Research of Lens MTF Measurement Software
With the development of CMOS technology, CMOS image sensors have been widely used in mobile phone camera modules. In 2005, global mobile phone shipments reached 795 million units, of which approximately 455 million mobile phones had camera functions, accounting for 57%. It is predicted that by 2008, 85% of mobile phones will have camera functions, and the shipment of camera phones will reach 800 million.The size of the mobile phone camera module market will also rise from about 2 billion US dollars in 2005 to 4.8 billion US dollars in 2008. This is a very promising market. Such a huge business opportunity has brought huge opportunities to major mobile phone camera module manufacturers, and it has also created challenges for major manufacturers. Since the small pixel (less than 2 million) mobile phone camera module adopts the fixed focus method instead of the automatic focus adjustment (AF) method, how to quickly and accurately complete the focus on the production line and quantitatively evaluate the entire mobile phone.
The imaging quality of the camera module has become an urgent problem for major manufacturers. Since the modulation transfer function (MTF) can objectively reflect the frequency response characteristics of an imaging system, it has been used as an important means to evaluate the quality of continuous imaging systems. Although CMOS is a discrete imaging device, it is still desirable to use MTF to evaluate its imaging quality.
In the conventional detection, many targets with different spatial frequencies are usually required for imaging, different wavelengths of light, and even different filters to be replaced. The operation is time-consuming and cannot be applied to the large and rapid detection requirements of the optical factory, so a computer-automated MTF detection method is proposed. The high-contrast black-and-white stripe target is illuminated by a uniform light source, and the image is acquired by using the CMOS image sensor of the mobile phone camera module, and then the image is analyzed, and the MTF of the system is calculated by the output curve of the image and the histogram of the image. Values do not need to meet some harsh conditions to calculate. For different lenses, the larger the MTF value, the higher the resolution of the lens; for the same lens, the lens always reaches its maximum position at the focus.
Therefore, the value of the MTF can be utilized as a criterion for focusing. At present, the system has been widely used in the production line of mobile phone camera module assembly, which greatly improves the production efficiency.