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快速双边滤波 附完整C代码

很早之前写过《双边滤波算法的简易实现bilateralFilter》。

当时学习参考的代码来自cuda的样例。

相关代码可以参阅:

https://github.com/johng12/cudaSamples/tree/master/cudaSamples/3_Imaging/bilateralFilter

由于算法逻辑非常清晰,就不多解释了。

需要补课的,请移步《o(1)复杂度之双边滤波算法的原理、流程、实现及效果。

代码见:bilateralFilter_cpu.cpp 文件。

#include <math.h>
#include <string.h>

////////////////////////////////////////////////////////////////////////////////
// export C interface
#define EPSILON 1e-3
extern "C" void updateGaussianGold(float delta, int radius);
extern "C" void bilateralFilterGold(unsigned int *pSrc,
                                    unsigned int *pDest,
                                    float e_d,
                                    int w, int h, int r);
//variables
float gaussian[50];

struct float4
{
    float x;
    float y;
    float z;
    float w;

    float4() {};
    float4(float value)
    {
        x = y = z = w = value;
    }
};

void updateGaussianGold(float delta, int radius)
{
    for (int i = 0; i < 2 * radius + 1; i++)
    {
        int x = i - radius;
        gaussian[i] = exp(-(x * x) /
                          (2 * delta * delta));
    }
}

float heuclideanLen(float4 a, float4 b, float d)
{
    float mod = (b.x - a.x) * (b.x - a.x) +
                (b.y - a.y) * (b.y - a.y) +
                (b.z - a.z) * (b.z - a.z) +
                (b.w - a.w) * (b.w - a.w);

    return exp(-mod / (2 * d * d));
}

unsigned int hrgbaFloatToInt(float4 rgba)
{
    unsigned int w = (((unsigned int)(fabs(rgba.w) * 255.0f)) & 0xff) << 24;
    unsigned int z = (((unsigned int)(fabs(rgba.z) * 255.0f)) & 0xff) << 16;
    unsigned int y = (((unsigned int)(fabs(rgba.y) * 255.0f)) & 0xff) << 8;
    unsigned int x = ((unsigned int)(fabs(rgba.x) * 255.0f)) & 0xff;

    return (w | z | y | x);
}

float4 hrgbaIntToFloat(unsigned int c)
{
    float4 rgba;
    rgba.x = (c & 0xff) * 0.003921568627f;       //  /255.0f;
    rgba.y = ((c>>8) & 0xff) * 0.003921568627f;  //  /255.0f;
    rgba.z = ((c>>16) & 0xff) * 0.003921568627f; //  /255.0f;
    rgba.w = ((c>>24) & 0xff) * 0.003921568627f; //  /255.0f;
    return rgba;
}

float4 mul(float a, float4 b)
{
    float4 ans;
    ans.x = a * b.x;
    ans.y = a * b.y;
    ans.z = a * b.z;
    ans.w = a * b.w;

    return ans;
}

float4 add4(float4 a, float4 b)
{
    float4 ans;
    ans.x = a.x + b.x;
    ans.y = a.y + b.y;
    ans.z = a.z + b.z;
    ans.w = a.w + b.w;

    return ans;
}

void bilateralFilterGold(unsigned int *pSrc,
                         unsigned int *pDest,
                         float e_d,
                         int w, int h, int r)
{
    float4 *hImage = new float4[w * h];
    float domainDist, colorDist, factor;

    for (int y = 0; y < h; y++)
    {
        for (int x = 0; x < w; x++)
        {
            hImage[y * w + x] = hrgbaIntToFloat(pSrc[y * w + x]);
        }
    }

    for (int y = 0; y < h; y++)
    {
        for (int x = 0; x < w; x++)
        {
            float4 t(0.0f);
            float sum = 0.0f;

            for (int i = -r; i <= r; i++)
            {
                int neighborY = y + i;

                //clamp the neighbor pixel, prevent overflow
                if (neighborY < 0)
                {
                    neighborY = 0;
                }
                else if (neighborY >= h)
                {
                    neighborY = h - 1;
                }

                for (int j = -r; j <= r; j++)
                {
                    domainDist = gaussian[r + i] * gaussian[r + j];

                    //clamp the neighbor pixel, prevent overflow
                    int neighborX = x + j;

                    if (neighborX < 0)
                    {
                        neighborX = 0;
                    }
                    else if (neighborX >= w)
                    {
                        neighborX = w - 1;
                    }

                    colorDist = heuclideanLen(hImage[neighborY * w + neighborX], hImage[y * w + x], e_d);
                    factor = domainDist * colorDist;
                    sum += factor;
                    t = add4(t, mul(factor, hImage[neighborY * w + neighborX]));
                }
            }

            pDest[y * w + x] = hrgbaFloatToInt(mul(1 / sum, t));
        }
    }

    delete[] hImage;
}

在网上很多人都采用双边滤波作为磨皮算法,包括比较知名的gpuimage库。

用的也是小半径的双边,而双边滤波有很多快速算法的变种。

详情可参阅:http://people.csail.mit.edu/sparis/bf/

而就在几个月前,github上有个朋友放出来了一份快速双边滤波的tiny版本代码。

https://github.com/ufoym/RecursiveBF/

代码见:rbf.hpp

#ifndef INCLUDE_RBF
#define INCLUDE_RBF
#include <math.h>
#include <string.h>
#define QX_DEF_CHAR_MAX 255

