Inherits DD::Image::PixelIop.
Public Member Functions | |
| ColorLookup (Node *node) | |
| void | _validate (bool) |
| void | _open () |
| void | pixel_engine (const Row &in, int y, int x, int r, ChannelMask channels, Row &out) |
| void | in_channels (int input, ChannelSet &channels) const |
| virtual float | lookup (int colour, float value) const =0 |
This is a base class that implements a lookup from input color values to output values. Values between 0 and range() are looked up in a 1282-entry lookup table indexed by the top 16 bits of the floating-point number, and linearly interpolated between those values. Values outside that range are linearly interpolated from the end entries in the table.
To subclass this you must set range() in your _validate(), and then call the base class _validate(). You must also implement lookup() which will be called many times to fill in the tables.
You can also implement mono() if all the channels use the same lookup table.
into output ones. The actual implementation calls this during _request() and uses it to set up a fast lookup table that is based on the top 16 bits of the floating point numbers. The subclass _validate() should also call set_out_channels() to the set that is not the identity, to avoid building tables for unchanging channels.
The resulting lookup curve is made of many linear segments and thus large second derivatives in the lookup function can produce mach banding. The range outside 0..1 is linearly extrapolated from the first and last segments.
| void ColorLookup::in_channels | ( | int | input, |
| ChannelSet & | channels | ||
| ) | const [virtual] |
Returns channels unchanged, since it only needs the same channel to produce the output.
Implements DD::Image::PixelIop.
| float DD::Image::ColorLookup::lookup | ( | int | z, |
| float | value | ||
| ) | const [pure virtual] |
Subclasses must implement this function. It returns the what value in a channel with DD::Image::colourIndex()==z should turn into.
Input values between zero and one are looked up in a table that is built during _open() by calling this. Values outside the zero to one range will linearly interpolate the ends of this table.