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Author Topic: First Face Scan, need tips  (Read 23916 times)

meshmaster

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Re: First Face Scan, need tips
« Reply #15 on: September 18, 2013, 03:01:11 PM »

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 ?

Trust me, a subject will move a lot in 2 seconds... I can't stress this enough, human beings are always in movement, the idea that someone can sit still is an illusion.

You need to be able to capture in fractions of a second... in order to stop movement.

Cheers,

Joe

Mfranquelo

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Re: First Face Scan, need tips
« Reply #16 on: September 18, 2013, 03:24:56 PM »

On Canon 600D Focal length 50 mm and distance 1,5m its 1,3888mm pixel size / real world, maybe the subject in 2 secs doesnt move 1,3888mm ?

Trust me, a subject will move a lot in 2 seconds... I can't stress this enough, human beings are always in movement, the idea that someone can sit still is an illusion.

You need to be able to capture in fractions of a second... in order to stop movement.

Cheers,

Joe


I know i need less than a fraction of a sec to stop movement, however, by 2 seconds, i meant the time lapse between the first photo, and the last one, being each photo's shutter speed 1/125.

What i mean is this:

If the subject, from the first photo, till the last one, moves less than 1,38mm > Then, what ive understood (which may be perfectly wrong) is that missalignment shouldnt be noticeable IF -> The distance from the lens to the subject is 1,5m & using a canon 600d with 50mm lens.

I understand that human beings are always in movement, as little as it can be, however if the accuracy is below that, you wont notice those movements. (heart pumps, micro muscle movements...)

This is what i meant, im not sure if thats what you meant also :)

Manuel.
« Last Edit: September 18, 2013, 03:27:08 PM by Mfranquelo »

meshmaster

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Re: First Face Scan, need tips
« Reply #17 on: September 18, 2013, 03:29:59 PM »

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 ?

Trust me, a subject will move a lot in 2 seconds... I can't stress this enough, human beings are always in movement, the idea that someone can sit still is an illusion.

You need to be able to capture in fractions of a second... in order to stop movement.

Cheers,

Joe


I know i need less than a fraction of a sec to stop movement, however, by 2 seconds, i meant the time lapse between the first photo, and the last one, being each photo's shutter speed 1/125.
If the subject, from the first photo, till the last one, moves less than 1,38mm > Then, what i?ve understood (which may be perfectly wrong), missalignment shouldnt be noticeable IF -> the distance from the lens to the subject is 1,5m & using a canon 600d with 50mm lens.

I understand that human beings are always in movement, as little as it can be, however if the accuracy is below that, you won?t notice those movements. (heart pumps, micro muscle movements...)

This is what i meant, im not sure if thats what you meant also :)


Look, many of us have travelled down this road before and our advice to you is that you simply are going to need more cameras and those cameras must fire in sync with each other with exposure times measured in a fraction of a second... that is if you want good results.   Honestly, we would all have been happy to use a lot less cameras if it were possible... but honestly,  it's not.

So my advice at least is the same as before, build your rig up little by little over time, eventually you will get to where you want/need to be.

Keep at it!

Cheers,

Joe

Infinite

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Re: First Face Scan, need tips
« Reply #18 on: September 18, 2013, 03:34:14 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 ?

I think as many cameras as you can, as close as possible. Fill the frame with the face. Details, focus and sharpness are key.
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meshmaster

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Re: First Face Scan, need tips
« Reply #19 on: September 18, 2013, 03:36:43 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 ?

I think as many cameras as you can, as close as possible. Fill the frame with the face. Details, focus and sharpness are key.


Honestly, this is the best advice you will get!  Listen to INFINITE... he knows of what he speaks!

Mfranquelo

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Re: First Face Scan, need tips
« Reply #20 on: September 18, 2013, 04:03:57 PM »
Thank you  :)

By the way i apologize for being insistent.

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 ?

I think as many cameras as you can, as close as possible. Fill the frame with the face. Details, focus and sharpness are key.

Ill do a test with 8 cameras. Connected and triggered using breeze software.

Cheers,
Manuel.

andy_s

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Re: First Face Scan, need tips
« Reply #21 on: September 19, 2013, 09:52:03 AM »
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

Hi Mfranquelo, Joe's [very correct] comment just reminded me [to remind you] that Chad is already getting pretty decent results using a small[ish] number of highly synchronised point&shoot here http://www.agisoft.ru/forum/index.php?topic=1378.0 and no flash [small sensor/large depth of field/larger aperture?], I can't remember if the exposure time was stated anywhere [on a related post] ?

I don't know the lighting for this http://www.martin-hoppe.com/indexMAIN.html - I believe it used 50 usb synchronised point&shoot.

[in my opinion] You shouldn't apologise for being 'persistent' - all this will only become easy when you 'know how' [and maybe not even then :-\ ???]...I admire persistence [maybe above everything] but I still haven't [much of] a clue  ;)
« Last Edit: September 19, 2013, 10:11:08 AM by andy_s »

Mfranquelo

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Re: First Face Scan, need tips
« Reply #22 on: September 19, 2013, 12:10:37 PM »
Hello Andy,
Thank you a lot :)

Would it be possible to combine for example, cameras with higher resolution for the main facial features of the head, and that point-to-shoot camera rig for the rest of the head ? (or maybe less important features) That would save a lot of money :)
For smoother results i could subdivide the mesh afterwards in ZBrush. Maybe tweak something.

- Very nice topic !

Manuel.

andy_s

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Re: First Face Scan, need tips
« Reply #23 on: September 19, 2013, 02:19:35 PM »
Would it be possible to combine for example, cameras with higher resolution for the main facial features of the head, and that point-to-shoot camera rig for the rest of the head ? (or maybe less important features) That would save a lot of money :)
For smoother results i could subdivide the mesh afterwards in ZBrush. Maybe tweak something.

