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Generate intrinsic matrix from exif values

Hi all! I'm trying to find the Essential Matrix in order to find the movement of one camera according to another.

I calculate F using SIFT matches, then findFundamentalMat with ransac to remove outliers then findFundamentalMat with LMEDS. The results seems good (the equation xEx' = 0 is nearly verified for each pairs (x,x'). Now, I would like to calculate E, using the formula E = K^(_2)^(t)FK^(_1). Since I don't know which camera was used to generate photos, I would like to create K from scratch, but without any way to calibrate it, so I would like to use Exif values to create it. Actually i'm doing so : K =
Fx 0 Cx
0 Fy Cy
0 0 1
with (Cx, Cy) = (image.width/2, image.height/2) (I have to assume that the principale point is the middle of the image).

But for (Fx, Fy) actually i'm really not sure of what I'm doing...

Fx = focal_length(mm) * X_res(DPI) / 25.4 (because 1inch = 25.4mm) and Fy = focal_length(mm) * Y_res(DPI) / 25.4

1^(st), i'm not sure if the formula is good and 2^(nd), I saw that openCV want pixel instead of mm for matrix but I don't understand...

Can someone help me?

Thanks!

Generate intrinsic matrix from exif values

Hi all! I'm trying to find the Essential Matrix in order to find the movement of one camera according to another.

I calculate F using SIFT matches, then findFundamentalMat with ransac to remove outliers then findFundamentalMat with LMEDS. The results seems good (the equation xEx' = 0 is nearly verified for each pairs (x,x'). Now, I would like to calculate E, using the formula E = K^(_2)^(t)FK^(_1). K'(t)FK. Since I don't know which camera was used to generate photos, I would like to create K from scratch, but without any way to calibrate it, so I would like to use Exif values to create it. Actually i'm doing so : K =
Fx 0 Cx
0 Fy Cy
0 0 1
with (Cx, Cy) = (image.width/2, image.height/2) (I have to assume that the principale point is the middle of the image).

But for (Fx, Fy) actually i'm really not sure of what I'm doing...

Fx = focal_length(mm) * X_res(DPI) / 25.4 (because 1inch = 25.4mm) and Fy = focal_length(mm) * Y_res(DPI) / 25.4

1^(st), 1st, i'm not sure if the formula is good and 2^(nd), 2nd, I saw that openCV want pixel instead of mm for matrix but I don't understand...

Can someone help me?

Thanks!

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updated 2018-03-14 06:36:40 -0500

berak gravatar image

Generate intrinsic matrix from exif values

Hi all! I'm trying to find the Essential Matrix in order to find the movement of one camera according to another.

I calculate F using SIFT matches, then findFundamentalMat with ransac to remove outliers then findFundamentalMat with LMEDS. The results seems good (the equation xEx' = 0 is nearly verified for each pairs (x,x'). Now, I would like to calculate E, using the formula E = K'(t)FK. Since I don't know which camera was used to generate photos, I would like to create K from scratch, but without any way to calibrate it, so I would like to use Exif values to create it. Actually i'm doing so : :

K = 
Fx 0 Cx
0 Fy Cy
0 0 1
0 0 1

with (Cx, Cy) = (image.width/2, image.height/2) (I have to assume that the principale point is the middle of the image).

But for (Fx, Fy) actually i'm really not sure of what I'm doing...

Fx = focal_length(mm) * X_res(DPI) / 25.4 (because 1inch  = 25.4mm)

and

Fy = focal_length(mm) * Y_res(DPI) / 25.4

25.4

1st, i'm not sure if the formula is good and 2nd, I saw that openCV want pixel instead of mm for matrix but I don't understand...

Can someone help me?

Thanks!

Generate intrinsic matrix from exif values

Hi all! I'm trying to find the Essential Matrix in order to find the movement of one camera according to another.

I calculate F using SIFT matches, then findFundamentalMat with ransac to remove outliers then findFundamentalMat with LMEDS. The results seems good (the equation xEx' = 0 is nearly verified for each pairs (x,x'). Now, I would like to calculate E, using the formula E = K'(t)FK. Since I don't know which camera was used to generate photos, I would like to create K from scratch, but without any way to calibrate it, so I would like to use Exif values to create it. Actually i'm doing so :

K =  
 Fx  0  Cx  
  0   Fy  Cy  
  0    0   1

with (Cx, Cy) = (image.width/2, image.height/2) (I have to assume that the principale point is the middle of the image).

But for (Fx, Fy) actually i'm really not sure of what I'm doing...

Fx = focal_length(mm) * X_res(DPI) / 25.4 (because 1inch  = 25.4mm)

and

Fy = focal_length(mm) * Y_res(DPI) / 25.4

1st, i'm not sure if the formula is good and 2nd, I saw that openCV want pixel instead of mm for matrix but I don't understand...

Can someone help me?

Thanks!