Image Performance and EMVA 1288

Image Performance and EMVA 1288

When it comes to evaluating the performance of high-speed cameras based on image quality, traditional methods have been inconsistent and qualitative, leading to difficulties in comparing cameras from different manufacturers, especially regarding sensitivity. Many users often rely on side-by-side comparisons to judge sensitivity by observing which camera produces a brighter image. However, this practice is scientifically inaccurate and can lead to misleading conclusions.

To address these challenges and provide a standardized approach, the European Machine Vision Association (EMVA) introduced EMVA 1288, an electronic standard designed to characterize the performance of industrial camera sensors using a scientific methodology. The goal is to have a consistent method for assessing image performance across different cameras.

The EMVA 1288 data sheet and summary include the following key information:

  1. Sensor Specifications: This section covers essential details about the camera sensor, such as pixel size, full pixel resolution, and the type of shutter (global or rolling).
  2. Test Parameters: The test parameters specify the camera’s frame rate, exposure settings, environmental conditions during testing, and the wavelength of the light source used to generate the report.
  3. Photon Transfer and Signal-to-Noise Ratio (SNR) Curves: These curves provide valuable insights into the camera’s performance in terms of sensitivity and noise levels. A higher SNR indicates better signal quality and the ability to detect small changes in light levels.
  4. Official EMVA 1288 Measurement Results: This section presents the final measurement results following the EMVA 1288 standard, offering a comprehensive evaluation of the camera’s image performance.

Now, let’s delve into the key parameters used in EMVA 1288 and their significance:

  1. Quantum Efficiency (QE × FF) – Percentage (%): QE represents the percentage of photons that get converted to electrons at a specific wavelength (λ). Higher QE values correspond to greater light sensitivity. To find the precise QE value at specific wavelengths, referring to the sensor’s spectral response curve is essential. The EMVA QE value takes into account the fill factor value, providing a more comprehensive assessment of sensitivity.
  2. Temporal Dark Noise – Electrons (e-): Also known as “Read Noise,” this parameter quantifies the noise present in the image when no incident light reaches the sensor (i.e., when the lens cap is on). A lower temporal dark noise value indicates a better dynamic range, superior low-light performance, and overall higher image quality for more accurate image analysis.
  3. Signal-to-Noise Ratio (SNRmax) – Decibels (dB): SNRmax represents the ratio of signal power to noise power. A higher SNRmax value indicates better signal quality and the camera’s ability to resolve subtle changes in light levels effectively.
  4. Absolute Sensitivity Threshold – Photons (p): This parameter specifies the quantity of photons required for a pixel to generate a signal equal to the noise level. A lower absolute sensitivity threshold indicates that the sensor can identify details in low-light applications more effectively.
  5. Saturation Capacity – Electrons (Ke-): Also known as “Full Well Capacity” (FWC), this parameter indicates the amount of charge a pixel can store. A higher saturation capacity correlates with a higher maximum SNR of the sensor, as SNR trends with the square root of FWC due to photon Shot noise.
  6. Dynamic Range – Decibels (dB): Dynamic range represents the ratio between the maximum pixel signal (or FWC) and the read noise. Higher dynamic range values result in better image quality because they enable the sensor to resolve fine grayscale features, even in dark areas. For instance, a 12-bit image can have a dynamic range of up to 72 dB.

By understanding and utilizing the EMVA 1288 standard and its associated parameters, users can make more informed and accurate assessments of high-speed cameras, facilitating better decision-making when selecting the most suitable camera for their specific applications.