Information about the resolution of the night vision camera

Resolution is an important indicator of night vision cameras and many optical imaging systems, which affects the ability of optical instruments to identify and observe. The night vision camera needs to be tested for its resolution before leaving the factory. At the same time, long-term use will also reduce the resolution, so the resolution needs to be checked regularly. So what is the relevant information about the resolution of the night vision camera? Let's take a look at it next.

Here is the content list:

• Detection principle

• Measures to Improve Positioning Accuracy

Detection principle

The basic principle of automatic resolution detection of night vision cameras is: firstly, locate the resolution pattern, then judge whether the resolution pattern is distinguishable according to the objective criterion of the resolution, and determine the resolution of the instrument according to the judgment result. Resolution auto-detection is performed as follows:

First, a camera is used to capture an image of a special resolution target plate, and the image is preprocessed. Then, the transformation algorithm is used to detect the positioning lines in the image. According to the positions of the four positioning lines, the position of the center of the resolution pattern in the whole image, the size of the pattern, and the inclination can be obtained. A resolution pattern consisting of stripes with equal spacing and the same direction is extracted, the contrast of each pattern is calculated, and whether the area is distinguishable is judged according to the size of the contrast. Contrast is calculated starting from the pattern with the widest line and working downward until it reaches an indistinguishable pattern. For the left and right resolution patterns in the same group, the one with low contrast is used as the contrast of the group of patterns. Take the number corresponding to the previous set of patterns of the indistinguishable pattern as the resolution of the night vision device under inspection. If the first group of resolution patterns is unqualified, it is determined that the resolution of the night vision device is lower than the corresponding value of this group; if the last group of resolution patterns is still distinguishable, it is determined that the resolution is higher than the corresponding value of this group. To achieve the purpose of automatic detection, it is necessary to study the objective criterion of night vision camera resolution and the method to improve the positioning accuracy.

Measures to Improve Positioning Accuracy

For the image of the night vision camera resolution target board, the pixels on the image can be divided into three categories: pixels in the resolution pattern area, pixels in the positioning line, and pixels in the noise. For noise pixels, it can be removed by opening operation; for pixels in the resolution pattern area, to achieve a good removal effect, you can first perform an opening operation on the entire image to remove the positioning line; then expand the image to appropriately expand the night vision camera resolution pattern area, and finally invert the image and the original image and perform AND operation with the source image to remove the resolution pattern area well. At this time, an image with only four positioning lines can be obtained, and high detection accuracy can be obtained by detecting this image. Since the night vision device belongs to an electronic imaging system, it will have a lot of random noise. Even when the human eye directly observes the image, it will find that there is noise and flickering in the image. This directly leads to the uneven brightness of the image, which will seriously affect the image positioning accuracy.

To reduce the influence of this factor, the method of taking the average of multiple images is adopted. After averaging, the noise in the image is significantly reduced, and the positioning line becomes very uniform, which is convenient for target segmentation and positioning. After several times of positioning the average results of different numbers of images, with the increase of the number of participating average images, the positioning accuracy shows a trend of improvement. When the number of averaged images reaches about 10, the positioning accuracy is basically below 2 pixels. Continuing to increase the number of images has little effect on its accuracy and will slow down the detection speed. Since the positioning accuracy is related to the number of images involved in averaging, the number of pixels occupied by each resolution pattern area is more than 90 × 90, and the pixels of the pattern boundary are removed in the final contrast calculation. (80% of the pixels are taken from the positioning center for contrast calculation), so a positioning error of 2 pixels will not affect the contrast calculation. Therefore, the average result of 10 images is taken in the program to achieve positioning. When the human eye directly observes the target through the night vision device, the image seen still has such electronic noise. To ensure that the detection result is consistent with the image observed by the human eye, the night vision camera resolution pattern area in a single image is still used. Perform resolution interpretation. To further reduce the detection error, in the contrast calculation of the night vision camera resolution pattern area, 80% of the pixels are taken from the positioning center for contrast calculation, excluding the influence of the pixels at the edge of the resolution pattern.

The above is the relevant information about the resolution of the night vision camera. If you are interested in the night vision camera, you can contact us.