/* ======================================================================
RecursiveBF: A lightweight library for recursive bilateral filtering.
-------------------------------------------------------------------------
Intro:      Recursive bilateral filtering (developed by Qingxiong Yang) 
            is pretty fast compared with most edge-preserving filtering 
            methods.
            -   computational complexity is linear in both input size and 
                dimensionality
            -   takes about 43 ms to process a one mega-pixel color image
                (i7 1.8GHz & 4GB memory)
            -   about 18x faster than Fast high-dimensional filtering 
                using the permutohedral lattice
            -   about 86x faster than Gaussian kd-trees for fast high-
                dimensional filtering
Usage:      // ----------------------------------------------------------
            // Basic Usage
            // ----------------------------------------------------------
            unsigned char * img = ...;                    // input image
            unsigned char * img_out = 0;            // output image
            int width = ..., height = ..., channel = ...; // image size
            recursive_bf(img, img_out, 
                         sigma_spatial, sigma_range, 
                         width, height, channel);
            // ----------------------------------------------------------
            // Advanced: using external buffer for better performance
            // ----------------------------------------------------------
            unsigned char * img = ...;                    // input image
            unsigned char * img_out = 0;            // output image
            int width = ..., height = ..., channel = ...; // image size
            float * buffer = new float[                   // external buf
                                 ( width * height* channel 
                                 + width * height
                                 + width * channel 
                                 + width) * 2];
            recursive_bf(img, img_out, 
                         sigma_spatial, sigma_range, 
                         width, height, channel, 
                         buffer);
            delete[] buffer;
Notice:     Large sigma_spatial/sigma_range parameter may results in 
            visible artifact which can be removed by an additional 
            filter with small sigma_spatial/sigma_range parameter.
-------------------------------------------------------------------------
Reference:  Qingxiong Yang, Recursive Bilateral Filtering,
            European Conference on Computer Vision (ECCV) 2012, 399-413.
====================================================================== */

inline void recursive_bf(
    unsigned char * img_in, 
    unsigned char *& img_out, 
    float sigma_spatial, float sigma_range, 
    int width, int height, int channel, 
    float * buffer /*= 0*/);

// ----------------------------------------------------------------------

inline void _recursive_bf(
    unsigned char * img,
    float sigma_spatial, float sigma_range, 
    int width, int height, int channel,
    float * buffer = 0)
{
    const int width_height = width * height;
    const int width_channel = width * channel;
    const int width_height_channel = width * height * channel;

    bool is_buffer_internal = (buffer == 0);
    if (is_buffer_internal)
        buffer = new float[(width_height_channel + width_height 
                            + width_channel + width) * 2];

    float * img_out_f = buffer;
    float * img_temp = &img_out_f[width_height_channel];
    float * map_factor_a = &img_temp[width_height_channel];
    float * map_factor_b = &map_factor_a[width_height]; 
    float * slice_factor_a = &map_factor_b[width_height];
    float * slice_factor_b = &slice_factor_a[width_channel];
    float * line_factor_a = &slice_factor_b[width_channel];
    float * line_factor_b = &line_factor_a[width];
    
    //compute a lookup table
    float range_table[QX_DEF_CHAR_MAX + 1];
    float inv_sigma_range = 1.0f / (sigma_range * QX_DEF_CHAR_MAX);
    for (int i = 0; i <= QX_DEF_CHAR_MAX; i++) 
        range_table[i] = static_cast<float>(exp(-i * inv_sigma_range));

    float alpha = static_cast<float>(exp(-sqrt(2.0) / (sigma_spatial * width)));
    float ypr, ypg, ypb, ycr, ycg, ycb;
    float fp, fc;
    float inv_alpha_ = 1 - alpha;
    for (int y = 0; y < height; y++)
    {
        float * temp_x = &img_temp[y * width_channel];
        unsigned char * in_x = &img[y * width_channel];
        unsigned char * texture_x = &img[y * width_channel];
        *temp_x++ = ypr = *in_x++; 
        *temp_x++ = ypg = *in_x++; 
        *temp_x++ = ypb = *in_x++;
        unsigned char tpr = *texture_x++; 
        unsigned char tpg = *texture_x++;
        unsigned char tpb = *texture_x++;

        float * temp_factor_x = &map_factor_a[y * width];
        *temp_factor_x++ = fp = 1;

