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Namespace: acl::filter (cpp) / acl::neon::filter (NEON)

gaussianBlur

Gaussian blur (low-pass filter), accelerated with a separable kernel (row kernel × column kernel).

Tier: Starter+
Channels: 1ch / 3ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`ST`	`uint8_t, uint16_t, float`	—
`DT`	`uint8_t, uint16_t, float`	—

CPP Version: `acl::filter::gaussianBlur`

template<class ST, class DT>
int gaussianBlur(
    const ST* srcImage, DT* dstImage,
    int width, int height, int cn,
    int srcStride, int dstStride,
    int kRadiusX, int kRadiusY,
    double sigmaX = 0.0, double sigmaY = 0.0,
    ST* constant = nullptr,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const ST` / `DT`	input / output; `dstImage` must be pre-allocated	non-null
`width`, `height`	`int`	Image size (pixels)	> 0
`cn`	`int`	Channel count	1 or 3
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto
`kRadiusX`, `kRadiusY`	`int`	Kernel radius; kernel size = 2r+1	≥ 1
`sigmaX`, `sigmaY`	`double`	Gaussian sigma	`0` = auto (`σ = 0.15·kSize + 0.35`)
`constant`	`ST*`	`BORDER_CONSTANT` fill-value pointer	`nullptr`
`bt`	`acl::BorderType`	Border handling	`BORDER_REFLECT_101`

NEON Version: `acl::neon::filter::gaussianBlur*` (`uint8_t` only)

The NEON layer provides fixed-kernel and generic entry points:

Entry point	Kernel	Channels	Tier	sigma configurable
`gaussianBlur3x3`	3×3	1	Starter+	—
`gaussianBlur3x3_3ch`	3×3	3	Starter+	—
`gaussianBlur5x5`	5×5	1	Starter+	—
`gaussianBlur11x11`	11×11	1	Starter+	—
`gaussianBlur` (generic)	any 2r+1	1	Starter+	✅
`gaussianBlur5x5_3ch`	5×5	3	Starter+	—

Trial package note: Trial does not include gaussianBlur. Use the resize wrappers acl::trial::resizeBilinear2xDown_cpp(const uint8_t*, uint8_t*) or acl::trial::resizeBilinear2xDown_neon(const uint8_t*, uint8_t*) for the Trial demo surface.

Fixed-kernel signature (3x3 / 5x5 / 11x11 / 3x3_3ch / 5x5_3ch share the same signature):

int gaussianBlur3x3(   // or gaussianBlur5x5 / gaussianBlur11x11 / gaussianBlur3x3_3ch / gaussianBlur5x5_3ch
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    uint8_t constant = 0,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Generic signature (supports arbitrary radius / sigma):

int gaussianBlur(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    int kRadiusX, int kRadiusY,
    double sigmaX = 0.0, double sigmaY = 0.0,
    int constant = 0,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Smart dispatch: when kSize ∈ {3, 5, 11} and sigma = 0, the generic version delivers the same throughput as the corresponding fixed-kernel variant; other (kSize, sigma) combinations fall back to the dynamic sepFilter2D performance profile.

Example

#include <acl/acl.h>
#include <acl/api.h>
acl::init("license.dat");

uint8_t srcImage[1920*1080], dstImage[1920*1080];

// Case 1: 3×3 fixed kernel (Starter+ paid API)
acl::neon::filter::gaussianBlur3x3(srcImage, dstImage, 1920, 1080);

// Case 2: 5×5 + custom sigma (Starter+)
acl::neon::filter::gaussianBlur(srcImage, dstImage, 1920, 1080, 0, 0, 2, 2, 1.5, 1.5);

boxFilter

Box (mean) filter; all pixels within the kernel are summed with equal weight. Optional normalization (when normalize=true the result is divided by the kernel size, which is the standard mean filter).

Tier: Starter+
Channels: 1ch / 3ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`ST, DT` (CPP)	`{uint8_t, uint16_t, float}`	—
`DT` (NEON)	`{uint8_t, int}` (src is `uint8_t`)	NEON-only

CPP Version: `acl::filter::boxFilter`

template<class ST, class DT>
int boxFilter(
    const ST* srcImage, DT* dstImage,
    int width, int height, int cn,
    int srcStride, int dstStride,
    int kRadius,
    bool isNormalize = true,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const ST` / `DT`	input / output	non-null
`width`, `height`	`int`	Image size (pixels)	> 0
`cn`	`int`	Channel count	1 or 3
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto
`kRadius`	`int`	Kernel radius (kSize = 2r+1)	≥ 1
`isNormalize`	`bool`	`true` → mean (divide by `kSize²`); `false` → sum	`true`
`bt`	`acl::BorderType`	Border handling	`BORDER_REFLECT_101`

NEON Version: `acl::neon::filter::boxFilter*` (`uint8_t` only)

Entry point	Kernel	Channels	Tier
`boxFilter3x3`	3×3	1	Starter+
`boxFilter5x5`	5×5	1	Starter+
`boxFilter` (generic)	any 2r+1	1	Starter+

There is no NEON entry point for 3 channels yet; use the CPP version acl::filter::boxFilter<uint8_t,uint8_t>(..., cn=3).

