环境光强度#
哪种类型的环境光有问题？#
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.
辐照度与照度#
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.
与此相反，可见光的感知亮度通常表示为照度。这是一个光度量，指的是光对人眼的感知亮度。照度以勒克斯 (lx) 为单位。
没有普遍有效的方法可以从辐照度值中得出照度值。这是因为不同光源的红外部分可能会发生很大变化，因此，每个光源的光谱都必须单独考虑。
比较示例方案#
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 | 环境光强度的辐射限制 （最大辐照度 @ 920–970 nm） | 环境光强度的光度限制 （最大照度，近似值） |
|---|---|---|
| 阳光a | 12.8 W/m² | ~60 klux |
| 白炽灯 (3200 K)b | 12.8 W/m² | ~8 klux |
| 在 920–970 nm 之间没有近红外发射的人造光源（例如可见光 LED，荧光灯等） | 12.8 W/m² | 没有实际限制 |
| blaze-102 and blaze-112 | Radiometric Limit for Ambient Light Robustness (max. Irradiance @ 830–880 nm) | 环境光强度的光度限制 （最大照度，近似值） |
|---|---|---|
| 阳光a | 6.8 W/m² | ~15 klux |
| 白炽灯 (3200 K)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 | 没有实际限制 |
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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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3200 K 色温的钨卤素灯
环境光的影响#
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.
信息
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.
确定相机的辐照度限制#
在以下条件下测试了相机：
- 平面白色目标，反射率 90％
- Target illuminated by 940 nm (blaze-101) or 850 nm (blaze-102, blaze-112) LED
- 目标和相机之间的距离为 6 m
- Exposure 时间为 250 µs
测试设置#
照相机直接对准 6 m 处白色平面目标。为了模拟环境光，可以使用与相机波长相同的附加光源照亮目标。目标上的发光度增加到相机仍可提供不会过曝的可用图像。测量照度并基于相机图像确定噪声的增加率。
测试结果#
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.