tips
« Reply #11 on: September 17, 2013, 07:11:19 PM »
"1m distance and you work on approx 50micron precision/deviation per pixel ( 18Mpix image )"
How you did this calculation ? Interesting.

Ill try a set up with 6 cameras on my next test (i just did the one with flashes, ill post results)
How do you syncronize them ? Pocketwizard or camera axe ?
Im using two 580ex ii flash at the moment with diffusers. 1/125 speed.


- Objects on a turntable move relative to the camera, why theres no pixel deviation here? you mean that the error is on the movement of our facial muscles, so the geometry doesnt match ?

Thanks for your kind answers :)

xManuel.

xManuel try read few things about photogrammetry, the basic, that you understand how it work, what cause problems and how to calculate thing like 50 microns precision. Learning this will help you in next step of planning proper equipment and save a lot of money.......
And try read older post, a lot of things was mentioned and EXPLAINED very well here.......

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meshmaster

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Re: First Face Scan, need tips
« Reply #12 on: September 17, 2013, 07:13:26 PM »
Okay i understand, im trying to reduce costs, maybe vertical 8 cameras mounted on a curved motorized rail. But if the error results to be to big i?ll consider on buying more cameras, (the motor would take maybe 20 secs from the start till the end.  I?d love to make a system balanced between accuracy and budget (i know its really hard :) )

What number of cameras do you suggest for a decent multicam face scan ? just the face, not the complete head / hair...

Thank you!

It all depends on your requirements.

Honestly, there is no such thing as doing this inexpensively.... sorry to say, but true.

My best advice to you is start with 8 cameras and start to build your set-up, little by little as you can afford to do so.

You will quickly find out that it is not just the cameras that are expensive, but the lenses, the lights, the cables, the stands...etc... the list goes on and on.

Scanning costs a lot less than it used to, but to do quality work... it still isn't inexpensive.

Slow and steady wins the race!

Cheers,

Joe

Infinite

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Re: First Face Scan, need tips
« Reply #13 on: September 18, 2013, 02:13:03 PM »
Some good advice here.

Trick is, as many cameras as you can. We always need to beat occlusion. The more cameras you have, the better the registration, the smoother the results.


Slow and steady wins the race!


There is no race, no gold cup, no final cheer ..just a never ending journey :)
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Mfranquelo

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Re: First Face Scan, need tips
« Reply #14 on: September 18, 2013, 02:55:27 PM »
Thanks for your kind responses  :)

Theres not much occlusion on a face i guess, maybe on the ears / nose. But of course you have infinite experience more than me on this :)

Maybe its better less megapixel, more distance from the subject (so the pixel size/reality is bigger) (less accuracy/resolution of course) > AND more cameras. ?

On Canon 600D Focal length 50 mm and distance 1,5m its 1,3888mm pixel size / real world, maybe the subject in 2 secs doesn?t move 1,3888mm ? I dont know, id like to find these kind of balances so i can adjust budget or to think about a instant capturing method, or semi instant.
What do you think ?