Saturday, December 19, 2009

Under the Hood: Camera

 You guys know how I keep on drawling on when i review the cameras of our smartphones. In a review I usually keep to the real-world performance of those cameras and stay away from the technical aspects as much as possible lest I bore my readers. But it seems some of my readers are fine with me going a bit more techy once in a while. So i decided to blog a bit about the technical aspects of a digi-cam. You also check stuff out under the hood of an accelerometer here.

We all know what a digi-cam does. It converts a 3D scene into a 2D image. The information contained in a 3D scene can be captured to a 2D image plane by a camera as follows: 
  1. A lens collects the incident illumination. 
  2. The light rays are deflected towards a focal point.
  3. The deflected rays create an image of the observed scene.

Now i'll describe the mathematical framework for mapping the 3D world space to the 2D image plane, the process of camera calibration and the geometry of stereo cameras. The matrix K can be referred to as the calibration matrix and its entries are called the intrinsic parameters of the camera. The principal point in the image plane is at position at the intersection of the optical axis with the image plane. The coefficients represent the focal length of the camera in terms of pixel dimensions in x and y directions. The focal length f of the camera, and mx and my represent the number of pixels per unit distance in image coordinates in x and y respectively. Therefore, a real-world camera can be represented by ten technical parameters.

But the physical properties of lenses make the previous image formation process geometrically deviate from the ideal pinhole model (u studied this in hi-skool).
And that is why Nokia uses Carl Zeis lenses for their flagship handsets. Carl Zeiss produces some of the best lenses in the market, and better quality lenses prevent deviation from the ideal design. Ofcourse it won't be perfect but it'll still be almost there.

If you're still reading this then you might want to check things out in a bit more depth at The Camera Model and similar techniques.

Another Techy Article: Desensitization Model.

Image from Letsgodigital.

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