I don't see why not Manuel - please have a look at some of Magnus's posts - he's getting great results with mixed 1100D [12MPix] & D3200 [24Mpix]. I still can't quite get my head around how photoscan works [apparently] so well with 'mixtures'. 

I'm actually thinking of a total point&shoot solution to start with [head/body - the lot] with a built in migration plan leading to mixed point&shoot / DSLR leading to full DSLR [if required]. That needs a bit more google / development though to hang it all together - chdk usbremote / chdkptp / arduino relay controller / integration signal to camera-axe for studio flash / dslr remote shutter release / smartshooter tether [and maybe a few prayers too  :o]. The EOS100D looks quite tasty for the head shots.

I just need to 'pull the finger out' and germinate some of those thought seeds into the real world.

Mfranquelo

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Re: First Face Scan, need tips
« Reply #24 on: September 19, 2013, 03:17:41 PM »
I see  :) thanks for the answer andy, i?ll have a look into that.

Chdk usbremote seems to be very nice to sync point to shoot cameras 0,1 milisec (Thats if you have only point to shoot cameras in the rig)
- But how do you sync point&shoot and dslrs ? thats what must be investigated right ?  :)
- Breeze software or Smartshooter / Phase one capture one is nice for tethered multi camera shooting but its only for DSLR's if im correct.
- Not sure how you want to use the arduino relay could you explain this a little bit more ?


---

I guess this is offtopic, but why would you prefer the eos100d over the 600d ? its like 50 euro more expensive i think.
1100d is 300 euro at the moment, not much difference in comparison to the 600d (in price) (maybe i could get a deal in a shop if i buy 6 cameras at once)

- Im going to do the investment soon, but i want to be really sure which camera should i buy, i?ve been reading the post that discusses that here in PS, and it seems like canon 600d is the winner.

germination process is slow,  but satisfying  :)

andy_s

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Re: First Face Scan, need tips
« Reply #25 on: September 19, 2013, 04:31:45 PM »
Chdk usbremote seems to be very nice to sync point to shoot cameras 0,1 milisec (Thats if you have only point to shoot cameras in the rig)
- But how do you sync point&shoot and dslrs ? thats what must be investigated right ?  :)

Correct - integration needs further investigation

chdk usbremote [the program running on from each cameras SD card]:
As you know, all the cameras wait to 'open' the shutter(s) until after the usb line drops to zero, for some camera types the time to open the shutters [of many cameras] appears to be very synchronised.

Part of what I don't yet know is if the delay period [until all the shutters are synchronously 'open'] is consistent across sequential shots. I suspect it isn't and that would hobble my DSLR integration plan. 




Update http://chdk.setepontos.com/index.php?topic=10687.msg105197#msg105197

"The standard USB remote code is capable of very precise shutter release timing if you use the right sequence.  With the switch mode set to "One Press" and "Sync" enabled, have your Arduino assert the 5V line prior to when you need to release the shutter and hold it high.  When you want to shoot,  set the 5V line to 0V.  You should get a shot less than a few milliseconds later and that delay will be very consistent from shot to shot."



For argument, assume it is a consistent period [update: not necessarily a big assumption any longer].
[I think] A 'relay' controller will be needed to open the USB network +5V lines to all the [point&shoot] cameras [to initiate the chdk usbremote firing sequence] . At that same time [or even before it depending on the DSLR shutter lag ;)] the controller must also provide an input signal to the camera-axe. As you [again] probably know, the camera-axe has chainable & programable flash / DSLR remote shutter outputs. In theory, that's Job Done   8):o 

- Breeze software or Smartshooter / Phase one capture one is nice for tethered multi camera shooting but its only for DSLR's if im correct.

Yes - smartshooter for DSLR cameras [I just think Breeze is too pricey] and chdkptp client [for Windows] for point&shoot [free  ;)]. A bit of filenaming automation needed for the downloaded files.

- Not sure how you want to use the arduino relay could you explain this a little bit more ?

that's the controller referred to above.

I guess this is offtopic, but why would you prefer the eos100d over the 600d ? its like 50 euro more expensive i think.

see the last part of the link referred to here http://www.agisoft.ru/forum/index.php?topic=1411.msg7127#msg7127


germination process is slow,  but satisfying  :)

in my case very slow - interesting nevertheless  ;)
« Last Edit: September 19, 2013, 09:54:02 PM by andy_s »

Mfranquelo

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Re: First Face Scan, need tips
« Reply #26 on: September 20, 2013, 11:32:19 AM »
Hm, what about this for "sync" :

Place the cameras on a extremely dark environment:

1. develop bulb mode for chdk :) (there?s someone doing this already, i read)
2. Open every camera's shutter - bulb mode
3. fire flashes
4. close shutters
5. everything should be in perfect sync.




andy_s

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Re: First Face Scan, need tips
« Reply #27 on: September 20, 2013, 01:38:07 PM »
Hi Manuel,

the Camera-Axe guys that take pictures of bursting balloons / bullets and the like all do it in dark rooms. The balloons don't mind the dark conditions but your subject might ?

I don't have any cams yet and haven't read about that funcionality - but, from a synch perspective it sounds fine.

From what I gather chdkptp client 'lua' code can be written to do just about anything - see this as an example that does not use the chdk usbremote previously referred to [but note in the listing "experimental code for shooting with multiple cameras not optimized for best sync, lots of loose ends"]   

http://trac.assembla.com/chdkptp/browser/trunk/lua/multicam.lua
« Last Edit: September 20, 2013, 02:34:38 PM by andy_s »