Scalar
subtraction
In this operation a scalar is subtracted from every pixel in a raster band, or the pixel value is subtracted from the scalar. The raster band is overwritten with the result of the subtracttion.
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.
High-level declaration (pixel value - scalar):
procedure DSpGMSubtractScalar(const r: TDSpRaster; const band, token: integer;
scalar: TDSpFloat64);
High-level declaration (scalar - pixel value):
procedure DSpGMScalarSubtract(const r: TDSpRaster; const band, token: integer;
scalar: TDSpFloat64);
Low-level declarations (scalar - pixel value):
procedure DSpGMScalarSubtractUInt32
procedure DSpGMScalarSubtractInt32
procedure DSpGMScalarSubtractInt64
procedure DSpGMScalarSubtractFloat32
procedure DSpGMScalarSubtractFloat64
(const data: pointer; pixels: integer;
fill, scalar: TDSpFloat64);
The low-level operations for
pixel value - scalar use the low-level procedures for scalar
addition, supplying -scalar as the scalar value.
| 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 can be any 32-bit or 64-bit data type. |
| token | The access token for the raster. The token has to be generated for write access. |
| scalar |
The value that is subtracted from every pixel of the raster band, or the value from which the pixel value is subtracted. 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. |