        // from left to right
        for (int x = 1; x < width; x++) 
        {
            unsigned char tcr = *texture_x++; 
            unsigned char tcg = *texture_x++; 
            unsigned char tcb = *texture_x++;
            unsigned char dr = abs(tcr - tpr);
            unsigned char dg = abs(tcg - tpg);
            unsigned char db = abs(tcb - tpb);
            int range_dist = (((dr << 1) + dg + db) >> 2);
            float weight = range_table[range_dist];
            float alpha_ = weight*alpha;
            *temp_x++ = ycr = inv_alpha_*(*in_x++) + alpha_*ypr; 
            *temp_x++ = ycg = inv_alpha_*(*in_x++) + alpha_*ypg; 
            *temp_x++ = ycb = inv_alpha_*(*in_x++) + alpha_*ypb;
            tpr = tcr; tpg = tcg; tpb = tcb;
            ypr = ycr; ypg = ycg; ypb = ycb;
            *temp_factor_x++ = fc = inv_alpha_ + alpha_*fp;
            fp = fc;
        }
        *--temp_x; *temp_x = 0.5f*((*temp_x) + (*--in_x));
        *--temp_x; *temp_x = 0.5f*((*temp_x) + (*--in_x));
        *--temp_x; *temp_x = 0.5f*((*temp_x) + (*--in_x));
        tpr = *--texture_x; 
        tpg = *--texture_x; 
        tpb = *--texture_x;
        ypr = *in_x; ypg = *in_x; ypb = *in_x;

        *--temp_factor_x; *temp_factor_x = 0.5f*((*temp_factor_x) + 1);
        fp = 1;

        // from right to left
        for (int x = width - 2; x >= 0; x--) 
        {
            unsigned char tcr = *--texture_x; 
            unsigned char tcg = *--texture_x; 
            unsigned char tcb = *--texture_x;
            unsigned char dr = abs(tcr - tpr);
            unsigned char dg = abs(tcg - tpg);
            unsigned char db = abs(tcb - tpb);
            int range_dist = (((dr << 1) + dg + db) >> 2);
            float weight = range_table[range_dist];
            float alpha_ = weight * alpha;

            ycr = inv_alpha_ * (*--in_x) + alpha_ * ypr; 
            ycg = inv_alpha_ * (*--in_x) + alpha_ * ypg; 
            ycb = inv_alpha_ * (*--in_x) + alpha_ * ypb;
            *--temp_x; *temp_x = 0.5f*((*temp_x) + ycr);
            *--temp_x; *temp_x = 0.5f*((*temp_x) + ycg);
            *--temp_x; *temp_x = 0.5f*((*temp_x) + ycb);
            tpr = tcr; tpg = tcg; tpb = tcb;
            ypr = ycr; ypg = ycg; ypb = ycb;

            fc = inv_alpha_ + alpha_*fp;
            *--temp_factor_x; 
            *temp_factor_x = 0.5f*((*temp_factor_x) + fc);
            fp = fc;
        }
    }
    alpha = static_cast<float>(exp(-sqrt(2.0) / (sigma_spatial * height)));
    inv_alpha_ = 1 - alpha;
    float * ycy, * ypy, * xcy;
    unsigned char * tcy, * tpy;
    memcpy(img_out_f, img_temp, sizeof(float)* width_channel);

    float * in_factor = map_factor_a;
    float*ycf, *ypf, *xcf;
    memcpy(map_factor_b, in_factor, sizeof(float) * width);
    for (int y = 1; y < height; y++)
    {
        tpy = &img[(y - 1) * width_channel];
        tcy = &img[y * width_channel];
        xcy = &img_temp[y * width_channel];
        ypy = &img_out_f[(y - 1) * width_channel];
        ycy = &img_out_f[y * width_channel];

        xcf = &in_factor[y * width];
        ypf = &map_factor_b[(y - 1) * width];
        ycf = &map_factor_b[y * width];
        for (int x = 0; x < width; x++)
        {
            unsigned char dr = abs((*tcy++) - (*tpy++));
            unsigned char dg = abs((*tcy++) - (*tpy++));
            unsigned char db = abs((*tcy++) - (*tpy++));
            int range_dist = (((dr << 1) + dg + db) >> 2);
            float weight = range_table[range_dist];
            float alpha_ = weight*alpha;
            for (int c = 0; c < channel; c++) 
                *ycy++ = inv_alpha_*(*xcy++) + alpha_*(*ypy++);
            *ycf++ = inv_alpha_*(*xcf++) + alpha_*(*ypf++);
        }
    }
    int h1 = height - 1;
    ycf = line_factor_a;
    ypf = line_factor_b;
    memcpy(ypf, &in_factor[h1 * width], sizeof(float) * width);
    for (int x = 0; x < width; x++) 
        map_factor_b[h1 * width + x] = 0.5f*(map_factor_b[h1 * width + x] + ypf[x]);

    ycy = slice_factor_a;
    ypy = slice_factor_b;
    memcpy(ypy, &img_temp[h1 * width_channel], sizeof(float)* width_channel);
    int k = 0; 
    for (int x = 0; x < width; x++) {
        for (int c = 0; c < channel; c++) {
            int idx = (h1 * width + x) * channel + c;
            img_out_f[idx] = 0.5f*(img_out_f[idx] + ypy[k++]) / map_factor_b[h1 * width + x];
        }
    }

    for (int y = h1 - 1; y >= 0; y--)
    {
        tpy = &img[(y + 1) * width_channel];
        tcy = &img[y * width_channel];
        xcy = &img_temp[y * width_channel];
        float*ycy_ = ycy;
        float*ypy_ = ypy;
        float*out_ = &img_out_f[y * width_channel];

