Thermalyze Operation

Camera Calibration

The topics in this section explain how to add and remove bad pixels, perform uniformity correction, and perform lens calibrations.

Bad Pixel Replacement Uniformity Correction Lens Calibration Lens Calibration Points

Bad Pixel Replacement

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Description

The Bad Pixel Replacement window (see Figure 1) contains controls for compensating for bad pixels on the camera detector. To open the Bad Pixel Replacement window, click the Bad Pixel Replacement item under the Setup menu.

Figure 1: Bad Pixel Replacement window

Bad pixels are detector elements whose electrical response has changed and can no longer be used to accurately represent radiometric temperature. Pixels response can change over time or due to exposure to high levels of infrared energy. While capturing images, the response of bad pixels is replaced by the response of a neighboring good pixel.

When your camera was calibrated at Optotherm, any bad pixels (called factory bad pixels) were identified and marked. You do not have access to, and cannot change, the file containing the factory bad pixels. However, if you notice any additional pixels whose response is suspect, you can mark them so that they are replaced when capturing images.

# Bad Pixels	This field displays the number of bad pixels that have been marked in the image.
Show Bad Pixels	Check this box to display a square enclosing each bad pixel that has been marked. Note: Bad pixels cannot be displayed while capturing images.
Bad Pixel Markers Color	Choose the color of the markers used to to display the bad pixels.
Add/Remove Bad Pixels	Choose the Add option and then click on a bad pixel in the Main Image to mark the pixel. Choose the Remove option and then click on a marked pixel to unmark it. Choose the No Change option when you are finished marking pixels. Note: Use the zoom and pan tools to aid in marking and unmarking pixels.
Remove All	Click this button to unmark all pixels.
Save Changes	Click this button to save the changes you have made. Note: Unless changes are saved, any changes will be discarded when Thermalyze closes.
Load Factory Data	Click this button to replace the current bad pixels with the factory bad pixels. Note: Changes to bad pixels will be lost when Thermalyze closes unless the Save Changes button is clicked.
Bad Row	Enter the index of the row to replace. The index of the first row is 0. Enter -1 for no bad row replacement.
Bad Column	Enter the index of the column to replace. The index of the first column is 0. Enter -1 for no bad column replacement.

Identify Bad Pixels

Follow this procedure to detect and correct bad pixels:

Place the lens cap on the lens.
Press the Image Size button to display the large image size.
Press the Capture Images button to begin capturing images.
Enable Image Averaging and set it to a minimum of 64 images.
Press the ON/OFF button in the Image Subtract panel to activate Image Subtraction.
Enter values of -1.00 and 1.00 into the Palette Min and Max boxes.
Click the Set Reference button in the Image Subtract panel and then examine the Main Image for pixels with white or black color (bad pixels). Stop capturing images when one or more bad pixels is identified.

Add Bad Pixels

Open the Bad Pixel Replacement window.
Check the Show Bad Pixels box.
Choose the best color (White or Black) to mark the bad pixels so that they can be clearly identified.
Zoom and Pan the Main Image so that the bad pixels can be selected.
Select the Add option and then click on the bad pixel in the Main Image.
If you select the wrong pixel, you can remove it by selecting the Remove option and then clicking on the pixel.
When finished adding bad pixel, click the Apply Changes button and then click the Save Changes button.

Uniformity Correction

Description

The toolbar (see Figure 2) in the top center of the Thermalyze window is used to setup and control image uniformity correction.

Figure 2: Uniformity Correction toolbar

Enable Uniformity Correction	Image uniformity refers to the consistency of pixel temperature values across a thermal image when viewing a constant temperature (blackbody) source. Uniformity correction is used to improve the uniformity of thermal images captured using lenses that have not been calibrated with an Optotherm IS640 thermal imaging camera.
Uniformity Correction Setup	Press this button to open the Uniformity Correction Setup window (see Figure 3). Controls in this window enable you to perform uniformity correction for each lens and range.

Uniformity Correction Setup window

Figure 3: Uniformity Correction Setup window

Uniformity correction can be applied by performing only one correction (low or high) or performing both low and high corrections. If only one correction is performed (either low or high), image uniformity will be acceptable only for measured temperatures near the correction temperature. If both low and high corrections are performed, image uniformity will be interpolated between correction temperatures, resulting in better uniformity at measured temperatures different than the low and high correction temperatures.

The low and high temperature values used in uniformity correction will depend on the temperatures to be measured. Use a low temperature value that is close to the lowest temperature to be measured, but at least 10°C higher than the range minimum. Likewise, use a high temperature value that is close to the highest temperature to be measured, but at least 10°C lower than the range maximum.

Required: Uniformity images must be set for each lens and range for which uniformity correction is required.

