ISO 16505 — Road Vehicles — Camera Monitor Systems

 

Test Targets

ISO 16505 Test Targets are available for purchase on the Imatest Store

Test Methods

Resolution

References ISO 12233:2014.   Hyperbolic wedge features can be analyzed by the Wedge or eSFR ISO module. Slanted edge features can be analyzed by the SFR, SFRplus, eSFR ISO, SFRreg , or Chekerboard modules.

We presented a paper, “Measuring MTF with wedges: pitfalls and best practices” at the Multi-camera and Embedded Systems for Autonomous Machines session of the Electronic Imaging Conference at San Francisco Airport on January 30, 2017. The paper focuses on difficulties with the ISO 16505 standard and how to overcome them— how to obtain good measurements despite ambiguities in the standard, which is in need of revision.

A key finding in the paper is that the primary resolution metric in ISO 16505, MTF10 derived from hyperbolic wedges, is not a reliable measurement of system performance. A poor quality camera can have a good MTF10 measurement. We recommend replacing MTF10 with the minimum of {MTF10, the Nyquist frequency, and the onset of aliasing (the spatial frequency where the bar count starts decreasing)}.

According to the standard, the contrast of the hyperbolic wedge should be greater than 20:1 or 40:1 (depending on where you look) so some lower contrast wedge test charts will not strictly comply with the standard. Very high contrast charts have problems with saturation or clipping.

The standard has some confusing and possibly erroneous statements on spatial frequency units.

  • Imatest calculates spatial frequencies directly from the wedge geometry itself. It does not use the numeric markings next to the wedges in any of its calculations. These numbers can be multiplied by 100 to obtain spatial frequency in Line Widths per Picture Height (LW/PH) if the image is framed so the top and bottom borders of the chart, which contain arrow marks (∇ and Δ), are at the exact edges of the frame. The problem is that charts are rarely framed this way in practice.
  • The fundamental units used by Imatest to calculate spatial frequency response are cycles per pixel (C/P), where 1 cycle = 1 line pair = 2 line widths.
  • Spatial frequency in Line Widths per Picture Height (LW/PH) is normally obtained by multiplying the C/P value by 2 * the Picture Height in pixels (typically the shortest dimension of the total picture).
  • ISO 16505 specifies a hypothetical square region inside the image for calculating LW/PH spatial frequencies. If Lpx is the length in pixels of a side of the square, then you can use the simple equation, LW/PH = 2 * Lpx * C/P. The standard has many confusing statements about units. This is most of what you need to know.

The units LW/PH can be selected in the settings windows, and a secondary readout of MTF10 can be selected to produce a compliant measurement.

Magnification

The ISO 16505 requires magnification to be mapped as a function of field distance. Imatest currently computes optical distortion as a function of field distance, but does not yet convert this into a magnification output.

Camera Monitor System (CMS) sharpness spatial frequency units

The spatial frequency units for MTF (sharpness) measurements in the ISO 16505 standard are very confusing. Although we haven’t fully addressed this issue (as of May 2017) we have recently published a page on how to determine spatial frequency units for calculating the MTF of camera monitor systems. These units (both Line Widths per (effective) Picture Height) allow the sharpness of the image inside the CMS (the output of the camera/input to the monitor) to be compared directly with the image taken of the monitor by a second camera. See Camera Monitor Systems (in the Solutions section).

 Aspect Ratio

The standard refers to aspect ratio across the field, and where that aspect ratio is at a minimum value. Imatest does not currently consider aspect ratio as a function of field distance and instead computes an overall aspect ratio.

Color

The ISO-16505 color chart can be analyzed in Multicharts and Multitest in Imatest 5.0+. The uv color angle in degrees and also the Pass/Fail limits (from section 6.9.3 and Figure 21 of the standard) and P/F indicator (0 or 1 for F or P) are displayed (only for the ISO-16505 color chart). Results are saved in the JSON and CSV output files. An example is shown on the right.

Multicharts uv results for the ISO 16505 color
chart. Click on the image to view full-sized.

Timing

There is currently no calculation of system latency produced by Imatest.

 See Also