Fixed-kernel signature (boxFilter3x3 / boxFilter5x5):

template<class DT>
int boxFilter3x3(   // or boxFilter5x5
    const uint8_t* srcImage, DT* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    int constant = 0,
    bool isNormalize = true,
    int cn = 1,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Generic signature:

template<class DT>
int boxFilter(
    const uint8_t* srcImage, DT* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    int kRadius, int constant,
    bool isNormalize = true,
    int cn = 1,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

DT supports uint8_t (normalize) / uint32_t (no normalize, overflow-safe). cn is a runtime parameter (1 or 3).

Example

uint8_t srcImage[1920*1080], dstImage[1920*1080];
uint32_t dstSum[1920*1080];

// 3×3 mean filter
acl::neon::filter::boxFilter3x3<uint8_t>(srcImage, dstImage, 1920, 1080, 0, 0);

// 5×5 sum (not normalized, u32 output)
acl::neon::filter::boxFilter5x5<uint32_t>(
    srcImage, dstSum, 1920, 1080, 0, 0,
    /*constant=*/0, /*isNormalize=*/false, /*cn=*/1,
    acl::BorderType::BORDER_REPLICATE);

filter2D

Generic 2D convolution (arbitrary kernel). Internally detects separable kernels; if separable, automatically converts to sepFilter2D for speedup.

Tier: Starter+
Channels: 1ch / 3ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`ST`	`uint8_t, uint16_t, float`	—
`DT`	`uint8_t, uint16_t, float`	—
`KT`	`uint8_t, uint16_t, float`	—

CPP Version: `acl::filter::filter2D`

template<class ST, class DT, class KT>
int filter2D(
    const ST* srcImage, DT* dstImage,
    int width, int height, int cn,
    int srcStride, int dstStride,
    const KT* kernel, int kRadiusX, int kRadiusY,
    const ST* constant = nullptr,
    bool isNormalize = true,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const ST` / `DT`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`cn`	`int`	Channel count	1 or 3
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto
`kernel`	`const KT*`	Kernel data, row-major, size `(2rX+1)×(2rY+1)`	non-null
`kRadiusX`, `kRadiusY`	`int`	Kernel radius	≥ 1
`constant`	`const ST*`	`BORDER_CONSTANT` fill-value pointer	`nullptr`
`isNormalize`	`bool`	When `true`, output is divided by sum of kernel elements	`true`
`bt`	`acl::BorderType`	Border handling	`BORDER_REFLECT_101`

NEON Version: `acl::neon::filter::filter2D` (`uint8_t` input only)

template<class DT, class KT>
int filter2D(
    const uint8_t* srcImage, DT* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    const KT* kernel, int kRadiusX, int kRadiusY,
    int constant = 0,
    bool isNormalize = true,
    int cn = 1,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

DT / KT: typically (uint8_t, float) or (int32_t, int32_t).

Example

uint8_t srcImage[1920*1080], dstImage[1920*1080];

// 5×5 Laplacian kernel (not normalized, sharpen)
int K[25] = { 0, 0,-1, 0, 0,
              0,-1,-2,-1, 0,
             -1,-2,17,-2,-1,
              0,-1,-2,-1, 0,
              0, 0,-1, 0, 0 };
acl::filter::filter2D<uint8_t, uint8_t, int>(
    srcImage, dstImage, 1920, 1080, 1, 0, 0, K, 2, 2,
    nullptr, /*isNormalize=*/false, acl::BorderType::BORDER_REPLICATE);

sepFilter2D

Separable 2D convolution: first convolves along rows with kernelX, then along columns with kernelY. Faster than filter2D: O(k) → O(2k).

Tier: Starter+
Channels: 1ch / 3ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`ST`	`uint8_t, uint16_t, float`	—
`DT`	`uint8_t, uint16_t, float`	—
`KT`	`uint8_t, uint16_t, float`	—

CPP Version: `acl::filter::sepFilter2D`

template<class ST, class DT, class KT>
int sepFilter2D(
    const ST* srcImage, DT* dstImage,
    int width, int height, int cn,
    int srcStride, int dstStride,
    const KT* kernelX, const KT* kernelY,
    int kRadiusX, int kRadiusY,
    const ST* constant = nullptr,
    bool isNormalize = true,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const ST` / `DT`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`cn`	`int`	Channel count	1 or 3
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto
`kernelX`, `kernelY`	`const KT*`	Row / column 1D kernels, lengths `2rX+1` / `2rY+1` respectively	non-null
`kRadiusX`, `kRadiusY`	`int`	Kernel radius	≥ 1
`constant`	`const ST*`	`BORDER_CONSTANT` fill-value pointer	`nullptr`
`isNormalize`	`bool`	If `true` divide by kernel sum	`true`
`bt`	`acl::BorderType`	Border-handling mode	`BORDER_REFLECT_101`