Low Temperature Image	Enter the temperature of the constant temperature (blackbody) source when performing the low temperature correction. Click the Set button to save the uniformity image and temperature value to file. The uniformity image and temperature are used to calculate uniformity correction coefficients that can be applied to captured thermal images. The checkbox on the right indicates that a uniformity image and temperature have been set.
High Temperature Image	Enter the temperature of the constant temperature (blackbody) source when performing the high temperature correction. Click the Set button to save the uniformity image and temperature value to file. The uniformity image and temperature are used to calculate uniformity correction coefficients that can be applied to captured thermal images. The checkbox on the right indicates that a uniformity image and temperature have been set.
Clear	Click this button to delete the uniformity image.

Performing a Uniformity Correction

In the following example, the thermal stage is used as a constant temperature (blackbody) source. The range of temperatures to be measures is assumed to be 20 to 60°C and therefore, the low temperature range will be used.

Install the lens on the camera, select the lens in the Camera Lens drop-down box, select the low temperature range in the Range drop-down box, and allow the lens temperature to stabilize.
Wipe off the top of the thermal stage.
Set the thermal stage temperature to 20°C and allow to stabilize.
Position the camera so that the lens is approximately 25mm above from the stage.
Enable Image Averaging and set to 128 images.
Open the Uniformity Correction Setup window.
Enter 20°C into the Low Temperature Image box and click the Set button on the right.
Set the thermal stage temperature to 60°C and allow to stabilize.
Enter 60°C into the High Temperature Image box and click the Set button on the right.
Close the Uniformity Correction Setup window.
Set the Enable Uniformity Correction button to .

Lens Calibration

Description

Prior to being shipped, each Optotherm thermal imaging camera undergoes a rigorous ambient temperature compensation process to account for detector response for fluctuating camera temperatures during operation. This process requires several days and involves controlling the camera and lens to a range of specifics temperatures while exposed to the infrared emittance from blackbodies regulated to precise temperatures. After ambient compensation is complete, each lens is installed on the camera for uniformity and radiometry calibration. Ambient compensation cannot be performed by a third party and can only be performed at Optotherm. Therefore, there are not a user interface for performing ambient compensation within Thermalyze.

Measurement Accuracy: Changing settings in this window will alter temperature measurement accuracy. Therefore, changes should be made only by experienced operators.

Lens Calibration

The Lens Calibration window (see Figure 4) is used by Optotherm technicians and experienced operators to calibrate an Optotherm thermal imaging camera with a specific lens. To open the Lens Calibration window, click the Lens Calibration item under the Setup menu.

Figure 4: Lens Calibration window

Lens calibration involves the following procedure:

Create low-noise images while staring at a blackbody set to two different temperatures in order to compensate for the optical performance of each lens.
Specify settings to compensate for lens temperature dependence of optical performance, temperature offset, and radial uniformity.
Apply a calibration curve to improve radiometry (temperature measurement accuracy).

Optical Correction Images

Low and high Temperature images are used to compensate for lens optical performance.

Create Low Noise Image

ON/OFF	While capturing images, press this button to the ON state to accumulate images. Accumulated images are averaged to create a low noise temperature image. Note: Accumulated images are recorded prior to application of lens calibration settings. Therefore, lens calibration does not need to be disabled when accumulating images.
Images	This field displays the number of accumulated images.
Reset	Click this button to delete all accumulated images.
Quadrant Average	Check this box to average corresponding pixels from each quadrant when creating the low noise image. Important: This feature is currently for development purposes only and should not be used.
Noise Reduction	Check this box to average neighboring pixels when creating the low noise image. Important: This feature is currently for development purposes only and should not be used.

Low/High Temperature Image

Scene Temp	Enter the blackbody temperature used to create the Low of High Temperature Image.
Set to Memory	Click this button to save the a low noise image to memory as the Low or High Temperature Image for use in optical correction.
Scene Temp (Image Set in Memory)	This field displays the Scene Temperature entered when the Set to Memory button was clicked, which is used in optical correction.
Detector Temp	This field displays the value of the detector temperature when the Set to Memory button was clicked, which is used for optical correction.
Save Image to File	Click this button to save to file the Low or High Temperature Image currently in memory. Saved Temperature Images are opened automatically upon program startup for use in optical correction. Note: A flag will appear next to this button when a Temperature Image has been set to memory but not yet saved.
Clear from Memory	Click this button to clear the Temperature Image from memory.

Lens Calibration Settings

Enable Lens Calibration

Check this box to enable lens calibration for the currently installed lens.

Optical Correction

Enable	Check this box to enable Optical Correction to improve scene uniformity by applying the Low and High Temperature Images. Note: Optical Correction is typically required for all lenses.
Scale Factor	Enter the magnitude of Optical Correction to apply. Important: This setting is usually determined at the factory and should only be altered by experienced operators.
Fine-Tune	Enter an adjustment to Optical Correction to compensate for scene non-uniformity. Caution: If this setting is not returned to zero after use, scene uniformity will continue to be affected.

