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Power
Power applies one of six non-linear operations to each pixel of the input image.
| Operation | What it does |
|---|---|
| power | Raises each pixel value to a constant power “a” (default 1.0) |
| exponential | Applies an exponential function to the pixel value |
| sinusoid | Applies a sine function to the pixel value |
| hyperbolic | Applies the hyperbolic tangent to the pixel value |
| logarithm | Takes the logarithm of the pixel value |
| abs | Takes the absolute value of the pixel value |
Choosing an operation
- A power greater than 1.0 emphasizes high-contrast information; a power less than 1.0 emphasizes low-contrast information.
- The logarithm emphasizes low-contrast information and can make dark elements brighter.
- The exponential and the sinusoid can emphasize either the highlights or the shadows of the image; choose which with “enhance”.
Constants
The power, exponential, sinusoid and hyperbolic operations use a constant for each band. Constants must be positive, and can be decimal numbers. Give one per band, or a single constant for all bands.
For the exponential, sinusoid and hyperbolic operations, the constant is a “max” value. The default is the maximum value for the bit depth: 255 for 8-bit, 65535 for 16-bit, or 1.0 for floating point. You can use the actual maximum of your data instead, or a lower or higher value to emphasize different values.
Non-integer powers of negative pixel values are not allowed. The output is floating point.