        xcf = &in_factor[y * width];
        float*ycf_ = ycf;
        float*ypf_ = ypf;
        float*factor_ = &map_factor_b[y * width];
        for (int x = 0; x < width; x++)
        {
            unsigned char dr = abs((*tcy++) - (*tpy++));
            unsigned char dg = abs((*tcy++) - (*tpy++));
            unsigned char db = abs((*tcy++) - (*tpy++));
            int range_dist = (((dr << 1) + dg + db) >> 2);
            float weight = range_table[range_dist];
            float alpha_ = weight*alpha;

            float fcc = inv_alpha_*(*xcf++) + alpha_*(*ypf_++);
            *ycf_++ = fcc;
            *factor_ = 0.5f * (*factor_ + fcc);

            for (int c = 0; c < channel; c++)
            {
                float ycc = inv_alpha_*(*xcy++) + alpha_*(*ypy_++);
                *ycy_++ = ycc;
                *out_ = 0.5f * (*out_ + ycc) / (*factor_);
                *out_++;
            }
            *factor_++;
        }
        memcpy(ypy, ycy, sizeof(float) * width_channel);
        memcpy(ypf, ycf, sizeof(float) * width);
    }

    for (int i = 0; i < width_height_channel; ++i)
        img[i] = static_cast<unsigned char>(img_out_f[i]);

    if (is_buffer_internal)
        delete[] buffer;
}


inline void recursive_bf(
    unsigned char * img_in,
    unsigned char *& img_out,
    float sigma_spatial, float sigma_range,
    int width, int height, int channel,
    float * buffer = 0)
{
    if (img_out == 0)
        img_out = new unsigned char[width * height * channel];
    for (int i = 0; i < width * height * channel; ++i)
        img_out[i] = img_in[i];
    _recursive_bf(img_out, sigma_spatial, sigma_range, width, height, channel, buffer);
}

#endif // INCLUDE_RBF

而这份代码的作者,真的很粗心,代码中有多处逻辑写错,代码风格也有待加强。

当然也有,有心者,在此基础上做了修正。

https://github.com/Fig1024/OP_RBF

这个作者还在这个基础上做了simd指令集优化。

优化代码暂时不看。

关注下基础实现的代码。即RBFilterPlain.cpp:

#include "stdafx.h"
#include "RBFilterPlain.h"
#include "stdafx.h"
#include <algorithm>

using namespace std;

#define QX_DEF_CHAR_MAX 255


CRBFilterPlain::CRBFilterPlain()
{

}

CRBFilterPlain::~CRBFilterPlain()
{
    releaseMemory();
}

// assumes 3/4 channel images, 1 byte per channel
void CRBFilterPlain::reserveMemory(int max_width, int max_height, int channels)
{
    // basic sanity check
    _ASSERT(max_width >= 10 && max_width < 10000);
    _ASSERT(max_height >= 10 && max_height < 10000);
    _ASSERT(channels >= 1 && channels <= 4);

    releaseMemory();

    m_reserve_width = max_width;
    m_reserve_height = max_height;
    m_reserve_channels = channels;

    int width_height = m_reserve_width * m_reserve_height;
    int width_height_channel = width_height * m_reserve_channels;

    m_left_pass_color = new float[width_height_channel];
    m_left_pass_factor = new float[width_height];

    m_right_pass_color = new float[width_height_channel];
    m_right_pass_factor = new float[width_height];

    m_down_pass_color = new float[width_height_channel];
    m_down_pass_factor = new float[width_height];

    m_up_pass_color = new float[width_height_channel];
    m_up_pass_factor = new float[width_height];
}

void CRBFilterPlain::releaseMemory()
{
    m_reserve_width = 0;
    m_reserve_height = 0;
    m_reserve_channels = 0;

    if (m_left_pass_color)
    {
        delete[] m_left_pass_color;
        m_left_pass_color = nullptr;
    }

    if (m_left_pass_factor)
    {
        delete[] m_left_pass_factor;
        m_left_pass_factor = nullptr;
    }

    if (m_right_pass_color)
    {
        delete[] m_right_pass_color;
        m_right_pass_color = nullptr;
    }

    if (m_right_pass_factor)
    {
        delete[] m_right_pass_factor;
        m_right_pass_factor = nullptr;
    }

    if (m_down_pass_color)
    {
        delete[] m_down_pass_color;
        m_down_pass_color = nullptr;
    }

    if (m_down_pass_factor)
    {
        delete[] m_down_pass_factor;
        m_down_pass_factor = nullptr;
    }

    if (m_up_pass_color)
    {
        delete[] m_up_pass_color;
        m_up_pass_color = nullptr;
    }

    if (m_up_pass_factor)
    {
        delete[] m_up_pass_factor;
        m_up_pass_factor = nullptr;
    }
}

int CRBFilterPlain::getDiffFactor(const unsigned char* color1, const unsigned char* color2) const
{
    int final_diff;
    int component_diff[4];

    // find absolute difference between each component
    for (int i = 0; i < m_reserve_channels; i++)
    {
        component_diff[i] = abs(color1[i] - color2[i]);
    }

