What Is a Display MTF Measurement System?
A display modulation transfer function (MTF) measurement system is a device for assessing display resolution using MTF, a spatial frequency characteristic of optical systems, commonly found in displays.
Display resolution depends on factors beyond pixel count and scanning lines, such as pixel arrangement, luminance, contrast, gamma characteristics, color reproduction range, color temperature, and white balance. MTF is a theoretically solid method for evaluating overall system resolution, from TV camera lenses to transmission systems, display characteristics, and human visual perception.
Optical property evaluation of displays includes glare, sharpness, anti-glare, and transmission distribution. Sharpness, or the blurriness of an image, is assessed using point spread function (PSF), line spread function (LSF), and amplitude transfer function (MTF).
MTF is plotted against spatial frequency, with higher values indicating better transfer characteristics and less blur.
Uses of Display MTF Measurement Systems
Display MTF measurement systems evaluate the sharpness of displays and their components, serving as vital quality control tools.
They are particularly used for assessing LCD panels in devices like 4K/8K TVs, cell phones, PCs, in-vehicle systems, and measuring instruments. MTF measurement features high accuracy, cost-effectiveness, and ease of operation.
Principle of Display MTF Measurement Systems
In MTF measurement, the input signal from a camera maintains a constant amplitude at high frequencies, with the output amplitude decreasing with increasing frequency. This output is the MTF.
MTF can be measured using three methods: slit, edge, and chart methods.
1. Slit Method
This method involves capturing a metal slit image and performing a Fourier transform. It is primarily used in the United States and requires relatively expensive test devices.
2. Edge Method
The edge method, recommended by the International Electrotechnical Commission (IEC), calculates MTF by Fourier transforming an edge image to obtain the LSF.
3. Chart Method
The chart method captures a square wave test pattern, corrects it to obtain the input/output contrast ratio of a sine wave, and is commonly used in Japan and Europe due to lower test device costs.
Features of Display MTF Measurement Systems
Display MTF measurement systems, combined with a signal generator and a measurement camera, can evaluate display MTF effectively. They can also measure graininess, luminance uniformity, and gradation curve with high accuracy.
Display MTF Measurement Systems Manufacturers
Few manufacturers specialize in display MTF measurement systems.
DM&S, a German company, offers the SMS-1000, measuring glare and evaluating sharpness, anti-glare, and transmission characteristics. Astrodesign Inc. provides the DT series, developed in collaboration with NHK, for real-time MTF measurement of displays. S.S. Giken Co., Ltd. offers the NS-2002 system, evaluating resolution, graininess, and tonality of X-ray display images using MTF.