NEON Version: `acl::neon::filter::sepFilter2D` (`uint8_t` only, 1ch / 3ch)

template<class KT>
int sepFilter2D(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    const KT* kernelX, const KT* kernelY,
    int kRadiusX, int kRadiusY,
    int constant = 0,
    int cn = 1,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

cn = 1 or 3 (channel count selected at runtime). KT: usually float.

Example

uint8_t srcImage[1920*1080], dstImage[1920*1080];

// Decompose Gaussian 5×5 into [1,4,6,4,1]/16 × [1,4,6,4,1]/16
float kx[5] = {1,4,6,4,1}, ky[5] = {1,4,6,4,1};
acl::neon::filter::sepFilter2D<float>(
    srcImage, dstImage, 1920, 1080, 0, 0, kx, ky, 2, 2, /*constant=*/0, /*cn=*/1);

sobel3x3

3×3 Sobel edge-detection operator. The runtime flag isGradX selects whether to compute Gx (horizontal gradient) or Gy (vertical gradient).

Tier: Starter+
Channels: 1ch (call separately per channel or use filter2D)
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`ST`	`{uint8_t, uint16_t, float}`	—
`DT`	typically `int16_t` / `int32_t` / `float`	—
Output type: `int16_t` (short) (since gradient values may be negative)

CPP Version: `acl::filter::sobel3x3`

template<class ST, class DT>
int sobel3x3(
    const ST* srcImage, DT* dstImage,
    int width, int height, int cn,
    int srcStride = 0, int dstStride = 0,
    const ST* constant = nullptr,
    bool isGradX = true,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const ST` / `DT`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`cn`	`int`	Channel count	1 or 3
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto
`constant`	`const ST*`	`BORDER_CONSTANT` fill value	`nullptr`
`isGradX`	`bool`	`true`: Gx (horizontal); `false`: Gy (vertical)	`true`
`bt`	`acl::BorderType`	Border-handling mode	`BORDER_REFLECT_101`

Both directions require two separate calls.

NEON Version: `acl::neon::filter::sobel3x3` (`uint8_t → int16_t` only, 1ch)

int sobel3x3(
    const uint8_t* srcImage, int16_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    int constant = 0,
    bool isGradX = true,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Example

int16_t gx[1920*1080], gy[1920*1080];
acl::neon::filter::sobel3x3(src_u8, gx, 1920, 1080, 0, 0, 0, /*isGradX=*/true);   // Gx
acl::neon::filter::sobel3x3(src_u8, gy, 1920, 1080, 0, 0, 0, /*isGradX=*/false);  // Gy
// Gradient magnitude can be composed via acl::arithmetic::phaseMagnitude

scharr

3×3 Scharr edge-detection operator. Offers better rotational symmetry than Sobel and slightly higher numerical precision.

Tier: Starter+
Channels: 1ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`ST`	`{uint8_t, uint16_t, float}`	—
`DT`	typically `int16_t` / `int32_t` / `float`	—
Output type: `int16_t`

CPP Version: `acl::filter::scharr`

template<class ST, class DT>
int scharr(
    const ST* srcImage, DT* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    const ST* constant = nullptr,
    bool isGradX = true,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Parameter semantics are the same as sobel3x3 (only the kernel coefficients are Scharr [-3, -10, -3; 0, 0, 0; 3, 10, 3] instead of Sobel).

NEON Version: `acl::neon::filter::scharr` (`uint8_t → int16_t` only)

int scharr(
    const uint8_t* srcImage, int16_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    bool isGradX = true,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Example

int16_t gx[1920*1080];
acl::neon::filter::scharr(src_u8, gx, 1920, 1080, 0, 0, /*isGradX=*/true);   // Gx (Scharr)

laplacian

Laplacian operator (second-order gradient), used for edge detection or sharpening. Internally performs two convolutions with a 3×3 or larger kernel.