    // based on number of components, produce a single difference value in the 0-255 range
    switch (m_reserve_channels)
    {
    case 1:
        final_diff = component_diff[0];
        break;

    case 2:
        final_diff = ((component_diff[0] + component_diff[1]) >> 1);
        break;

    case 3:
        final_diff = ((component_diff[0] + component_diff[2]) >> 2) + (component_diff[1] >> 1);
        break;

    case 4:
        final_diff = ((component_diff[0] + component_diff[1] + component_diff[2] + component_diff[3]) >> 2);
        break;

    default:
        final_diff = 0;
    }

    _ASSERT(final_diff >= 0 && final_diff <= 255);

    return final_diff;
}

// memory must be reserved before calling image filter
// this implementation of filter uses plain C++, single threaded
// channel count must be 3 or 4 (alpha not used)
void CRBFilterPlain::filter(unsigned char* img_src, unsigned char* img_dst,
    float sigma_spatial, float sigma_range,
    int width, int height, int channel)
{
    _ASSERT(img_src);
    _ASSERT(img_dst);
    _ASSERT(m_reserve_channels == channel);
    _ASSERT(m_reserve_width >= width);
    _ASSERT(m_reserve_height >= height);

    // compute a lookup table
    float alpha_f = static_cast<float>(exp(-sqrt(2.0) / (sigma_spatial * 255)));
    float inv_alpha_f = 1.f - alpha_f;


    float range_table_f[QX_DEF_CHAR_MAX + 1];
    float inv_sigma_range = 1.0f / (sigma_range * QX_DEF_CHAR_MAX);
    {
        float ii = 0.f;
        for (int i = 0; i <= QX_DEF_CHAR_MAX; i++, ii -= 1.f)
        {
            range_table_f[i] = alpha_f * exp(ii * inv_sigma_range);
        }
    }

    ///////////////
    // Left pass
    {
        const unsigned char* src_color = img_src;
        float* left_pass_color = m_left_pass_color;
        float* left_pass_factor = m_left_pass_factor;

        for (int y = 0; y < height; y++)
        {
            const unsigned char* src_prev = src_color;
            const float* prev_factor = left_pass_factor;
            const float* prev_color = left_pass_color;

            // process 1st pixel separately since it has no previous
            *left_pass_factor++ = 1.f;
            for (int c = 0; c < channel; c++)
            {
                *left_pass_color++ = *src_color++;
            }

            // handle other pixels
            for (int x = 1; x < width; x++)
            {
                // determine difference in pixel color between current and previous
                // calculation is different depending on number of channels
                int diff = getDiffFactor(src_color, src_prev);
                src_prev = src_color;

                float alpha_f = range_table_f[diff];

                *left_pass_factor++ = inv_alpha_f + alpha_f * (*prev_factor++);

                for (int c = 0; c < channel; c++)
                {
                    *left_pass_color++ = inv_alpha_f * (*src_color++) + alpha_f * (*prev_color++);
                }
            }
        }
    }

    ///////////////
    // Right pass
    {
        // start from end and then go up to begining 
        int last_index = width * height * channel - 1;
        const unsigned char* src_color = img_src + last_index;
        float* right_pass_color = m_right_pass_color + last_index;
        float* right_pass_factor = m_right_pass_factor + width * height - 1;

        for (int y = 0; y < height; y++)
        {
            const unsigned char* src_prev = src_color;
            const float* prev_factor = right_pass_factor;
            const float* prev_color = right_pass_color;

            // process 1st pixel separately since it has no previous
            *right_pass_factor-- = 1.f;
            for (int c = 0; c < channel; c++)
            {
                *right_pass_color-- = *src_color--;
            }

            // handle other pixels
            for (int x = 1; x < width; x++)
            {
                // determine difference in pixel color between current and previous
                // calculation is different depending on number of channels
                int diff = getDiffFactor(src_color, src_color - 3);
                //    src_prev = src_color;

                float alpha_f = range_table_f[diff];

                *right_pass_factor-- = inv_alpha_f + alpha_f * (*prev_factor--);

                for (int c = 0; c < channel; c++)
                {
                    *right_pass_color-- = inv_alpha_f * (*src_color--) + alpha_f * (*prev_color--);
                }
            }
        }
    }

    // vertical pass will be applied on top on horizontal pass, while using pixel differences from original image
    // result color stored in 'm_left_pass_color' and vertical pass will use it as source color
    {
        float* img_out = m_left_pass_color; // use as temporary buffer
        const float* left_pass_color = m_left_pass_color;
        const float* left_pass_factor = m_left_pass_factor;
        const float* right_pass_color = m_right_pass_color;
        const float* right_pass_factor = m_right_pass_factor;

        int width_height = width * height;
        for (int i = 0; i < width_height; i++)
        {
            // average color divided by average factor
            float factor = 1.f / ((*left_pass_factor++) + (*right_pass_factor++));
            for (int c = 0; c < channel; c++)
            {
                *img_out++ = (factor * ((*left_pass_color++) + (*right_pass_color++)));
            }
        }
    }