Offset Correction

Enable	Check this box to enable Offset Correction to improve measurement accuracy by applying a temperature offset to improve measurement accuracy. Note: Offset Correction may not be required for all lenses.
Scale Factor	Enter the magnitude of Offset Correction to apply. Important: This setting is usually determined at the factory and should only be altered by experienced operators.
Fine-Tune	Enter an adjustment to Offset Correction to compensate for temperature measurement offset errors. Caution: If this settings is not returned to zero after use, temperature measurements will continue to be affected.

Radial Correction

Enable	Check this box to enable Radial Correction to correct for image artifacts characterized by a bull's eye pattern in the center of the image and extending radially outward to the image corners. Note: Radial Correction may not be required for all lenses.
Scale Factor	Enter the magnitude of Radial Correction to apply. Important: This setting is usually determined at the factory and should only be altered by experienced operators.
Fine-Tune	Enter an adjustment to Radial Correction to compensate for radial image artifacts. Caution: If this setting is not returned to zero after use, radial compensation will continue to be affected.

Lens Calibration Curve

Enable	Check this box to apply a calibration curve to correct non-radiometric temperature measurements.
Lens Calibration Points	Click this button to open the Lens Calibration Points window.

Save Settings to File

Click this button to save Lens Calibration Settings to file. Saved settings are opened automatically upon program startup.

Note: A flag

will appear next to this button when Lens Calibration settings have been changes but not yet saved.

Factory Defaults

Temperature images and lens calibration settings (including lens calibration points) are loaded from C:\Optotherm\Thermalyze\Lens Calibration upon program startup. Thermalyze operators have the ability to make changes which will replace the data currently stored in C:\Optotherm\Thermalyze\Lens Calibration. Because measurement accuracy depends on this data, operators have the ability to load factory default data back into memory. Factory default data is stored in C:\Program Files\Optotherm\Thermalyze\Calibration\Lens Calibration.

Load Factory Defaults	Click this button to load factory default temperature images and lens calibration settings for the currently installed Lens and Calibration Range into memory. Important: The factory default data that is loaded back into memory must be saved so that it can be opened automatically upon program startup. Temperature images, calibration settings, and calibration points must all be saved to file.
Restore Factory Defaults	Click this button to load factory default temperature images and lens calibration settings for all lenses and calibration ranges into memory and then saved.

Lens Calibration Points

Description

The Lens Calibration Points window (see Figure 5) is used by Optotherm technicians and experienced operators to enter calibration data points that are used to create a calibration curve to correct for non-radiometric temperature measurements. To open the Lens Calibration Points window, click the Lens Calibration Points button on the Lens Calibration window.

Measurement Accuracy: Changing settings in this window will alter temperature measurement accuracy. Therefore, changes should be made only by experienced operators.

Figure 5: Lens Calibration Points window

Toolbar

Add Cal Point	Click this button to add a new calibration point. If a row is selected, the new calibration point is added above the selected row. If no row is selected, the new calibration point is added below the last row. Tip: Select a row by clicking in the # column.
Shift Cal Point Up	Click this button to shift the currently selected calibration point up one row.
Shift Cal Point Down	Click this button to shift the currently selected calibration point down one row.
Delete Cal Point	Click this button to delete the currently selected calibration point.
Delete All Cal Points	Click this button to delete all calibration points.

Temperature Calibration Points

Calibration points are created by imaging a blackbody set to a stable target temperature and then entering the measurement reading and target temperature.

#	Displays the number of each calibration point.
Reading	Enter the thermal camera measurement.
Target	Enter the blackbody temperature.

Create End Point

Create End Point	Calibration points are used to create polynomial calibration curve coefficients. The behavior of a polynomial curve fit beyond the range of calibration points can sometimes lead to considerable inaccuracy. To prevent this behavior, simulated calibration points can be added at both ends of the range. Simulated calibration points are created by linear extrapolation using the nearest two calibration points. To create a low temperature end point, enter a target temperature below the lowest calibration point target temperature and then click the Create button. To create a high temperature end point, enter a target temperature above the highest calibration point target temperature and then click the Create button.
Polynomial Fit Order	Enter the order of polynomial curve fit. Note: The order must be less than the number of calibration points.
Reload from Memory	Click this button to load the calibration point in memory for the currently installed lens into the calibration points table.
Set to Memory	Click this button to save the calibration points in the table to memory. Note: A flag will appear next to this button when calibration points have been changed but not yet set to memory.
Save to File	Click this button to save the calibration points in memory to file. Saved calibration points are opened automatically upon program startup to create a lens calibration curve. Note: A flag will appear next to this button when calibration points have been changed in memory but not yet saved.

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