As mentioned in About enlarging, if the requested final size is too big, the rescaling is automatically divided in steps.

For example, let us suppose that we have created an LqrCarver object from a 100 by 100 pixels image, and that we call lqr_carver_resize with 600 and 100 as width and height arguments. With the default settings, the rescaling of the width will be performed in 3 steps: first, from 100 to 199, then from 199 to 397, and finally from 397 to 600.

The rule here is that the maximum size which can be reached in a single step is equal to twice the original size minus one, and that at each step the original size is reset to the current size (through an internal call to lqr_carver_flatten).

In most situations, however, the steps should be smaller in order to obtain good results. This can be set with this function:

The value of enl_step must be strictly grater then 1.0 and less then (or equal to) 2.0. The default value is 2.0 (for back-compatibility reasons); any other value will result in the function returning an error. The new maximum size for a step will then be obtained by multiplying the original size by the enlargement step and subtracting 1.

The current value of the enlargement step can be retrieved with this function:

When the function lqr_carver_resize is asked to resize along both directions in a single step, it has to choose which direction to resize first. The resize order can be changed through this function:

The possible values for resize_order are:

When the function lqr_carver_resize is invoked, it chooses at each step the optimal seam to carve based on the relvance value for each pixel. However, in the case two seams are equivalent (which may happen when large portions of the image have the same colour, for example), the algorithm always chooses the seams from one side, which might be a problem (e.g. an object centered in the original image might not be centered any more in the resulting image).

In order to overcome this effect, an option is given to automatically switch the favoured side during rescaling, at the cost of a slightly worse performance. The number of times such a switching event occurs for each rescale operation can be set using the function:

The default value for newly created LqrCarver objects is 0, which is equivalent to disabling this feature. Giving a value greater than the number of pixels by which to rescale produces a switch for each pixel, therefore you could set switch_freqency to a ridicolously high value in order to be sure to get this effect.

As for the final result, a very small value (e.g. 1 to 4) will normally suffice to balance the left and right side of the image (or the top and the bottom sides for vertical rescalings), without noticeable computational costs. However, in order to obtain a smoother behaviour for the visibiliy map, i.e. for the intermediate steps, higher values may be required.

By default, the library tries to cache some quantities in order to save computational time. The cache may be disabled in order to save memory instead, using this function:

To disable the cache, set use_cache to FALSE. To re-enable it back, set it to TRUE.