    ///////////////
    // Down pass
    {
        const float* src_color_hor = m_left_pass_color; // result of horizontal pass filter

        const unsigned char* src_color = img_src;
        float* down_pass_color = m_down_pass_color;
        float* down_pass_factor = m_down_pass_factor;

        const unsigned char* src_prev = src_color;
        const float* prev_color = down_pass_color;
        const float* prev_factor = down_pass_factor;

        // 1st line done separately because no previous line
        for (int x = 0; x < width; x++)
        {
            *down_pass_factor++ = 1.f;
            for (int c = 0; c < channel; c++)
            {
                *down_pass_color++ = *src_color_hor++;
            }
            src_color += channel;
        }

        // handle other lines
        for (int y = 1; y < height; y++)
        {
            for (int x = 0; x < width; x++)
            {
                // determine difference in pixel color between current and previous
                // calculation is different depending on number of channels
                int diff = getDiffFactor(src_color, src_prev);
                src_prev += channel;
                src_color += channel;

                float alpha_f = range_table_f[diff];

                *down_pass_factor++ = inv_alpha_f + alpha_f * (*prev_factor++);

                for (int c = 0; c < channel; c++)
                {
                    *down_pass_color++ = inv_alpha_f * (*src_color_hor++) + alpha_f * (*prev_color++);
                }
            }
        }
    }

    ///////////////
    // Up pass
    {
        // start from end and then go up to begining 
        int last_index = width * height * channel - 1;
        const unsigned char* src_color = img_src + last_index;
        const float* src_color_hor = m_left_pass_color + last_index; // result of horizontal pass filter
        float* up_pass_color = m_up_pass_color + last_index;
        float* up_pass_factor = m_up_pass_factor + (width * height - 1);

        //    const unsigned char* src_prev = src_color;
        const float* prev_color = up_pass_color;
        const float* prev_factor = up_pass_factor;

        // 1st line done separately because no previous line
        for (int x = 0; x < width; x++)
        {
            *up_pass_factor-- = 1.f;
            for (int c = 0; c < channel; c++)
            {
                *up_pass_color-- = *src_color_hor--;
            }
            src_color -= channel;
        }

        // handle other lines
        for (int y = 1; y < height; y++)
        {
            for (int x = 0; x < width; x++)
            {
                // determine difference in pixel color between current and previous
                // calculation is different depending on number of channels
                src_color -= channel;
                int diff = getDiffFactor(src_color, src_color + width * channel);

                float alpha_f = range_table_f[diff];

                *up_pass_factor-- = inv_alpha_f + alpha_f * (*prev_factor--);

                for (int c = 0; c < channel; c++)
                {
                    *up_pass_color-- = inv_alpha_f * (*src_color_hor--) + alpha_f * (*prev_color--);
                }
            }
        }
    }

    ///////////////
    // average result of vertical pass is written to output buffer
    {
        const float* down_pass_color = m_down_pass_color;
        const float* down_pass_factor = m_down_pass_factor;
        const float* up_pass_color = m_up_pass_color;
        const float* up_pass_factor = m_up_pass_factor;

        int width_height = width * height;
        for (int i = 0; i < width_height; i++)
        {
            // average color divided by average factor
            float factor = 1.f / ((*up_pass_factor++) + (*down_pass_factor++));
            for (int c = 0; c < channel; c++)
            {
                *img_dst++ = (unsigned char)(factor * ((*up_pass_color++) + (*down_pass_color++)));
            }
        }
    }
}

这份代码把算法逻辑梳理得非常清晰。

一开始我也觉得这个代码效果和速度都很不错了。

但是没有仔细看,经过朋友的提醒,说是这个算法有严重的bug,会有线条瑕疵。

把对应的参数值调大之后,的确。特别明显的条纹效应,直接毁图了。

后来我经过一段时间的思考和研究,明确了算法的问题所在。

针对这个算法的修复,已经有明确思路了。

在这里,暂时先放出我经过稍加整理了OP_RBF的完整C代码版本。

做了一些代码逻辑上的优化,降低内存的使用。

 
int   getDiffFactor(const unsigned char* color1, const unsigned char* color2, const  int & channels)
{
    int final_diff;
    int component_diff[4];

    // find absolute difference between each component
    for (int i = 0; i < channels; i++)
    {
        component_diff[i] = abs(color1[i] - color2[i]);
    }

    // based on number of components, produce a single difference value in the 0-255 range
    switch (channels)
    {
    case 1:
        final_diff = component_diff[0];
        break;

    case 2:
        final_diff = ((component_diff[0] + component_diff[1]) >> 1);
        break;

    case 3:
        final_diff = ((component_diff[0] + component_diff[2]) >> 2) + (component_diff[1] >> 1);
        break;

    case 4:
        final_diff = ((component_diff[0] + component_diff[1] + component_diff[2] + component_diff[3]) >> 2);
        break;

    default:
        final_diff = 0;
    }

    _ASSERT(final_diff >= 0 && final_diff <= 255);

    return final_diff;
}

void CRB_HorizontalFilter(unsigned char* Input, unsigned char* Output, int Width, int Height, int Channels, float * range_table_f, float inv_alpha_f, float* left_Color_Buffer, float* left_Factor_Buffer, float* right_Color_Buffer, float* right_Factor_Buffer)
{