Tier: Starter+
Channels: 1ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`ST`	`{uint8_t, uint16_t, float}`	—
`DT`	typically `int16_t` / `int32_t` / `float`	—
Output type: `int16_t` (second-order gradient may be negative)

CPP Version: `acl::filter::laplacian`

template<class ST, class DT>
int laplacian(
    const ST* srcImage, DT* dstImage,
    int width, int height, int cn,
    int srcStride = 0, int dstStride = 0,
    int ksize = 1, double scale = 1.0, double delta = 0.0,
    const ST* constant = nullptr,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const ST` / `DT`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`cn`	`int`	Channel count	1
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto
`ksize`	`int`	Kernel aperture size	`1` (= 3×3 standard Laplacian)
`scale`	`double`	Output scaling factor	`1.0`
`delta`	`double`	Output offset	`0.0`
`constant`	`const ST*`	`BORDER_CONSTANT` fill value	`nullptr`
`bt`	`acl::BorderType`	Border-handling mode	`BORDER_REFLECT_101`

NEON Version: `acl::neon::filter::laplacian` (`uint8_t → int16_t` only)

int laplacian(
    const uint8_t* srcImage, int16_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    int ksize = 1, int constant = 0,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

The NEON version omits scale / delta (fixed at 1.0 / 0.0). For scaling, use the CPP version.

Example

uint8_t srcImage[1920*1080];
int16_t dstImage[1920*1080];
acl::neon::filter::laplacian(srcImage, dstImage, 1920, 1080);

canny

Canny edge detection. Typical pipeline: Gaussian blur → gradient → non-maximum suppression → double-threshold linking.

Tier: Starter+
Channels: 1ch (grayscale input)
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`Src_T`	`uint8_t`, `uint16_t`	CPP backend
`Src_T`	`uint8_t`	NEON backend

NEON Version: `acl::neon::filter::canny` (`uint8_t` only)

int canny(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int low_thresh, int high_thresh,
    int aperture_size = 3,
    int srcStride = 0, int dstStride = 0,
    bool l2GradFlag = true);

Parameter	Type	Meaning	Default
`srcImage`	`const uint8_t*`	Input grayscale image	non-null
`dstImage`	`uint8_t*`	Output binary edge image (0 / 255)	non-null
`width`, `height`	`int`	Image size	> 0
`low_thresh`, `high_thresh`	`int`	Low / high double thresholds	`low < high`
`aperture_size`	`int`	Sobel kernel aperture	`3` (only 3 is supported)
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto
`l2GradFlag`	`bool`	`true`: L2 Euclidean gradient; `false`: L1 gradient (faster)	`true`

Example

uint8_t srcImage[1920*1080], dstImage[1920*1080];
acl::neon::filter::canny(srcImage, dstImage, 1920, 1080, 50, 150);

morphology (erode / dilate)

Basic morphological operators: erosion (erode, taking the minimum over kernel coverage) and dilation (dilate, taking the maximum). Uses the O(N) van Herk / Gil-Werman algorithm; runtime is independent of kernel size.

Tier: Starter+
Channels: 1ch / 3ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`T`	`uint8_t, uint16_t, float`	—
Kernel shape: square (determined by `radius`; actual kernel size = 2r+1)

CPP Version: `acl::filter::erode` / `acl::filter::dilate`

template<class T>
int erode(
    const T* srcImage, T* dstImage,
    int width, int height, int cn, int radius,
    int srcStride = 0, int dstStride = 0);

template<class T>
int dilate(
    const T* srcImage, T* dstImage,
    int width, int height, int cn, int radius,
    int srcStride = 0, int dstStride = 0);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const T` / `T`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`cn`	`int`	Channel count	1 or 3
`radius`	`int`	Structuring-element radius (square kernel, size = 2r+1)	≥ 1
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto

NEON Version: `acl::neon::filter::erode` / `acl::neon::filter::dilate` (`uint8_t` only)

int erode(   // or dilate
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height, int cn, int radius,
    int srcStride = 0, int dstStride = 0);

Parameter semantics match the CPP version.

Example

uint8_t srcImage[1920*1080], dstImage[1920*1080];

// 3×3 erosion (radius=1)
acl::filter::erode<uint8_t>(srcImage, dstImage, 1920, 1080, 1, 1);

// 11×11 dilation (radius=5; the O(N) algorithm is unaffected by size)
acl::filter::dilate<uint8_t>(srcImage, dstImage, 1920, 1080, 1, 5);

medianFilter

3×3 median filter — outputs the median of the 9 pixels within the kernel. Typical use: salt-and-pepper noise removal.

Tier: Starter+
Channels: 1ch / 3ch
Inplace: supported (src == dst OK)
Types:

Template parameter	Allowed types	Constraint
`DT`	`uint8_t, uint16_t, float`	—
Kernel size: 3×3 only (5×5 and larger are not implemented)

CPP Version: `acl::filter::medianFilter3x3`

template<class DT>
int medianFilter3x3(
    const DT* srcImage, DT* dstImage,
    int width, int height,
    int cn = 1,
    int srcStride = 0, int dstStride = 0,
    DT borderValue = 0,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const DT` / `DT`	input / output (inplace supported)	non-null
`width`, `height`	`int`	Image size	> 0
`cn`	`int`	Channel count	`1`
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto
`borderValue`	`DT`	`BORDER_CONSTANT` fill value	`0`
`bt`	`acl::BorderType`	Border-handling mode	`BORDER_REFLECT_101`

