Application of telecentric lens in mobile phone screen detection

At 1 am on September 10, 2015, Apple held a press conference to announce that the new iPhone 6S and iPhone 6S Plus phones will be released on September 25. This heavy news quickly occupied the headlines of major information websites. And caused the concern of fruit powder. As a visual equipment supplier that provides screen detection solutions to Apple, iJUNCO also expressed great interest in this news. Now we take advantage of this boom to introduce you to a new concern in mobile screen detection applications Technology-telecentric lens.

    The main problem of mobile phone screen detection is the contradiction between "large" and "small". "Large" means that when a lens with a large magnification is used, a very clear picture can be obtained for easy analysis, as shown below:

Phone screen detection

  However, the scope of such a solution is too small each time, a 5.0-inch screen may take hundreds of times to complete the shooting, and the efficiency is conceivable. Such a scheme is feasible in the laboratory, but it cannot be competent if it is to be applied to actual production testing.

  What does "small" mean? When we use a high-resolution (500W-2900 W) industrial camera and a normal high-resolution industrial lens (500W pixel fixed focus lens) to take the overall picture of the screen, we get The picture is as follows:

Phone screen detection

There are two problems here. First, the resolution is not enough to obtain an effective image that can distinguish the situation of each pixel. After reading this image with software, it will be found that the number of pixels and color values on each physical pixel are very unstable, and accurate detection results cannot be obtained based on the gray and RGB values of the pixels, that is, the detection is simply impossible achieve. Second, moire cannot be eliminated. Moiré is the high-frequency interference of the light-sensitive elements on the device, which will cause the picture to appear colored high-frequency stripes. Because moiré is irregular, there is no obvious shape rule, so filtering and other methods cannot be used in image processing to denoise, which seriously affects the detection process.

In order to solve the above problems, we introduced a bi-telecentric lens into the screen detection system, and the situation immediately changed. Let's take a look at two screen pictures obtained with a BTOS telecentric lens and an area scan camera. Due to the image quality loss caused by the presentation method, it does not look as high as the actual image quality, but the contrast between these images and ordinary lens images is obvious Amazing enough.

Phone screen detection


The picture above shows a 4.0-inch smartphone screen shot with the MV-EM200M (200W CCD chip monochrome Gigabit network camera) + BTOS telecentric lens FML05X110C (0.5x magnification, 110mm working distance).

Phone screen detection

The picture above shows the MV-EM510C (500W CCD chip color Gigabit network camera) + BTOS dual telecentric lens BT-2364 shooting iphone6 mobile phone screen.

   In addition, we also tested the use of high-resolution line-array cameras, 2900W high-resolution area-array cameras and other large-format lenses (such as F-192 lenses) to shoot mobile phone screens. , And found the balance between "big" and "small" problems, and solved the problem of mobile phone screen detection. At present, Beijing Branch has successfully applied this solution to the project solutions of well-known smart phone brands such as Apple, Samsung mobile phones, Huawei and Motorola.

Obviously, with the popularity of smart phones, the application prospects of this technology are limitless.