    // Left pass and Right pass 

    int Stride = Width * Channels;
    const unsigned char* src_left_color = Input;
    float* left_Color = left_Color_Buffer;
    float* left_Factor = left_Factor_Buffer;

    int last_index = Stride * Height - 1;
    const unsigned char* src_right_color = Input + last_index;
    float* right_Color = right_Color_Buffer + last_index;
    float* right_Factor = right_Factor_Buffer + Width * Height - 1;

    for (int y = 0; y < Height; y++)
    {
        const unsigned char* src_left_prev = Input;
        const float* left_prev_factor = left_Factor;
        const float* left_prev_color = left_Color;

        const unsigned char* src_right_prev = src_right_color;
        const float* right_prev_factor = right_Factor;
        const float* right_prev_color = right_Color;

        // process 1st pixel separately since it has no previous
        {
            //if x = 0 
            *left_Factor++ = 1.f;
            *right_Factor-- = 1.f;
            for (int c = 0; c < Channels; c++)
            {
                *left_Color++ = *src_left_color++;
                *right_Color-- = *src_right_color--;
            }
        }
        // handle other pixels
        for (int x = 1; x < Width; x++)
        {
            // determine difference in pixel color between current and previous
            // calculation is different depending on number of channels
            int left_diff = getDiffFactor(src_left_color, src_left_prev, Channels);
            src_left_prev = src_left_color;

            int right_diff = getDiffFactor(src_right_color, src_right_color - Channels, Channels);
            src_right_prev = src_right_color;

            float left_alpha_f = range_table_f[left_diff];
            float right_alpha_f = range_table_f[right_diff];
            *left_Factor++ = inv_alpha_f + left_alpha_f * (*left_prev_factor++);
            *right_Factor-- = inv_alpha_f + right_alpha_f * (*right_prev_factor--);

            for (int c = 0; c < Channels; c++)
            {
                *left_Color++ = (inv_alpha_f * (*src_left_color++) + left_alpha_f * (*left_prev_color++));
                *right_Color-- = (inv_alpha_f * (*src_right_color--) + right_alpha_f * (*right_prev_color--));
            }
        }
    }
    // vertical pass will be applied on top on horizontal pass, while using pixel differences from original image
    // result color stored in 'leftcolor' and vertical pass will use it as source color
    {
        unsigned char* dst_color = Output; // use as temporary buffer  
        const float* leftcolor = left_Color_Buffer;
        const float* leftfactor = left_Factor_Buffer;
        const float* rightcolor = right_Color_Buffer;
        const float* rightfactor = right_Factor_Buffer;

        int width_height = Width * Height;
        for (int i = 0; i < width_height; i++)
        {
            // average color divided by average factor
            float factor = 1.f / ((*leftfactor++) + (*rightfactor++));
            for (int c = 0; c < Channels; c++)
            {

                *dst_color++ = (factor * ((*leftcolor++) + (*rightcolor++)));

            }
        }
    }
}

void CRB_VerticalFilter(unsigned char* Input, unsigned char* Output, int Width, int Height, int Channels, float * range_table_f, float inv_alpha_f, float* down_Color_Buffer, float* down_Factor_Buffer, float* up_Color_Buffer, float* up_Factor_Buffer)
{

    // Down pass and Up pass 
    int Stride = Width * Channels;
    const unsigned char* src_color_first_hor = Output; // result of horizontal pass filter 
    const unsigned char* src_down_color = Input;
    float* down_color = down_Color_Buffer;
    float* down_factor = down_Factor_Buffer;

    const unsigned char* src_down_prev = src_down_color;
    const float* down_prev_color = down_color;
    const float* down_prev_factor = down_factor;


    int last_index = Stride * Height - 1;
    const unsigned char* src_up_color = Input + last_index;
    const unsigned char* src_color_last_hor = Output + last_index; // result of horizontal pass filter
    float* up_color = up_Color_Buffer + last_index;
    float* up_factor = up_Factor_Buffer + (Width * Height - 1);

    const float* up_prev_color = up_color;
    const float* up_prev_factor = up_factor;

    // 1st line done separately because no previous line
    {
        //if y=0 
        for (int x = 0; x < Width; x++)
        {
            *down_factor++ = 1.f;
            *up_factor-- = 1.f;
            for (int c = 0; c < Channels; c++)
            {
                *down_color++ = *src_color_first_hor++;
                *up_color-- = *src_color_last_hor--;
            }
            src_down_color += Channels;
            src_up_color -= Channels;
        }
    }
    // handle other lines 
    for (int y = 1; y < Height; y++)
    {
        for (int x = 0; x < Width; x++)
        {
            // determine difference in pixel color between current and previous
            // calculation is different depending on number of channels
            int down_diff = getDiffFactor(src_down_color, src_down_prev, Channels);
            src_down_prev += Channels;
            src_down_color += Channels;
            src_up_color -= Channels;
            int up_diff = getDiffFactor(src_up_color, src_up_color + Stride, Channels);
            float down_alpha_f = range_table_f[down_diff];
            float up_alpha_f = range_table_f[up_diff];