NEON Version: `acl::neon::filter::medianFilter3x3` / `medianFilter3x3_3ch` (`uint8_t` only)

Entry point	Channels	Tier
`medianFilter3x3`	1	Starter+
`medianFilter3x3_3ch`	3	Starter+

int medianFilter3x3(   // or medianFilter3x3_3ch
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    uint8_t borderValue = 0,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Example

uint8_t srcImage[1920*1080];

// Salt-and-pepper denoise (in-place)
acl::neon::filter::medianFilter3x3(srcImage, srcImage, 1920, 1080);

bilateralFilter

Edge-preserving smoothing — bilateral filter; simultaneously considers spatial distance and pixel-value difference, denoising while preserving edges.

Tier: Pro+
Channels: 1ch / 3ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`T` (CPP)	`uint8_t, uint16_t, float`	—
`T` (NEON)	`uint8_t`	NEON-only

CPP Version: `acl::filter::bilateralFilter`

template<class T = uint8_t>
int bilateralFilter(
    const T* srcImage, T* dstImage,
    int width, int height, int cn,
    int srcStride, int dstStride,
    int d, double sigmaColor, double sigmaSpace,
    const T* constant = nullptr,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const T` / `T`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`cn`	`int`	Channel count	1 or 3
`srcStride`, `dstStride`	`int`	Bytes per row	required
`d`	`int`	Filter radius (kernel = 2d+1)	≥ 1
`sigmaColor`	`double`	Standard deviation in color space	typically 10-100
`sigmaSpace`	`double`	Standard deviation in coordinate space	typically 10-100
`constant`	`const T*`	`BORDER_CONSTANT` fill value	`nullptr`
`bt`	`acl::BorderType`	Border handling	`BORDER_REFLECT_101`

NEON Version: `acl::neon::filter::bilateralFilter` (`uint8_t` only, 1ch / 3ch)

int bilateralFilter(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    int d, double sigmaColor, double sigmaSpace,
    int constant = 0,
    int cn = 1,
    acl::BorderType bt = acl::BorderType::BORDER_REFLECT_101);

cn = 1 or 3 (channel count, runtime).

Example

uint8_t srcImage[1920*1080], dstImage[1920*1080];

// Edge-preserving denoising, d=5, sigmaColor=sigmaSpace=30
acl::neon::filter::bilateralFilter(
    srcImage, dstImage, 1920, 1080, 0, 0, 5, 30.0, 30.0);

nlMeansDenoising

Non-Local Means denoising — searches for similar patches within the entire search window and forms a weighted average, denoising while preserving details.

Tier: Pro+
Channels: 1ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`T` (CPP)	`uint8_t, uint16_t, float`	—
`T` (NEON)	`uint8_t`	NEON-only

CPP Version: `acl::filter::nlMeansDenoising`

template<class T = uint8_t>
int nlMeansDenoising(
    const T* srcImage, T* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    float h,
    int patchRadius = 3,
    int searchRadius = 10);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const T` / `T`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`srcStride`, `dstStride`	`int`	Bytes per row	required
`h`	`float`	Denoising strength (larger = smoother; typically 5-15)	required
`patchRadius`	`int`	Patch radius (patch = 2r+1)	`3` (= 7×7)
`searchRadius`	`int`	Search-window radius	`10` (= 21×21)

NEON Version: `acl::neon::filter::nlMeansDenoising` (`uint8_t` only)

int nlMeansDenoising(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    float h,
    int patchRadius = 3,
    int searchRadius = 10);

Non-templated; the signature matches the CPP version with the template <T> removed.

Example

uint8_t srcImage[1920*1080], dstImage[1920*1080];

// Light denoising (h=10, patch 7×7, search 21×21 — defaults)
acl::neon::filter::nlMeansDenoising(srcImage, dstImage, 1920, 1080, 0, 0, 10.0f);

// Stronger denoising + larger search window
acl::neon::filter::nlMeansDenoising(srcImage, dstImage, 1920, 1080, 0, 0, 15.0f, 3, 15);

guidedFilter

Guided filter — edge-aware smoothing of the input image based on the guide image (guideImage). O(N) complexity (does not grow with kernel size).

