Kakadu Hyper-Doc (jp2_channels::set_colour

void set_colour_mapping( int colour_idx, int codestream_component, int lut_idx=-1, int codestream_idx=0)

Synopsis

This function is used, together with set_opacity_mapping and set_premult_mapping, to establish the relationship, if any, between code-stream image components and the reproduction functions of colour intensity, opacity and pre-multiplied opacity. The present function is most important, establishing the source of colour intensity information.

Each colour's intensity may be directly assigned to some code-stream image 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.

The colour_idx argument identifies the particular intensity channel whose mapping is being defined. A complete jp2_channels object must have an intensity mapping for each colour channel. However, the init function automatically installs a default mapping which directly associates the first num_colours code-stream components of code-stream 0 with the num_colours intensity channels. If this is what you want, there is no need to explicitly call the present function.

Arguments

colour_idx [int]

The meaning of this argument depends upon the colour space. Some common examples are:

For monochrome (greyscale) imagery, the only legal value is 0.
For RGB spaces, a colour index of 0 means red, 1 means green and 2 mean blue.
For CMYK, 0 means cyan, 1 means magenta, 2 means yellow and 3 means black.

codestream_component [int]

Identifies the image component (starting from 0) of the code-stream identified by codestream_idx which is used to create the relevant colour intensity channel, either by direct assignment or after mapping through a palette LUT.

lut_idx [int]

Set to -1 (the default) if the code-stream image component is to be assigned directly to the relevant colour intensity 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.

codestream_idx [int]

Index of the code-stream whose components and palette lookup tables (if required) are used to generate this colour intensity channel. The meaning of the index for various file formats is as follows:

For JP2 files, there is only one code-stream which can be interpreted by the file reader and it must have index 0.
For JPX files, index 0 refers to the first code-stream (first contiguous code-stream or fragment table) and the first code-stream header box (if any) in the file. Subsequent code-stream / code-stream header box pairs are identified by consecutive integers. Note that the same code-stream may be used to define intensity channels in different JPX compositing layers.
For MJ2 files, all code-streams must have the same reproduction rules and the index used here must be 0.