Gaussian Blur Filters

Gaussian blur image filters. More...

Functions
SIMD_API void	SimdGaussianBlur3x3 (const uint8_t *src, size_t srcStride, size_t width, size_t height, size_t channelCount, uint8_t *dst, size_t dstStride)
	Performs 3x3 Gaussian blur for an 8-bit interleaved image. More...
SIMD_API void *	SimdGaussianBlurInit (size_t width, size_t height, size_t channels, const float *sigma, const float *epsilon)
	Creates a context for separable Gaussian blurring of an 8-bit interleaved image. More...
SIMD_API void	SimdGaussianBlurRun (const void *filter, const uint8_t *src, size_t srcStride, uint8_t *dst, size_t dstStride)
	Performs image Gaussian blurring with a context created by SimdGaussianBlurInit. More...

Detailed Description

Gaussian blur image filters.

Function Documentation

SimdGaussianBlur3x3()

void SimdGaussianBlur3x3	(	const uint8_t *	src,
		size_t	srcStride,
		size_t	width,
		size_t	height,
		size_t	channelCount,
		uint8_t *	dst,
		size_t	dstStride
	)

Performs 3x3 Gaussian blur for an 8-bit interleaved image.

The function applies the same separable 3x3 kernel to every channel independently. For every channel c of pixel (x, y):

sx0 = Max(x - 1, 0);
sx1 = x;
sx2 = Min(x + 1, width - 1);
sy0 = Max(y - 1, 0);
sy1 = y;
sy2 = Min(y + 1, height - 1);

dst[x, y, c] = (src[sx0, sy0, c] + 2*src[sx1, sy0, c] + src[sx2, sy0, c] +
              2*(src[sx0, sy1, c] + 2*src[sx1, sy1, c] + src[sx2, sy1, c]) +
                 src[sx0, sy2, c] + 2*src[sx1, sy2, c] + src[sx2, sy2, c] + 8) / 16;

The source and destination images must have the same width, height and number of interleaved 8-bit channels. Valid channel counts are 1, 2, 3 and 4.

Note

This function has a C++ wrapper Simd::GaussianBlur3x3(const View<A>& src, View<A>& dst).

Parameters

[in]	src	- a pointer to pixels data of source image.
[in]	srcStride	- a row size of the src image (in bytes).
[in]	width	- an image width.
[in]	height	- an image height.
[in]	channelCount	- a number of 8-bit channels per pixel.
[out]	dst	- a pointer to pixels data of destination image.
[in]	dstStride	- a row size of the dst image (in bytes).

SimdGaussianBlurInit()

void * SimdGaussianBlurInit	(	size_t	width,
		size_t	height,
		size_t	channels,
		const float *	sigma,
		const float *	epsilon
	)

Creates a context for separable Gaussian blurring of an 8-bit interleaved image.

The context stores image parameters and normalized 1D Gaussian coefficients used by SimdGaussianBlurRun:

half = floor(sqrt(-log(epsilon[0])) * sigma[0]);
kernel = 2*half + 1;
weight[kernel];

for(x = -half; x <= half; ++x)
    weight[x + half] = exp(-Square(x/sigma[0])/2);

sum = 0;
for(x = -half; x <= half; ++x)
    sum += weight[x + half];

for(x = -half; x <= half; ++x)
    weight[x + half] /= sum;

Parameters

[in]	width	- a width of input and output image.
[in]	height	- a height of input and output image.
[in]	channels	- a number of 8-bit channels per pixel. Its value must be in range [1..4].
[in]	sigma	- a pointer to sigma parameter (blur radius). Its value must be greater than or equal to 0.000001.
[in]	epsilon	- a pointer to epsilon parameter (permissible relative error). Its value must be in range [0.000001..1.0]. Pointer can be NULL and by default value 0.001 is used.

Returns

a pointer to filter context. On error it returns NULL. This pointer is used by SimdGaussianBlurRun and must be released by SimdRelease.

SimdGaussianBlurRun()

void SimdGaussianBlurRun	(	const void *	filter,
		const uint8_t *	src,
		size_t	srcStride,
		uint8_t *	dst,
		size_t	dstStride
	)

Performs image Gaussian blurring with a context created by SimdGaussianBlurInit.

The function applies the context's normalized 1D kernel horizontally and vertically to every channel independently. Border pixels are handled by nearest-pixel replication:

sum = 0;
for(y = -half; y <= half; ++y)
{
    sy = Min(Max(0, dy + y), height - 1);
    for(x = -half; x <= half; ++x)
    {
        sx = Min(Max(0, dx + x), width - 1);
        sum += src[sx, sy, c]*weight[x + half]*weight[y + half];
    }
}
dst[dx, dy, c] = Round(sum);

Parameters

[in]	filter	- a filter context. It must be created by function SimdGaussianBlurInit and released by function SimdRelease.
[in]	src	- a pointer to pixels data of the original input image.
[in]	srcStride	- a row size (in bytes) of the input image.
[out]	dst	- a pointer to pixels data of the filtered output image.
[in]	dstStride	- a row size (in bytes) of the output image.