環境光に対する堅牢性#
どのような種類の環境光が問題となるか？#
blaze cameras emit invisible infrared light:
- blaze-101 cameras emit light at a wavelength of 940 nm
- blaze-102 and blaze-112 cameras emit light at a wavelength of 850 nm
Invisible infrared light in the ranges of 920–970 nm (blaze-101) or 830–880 nm (blaze-102, blaze-112) is detected by the cameras' image sensors and interferes with the cameras' own light sources, thus affecting the resulting measurements. It can therefore be considered the main cause of disturbance. The effect of light of other wavelengths is negligible in this regard.
放射照度と照度#
Because of the cameras mainly being susceptible to invisible infrared light, the ambient light robustness is specified in terms of irradiance, a radiometric quantity suited for invisible light. Irradiance is measured in W/m². It refers to the light in terms of its radiant flux (power) that is received by a surface per unit area.
これとは対照的に、可視光において知覚される明るさは通常、照度として表されます。これは、人間の目で知覚される明るさにより光を示す光度測定量です。照度はlux（lx）で測定されます。
放射照度の値から照度を導き出す、普遍的に有効な方法はありません。これは、光源によって赤外線の部分が大きく異なる可能性があり、各光源のスペクトルを個別に考慮する必要があるためです。
サンプルシナリオの比較#
To offer some guidance, Basler has examined three different scenarios to show how irradiance relates to the illuminance values of different light sources. The measurements were taken under the following conditions:
- The irradiance limit of blaze-101 cameras is 12.8 W/m², and the irradiance limit of blaze-102 and blaze-112 cameras is 6.8 W/m² (determined by Basler under specific test conditions).
- The total spectral irradiance of typical light sources, e.g., sunlight or halogen light, was chosen in such a way that the irradiance registered by the cameras' image sensors was equal to the cameras' irradiance limits of 12.8 W/m² and 6.8 W/m².
The illuminance in the visible light range under these conditions was then calculated taking into account the spectrum of the light source and the luminous efficiency function. Also included were the quantum efficiency of the image sensor, the transfer function of the cameras' bandpass filter (passband and stopband), and some other relevant camera properties.
The following tables list the results:
| blaze -101 | 環境光に対する堅牢性の放射測定制限 （920～970nmでの最大放射照度） | 環境光に対する堅牢性の光度測定制限 （最大照度、近似） |
|---|---|---|
| 太陽光a | 12.8W／m² | ～60klux |
| 白熱灯（3200K）b | 12.8W／m² | ～8klux |
| 920～970nmの近赤外線放射のない人工光源（可視LED、蛍光灯など） | 12.8W／m² | 実際的な制限なし |
| blaze-102 and blaze-112 | Radiometric Limit for Ambient Light Robustness (max. Irradiance @ 830–880 nm) | 環境光に対する堅牢性の光度測定制限 （最大照度、近似） |
|---|---|---|
| 太陽光a | 6.8 W/m² | ~15 klux |
| 白熱灯（3200K）b | 6.8 W/m² | ~5 klux |
| Artificial light sources without near-IR emission between 830–880 nm (e.g., visible LED, fluorescent lamp, etc.) | 6.8 W/m² | 実際的な制限なし |
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Bright, sunny day with blue sky in the northern hemisphere: day of summer solstice; solar time 12:00:00; latitude 53.692540; longitude 10.266444; target tilt 90° (perpendicular to ground); target azimuth 180° (south-facing); surface albedo 0.2; camera normal to target
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タングステンハロゲンランプ、3200K色温度
環境光の影響#
The effects of ambient light on the cameras' image quality are most pronounced in the depth map or point cloud. In scenes with strong ambient light in the ranges of 920–970 nm or 830–880 nm, the depth noise increases, thus reducing the precision of the depth measurement.
If the ambient light is relatively weak (irradiance up to 5 W/m²), the increase in noise remains below a factor of about 2. Under strong ambient light, close to the specified limit of daylight robustness (irradiance 12.8 W/m²), the noise increases by a factor of 7. If the irradiance of the ambient light is increased further beyond this limit, the cameras' image sensors saturate. When this happens, the intensity image appears white and depth measurements are no longer possible.
情報
Ambient light isn't visible in the cameras' intensity image. This means that ambient light changes can't be observed as brightness changes but only as changes in the image noise. The transition from a well-exposed image to an oversaturated image may therefore appear very sudden.
カメラの放射照度制限の決定#
カメラは、次の条件でテストされました。
- 90%の反射性を備えた白の平らな対象物
- Target illuminated by 940 nm (blaze-101) or 850 nm (blaze-102, blaze-112) LED
- 6mの距離（対象物とカメラの間）
- 露光時間250µs
試験のセットアップ#
カメラは、6メートルの距離にある平らな白いターゲットに直接向けられました。周囲光をシミュレートするために、ターゲットはカメラと同じ波長を使用して追加の光源によって照射されました。ターゲットの照射輝度は、過剰照射を行わずにカメラが使用可能な画像を照射したポイントまで上昇しました。放射照度を測定し、カメラの画像に基づいてノイズの増加を判定しました。
試験結果#
The blaze-101 camera still delivered usable images at an ambient irradiance of 12.8 W/m² for ambient light sources between 920–970 nm. The image noise increased by a factor of 7.
The blaze-102 camera still delivered usable images at an ambient irradiance of 6.8 W/m² for ambient light sources between 830–880 nm. The image noise increased by a factor of 7.