Messages

151

General / Different Lighting source for feature detection

« on: November 18, 2013, 02:47:07 AM »

Hello 

I have a question:

- If its okay for Agisoft to have 2 different images (for stereo photogrammetry measurements) with different lighting sources on the subject.
I guess this could affect the feature detection if the same "features" are in a different lighting condition, for example in one image light is coming from the zenith and on the other one its coming from the front.

Could anyone clarify this please?
Is this very critical ?

Thank you a lot,
Manuel.

152

General / Re: Scanning sculptures of a facade

« on: September 27, 2013, 04:58:16 PM »

Very nice post James, thank you for pointing it out.

Im not sure what advantages i could take of that system however (maybe i need to think a little bit more), -> I could fire 2 strobes of light, one without the transparent film and the other one with the film to project the noise pattern, each of them syncronized with the camera.

I cannot think of other advantages of using it and not using the conventional projector. Everything would be in perfect sync using flashes. even the projected pattern.

I?ll read a little bit more about the distance. thank you.

153

General / Re: Scanning sculptures of a facade

« on: September 26, 2013, 02:13:37 PM »

Hello bisenberger

Thank you for your answer.
I know i need a high amount of overlap, cameras would be facing to a central point P so that each image is in 90% overlap (maximun) with its pair one. That is not critically affected by the distance between each cameras but the angle.

Any thoughts on the noise projection ?

154

General / Scanning sculptures of a facade

« on: September 25, 2013, 06:49:44 PM »

Dear all,

Im going to do a little project next week which involves scanning the back of sculptures on a facade that cannot be reached using structured light scanners (or maybe they can, but its a much slower process) I dont need extremely high resolution.

Ive thought of mounting two 5d's 50mm lens with two flashes on an horizontal rail. (Synced) acting as a stereo pair.

The sculptures dont have any visible features, at least NOT many, to my eye. So i may need to use projected noise pattern? In this case, i guess i can project any pattern. Is just a standard noise pattern good enough ? or are there better pattern for feature recogniziton ? how big should the pattern be in relation to the object?

Are there any benefits of using a stereo pair set up ? Its easier for math operations knowing the distance between each camera's i guess ? whats the recommended distance from camera to camera ? Ive read 6,37cm somewhere.. but on the OpenCV book i read that 12cm is recommended.


Manuel.

155

Face and Body Scanning / Re: First Face Scan, need tips

« 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.

156

Face and Body Scanning / Re: First Face Scan, need tips

« 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 

157

Face and Body Scanning / Re: First Face Scan, need tips

« 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.

158

Face and Body Scanning / Re: First Face Scan, need tips

« 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.

159

Face and Body Scanning / Re: First Face Scan, need tips

« 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.

160

Face and Body Scanning / Re: First Face Scan, need tips

« 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 ?

161

Face and Body Scanning / Re: First Face Scan, need tips

« 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!

162

Face and Body Scanning / Re: First Face Scan, need tips

« 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.

163

Face and Body Scanning / Re: First Face Scan, need tips

« 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.

164

Face and Body Scanning / Re: First Face Scan, need tips

« on: September 17, 2013, 12:44:53 PM »

Hello Milos,
Sure, sorry for that.

165

Face and Body Scanning / Re: Single camera, different views, drawbacks?

« 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 ?