NAME

       lqr_carver_bias_set_energy_function - set a custom energy function for a LqrCarver object

SYNOPSIS

       #include <lqr.h>

       LqrRetVal lqr_carver_set_energy_function(LqrCarver* carver, LqrEnergyFunc en_func,
                                                gint radius, LqrEnergyReaderType reader_type,
                                                gpointer extra_data);

DESCRIPTION

       The function lqr_carver_set_energy_function assigns the energy function en_func to the
       LqrCarver object pointed to by carver (see below for more details on custom functions
       definitions).

       The parameter radius determines the size of the square region which affects the
       computation around each pixel (the side of the square will be 2 * radius + 1 pixels long).

       The parameter reader_type sets the reader type used when reading the image, and therefore
       it determines what quantity will be passed on to the function en_func (see below for more
       details on reader types).

       The parameter extra_data is a (void) pointer which can be used to pass on additional
       values to the function ef_func.

CUSTOM FUNCTIONS DEFINITION

       The function en_func must be of type LqrEnergyFunc, whose prototype is defined by:

           typedef gfloat (*LqrEnergyFunc) (gint x, gint y, gint img_width, gint img_height, LqrReadingWindow * rwindow, gpointer extra_data);

       Such a function is expected to compute the energy at pixel x, y based on the knowledge of
       the current image size (obtained from width and height) and the content of the image in a
       square around that pixel, which is passed through the rwindow reading window.

       In most cases, the parameters x, y, width and height would only be used to determine
       whether the region under consideration is at the image boundary or not.

       The rwindow content must be read using the function lqr_rwindow_read(3).

READER TYPES

       The LqrEnergyReaderType is an enum which can take these values (also noted is the number
       of channels of the corresponging reading window):

       LQR_ER_BRIGHTNESS
           brightness (1 channel)

       LQR_ER_BRIGHTNESS
           luma (1 channel)

       LQR_ER_RGBA
           RGBA (4 channels)

       LQR_ER_CUSTOM
           read the normalised image channels as they are (as many channels as the image has)
       These readouts always return values beetween 0 and 1.

       Note that these readouts may have special meanings depending on the image type:

       •   for LQR_GREY_IMAGE, LQR_GREYA_IMAGE and LQR_CUSTOM_IMAGE images, the LQR_ER_LUMA
           readout will yield the same result as LQR_ER_BRIGHTNESS

       •   for LQR_CUSTOM_IMAGE images, the LQR_ER_BRIGHTNESS readout will return the average
           pixel value (additive, i.e. if a black channel is present the channel values will be
           inverted and multiplied by the black channel inverse), multiplied by the alpha channel
           value.

       •   for LQR_CUSTOM_IMAGE images, the LQR_ER_RGBA readout cannot be used: it will always
           return 0

RETURN VALUE

       The return value follows the Liquid Rescale library signalling system.

SEE ALSO

       lqr_carver_set_energy_function_builtin(3), lqr_carver_get_energy(3), lqr_rwindow_read(3),
       lqr_rwindow_get_read_t(3), lqr_rwindow_get_radius(3), lqr_rwindow_get_channels(3)

COPYRIGHT

       Copyright © 2007-2009 Carlo Baldassi