Logarithmics
In these operations a logithmical function is applied to the value of every pixel in a raster band. The raster band is overwritten with the result of the addition.
The operation is provided in a high-level and a low-level format. In the high-level format a raster object, a band identifier and a token are specified, together with the scalar. The operation applies to all pixels and the result is stored in the specified band. In the low-level format the operation is applied to a block of contiguous memory containing a specified number of pixels. The low-level format is useful to chain a number of operations without the overhead of storing intermediate results.
If you want to preserve the original raster band, you should make a copy of the band first.
The operations can be summarized as follows:
| Operation | Description |
| DSpGMLn |
ln(pixel) |
| DSpGMLog2 | log2(pixel) |
| DSpGMLog10 | log10(pixel) |
| DSpGMLogN | logN(pixel) |
High-level declarations:
procedure DSpGMLn(const r: TDSpRaster; const band, token: integer);
procedure DSpGMLog2(const r: TDSpRaster; const band, token: integer);
procedure DSpGMLog10(const r: TDSpRaster; const band, token: integer);
procedure DSpGMLogN(const r: TDSpRaster; const band, token: integer;
base: TDSpFloat64);
Low-level declarations:
procedure DSpGMLnFloat32
procedure DSpGMLnFloat64
procedure DSpGMLog2Float32
procedure DSpGMLog2Float64
procedure DSpGMLog10Float32
procedure DSpGMLog10Float64
(const data: pointer; pixels: integer;
fill: TDSpFloat64);
procedure DSpGMLogNFloat32
procedure DSpGMLogNFloat64
(const data: pointer; pixels: integer;
fill, base: TDSpFloat64);
| Parameter | Description |
| r | A valid raster object. It must be opened for write access. |
| band | The identifier of the raster band. The band must exist in the raster, and it can be of any type. The data type must be 32-bit or 64-bit floating point. |
| token | The access token for the raster. The token has to be generated for write access. |
| base |
The scalar value which is the base of the logarithm. This value will be converted to the data type of the raster band before the operation. |
| data | A pointer to a block of memory containing pixels pixel values. |
| pixels | Number of pixels in the data block of memory. |
| fill | The missing data value of the raster band. |