Camera parameters and sensor characteristics

•Due to the method of functioning this sensor does not provide an exposure time (see also chapters Functionality of the uEye HDR sensor: Exposure).

•Pixel values are read out line by line (rolling readout) with the NSC0806. Due to the slight time offset between reading out one line and the next, the so-called rolling-shutter effect may be seen (see also Functionality of the uEye HDR sensor: Readout).

•Recommended pixel clock range 10–15 MHz. A pixel clock above 20 MHz may cause slight horizontal blurring.

•GigE uEye cameras only: To make full use of the dynamic range of HDR images, you should transfer the image data with a bit depth of 12 bits.

•In situations with extreme brightness, black pixels may become visible in the brightest image parts. This is a physical effect due to the CMOS technology. Slightly close the aperture to avoid that effect.

Contrast adjustment (black level/white level and gain)

•The sensor's black level shifts down with increasing operating temperatures. To avoid black level clipping, you should always enable automatic correction or manually set the black level to 255 (see is_Blacklevel()).

•When you use auto gain control, higher gain values can be achieved than with a manual setting. The sensor reaches white image values (255) only when auto gain is used (see is_SetAutoParameter()).

•The values for auto gain control and automatic black level correction are computed in the camera based on the histogram of the previous image. If you want to use the automatic adjustment also in trigger mode, you therefore have to capture two images at a time.

•Gain uses a bit depth of 14 bits on a digital basis. The use of gain factors over 4x will cause gaps in the histogram even with 12 bit transfer; it is therefore not recommended.
To transfer the sensor's raw data uncorrected, the automatic brightness control functions (see is_SetAutoParameter()) have to be disabled. In addition, set the gain setting to 0 (see is_SetHardwareGain()) and the black level to 255 (see is_Blacklevel()).

Selecting lenses

•The sensor has a high sensitivity in the near-infrared range. To ensure sharp images in the visible range, the camera should be fitted with an IR cut filter. All uEye HDR cameras use an HQ IR cut filter by default (see Filter types).

•Due to the extremely high dynamic range of the HDR sensor, any lens reflections always emerge more pronounced in lenses than when conventional sensors are used. With untempered lenses, the reflection can be more than 4 % of the amount of light captured. Light reflected in this way is mirrored on successive lens elements and ultimately appears as a distracting light spot in the image. To achieve good results with cameras featuring HDR sensors, the individual elements of the lens must be given a high-quality anti-reflective coating.

Flash mode and pulsed lighting

Since HDR sensors such as the NSC0806 do not integrate charges like conventional sensors, there are limitations in flash mode.

•When reading out the sensor, the amount of light striking each pixel at that exact moment in time is measured. For this reason, a flash must remain active during the entire readout duration to light up the entire image. In the case of a sensor with rolling readout, the light source would have to be illuminated during the entire readout duration (t = 1/frame rate) to light up the image evenly, which is generally not possible with high-power flashes.

•Another effect of the lack of integration on the sensor results from quickly pulsating light, such as that originating from LED and laser light sources and electric arc welding. The fluctuations in the brightness of the light source caused by the pulsation are visible as transitions from light to dark in the image, where their spacing depends on the light source frequency.

Display and processing of HDR images

We recommend not to perform contrast adjustment when image data is to be used for image analysis tasks. In order to be able to use the complete dynamic range of HDR images, you should transfer the image data with a bit depth of 12 bit. This will allow for processing the relevant image data in the best possible quality.

Images captured with HDR sensors may seem dull when displayed on a monitor. If HDR images will be solely used for visualization purposes, we recommend to perform contrast adjustment in the camera. This can either be performed manually using the functions "Black level correction" and "Gain" or automatically by the uEye driver. When you choose automatic adjustment the driver sets the black and white levels in such a way that the image brightness values are ideally distributed in the histogram.

The black level adjustment is always performed in the camera and does not affect image quality. When a uEye HDR camera is opened the automatic black level adjustment and the camera-internal white level adjustment are activated by default. You find more information to HDR in the Whitepaper "High Dynamic Range Imaging: Images and Sensors" on our website.