Geometrical transformations

A geometrical transformation consists in applying a spatial transformation to a set of pixels in order to modify their coordinates and then to carry out an interpolation of their values in order to correct the position error.

Indeed, since pixel coordinates are integer values, after the transformation their coordinates are approximate. Thus, the interpolation process consists in regenerating the missing approximate values for the luminosity levels of neighbouring pixels.

The main spatial transformations are:

• Vertical reversal
• Horizontal reversal
• Transposition
• Translation
• Scaling
• Rotation
• Cropping

Vertical reversal

LThe vertical reversal (also called mirror) consists in applying vertical symmetry to the image:

Horizontal reversal

The horizontal reversal (flip) consists in applying horizontal symmetry to the image:

Scaling

The transformation called scaling consists in multiplying the image pixel coordinates by a factor (scaling factor). The result of this transformation is an enlarging (zoom forward) or a contracting of the image (zoom back).

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