retina model parameters structure 
For better clarity, check explenations on the comments of methods : setupOPLandIPLParvoChannel and setupIPLMagnoChannel
Here is the default configuration file of the retina module. It gives results such as the first retina output shown on the top of this page.
<?xml version="1.0"?>
<opencv_storage>
<OPLandIPLparvo>
    <colorMode>1</colorMode>
    <normaliseOutput>1</normaliseOutput>
    <photoreceptorsLocalAdaptationSensitivity>7.5e-01</photoreceptorsLocalAdaptationSensitivity>
    <photoreceptorsTemporalConstant>9.0e-01</photoreceptorsTemporalConstant>
    <photoreceptorsSpatialConstant>5.3e-01</photoreceptorsSpatialConstant>
    <horizontalCellsGain>0.01</horizontalCellsGain>
    <hcellsTemporalConstant>0.5</hcellsTemporalConstant>
    <hcellsSpatialConstant>7.</hcellsSpatialConstant>
    <ganglionCellsSensitivity>7.5e-01</ganglionCellsSensitivity></OPLandIPLparvo>
<IPLmagno>
    <normaliseOutput>1</normaliseOutput>
    <parasolCells_beta>0.</parasolCells_beta>
    <parasolCells_tau>0.</parasolCells_tau>
    <parasolCells_k>7.</parasolCells_k>
    <amacrinCellsTemporalCutFrequency>2.0e+00</amacrinCellsTemporalCutFrequency>
    <V0CompressionParameter>9.5e-01</V0CompressionParameter>
    <localAdaptintegration_tau>0.</localAdaptintegration_tau>
    <localAdaptintegration_k>7.</localAdaptintegration_k></IPLmagno>
</opencv_storage>
Here is the 'realistic" setup used to obtain the second retina output shown on the top of this page.
<?xml version="1.0"?>
<opencv_storage>
<OPLandIPLparvo>
  <colorMode>1</colorMode>
  <normaliseOutput>1</normaliseOutput>
  <photoreceptorsLocalAdaptationSensitivity>8.9e-01</photoreceptorsLocalAdaptationSensitivity>
  <photoreceptorsTemporalConstant>9.0e-01</photoreceptorsTemporalConstant>
  <photoreceptorsSpatialConstant>5.3e-01</photoreceptorsSpatialConstant>
  <horizontalCellsGain>0.3</horizontalCellsGain>
  <hcellsTemporalConstant>0.5</hcellsTemporalConstant>
  <hcellsSpatialConstant>7.</hcellsSpatialConstant>
  <ganglionCellsSensitivity>8.9e-01</ganglionCellsSensitivity></OPLandIPLparvo>
<IPLmagno>
  <normaliseOutput>1</normaliseOutput>
  <parasolCells_beta>0.</parasolCells_beta>
  <parasolCells_tau>0.</parasolCells_tau>
  <parasolCells_k>7.</parasolCells_k>
  <amacrinCellsTemporalCutFrequency>2.0e+00</amacrinCellsTemporalCutFrequency>
  <V0CompressionParameter>9.5e-01</V0CompressionParameter>
  <localAdaptintegration_tau>0.</localAdaptintegration_tau>
  <localAdaptintegration_k>7.</localAdaptintegration_k></IPLmagno>
</opencv_storage>