TRANSMISSIVE CERTIFICATE OECF20 10.000:1 (X-VERSION) ISO 14524 OECF Camera Test Chart

The specification of TE270X D is derived from ISO 14524.

Standard versions of OECF charts use a screening to form the gray levels. This may lead to increased noise levels or artefacts in the images of high resolution cameras that can resolve the screening but cannot defocused slightly (e. g. mobile phones). TE270X uses continuous tone film and therefore does not show these structures.

The center of the is equipped with two polarizing filters. For cameras that do not allow a manual adjustment of the exposure, the automatic exposure control (AEC) is fooled by modifying the density (transmission) of the central part of the chart. So the correct exposure of the chart can be reached. This feature is especially made for cameras and camera modules in mobile devices which often do not have a manual exposure adjustment.

OECF MEASUREMENT

The opto electronic conversion function (described in ISO 14524) is one of the most important characteristics of a digital camera. It describes how the camera transforms luminance values of an object or illuminance values on the sensor plane into digital code values in the digital image.

The OECF is typically measured from a gray scale. Depending on the type of camera different versions of test charts are used. It is a test chart with a circular arrangement of the gray levels. These may be affected by lens and camera related shading but since most optical systems are rotationally symmetric they will fall on the same shading level for all patches.

ISO 14524 describes how the densities to manufacture the chart are calculated. The

An integrating sphere like the LE6 or LE7 provides the best uniformity for the illumination of the OECF targets. Although the targets usually come with density levels and the integrating sphere has a build in illuminancemeter we recommend to use a luminance meter in combination with the charts because the conversion to luminances from densities and illuminances requires a calibration factor. A low cost but accurate device is the Gossen Mavo Monitor.

Note: Do not use a teleluminance meter for the measurements!!! These devices are affected by stray light and do not deliver accurate values for the dark patches!!!

The measured values for the patches can be used to create your specific reference file for the evaluation in the iQ-Analyzer. To type in the values use the “Luminance and Density Data” button in the advanced settings of the OECF module.

Images taken from a single gray scale target can be used to answer all of the following questions:

• What is the maximum contrast in a scene that can be captured by the camera in all its tonal details (dynamic range)?

• Is the white balancing o.k.?

• Does the camera use all possible digital values in the image?

• Is there a gamma or tonal correction applied to the captured linear image?

• What is the signal to noise ratio for different gray levels?

• What is the ISO speed of the camera?

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