            *down_factor++ = inv_alpha_f + down_alpha_f * (*down_prev_factor++);
            *up_factor-- = inv_alpha_f + up_alpha_f * (*up_prev_factor--);

            for (int c = 0; c < Channels; c++)
            {
                *down_color++ = inv_alpha_f * (*src_color_first_hor++) + down_alpha_f * (*down_prev_color++);
                *up_color-- = inv_alpha_f * (*src_color_last_hor--) + up_alpha_f * (*up_prev_color--);
            }
        }
    }

    // average result of vertical pass is written to output buffer
    {
        unsigned char *dst_color = Output;
        const float* downcolor = down_Color_Buffer;
        const float* downfactor = down_Factor_Buffer;
        const float* upcolor = up_Color_Buffer;
        const float* upfactor = up_Factor_Buffer;

        int width_height = Width * Height;
        for (int i = 0; i < width_height; i++)
        {
            // average color divided by average factor
            float factor = 1.f / ((*upfactor++) + (*downfactor++));
            for (int c = 0; c < Channels; c++)
            {
                *dst_color++ = (factor * ((*upcolor++) + (*downcolor++)));
            }
        }
    }
}

// memory must be reserved before calling image filter
// this implementation of filter uses plain C++, single threaded
// channel count must be 3 or 4 (alpha not used)
void    CRBFilter(unsigned char* Input, unsigned char* Output, int Width, int Height, int Stride, float sigmaSpatial, float sigmaRange)
{
    int Channels = Stride / Width;
    int reserveWidth = Width;
    int reserveHeight = Height;
    // basic sanity check
    _ASSERT(Input);
    _ASSERT(Output);
    _ASSERT(reserveWidth >= 10 && reserveWidth < 10000);
    _ASSERT(reserveHeight >= 10 && reserveHeight < 10000);
    _ASSERT(Channels >= 1 && Channels <= 4);

    int reservePixels = reserveWidth * reserveHeight;
    int numberOfPixels = reservePixels * Channels;

    float* leftColorBuffer = (float*)calloc(sizeof(float)*numberOfPixels, 1);
    float* leftFactorBuffer = (float*)calloc(sizeof(float)*reservePixels, 1);
    float* rightColorBuffer = (float*)calloc(sizeof(float)*numberOfPixels, 1);
    float* rightFactorBuffer = (float*)calloc(sizeof(float)*reservePixels, 1);

    if (leftColorBuffer == NULL || leftFactorBuffer == NULL || rightColorBuffer == NULL || rightFactorBuffer == NULL)
    {
        if (leftColorBuffer)  free(leftColorBuffer);
        if (leftFactorBuffer) free(leftFactorBuffer);
        if (rightColorBuffer) free(rightColorBuffer);
        if (rightFactorBuffer) free(rightFactorBuffer);

        return;
    }
    float* downColorBuffer = leftColorBuffer;
    float* downFactorBuffer = leftFactorBuffer;
    float* upColorBuffer = rightColorBuffer;
    float* upFactorBuffer = rightFactorBuffer;
    // compute a lookup table
    float alpha_f = static_cast<float>(exp(-sqrt(2.0) / (sigmaSpatial * 255)));
    float inv_alpha_f = 1.f - alpha_f;


    float range_table_f[255 + 1];
    float inv_sigma_range = 1.0f / (sigmaRange * 255);

    float ii = 0.f;
    for (int i = 0; i <= 255; i++, ii -= 1.f)
    {
        range_table_f[i] = alpha_f * exp(ii * inv_sigma_range);
    }
    CRB_HorizontalFilter(Input, Output, Width, Height, Channels, range_table_f, inv_alpha_f, leftColorBuffer, leftFactorBuffer, rightColorBuffer, rightFactorBuffer);

    CRB_VerticalFilter(Input, Output, Width, Height, Channels, range_table_f, inv_alpha_f, downColorBuffer, downFactorBuffer, upColorBuffer, upFactorBuffer);

    if (leftColorBuffer)
    {
        free(leftColorBuffer);
        leftColorBuffer = NULL;
    }

    if (leftFactorBuffer)
    {
        free(leftFactorBuffer);
        leftFactorBuffer = NULL;
    }

    if (rightColorBuffer)
    {
        free(rightColorBuffer);
        rightColorBuffer = NULL;
    }

    if (rightFactorBuffer)
    {
        free(rightFactorBuffer);
        rightFactorBuffer = NULL;
    }
}

void    CRBFilter(unsigned char* Input, unsigned char* Output, int Width, int Height, int Stride, float sigmaSpatial, float sigmaRange);

就这样一个简单的接口函数。

代码也比较清晰,不多做解释了。

上个效果演示图。

前后对比,注意看人物的眼袋部分,有明显的条纹效应。

好久没上来发文了,最近有好多网友,询问关于《票据OCR前预处理 (附Demo)》一些算法相关的细节。

说实话,这个代码写得有点久了,逻辑记不太清楚了。

待后面有时间,把代码梳理一下,再写篇博客分享完整逻辑代码。

俺的联系方式如下:

邮箱: gaozhihan@vip.qq.com

联系我时请说明来意,不然一律忽略,谢谢。 

本文参与腾讯云自媒体分享计划,欢迎正在阅读的你也加入,一起分享。

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