Generate Portable Code for Image Filtering Algorithm

R2026b

This example shows how to instruct the code generator to avoid using precompiled libraries for MATLAB^® functions. By default, the code generator uses optimized, platform-specific, precompiled libraries for MATLAB functions if such libraries are available. Precompiled libraries can improve the performance of the generated code on the target platform. However, if you want to create portable applications that can run on many platforms, you can instruct the code generator to avoid using precompiled libraries if alternative implementations of their algorithms are available.

Because this example uses an image processing function, you must have the Image Processing Toolbox™ to run this example.

Create a MATLAB entry-point function libraryUsageTest that uses the imfilter (Image Processing Toolbox) function to filter an input image.

function filteredImage = libraryUsageTest(unfilteredImage)
h = [-1 0 1];
filteredImage = imfilter(unfilteredImage,h);
end

Generate a static C library for the libraryUsageTest function by using the codegen command. Create a code configuration object for a static library and set the InstructionSetExtensions property to "None". Use the -args argument to specify that the input argument is an 8-by-8 array of doubles and use the -report option to generate a code generation report.

cfg = coder.config("lib");
cfg.InstructionSetExtensions = "None";
codegen -config cfg -report libraryUsageTest -args {zeros(8)}

Open the code generation report and inspect the generated C function imfilter. The last line of this function calls the precompiled library ippfilter_real64.

void imfilter(const double varargin_1[64], double b[64])
{
  double aTmp[80];
  int i;
  for (i = 0; i < 8; i++) {
    aTmp[i] = 0.0;
    aTmp[i + 72] = 0.0;
    memcpy(&aTmp[i * 8 + 8], &varargin_1[i * 8], 8U * sizeof(double));
  }
  double kernel[3];
  double kernelSizeT[2];
  double outSizeT[2];
  double padSizeT[2];
  outSizeT[0] = 8.0;
  padSizeT[0] = 8.0;
  outSizeT[1] = 8.0;
  padSizeT[1] = 10.0;
  kernel[0] = -1.0;
  kernel[1] = 0.0;
  kernel[2] = 1.0;
  kernelSizeT[0] = 1.0;
  kernelSizeT[1] = 3.0;
  ippfilter_real64(&aTmp[0], &b[0], &outSizeT[0], 2.0, &padSizeT[0], &kernel[0],
                   &kernelSizeT[0], false);
}

To generate portable C code that implements the image filtering algorithm, instruct the code generator to avoid precompiled libraries. Use one of these approaches:

• In a MATLAB Coder™ code configuration object, set the UsePrecompiledLibraries property to "Avoid".

• In the MATLAB Coder Code Generation Settings dialog box, set Use precompiled libraries to Avoid precompiled libraries when possible.

• In the Simulink^® Configuration Parameters dialog box, set Use precompiled libraries for MATLAB functions (Simulink) to Avoid precompiled libraries when possible.

For this example, set the UsePrecompiledLibraries property of the code configuration object to "Avoid". Generate code for the libraryUsageTest function.

cfg.UsePrecompiledLibraries = "Avoid";
codegen -config cfg -report libraryUsageTest -args {zeros(8)}

Open the code generation report and inspect the generated C function imfilter. This function does not contain calls to precompiled libraries.

void imfilter(const double varargin_1[64], double b[64])
{
  double a_padded[80];
  int b_i;
  int i;
  int jb;
  for (i = 0; i < 8; i++) {
    a_padded[i] = 0.0;
    a_padded[i + 72] = 0.0;
    memcpy(&a_padded[i * 8 + 8], &varargin_1[i * 8], 8U * sizeof(double));
  }
  memset(&b[0], 0, 64U * sizeof(double));
  for (i = 0; i < 8; i++) {
    int cColOffset;
    cColOffset = i << 3;
    for (jb = 0; jb < 3; jb++) {
      int ia;
      ia = (i + jb) << 3;
      for (b_i = 0; b_i < 8; b_i++) {
        int b_tmp;
        b_tmp = cColOffset + b_i;
        b[b_tmp] += (-(2.0 - (double)jb) + 1.0) * a_padded[ia + b_i];
      }
    }
  }
}