Howtosignalprocessing
- What is scale space in SIFT?
- What does scale mean in space?
- What is scale space extrema detection?
- What are octaves in an image?
What is scale space in SIFT?
Scale spaces in SIFT
SIFT takes scale spaces to the next level. You take the original image, and generate progressively blurred out images. Then, you resize the original image to half size. And you generate blurred out images again.
What does scale mean in space?
Spatial scale is a specific application of the term scale for describing or categorizing (e.g. into orders of magnitude) the size of a space (hence spatial), or the extent of it at which a phenomenon or process occurs.
What is scale space extrema detection?
Scale-Space Extrema Detection
To detect the local maxima and minima of D(x, y, σ) each point is compared with its 8 neighbours at the same scale, and its 9 neighbours up and down one scale. If this value is the minimum or maximum of all these points then this point is an extrema.
What are octaves in an image?
When you are talking about frequencies, an octave higher means double the frequency, and an octave lower is half the frequency. In vision and images every octave (usually in an image pyramid where the source image is scaled down at a fixed rate e.g. 1.2x each time) is a doubling or halving of the size/scale.
