lqr_carver_bias_set_energy_function(3) set a custom energy function for a LqrCarver object


#include <lqr.h>

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


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.


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).


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


brightness (1 channel)


luma (1 channel)


RGBA (4 channels)


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


The return value follows the Liquid Rescale library signalling system.


Copyright © 2007-2009 Carlo Baldassi