HDR (High Dynamic Range)#

HDR (High Dynamic Range) is an imaging technology that improves the brightness and contrast of an image.

HDR images show details within the image rather exactly, which makes them ideal for high-resolution image processing.

Using the Feature#

The dynamic range of an image is the ratio between the highest and lowest brightness that can be displayed. Images with a wide dynamic range capture the actual contrast of the scene very well, so more details in dark and light sections can bee seen.

HDR allows capturing a wider dynamic range by acquiring images with different exposures.

Interleaved HDR#

Some camera models, support interleaved HDR (iHDR). The iHDR feature allows you to set different exposure times for even and odd pixel lines of the sensor. For example, you can specify a long exposure time for lines 1, 3, 5, etc. and a reduced exposure time for lines 2, 4, 6, etc. The different exposures start simultaneously. This creates a "striped" image with bright and dark lines.

The following drawing visualizes the different exposures per sensor line.

To set the exposure times for iHDR:

1. Set the ExposureTimeMode parameter to Individual.
2. Set the ExposureTimeSelector parameter to Stage 1.
3. Specify the exposure time for stage 1.
   The value specified for stage 1 applies to the even pixel lines of the sensor.
4. Set the ExposureTimeSelector parameter to Stage 2.
5. Specify the exposure time for stage 2.
   The value specified for stage 2 applies to the odd pixel lines of the sensor.

Use an external post-processing program to combine the bright and dark lines to generate a high dynamic range image.

Quad HDR#

Some camera models support Quad HDR (QHDR). The QHDR feature allows you to set individual exposure times for pixels within pixel units. These are areas of 2×2 pixels, also called quad pixels, which includes two pixels in horizontal direction and two pixels in vertical direction.

Short and long exposures can be set for each of these four pixels included in each pixel unit. With this, you can extract the information in both the dark and bright regions of the image with every single image acquired.

The following drawing illustrates the different exposures per pixel unit:

To set the exposure times for QHDR:

1. Set the ExposureTimeMode parameter to Individual.
2. Set the ExposureTimeSelector parameter to Stage 1.
3. Specify the exposure time for stage 1.

4. Repeat steps 2 and 3 for the other stages.

   The individual stages refer to the following pixels of each pixel unit:

   • Stage 1: The specified value applies to the upper left pixel.
   • Stage 2: The specified value applies to the upper right pixel.
   • Stage 3: The specified value applies to the lower left pixel.
   • Stage 4: The specified value applies to the lower right pixel.

   Info

   You can find the minimum and maximum exposure time values of your camera model in the Specifics section of the Exposure Time topic.

Use an external post-processing program to combine the information within each pixel unit to generate a high dynamic range image.

Specifics#

Show only your camera model

Sample Code#

// Set the exposure time mode to Individual
camera.ExposureTimeMode.SetValue(ExposureTimeMode_Individual);
// Select stage 1
camera.ExposureTimeSelector.SetValue(ExposureTimeSelector_Stage1);
// Set the exposure time to 1000 microseconds
camera.ExposureTime.SetValue(1000.0);
// Select stage 2
camera.ExposureTimeSelector.SetValue(ExposureTimeSelector_Stage2);
// Set the exposure time to 1000000 microseconds
camera.ExposureTime.SetValue(1000000.0);

INodeMap& nodemap = camera.GetNodeMap();
// Set the exposure time mode to Individual
CEnumParameter(nodemap, "ExposureTimeMode").SetValue("Individual");
// Select stage 1
CEnumParameter(nodemap, "ExposureTimeSelector").SetValue("Stage1");
// Set the exposure time to 1000 microseconds
CFloatParameter(nodemap, "ExposureTime").SetValue(1000.0);
// Select stage 2
CEnumParameter(nodemap, "ExposureTimeSelector").SetValue("Stage2");
// Set the exposure time to 1000000 microseconds
CFloatParameter(nodemap, "ExposureTime").SetValue(1000000.0);

// Set the exposure time mode to Individual
camera.Parameters[PLCamera.ExposureTimeMode].SetValue(PLCamera.ExposureTimeMode.Individual);
// Select stage 1
camera.Parameters[PLCamera.ExposureTimeSelector].SetValue(PLCamera.ExposureTimeSelector.Stage1);
// Set the exposure time to 1000 microseconds
camera.Parameters[PLCamera.ExposureTime].SetValue(1000.0);
// Select stage 2
camera.Parameters[PLCamera.ExposureTimeSelector].SetValue(PLCamera.ExposureTimeSelector.Stage2);
// Set the exposure time to 1000000 microseconds
camera.Parameters[PLCamera.ExposureTime].SetValue(1000000.0);

/* Macro to check for errors */
#define CHECK(errc) if (GENAPI_E_OK != errc) printErrorAndExit(errc)
GENAPIC_RESULT errRes = GENAPI_E_OK;  /* Return value of pylon methods */
/* Set the exposure time mode to Individual */
errRes = PylonDeviceFeatureFromString(hdev, "ExposureTimeMode", "Individual");
CHECK(errRes);
/* Select stage 1 */
errRes = PylonDeviceFeatureFromString(hdev, "ExposureTimeSelector", "Stage1");
CHECK(errRes);
/* Set the exposure time to 1000 microseconds */
errRes = PylonDeviceSetFloatFeature(hdev, "ExposureTime", 1000.0);
CHECK(errRes);
/* Select stage 2 */
errRes = PylonDeviceFeatureFromString(hdev, "ExposureTimeSelector", "Stage2");
CHECK(errRes);
/* Set the exposure time to 1000000 microseconds */
errRes = PylonDeviceSetFloatFeature(hdev, "ExposureTime", 1000000.0);
CHECK(errRes);

# Set the exposure time mode to Individual
camera.ExposureTimeMode.Value = "Individual"
# Select stage 1
camera.ExposureTimeSelector.Value = "Stage1"
# Set the exposure time to 1000 microseconds
camera.ExposureTime.Value = 1000.0
# Select stage 2
camera.ExposureTimeSelector.Value = "Stage2"
# Set the exposure time to 1000000 microseconds
camera.ExposureTime.Value = 1000000.0

You can also use the pylon Viewer to easily set the parameters.