- Form : LN source [INV]
LN replaces the pixel values in the image 'source' by their base-e
logarithm values. Any pixels whose original values were less than or equal
to 0 are replaced by -30 in the resulting image. If the INV keyword is
specified, the inverse log is taken
Example:
- LN 3
- take the natural log of each pixel in buffer 3.