Method
VipsImageunpremultiply
Declaration [src]
int
vips_unpremultiply (
VipsImage* in,
VipsImage** out,
...
)
Description [src]
Unpremultiplies any alpha channel.
Band alpha_band (by default the final band) contains the alpha and all
other bands are transformed as:
alpha = (int) clip(0, in[in.bands - 1], max_alpha);
norm = (double) alpha / max_alpha
if (alpha == 0)
out = [0, ..., 0, alpha]
else
out = [in[0] / norm, ..., in[in.bands - 1] / norm, alpha]
So for an N-band image, the first N - 1 bands are divided by the clipped and normalised final band, the final band is clipped. If there is only a single band, the image is passed through unaltered.
The result is VipsBandFormat unless the input format is
VipsBandFormat, in which case the output is double as well.
max_alpha has the default value 255, or 65535 for images tagged as
VipsInterpretation or VipsInterpretation, and
1.0 for images tagged as [enum@Vips.Interpretation.scRGB.
Non-complex images only.
::: tip “Optional arguments”
* max_alpha: gdouble, maximum value for alpha
* alpha_band: gint, band containing alpha data
::: seealso
vips_premultiply(), vips_flatten().
Parameters
out |
VipsImage |
Output image. |
|
| The argument will be set by the function. | |
| The instance takes ownership of the data, and is responsible for freeing it. | |
... |
none |
|