Tier: Pro+
Channels: 1ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`T`	`uint8_t, uint16_t, float`	—

CPP Version: `acl::filter::guidedFilter`

template<class T>
int guidedFilter(
    const T* guideImage,
    const T* srcImage,
    T* dstImage,
    int width, int height,
    int guideStride, int srcStride, int dstStride,
    int radius, double eps);

Parameter	Type	Meaning	Default
`guideImage`	`const T*`	Guide image (often identical to srcImage; another image also works)	non-null
`srcImage`, `dstImage`	`const T` / `T`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`guideStride`, `srcStride`, `dstStride`	`int`	Respective bytes per row	required
`radius`	`int`	Window radius (window size = 2r+1)	≥ 1
`eps`	`double`	Regularization parameter	typically `0.01` (integer images `1.0`-`100.0`)

NEON Version: `acl::neon::filter::guidedFilter` (`uint8_t` only)

int guidedFilter(
    const uint8_t* guideImage,
    const uint8_t* srcImage,
    uint8_t* dstImage,
    int width, int height,
    int guideStride, int srcStride, int dstStride,
    int radius, double eps);

Example

// Use the source image itself as the guide; radius=8, eps=1000
acl::filter::guidedFilter<uint8_t>(
    srcImage, srcImage, dstImage, 1920, 1080, 1920, 1920, 1920, 8, 1000.0);

stackBlur

O(1) approximate Gaussian blur (complexity independent of kernel size); suitable for large-kernel scenarios. The effect is close to Gaussian but slightly different; used where exact Gaussian is not required (e.g. UI blurred backgrounds).

Tier: Starter+
Channels: 1ch / 3ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`T`	`uint8_t, uint16_t, float`	—

CPP Version: `acl::filter::stackBlur`

template<class T>
int stackBlur(
    const T* srcImage, T* dstImage,
    int width, int height, int cn,
    int srcStride = 0, int dstStride = 0,
    int kSizeX = 3, int kSizeY = 3);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const T` / `T`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`cn`	`int`	Channel count	1 or 3
`srcStride`, `dstStride`	`int`	Bytes per row	`0` = auto
`kSizeX`, `kSizeY`	`int`	Horizontal / vertical kernel size (must be odd)	`3`

NEON Version: `acl::neon::filter::stackBlur` (`uint8_t` only)

int stackBlur(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height, int cn,
    int srcStride = 0, int dstStride = 0,
    int kSizeX = 3, int kSizeY = 3);

Example

// 21×21 blur (well beyond Gaussian 11×11; the O(1) algorithm does not degrade)
acl::filter::stackBlur<uint8_t>(srcImage, dstImage, 1920, 1080, 1, 0, 0, 21, 21);

unsharpMask

Unsharp Mask — subtracts a blurred image from the source to produce a sharpening enhancement. amount controls the sharpening strength.

Tier: Pro+
Channels: 1ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`T`	`uint8_t, uint16_t, float`	—

CPP Version: `acl::filter::unsharpMask`

template<class T>
int unsharpMask(
    const T* srcImage, T* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    int kRadius, double sigma, float amount);

Parameter	Type	Meaning	Default
`srcImage`, `dstImage`	`const T` / `T`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`srcStride`, `dstStride`	`int`	Bytes per row	required
`kRadius`	`int`	Gaussian kernel radius	≥ 1
`sigma`	`double`	Gaussian sigma (controls blur strength)	typically `1.0` ~ `2.0`
`amount`	`float`	Sharpening strength	typically `0.5` ~ `2.0` (`1.0` = original strength)

NEON Version: `acl::neon::filter::unsharpMask` (`uint8_t` only)

int unsharpMask(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    int kRadius, double sigma, float amount);

Example

// Light sharpening (radius=2, sigma=1.5, amount=1.2)
acl::filter::unsharpMask<uint8_t>(
    srcImage, dstImage, 1920, 1080, 0, 0, 2, 1.5, 1.2f);

gaborFilter

Gabor filter — sinusoidal × Gaussian-modulated kernel used for texture analysis and direction-sensitive edge detection.

Tier: Pro+
Channels: 1ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`T`	`uint8_t, uint16_t, float`	—

CPP Version: `acl::filter::gaborFilter`

template<class T>
int gaborFilter(
    const T* srcImage, T* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    int ksize, double sigma, double theta,
    double lambd, double gamma, double psi);

Parameter	Type	Meaning	Typical value
`srcImage`, `dstImage`	`const T` / `T`	input / output	non-null
`width`, `height`	`int`	Image size	> 0
`srcStride`, `dstStride`	`int`	Bytes per row	required
`ksize`	`int`	Kernel size (typically odd)	`21` / `31`
`sigma`	`double`	Gaussian envelope sigma	`4.0`-`8.0`
`theta`	`double`	Direction (radians)	`0` (horizontal) ~ `π`
`lambd`	`double`	Sinusoidal wavelength	`10.0`
`gamma`	`double`	Spatial aspect ratio	`0.5`
`psi`	`double`	Phase offset	`0`

NEON Version: `acl::neon::filter::gaborFilter` (`uint8_t` only)

int gaborFilter(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride, int dstStride,
    int ksize, double sigma, double theta,
    double lambd, double gamma, double psi);

Example

uint8_t srcImage[1920*1080], dstImage[1920*1080];

// Horizontal-direction Gabor kernel
acl::neon::filter::gaborFilter(srcImage, dstImage, 1920, 1080, 0, 0,
    21, 4.0, 0.0, 10.0, 0.5, 0.0);

edgePreservingFilter / detailEnhance

Edge-preserving filtering — O(N) edge-preserving smoothing based on recursive domain transforms (Gastal & Oliveira, SIGGRAPH 2011).
edgePreservingFilter smooths while preserving edges; detailEnhance uses it in reverse to enhance details.

