Method

VipsImagestdif

Declaration [src]

int
vips_stdif (
  VipsImage* in,
  VipsImage** out,
  int width,
  int height,
  ...
)

Description [src]

vips_stdif() performs statistical differencing according to the formula given in page 45 of the book “An Introduction to Digital Image Processing” by Wayne Niblack.

This transformation emphasises the way in which a pel differs statistically from its neighbours. It is useful for enhancing low-contrast images with lots of detail, such as X-ray plates.

At point (i,j) the output is given by the equation:

vout(i,j) = @a * @m0 + (1 - @a) * meanv +
      (vin(i,j) - meanv) * (@b * @s0) / (@s0 + @b * stdv)

Values a, m0, b and s0 are entered, while meanv and stdv are the values calculated over a moving window of size width, height centred on pixel (i,j). m0 is the new mean, a is the weight given to it. s0 is the new standard deviation, b is the weight given to it.

Try:

vips stdif $VIPSHOME/pics/huysum.v fred.v 0.5 128 0.5 50 11 11

The operation works on one-band uchar images only, and writes a one-band uchar image as its result. The output image has the same size as the input.

::: tip “Optional arguments” * a: gdouble, weight of new mean * m0: gdouble, target mean * b: gdouble, weight of new deviation * s0: gdouble, target deviation

::: seealso vips_hist_local().

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.
`width`	`int`
	Width of region.
`height`	`int`
	Height of region.
`...`	`none`
	`NULL`-terminated list of optional named arguments.

Return value

Returns:	`int`
	0 on success, -1 on error.