The automatic feature detection can be driven manually by adding a bias to the pixels of the image.
For example, it is possible to protect regions of the image by adding a positive bias to the corresponding pixels. This will make the seams more unlikely to cross those regions, thus avoiding distortion (but increasing distortion of the other regions).
It is also possible to make the seams more likely to cross some regions by adding a negative bias to them. In this case, reducing the size of the image will tend to erase those regions, while (possibly) keeping the rest of the image in a consistent state.
The bias has to be added before the resizing takes place (but it can be added before initialisation since version 0.4).
In all of the bias-related functions, the bias is added on top of the existing one, so that all of the functions can be called multiple times.
The function to use in order to add a bias to a given pixel is:
LqrRetVal lqr_carver_bias_add_xy( | LqrCarver* carver, |
| gdouble bias, | |
| gint x, | |
gint y); |
Typical values for the bias parameter would be between 100
and 10000 in module.
It is possible to use a whole array of floating points at once through this function:
LqrRetVal lqr_carver_bias_add( | LqrCarver* carver, |
| gdouble* buffer, | |
gint bias_factor); |
Here, buffer is an array contining the bias values, and it is assumed to have
the same size as the image loaded in carver, while
bias_factor is an overall bias factor, which can be used to affect the global
bias level: if the elements of buffer are of order 1, a standard choice for
the bias_factor would be between 100 and 10000 (in module).
This function, and all the following, will not swallow the buffer (to the contrary of what
happens e.g. when creating a new LqrCarver object and allowing the default behaviour),
therefore the buffer must be freed by the user afterwards.
The bias can also be read from an 8-bit rgb buffer. This buffer has to be in the same format as the one used in the 8-bit LqrCarver constructor (but may have a different number of colours per channel). The function is:
LqrRetVal lqr_carver_bias_add_rgb( | LqrCarver* carver, |
| guchar* buffer, | |
| gint bias_factor, | |
gint channels); |
As in the previous case, buffer is assumed to hold and image of the same size
as the one in the carver.
The buffer contents will be transformed into floating-points by averaging the
colour components and multiplying the result by the alpha channel (transparency) value.
The existence of an alpha channel is inferred from the channels value: if
this is 1 or 3, no alpha channel is assumed, if it is 2 or 4 or greater, it is assumed that the
last channel holds the alpha value. If this is not what you want, you should resort to one of
the previous methods.
The two previously described functions operate on the whole LqrCarver image. It is also possible
to access specific image regions in a similar way; for the floating point case use:
LqrRetVal lqr_carver_bias_add_area( | LqrCarver* carver, |
| gdouble* buffer, | |
| gint bias_factor, | |
| gint width, | |
| gint height, | |
| gint x_off, | |
gint y_off); |
while for the rgb image case use:
LqrRetVal lqr_carver_bias_add_rgb_area( | LqrCarver* carver, |
| guchar* buffer, | |
| gint bias_factor, | |
| gint channels, | |
| gint width, | |
| gint height, | |
| gint x_off, | |
gint y_off); |
In both functions, width and height are used to specify the size of the area of interest,
while x_off and y_off specify its offset. For the
rest, both functions work in the same way as their global couterpart.
The provided buffers have to be of size width * heightwidth * height * channelsLqrCarver image area: only the parts which
overlap with it will be used. For example, the offsets can also be negative.