Tier: Business
Channels: 3ch (RGB)
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`T`	`uint8_t`	—

CPP Signature

int edgePreservingFilter(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    float sigmaS = 60.0f, float sigmaR = 0.4f,
    int numIter = 3);

int detailEnhance(
    const uint8_t* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    float sigmaS = 10.0f, float sigmaR = 0.15f);

Parameter	Type	Meaning	Default
`sigmaS`	`float`	Spatial sigma (larger → larger smoothing range)	60.0 (edge-preserving) / 10.0 (detail)
`sigmaR`	`float`	Color-value sigma	0.4 / 0.15
`numIter`	`int`	Number of iterations (edge-preserving)	3

Example

uint8_t rgbSrc[1920*1080*3], rgbDst[1920*1080*3];

// Cartoon-style effect
acl::filter::edgePreservingFilter(rgbSrc, rgbDst, 1920, 1080, 0, 0, 60.0f, 0.4f, 3);

// Detail enhancement
acl::filter::detailEnhance(rgbSrc, rgbDst, 1920, 1080);

tonemap

HDR tone mapping — compresses a float HDR image into the uint8_t LDR display space. Provides 3 classic algorithms.

Tier: Business
Channels: 1ch / 3ch
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
Input	`float`	—
Output	`uint8_t`	—

CPP Signature

// Linear exposure (simple gamma)
int tonemapLinear(
    const float* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    float gamma = 2.2f, float exposure = 1.0f);

// Reinhard (global key control)
int tonemapReinhard(
    const float* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    float gamma = 2.2f,
    float key = 0.18f,
    float lWhite = 0.0f);

// Drago (logarithmic mapping, suitable for high dynamic range)
int tonemapDrago(
    const float* srcImage, uint8_t* dstImage,
    int width, int height,
    int srcStride = 0, int dstStride = 0,
    float gamma = 2.2f,
    float saturation = 1.0f,
    float bias = 0.85f);

Parameter	Meaning	Typical value
`gamma`	Output gamma correction	`2.2`
`exposure` (Linear)	Exposure multiplier	`1.0`
`key` (Reinhard)	Mean-luminance key	`0.18`
`lWhite` (Reinhard)	White point (`0` = auto-take max)	`0.0`
`saturation` (Drago)	Saturation	`1.0`
`bias` (Drago)	Bias	`0.85`

Example

float hdr[1920*1080];
uint8_t ldr[1920*1080];

// Simplest: linear + gamma
acl::filter::tonemapLinear(hdr, ldr, 1920, 1080);

// Use Reinhard when the scene is too bright
acl::filter::tonemapReinhard(hdr, ldr, 1920, 1080, 0, 0, 2.2f, 0.18f);

mergeMertens

Multi-exposure image fusion (Mertens et al. 2007) — fuses multiple images at different exposures into a single balanced-exposure output. A simpler alternative to the HDR + tonemap pipeline.

Tier: Business
Channels: 3ch (RGB)
Inplace: not supported
Types:

Template parameter	Allowed types	Constraint
`T`	`uint8_t`	—

CPP Signature

int mergeMertens(
    const uint8_t** images, int numImages,
    uint8_t* dstImage,
    int width, int height,
    const int* strides = nullptr,
    int dstStride = 0,
    float wContrast = 1.0f,
    float wSaturation = 1.0f,
    float wExposure = 1.0f);

Parameter	Meaning	Typical value
`images`	Input image pointer array (3ch RGB)	`numImages` images
`numImages`	Number of input images	typically `3` (underexposed / normal / overexposed)
`strides`	Per-image stride array; when `nullptr`, all treated as `width*3`	optional
`wContrast`	Contrast weight	`1.0`
`wSaturation`	Saturation weight	`1.0`
`wExposure`	Exposure-quality weight	`1.0`

Example

uint8_t under[1920*1080*3], normal[1920*1080*3], over[1920*1080*3];
uint8_t fused[1920*1080*3];

const uint8_t* imgs[3] = { under, normal, over };
acl::filter::mergeMertens(imgs, 3, fused, 1920, 1080);

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API‐Filter

Filter

gaussianBlur

CPP Version: acl::filter::gaussianBlur

NEON Version: acl::neon::filter::gaussianBlur* (uint8_t only)

