How to find out the pixel size in Camera Calibration?

[Toshi_OK]

Hi everyone,

Could somebody let me know how to find out the pixel size in Camera Calibration to accurate more?

The basic calculation what I know is below
"Square root of the area of the image pickup element divided by the number of pixels"

Then the parameter and the calculation will be...
---sample parameter---
Senser Size (mm) = 5.9 x 4.4  = 25.96 mm area
Resolusion  size = 4608 x 3456 = 15925248 area

Formula
SQRT( 26 / 15925248 ) = approx "0.00127676"
----

However the parameter based on EXIF shows slightly different such as "0.00133853" as in attached photo.

So the questions are...
* Which EXIF parameter the Photoscan actually use for?
* Actual formula
---

I saw the thread below, and I would like to know more specific if i could.
http://www.agisoft.com/forum/index.php?topic=4001.msg20706#msg20706

[stihl]

Taken from this website: http://www.digicamdb.com/specs/canon_ixus-125-hs/

The pixel pitch( pixel size) of your camera is 1.33 microns which is 0.0013 mm for photoscan.
Not sure where it went wrong with your calculation. But the EXIF data is usually correct. In some scenarios this information night be missing, best option then  is to look up the camera specs online.

[Alexey Pasumansky]

Hello Toshi_OK,

PhotoScan is using the following EXIF information to fill up the pixel size fields:

Code: [Select]

pixel_width = 1 / FocalPlaneXResolution
pixel_height = 1 / FocalPlaneYResolution
If the difference between two values are minimal, they are averaged.

[Toshi_OK]

Hi stihl,
Hi Alexey,

Thank you so much for your kind reply.
That's exactly what I wanted to know.

Thanks again.

[Alexey Pasumansky]

Hello Toshi_OK,

Just an additional comment, in case Focal Plane Resolution tags are missing, PhotoScan will use crop factor (focal length / focal length in 35 mm eq.) to calculate the pixel size:

Code: [Select]

pixel_size = pixel_size_35mm * focal_length / focal_length_35mm