Method

VipsImagesharpen

Declaration [src] 

int
vips_sharpen (
  VipsImage* in,
  VipsImage** out,
  ...
)

Description [src]

Optional arguments:

  • sigma: sigma of gaussian
  • x1: flat/jaggy threshold
  • y2: maximum amount of brightening
  • y3: maximum amount of darkening
  • m1: slope for flat areas
  • m2: slope for jaggy areas

Selectively sharpen the L channel of a LAB image. The input image is transformed to #VIPS_INTERPRETATION_LABS.

The operation performs a gaussian blur and subtracts from in to generate a high-frequency signal. This signal is passed through a lookup table formed from the five parameters and added back to in.

The lookup table is formed like this:

.                     ^
.                  y2 |- - - - - -----------
.                     |         /
.                     |        / slope m2
.                     |    .../
.             -x1     | ...   |
. -------------------...---------------------->
.             |   ... |      x1
.             |... slope m1
.             /       |
.            / m2     |
.           /         |
.          /          |
.         /           |
.        /            |
. ______/ _ _ _ _ _ _ | -y3
.                     |

For screen output, we suggest the following settings (the defaults):

  sigma == 0.5
  x1 == 2
  y2 == 10         (don't brighten by more than 10 L*)
  y3 == 20         (can darken by up to 20 L*)
  m1 == 0          (no sharpening in flat areas)
  m2 == 3          (some sharpening in jaggy areas)

If you want more or less sharpening, we suggest you just change the m2 parameter.

The sigma parameter changes the width of the fringe and can be adjusted according to the output printing resolution. As an approximate guideline, use 0.5 for 4 pixels/mm (display resolution), 1.0 for 12 pixels/mm and 1.5 for 16 pixels/mm (300 dpi == 12 pixels/mm). These figures refer to the image raster, not the half-tone resolution.

See also: vips_conv().

This method is not directly available to language bindings.

Parameters

out

Type: VipsImage

Output image.

The argument will be set by the function.
The caller of the method takes ownership of the returned data, and is responsible for freeing it.
...

Type: 

NULL-terminated list of optional named arguments.

Return value

Type: int

0 on success, -1 on error.