OECF измерительная Тестовая карта диаграмма индивидуальная версия калибровки камера Тестовая карта бесплатная доставка

光电转换功能（在ISO14524中描述）是数码相机的重要的特征之一。它描述了照相机如何把变换的传感器平面物体照度值或亮度值转换成数字图像中的数字代码值。

该OECF是典型地从一个灰度进行测定的。根据相机的不同使用不同版本的测试卡。TE264D是按照ISO14524规格制造的。它是与灰度级的圆形排列的测试图。它是与灰度级圆形排列的测试图。这些可以通过镜头和相机相关的阴影的影响，但是大部分光学系统旋转对称称为theywill落在了所有补丁一样阴影水平。

ISO 14524描述了测试卡的密度如何计算。这个值取决于所需的动态范围图卡。为了测量一个相机的测试卡的对比度应该在超出相机动态范围之内测试。这就是为什么今天的目标典型对比度为10000:1和有时甚至超过1000000:1。虽然有较少可用12级灰阶和无声的测试图卡，我们建议使用至少在TE264和20补丁具有用于计算足够支撑点。TE264的标准版本使用筛选，形成灰阶级。筛选解决问题可能导致高分辨率摄像机图像噪声水平或假象的增加。为了避免这个问题的图卡应该适合有限的图像高度和/或相机可以在过程中定义的标准相比,有点散焦。TE264X可以做到使用连续色调膜，因此不会出现这个麻烦。

OECF MEASUREMENT 

The opto electronic conversion function (described in ISO 14524) is one 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 grey scale. Depending on the type of camera different versions of test charts are used. The specification of TE264 D is derived from ISO 14524. It is a test chart with a circular arrangement of the grey 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 values depend on the desired dynamic range of the chart. In order to measure a camera the contrast of the chart should exceed the dynamic range of the camera under test. This is the reason why typical contrast ranges of today’s targets are 10.000:1 and sometimes even more than 1.000.000:1. Although there are still charts with 12 gray steps and less available, we recommend using at least the TE 264 with 20 patches to have enough supporting points for the calculation. The standard version of TE264 uses 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. To avoid this problem the chart should fit a limited image height and/or the cameras may, in contrast to the procedure defined in the standard, be slightly defocused. TE 264X is available that uses continuous tone film and therefore does not show this problem. 

An integrating sphere like the LE6 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 illuminance meter 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 grey levels? 

» What is the ISO speed of the camera?