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The Lens Distortion Correction tool is a DevWare DevWareX plug-in. It is intended for use with the MT9V126, MT9V128, and ASX343AT System on Chip (SOC).
The Distortion Correction tool can be used to generate Distortion Correction configuration settings for wide angle lens sensor module. It provides:
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- To start the Distortion Correction tool GUI window, follow the following steps are:
Run DevWareDevWareX, go to the main menu->Plug-ins-> Lens Distortion Correction Tools (Ver 2.0), DeWarp) Tools and the Lens Distortion Correction (DeWarp) Tools dialog is shown as follows: 
Fig. 1 Distortion Correction DevWare DevWareX Plug-in
The tool can operate in one of two modes: MT9V126 SOC Hardware or Software Simulation. In MT9V126 SOC Hardware mode the process of correcting the lens distortion and adjusting the perspective of the image are done by the system hardware. In the Software Simulation mode, these processes are done by a simulation of the system hardware by DevWare. In order to operate in MT9V126 SOC Hardware an Aptina Imaging Demo camera has to be installed connected to your computer.
When selecting one of these modes, DevWare DevWareX will automatically switch the sensor to the output format which corresponds with your selected mode. For MT9V126 SOC Hardware DevWare DevWareX will set the sensor to output Dewarp+Overlay CCIR656 Interlaced image. For Software Simulation DevWare DevWareX will set the sensor to output 640x480 YCbCr/RGB Progressive image.
You can also change the sensor output mode directly by clicking the Control button in the DevWare DevWareX toolbar, which brings up the Sensor Control dialog. In there access Digital Video Output and make sure 640x480 YCbCr/RGB Progressive is selected if you want to apply Distortion Correction settings to Devware DevWareX software simulator, Or Dewarp+Overlay CCIR656 Interlaced if you want to apply the current Distortion Correction setting to sensor.
- In Software Simulation mode, the Distortion Correction output format can be specified via Format: in the Output Mode group. Three modes supported: NTSC, PAL and Progressive. In MT9V126 SOC Hardware the output format is determined by the sensor settings and it can be modified by the DevWare DevWareX sensor control pages.
- In Software Simulation mode the Distortion Correction effect can be seen more clearly by selecting Circle Overlay, ten circles with different image heights will be shown on the current frame sensor output, check Enable and you can see what will happen to those circles after Distortion Correction processing. Check Open picture-in-picture if you want to see both images before and after Distortion Correction at the same time. These options are available in Software Simulation mode only.
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You can find default settings which come with the tool in the folder
<installation-path>\Plugins\Default Lens Correction
You can apply the current Distortion Correction tool setting to either the software simulator or to the sensor by clicking the corresponding radio box at the bottom of Distortion Correction Tools, and then click on Apply button. If Software Simulation is selected, make sure Enable gets checked so that the new Distortion Correction setting can take effect in the Devware DevWareX display window.
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Computer with two monitors with each monitor on a separate table are required, one is for displaying target images and the other is for Devware DevWareX operations. Two tables should be used in order to minimize the table vibration during image capturing. The vibration needs to be less than 1 pixel in the sensor.
Other hardware includes Demo2 system with fine adjustment for height control and SOC 360 or MI360 with a wide angle lens mount.
The key issues to consider are [1]:
The monitor must be normal to the optical bench (no tilt)
The camera must be parallel to the monitor
An accurate measurement of the optical center of the lens is very important; the Cross-Hair image target can be used for this purpose.
An accurate flat-fielding of the image, make sure the experiment setup is not touched during image capturing.
The illumination of the room can be controlled ( lights need to be turned off during data collections)
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- Click on Load Crosshair Target button, the cross-hair target image will be displayed on one of the monitors, double click to maximize the image.
- Adjust lens focus; adjust camera height so that the image of the crosshairs shows up as straight lines at the center (co-ordinates [319,239]) of the Devware DevWareX display. If it is not possible to adjust the camera so that the straight –lines line up the center of the display, then the optical center of the lens is not at the center of the sensor. Record the values of the horizontal and vertical co-ordinates where the cross-hair lines are straight (from Devware) and enter them in the Horizontal and Vertical edit boxes respectively, click on Capture Crosshair Target button.
- Click on Load Flatfield Target button, double click to maximize the image.
- Adjust Devware DevWareX gains and exposure so that the average intensity in the image is around 200 digital counts and no part of the image is saturated. To check the average digital count, draw a graph through a column / row near the center of the image. Make sure aperture correction is disabled in Devware. Click on Capture Flatfield Target button.
- Click on Load Scene Target button, double click to maximize the image
- Click on Capture Scene Target button.
- Click on Calibrate Button to initiate the distortion measurements.
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The Advanced tool gives the user the option to export and import the Distortion Correction configuration in several formats.
Import/Export Dewarp Settings is an option which is useful for capturing and restoring the mathematical model of the lens distortion and perspective correction.
Write to INI File allows exporting the configuration into a presets file which can then be used in order to program the sensor using DevWare DevWareX Presets.
To Flash Image produces a binary file which is compatible with the SPI flash tool requirement for the Distortion Correction data.
Fig. 9 Perspective Correction Page
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