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void set_opacity_mapping( int colour_idx, int codestream_component, int lut_idx=-1, int codestream_idx=0)
Java: void Set_opacity_mapping( int colour_idx, int codestream_component, int lut_idx, int codestream_idx)
[Declared in "../apps/compressed_io/jp2.h"]
This function is used, together with set_colour_mapping and set_premult_mapping, to establish the relationship, if any, between the code-stream image components and the reproduction functions of colour intensity, opacity and pre-multiplied opacity. The present function may be used to provide opacity definitions. There is no obligation to provide opacity mappings; indeed, the default configuration created by init provides no opacity information.
Each opacity channel (there can be one for each colour) may be directly assigned to some code-stream component. Alternatively, it may be associated with the output of a palette lookup table (LUT), together with a code-stream image component which provides indices into the LUT.
Identifies the colour intensity channel whose opacity is being described. The meaning of this argument is identical to that explained in connection with the set_colour_mapping function.
Identifies the code-stream image component (starting from 0) which is used to create the relevant opacity channel, either by direct assignment or after mapping through a palette LUT.
Set to -1 (the default) if the code-stream image component is to be assigned directly to the opacity channel. Otherwise, the code-stream component samples are indices to a lookup table, where lut_idx gives the index of the lookup table (starting from 0), as it appears in the jp2_palette object.
Index of the code-stream whose components and palette lookup tables (if required) are used to generate this opacity channel. See the discussion which accompanies the set_colour_mapping function for more details on the meaning of this index and how it should be used with different file formats.