Foreword

All the functions described in this page are used to add a rigidity mask to LqrCarver objects. Whenever one of these functions is called, a rigidity mask is activated for the whole image; the mask contains coefficients which modulate the value of the rigidity (which is set with lqr_carver_init(3)) in different areas of the image.

It is very important to note that using no rigidity masks at all is equivalent to use a rigidity mask over the whole image with all the values set to 1.0, but, when first adding a rigidity mask to a LqrCarver object, all the pixels outside the affected area will have their rigidity set to zero; therefore, the functions lqr_carver_rigmask_add_xy, lqr_carver_rigmask_add_area and lqr_carver_rigmask_add_rgb_area actually affect the whole image, despite their name.

All the functions must be called after lqr_carver_init and before lqr_carver_resize. If called multiple times over the same area, new values will replace the old ones.

Setting the rigidity mask pixel by pixel

The function lqr_carver_rigmask_add_xy sets the rigidity mask value of the x, y pixel of the image loaded into the LqrCarver object pointed to by carver

Setting the rigidity mask from a buffer

The function lqr_carver_rigmask_add_area adds a rigidity mask to an area of the image loaded in the LqrCarver object pointed to by carver.

The parameter buffer must point to an array of doubles of size width * height, ordered first by rows, then by columns.

The offset of the area relative to the image are specified through x_off and y_off. The rigidity mask area can exceed the boundary of the image, and the offsets can be negative.

The values in the given buffer are scaled by the overall rigidity value set when calling the function lqr_carver_init.

The function lqr_carver_rigmask_add can be used when the area to add is of the same size of the image loaded in the LqrCarver object and the offsets are 0.

Setting the rigidity mask from an image

The functions lqr_carver_rigmask_add_rgb_area and lqr_carver_rigmask_add_rgb are very similar to lqr_carver_rigmask_add_area and lqr_carver_rigmask_add, but use 8-bit multi-channel images as inputs.

The number of channels in the image is passed via the parameter channels. The last channel is assumed to be the alpha (opacity) channel if channels is equal to 2 or greater than 3 (if this is not the case, use the previous functions).

The rigidity value is computed from the average of the colour channels, multiplied by the value of the alpha channel if present. For example, in RGBA images a white, nontransparent pixel is equivalent to a value of 1.0 when using a buffer in lqr_carver_rigmask_add_area.

Return value

The return values follow the Liquid Rescale library signalling system.

See also

LqrRetVal(3), lqr_carver_init(3), lqr_carver_bias_add(3)