xil_lookup_create(3)

NAME

xil_lookup_create, xil_lookup_create_copy, xil_lookup_destroy − create or destroy lookup tables

SYNOPSIS

#include <xil/xil.h>

XilLookup xil_lookup_create ( XilSystemState State,

XilDataType input_datatype,
XilDataType output_datatype,
unsigned int output_nbands,
unsigned int num_entries,
short first_entry_offset,
void ∗data);

XilLookup xil_lookup_create_copy ( XilLookup lookup);

void xil_lookup_destroy ( XilLookup lookup);

DESCRIPTION

These routines create and destroy lookup tables. Lookup tables are used in transforming data, and specialized lookup tables are used as colormap attributes of images.

xil_lookup_create () creates a lookup table for one band of input data. It can be used to create a single lookup table for converting a single-band input image to a single-band or multiband destination image. Or it can be used to create n single lookup tables for a multiband input image with n bands; when used for multiband input images, the single lookups created for the input bands must be combined into a combined lookup table by calling the xil_lookup_create_combined(3) function.

When used to convert a single-band input image to a multiband image, the lookup table must have multiple output data elements per input value; the number of elements must match the number of output_nbands specified. When used for converting a single band of input data, the lookup table can have only one output data element per input value, and the destination output_nbands must equal 1.

Regardless of whether it is created for single-band or multiband input data, a lookup table allows an offset that describes the input value corresponding to the first table value. Table data can represent any of the allowed image data types, but 1-bit data is stored in an unpacked format as the least significant bit in an 8-bit entry. The tables created for multiband input data can use different offsets, but they must all use the same data types.

The maximum number of entries allowed in the lookup table is determined by the input data type and by the first_entry_offset, as specified in the xil_lookup_create () call. This ensures that inaccessible lookup table entries are not created. Lookup tables with a first_entry_offset of 0 and an input data type of XIL_BYTE may have at most 256 entries. Lookup tables with a first_entry_offset of -32768 and an input data type of XIL_SHORT may have at most 65536 entries. Lookup tables with a first_entry_offset of 0 and a data type of XIL_SHORT may have at most 32768 entries. This function accepts NULL as a valid value for any of its arguments. XIL lookups cannot have XIL_FLOAT as an input datatype.

xil_lookup_create_copy () returns a copy of the specified lookup table. Copies of lookup objects have the same XilVersion number as the original lookup object. The name of a copy is initially empty (NULL).

xil_lookup_destroy () destroys the specified lookup table. For multiband input data, the tables created for each input band must be destroyed individually; the combined table must also be destroyed.

ERRORS

For a complete list of XIL error messages by number, consult Appendix B of the XIL Programmer’s Guide.

EXAMPLES

Create a lookup table for converting an 8-bit pseudocolor image to a 24-bit color image given the colormap components red, green, blue:

XilSystemState State;
XilLookup lookup_table;
Xil_unsigned8 red[256];/∗ red component of colormap ∗/
Xil_unsigned8 green[256];/∗ green component of colormap ∗/
Xil_unsigned8 blue[256];/∗ blue component of colormap ∗/
Xil_unsigned8 data[256∗3];/∗ lookup table data ∗/
int i, j;
for(j=0,i=0; i<256; i++, j+=3) {
    data[j]     = blue[i];
    data[j+1] = green[i];
    data[j+2] = red[i];
}
lookup_table = xil_lookup_create (State, XIL_BYTE, XIL_BYTE, 3, 256, 0, data);

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