Computer Vision MT25, Image transformations
Flashcards
Suppose we represent an image via a 2D function $f$. @Describe the differences between:
- a pointwise transformation
- a geometric transformation
- image filtering
In all cases, we make a new image $g$ from $f$.
- Pointwise: $g(x, y) = t(f(x,y))$ where $t$ is some function
- Geometric: $g(x, y) = f(T(x,y))$ where $T$ is some function
- Filtering: $g(x, y) = F(N(x, y))$ where $F$ is some function and $N$ is a neighbourhood
Suppose we represent an image via a 2D function $f$. @Define the gamma correction filter.
Warps
@State the name of the technique for applying a transformation to an image by iterating over source pixels and drawing them at the target location, and state a problem with this.
This is called a forward warp, the problem is that there may be “holes” in the generated image.
@Define the technique of applying transformations via a forward warp.
Iterating over source pixels and drawing them at target locations.
@State the name of the technique for applying a transformation to an image by iterating over output pixels and computing where the pixels come from, possibly interpolating if the source location is between pixels.
Backward warp.
@Define the technique of applying transformations via a backward warp.
Iterating over output pixels and computing where the pixels come from, possible interpolating if the source location is between source locations.
@Define the optical axis. What does rotation around this axis and translation correspond to?
The axis passing through the centre of the camera and the centre of the image plane.
- Rotation: Rotation of the image.
- Translation: Scales the image around its centre.
@visualise~