See before: Infrared Illuminators in VideoCAD.
There is an IR illuminator. It is necessary to measure efficiency of this illuminator for a black/white camera in relation to the halogen incandescent lamp and create model of this illuminator in VideoCAD.
The matter of testing IR illuminator is the achievement of equal average brightness of the same pixel on the image, when the scene is illuminated by the test IR illuminator and a tungsten halogen lamp. When the scene is illuminated by the tungsten halogen lamp, a Luxmeter will show illumination, which is equivalent to IR illumination (irradiance) created by the IR illuminator for this camera.
|•||Luxmeter (a device for measuring illumination). Almost any kind of such a device with standard CIE spectral response will suit.|
|•||Any PC-based video capture system, TV-tuner with video input, etc. The System should allow to display live video on the computer screen.|
|•||Compact tungsten halogen lamp 12V, 10W.|
|•||Stabilized power supply unit for the lamp. 12V DC, without considerable ripples of output voltage.|
|•||Manual Iris Lens, focal length is 4-8mm.|
|•||Stand. It is recommended for convenience and accuracy.|
|•||Measuring should be carried out in a dark room.|
1. Switch off all image processing options and AGC in the camera.
AGC switching off increases accuracy and allows working with illumination of 5..10lx, even if the camera has sensitivity of 0.2..1lx.
2. Mount the manual iris lens on the camera, mount the camera on stand, direct it towards sheet of paper, connect to computer, display image on the screen.
3. On the sheet of paper, in the camera field-of-view place the luxmeter sensor.
4. Close to the sensor window directly on the sensor, fix a small piece of even white paper.
5. Fix the testing IR illuminator at the distance of 1-2 meter from the luxmeter sensor (not closer than 20-times size of the illuminator radiant window), direct illuminator axis of radiation on the sheet of paper on the sensor perpendicularly to the sheet of paper.
6. Run the Video Analyzer. Switch to the One pixel test tab. Mark Cycle box, click Start. After that move fast the mouse cursor to the small piece of even white paper on the screen, close to the sensor window.
7. Switch of common light. supply the illuminator by nominal voltage. If a LED IR illuminator is being tested, warm up the illuminator not less than 1 hour.
During warming up the power of the LED IR illuminator decreases by 15-20% and more in dependence of heatsink construction.
8. By adjusting aperture, obtain that the Average brightness measured by the Video analyzer would be equal to 0.22-0.25 after finishing measuring cycle by 100 frames.
The objects on the image should be recognized.
9. Switch OF the IR illuminator. Switch ON the tungsten halogen lamp.
10. By changing the distance from the lamp to the sheet of paper, obtain equal with step 8 value of Average brightness after finishing measuring cycle by 100 frames.
You must not change the lamp supply voltage. It should be equal to nominal lamp supply voltage. Change Illumination only be means of distance variation between the lamp and the sheet of paper.
Be sure, that the luxmeter sensor window and the small piece of paper on the sensor have visually equal illumination.
11. Record the luxmeter reading.
The luxmeter shows illumination Eeq., which is equivalent to IR illumination (irradiance) created by the IR illuminator for this camera.
12. Calculate the irradiance Eir (watt/m2), created by the illuminator according to the formula:
Eeq - equivalent illumination, measured in step 11;
Kse - relative spectral efficiency factor of IR radiation (lumen/watt) for white paper and black/white CCD sensor.
The Kse values are obtained by practical measurements in the laboratory of CCTVCAD Software http://cctvcad.com with IR illuminators calibrated in radiometric laboratory of Micrel.Ltd http://micrel.spb.ru.
The Kse values are correct for white paper. Closer Kse values are obtained for a human body. For green grass Kse have 2.2 times more values..
Green grass reflects IR radiation better than the visible light. Paper and human body reflect IR radiation worse than the visible light.
Theoretical calculation gives average result. The theoretical result did not take into account difference in reflection power in visible and IR lights.
During designing, it is necessary to use Kse value for paper and human body.
Switching the Kse values for day/night cameras in VideoCAD is performed automatically in dependence on camera type.
13. Open the Illuminator calculation box in VideoCAD. Enter:
|•||Lamp type - IR LED of known wavelength;|
|•||Lamp power - consumed electric power of the IR illuminator;|
|•||LED quantity - 1;|
|•||Projector - mark;|
|•||Angle of radiation - radiation angle of the IR illuminator (0.5 radiation intencity);|
|•||Concentration - 0.5;|
If there is a specification with the light intensity curves, by choosing Concentration try to obtain close rediant intensity distribution.
|•||Distance - the distance between the IR illuminator and the small piece of even white paper on the sensor window (meter).|
14. Choose value in the Efficiency factor box to obtain in the Irradiance (watt/m2) box the value, which is equal to Eir calculated in step 12
The Efficiency factor values obtained by measuring some real IR illuminators:
|•||Efficiency factor=0.3 for narrow angle illuminator (angle of radiation is 20-50 degrees);|
|•||Efficiency factor=0.5 for wide angle illuminator (angle of radiation is 60-120 degrees).|
Total efficiency factor of the IR illuminator is a product of efficiency factor of IR LED (0..5..0.15) multiplied by the chosen efficiency factor of the illuminator.
15. Thus, we have obtained the model of available LED IR illuminator. Using obtained model we can get image models from different cameras at illumination produced by this illuminator with sufficient accuracy for practice.
See also: Measuring camera sensitivity, IR illuminators (in VideoCAD).