With this post there are 2 files attached:

emboss.c
CMakeLists.txt

When these files are placed in Freir0r .../src/filters/emboss -folder
they will compile into plugin for Frei0r.

The file .../src/CMakeLists.txt will need to be updated to include the
new folder for successful build.

I request that someone with commit access to Frei0r repository
includes these in Frei0r distribution.

Janne Liljeblad
set (SOURCES emboss.c)
set (TARGET emboss)

if (MSVC)
set_source_files_properties (emboss.c PROPERTIES LANGUAGE CXX)
set (SOURCES ${SOURCES} ${FREI0R_DEF})
endif (MSVC)

add_library (${TARGET} MODULE ${SOURCES})
set_target_properties (${TARGET} PROPERTIES PREFIX "")

install (TARGETS ${TARGET} LIBRARY DESTINATION ${LIBDIR})
/*
* This file is a port of com.jhlabs.image.EmbossFilter.java
* Copyright 2006 Jerry Huxtable
*
* emboss.c
* Copyright 2012 Janne Liljeblad
*
* This file is a Frei0r plugin.
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#include <stdlib.h>
#include <assert.h>
#include <math.h>

#include "frei0r.h"

double PI = 3.14159;
double pixelScale = 255.9;

typedef struct emboss_instance
{
  unsigned int width;
  unsigned int height;
    double azimuth;
  double elevation;
    double width45;
} emboss_instance_t;

int f0r_init()
{
return 1;
}

void f0r_deinit()
{ /* no initialization required */ }

void f0r_get_plugin_info(f0r_plugin_info_t* emposs_info)
{
emposs_info->name = "emboss";
emposs_info->author = "Janne Liljeblad";
emposs_info->plugin_type = F0R_PLUGIN_TYPE_FILTER;
emposs_info->color_model = F0R_COLOR_MODEL_RGBA8888;
emposs_info->frei0r_version = FREI0R_MAJOR_VERSION;
emposs_info->major_version = 0;
emposs_info->minor_version = 1;
emposs_info->num_params = 3;
emposs_info->explanation = "Creates embossed relief image of source image";
}

void f0r_get_param_info(f0r_param_info_t* info, int param_index)
{
  switch(param_index)
  {
  case 0:
    info->name = "azimuth";
    info->type = F0R_PARAM_DOUBLE;
    info->explanation = "Light direction";
    break;
  case 1:
    info->name = "elevation";
    info->type = F0R_PARAM_DOUBLE;
    info->explanation = "Background lightnes";
    break;
  case 2:
    info->name = "width45";
    info->type = F0R_PARAM_DOUBLE;
    info->explanation = "Bump height";
    break;
  }
}

f0r_instance_t f0r_construct(unsigned int width, unsigned int height)
{
    emboss_instance_t* inst = (emboss_instance_t*)calloc(1, sizeof(*inst));
    inst->width = width; 
  inst->height = height;
  inst->azimuth = 135.0;
  inst->elevation = 30.0;
  inst->width45 = 3.0;
    return (f0r_instance_t)inst;
}

void f0r_destruct(f0r_instance_t instance)
{
free(instance);
}

void f0r_set_param_value(f0r_instance_t instance, 
                         f0r_param_t param, int param_index)
{
  assert(instance);
  emboss_instance_t* inst = (emboss_instance_t*)instance;

  switch(param_index)
  {
  case 0:
    inst->azimuth = *((double*)param);
    break;
  case 1:
    inst->elevation = *((double*)param);
    break;
  case 2:
    inst->width45 = *((double*)param);
    break;
  }
}

void f0r_get_param_value(f0r_instance_t instance,
                         f0r_param_t param, int param_index)
{
  assert(instance);
  emboss_instance_t* inst = (emboss_instance_t*)instance;

  switch(param_index)
  {
  case 0:
    *((double*)param) = inst->azimuth;
    break;
  case 1:
    *((double*)param) = inst->elevation;
    break;
  case 2:
    *((double*)param) = inst->width45;
    break;
  }
}

void f0r_update(f0r_instance_t instance, double time,
                const uint32_t* inframe, uint32_t* outframe)
{
  // Check and cast instance
  assert(instance);
  emboss_instance_t* inst = (emboss_instance_t*)instance;

  // Get render params
    double azimuth = inst->azimuth * PI / 180.0; 
  double elevation = inst->elevation * PI / 180.0;
    double width45 = inst->width45;

  // Create brightness image
  unsigned int len = inst->width * inst->height;
  unsigned char bumpPixels[len];
  unsigned int index, r, g, b = 0;
  const unsigned char* src = (unsigned char*)inframe;
  while (len--)
  {
    r = *src++;
    g = *src++;
    b = *src++;
    *src++;//alpha not needed

    bumpPixels[index++] = (r + g + b)/3;
  }

// Create embossed image from brightness image
unsigned char* dst = outframe;
unsigned char shade, background = 0;
int Nx, Ny, Nz, Lx, Ly, Lz, Nz2, NzLz, NdotL;

Lx = (int)(cos(azimuth) * cos(elevation) * pixelScale);
Ly = (int)(sin(azimuth) * cos(elevation) * pixelScale);
Lz = (int)(sin(elevation) * pixelScale);

Nz = (int)(6 * 255 / width45);
Nz2 = Nz * Nz;
NzLz = Nz * Lz;

  background = Lz;
  int bumpIndex = 0;
  int width = inst->width;
  int height = inst->height;
  int s1, s2, s3 = 0;
  int x, y = 0;
  for (y = 0; y < height; y++, bumpIndex += width) 
  {
    s1 = bumpIndex;
    s2 = s1 + width;
    s3 = s2 + width;
    for (x = 0; x < width; x++, s1++, s2++, s3++) 
    {
        if (y != 0 && y < height-2 && x != 0 && x < width-2) 
      {
            Nx = bumpPixels[s1-1] + bumpPixels[s2-1] + bumpPixels[s3-1] - bumpPixels[s1+1] - bumpPixels[s2+1] - bumpPixels[s3+1];
            Ny = bumpPixels[s3-1] + bumpPixels[s3] + bumpPixels[s3+1] - bumpPixels[s1-1] - bumpPixels[s1] - bumpPixels[s1+1];
            if (Nx == 0 && Ny == 0)
                shade = background;
            else if ((NdotL = Nx*Lx + Ny*Ly + NzLz) < 0)
                shade = 0;
            else
                shade = (int)(NdotL / sqrt(Nx*Nx + Ny*Ny + Nz2));
        } 
      else
      {
            shade = background;
      }

      // Write value
      *dst++ = shade;
      *dst++ = shade;
      *dst++ = shade;
      *dst++;
    }  
  }
}