Example

boxFilter

CPP Version: acl::filter::boxFilter

NEON Version: acl::neon::filter::boxFilter* (uint8_t only)

Example

filter2D

CPP Version: acl::filter::filter2D

NEON Version: acl::neon::filter::filter2D (uint8_t input only)

Example

sepFilter2D

CPP Version: acl::filter::sepFilter2D

NEON Version: acl::neon::filter::sepFilter2D (uint8_t only, 1ch / 3ch)

Example

sobel3x3

CPP Version: acl::filter::sobel3x3

NEON Version: acl::neon::filter::sobel3x3 (uint8_t → int16_t only, 1ch)

Example

scharr

CPP Version: acl::filter::scharr

NEON Version: acl::neon::filter::scharr (uint8_t → int16_t only)

Example

laplacian

CPP Version: acl::filter::laplacian

NEON Version: acl::neon::filter::laplacian (uint8_t → int16_t only)

Example

canny

NEON Version: acl::neon::filter::canny (uint8_t only)

Example

morphology (erode / dilate)

CPP Version: acl::filter::erode / acl::filter::dilate

NEON Version: acl::neon::filter::erode / acl::neon::filter::dilate (uint8_t only)

Example

medianFilter

CPP Version: acl::filter::medianFilter3x3

NEON Version: acl::neon::filter::medianFilter3x3 / medianFilter3x3_3ch (uint8_t only)

Example

bilateralFilter

CPP Version: acl::filter::bilateralFilter

NEON Version: acl::neon::filter::bilateralFilter (uint8_t only, 1ch / 3ch)

Example

nlMeansDenoising

CPP Version: acl::filter::nlMeansDenoising

NEON Version: acl::neon::filter::nlMeansDenoising (uint8_t only)

Example

guidedFilter

CPP Version: acl::filter::guidedFilter

NEON Version: acl::neon::filter::guidedFilter (uint8_t only)

Example

stackBlur

CPP Version: acl::filter::stackBlur

NEON Version: acl::neon::filter::stackBlur (uint8_t only)

Example

unsharpMask

CPP Version: acl::filter::unsharpMask

NEON Version: acl::neon::filter::unsharpMask (uint8_t only)

Example

gaborFilter

CPP Version: acl::filter::gaborFilter

NEON Version: acl::neon::filter::gaborFilter (uint8_t only)

Example

edgePreservingFilter / detailEnhance

CPP Signature

Example

tonemap

CPP Signature

Example

mergeMertens

CPP Signature

Example

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

CPP Version: `acl::filter::gaussianBlur`

NEON Version: `acl::neon::filter::gaussianBlur*` (`uint8_t` only)

CPP Version: `acl::filter::boxFilter`

NEON Version: `acl::neon::filter::boxFilter*` (`uint8_t` only)

CPP Version: `acl::filter::filter2D`

NEON Version: `acl::neon::filter::filter2D` (`uint8_t` input only)

CPP Version: `acl::filter::sepFilter2D`

NEON Version: `acl::neon::filter::sepFilter2D` (`uint8_t` only, 1ch / 3ch)

CPP Version: `acl::filter::sobel3x3`

NEON Version: `acl::neon::filter::sobel3x3` (`uint8_t → int16_t` only, 1ch)

CPP Version: `acl::filter::scharr`

NEON Version: `acl::neon::filter::scharr` (`uint8_t → int16_t` only)

CPP Version: `acl::filter::laplacian`

NEON Version: `acl::neon::filter::laplacian` (`uint8_t → int16_t` only)

NEON Version: `acl::neon::filter::canny` (`uint8_t` only)

CPP Version: `acl::filter::erode` / `acl::filter::dilate`

NEON Version: `acl::neon::filter::erode` / `acl::neon::filter::dilate` (`uint8_t` only)

CPP Version: `acl::filter::medianFilter3x3`

NEON Version: `acl::neon::filter::medianFilter3x3` / `medianFilter3x3_3ch` (`uint8_t` only)

CPP Version: `acl::filter::bilateralFilter`

NEON Version: `acl::neon::filter::bilateralFilter` (`uint8_t` only, 1ch / 3ch)

CPP Version: `acl::filter::nlMeansDenoising`

NEON Version: `acl::neon::filter::nlMeansDenoising` (`uint8_t` only)

CPP Version: `acl::filter::guidedFilter`

NEON Version: `acl::neon::filter::guidedFilter` (`uint8_t` only)

CPP Version: `acl::filter::stackBlur`

NEON Version: `acl::neon::filter::stackBlur` (`uint8_t` only)

CPP Version: `acl::filter::unsharpMask`

NEON Version: `acl::neon::filter::unsharpMask` (`uint8_t` only)

CPP Version: `acl::filter::gaborFilter`

NEON Version: `acl::neon::filter::gaborFilter` (`uint8_t` only)