transform a plane from a camera still to a 2d image without perspective using a calibration plate

I have a camera mounted at an angle to a calibration plate. I would like to transform the plane in which the calibration sheet sits to a 'flat' 2d image.

put another way, my calibration sheet appear as a trapezium in the camera frame, i want to transform the image so that the calibration sheet appears square.

A linear transform would be fine there is very little camera distortion, it is only the perspective distortion to the calibration plane which i want to correct.

I am aware of the camera calibration tool box http://www.vision.caltech.edu/bouguetj/calib_doc/index.html but it appears to find the camera distortion, if anyone is familiar with the package is it easy to create a 'flat' image with that information.

alternatively can imtransform be used?

i say easy because i am a matlab novice.

Many thanks

James

Answer 1

[Image Analyst]

Read this:

http://blogs.mathworks.com/steve/2006/08/04/spatial-transformations-defining-and-applying-custom-transforms/

[james]

thanks for the reply. okay so i now know how to apply a custom transform. how do i find out what that transform should be? will the afore mentioned camera calibration tool box tell me that?

I need something that allows me to define a box with non parallel sides. when the box is defined i want to know the transform needed to make it square.

many thanks

James

[Image Analyst]

I haven't seen your image. I imagine you'd find the corners of your calibration sheet and then map those to the corners of your image. I've done it before. You just have 4 actual points, and their 4 desired locations and pass it in to maketform and then call tformfwd or something like that.

[james]

okay thanks