Xinsheng IntelligentCompany NewsBasic knowledge of machine vision inspection ~ camera

Is the CCD we often say is the camera?

First, is the camera a CCD?

Usually, we call all cameras CCD, and CCD has become synonymous with cameras. What is using what is called CCD is most likely CMOS. In fact, both CCD and CMOS are called photosensitive elements, which are semiconductor elements that convert optical images into electronic signals. They both use photodiodes to detect light, but differ in how the signal is read and fabricated. The difference between the two is as follows:

Second, pixels.

A pixel is the smallest unit of an image. An image in a computer is represented by a collection of regularly arranged points called pixels (or PIXEL). Each point has color information such as hue and gradation, so that a color image can be depicted.

▼Example: “Resolution: 1280×1024” will be displayed on the LCD monitor. This means that the number of pixels in the horizontal direction is 1280 and the number of pixels in the vertical direction is 1024. The total number of pixels of such a display is 1280×1024=1,310,720. Since the higher the number of pixels, the more detailed the image can be expressed, so it can also be said that "the definition is higher".

Third, the pixel diameter.

The so-called pixel diameter refers to the size of each CCD element, usually using μm as the unit. Strictly speaking, this size includes the light-receiving element and the signal transmission path. (= pixel pitch, that is, the distance from the center of a pixel to the center of an adjacent pixel.). That is, the pixel diameter is the same value as the pixel pitch. If the pixel diameter is smaller, the image will be delineated with smaller pixels, so a finer image can be obtained. The size of the light-receiving portion of the CCD element can be obtained from the pixel diameter and the number of effective pixels.

Suppose the conditions of a CCD element are as follows:

· Effective pixel count…768 × 484

Pixel diameter...8.4 μm × 9.8 μm

Then the size of the light-receiving part is

· Horizontal 768 × 8.4 μm = 6.4512 mm

·Vertical 484 × 9.8 μm = 4.7432 mm

Fourth, the size of the CCD.

▼The size of the CCD sensor is generally divided into two ways: expressed in inches and expressed in APS-C size. When expressed in inches, the size is not the actual size of the shot, but the diagonal length of the camera tube. For example, a 1/2-inch CCD means "having a shooting range equivalent to a 1/2-inch camera tube". Why is this calculated? This is because the original purpose of manufacturing CCD is to replace the camera tube of TV recorder. At the time, there was a strong demand for continued use of optics such as lenses, and this strange specification was born. The dimensions of the main inch specifications are shown in the table below.

Fifth, the shutter speed.

Indicates the time for accumulating charge in the CCD or CMOS sensor. If the shutter speed is 1/250, the time to accumulate light is 1/250 second. The faster the shutter speed, the less the amount of light received by the element, and the lower the shutter speed, the more the amount of light received by the element. It can also be said that the shutter speed will play a role in adjusting the amount of light. The following relationship exists between the shutter speed and the amount of light received (correctly, it should be called the amount of accumulated charge).

Example: If the shutter speed benchmark is 1/1000 of a second, then

・When the shutter speed is changed to 1/500 second, the amount of light received is doubled.

・When the shutter speed becomes 1/2000 second, the amount of light received becomes 1/2.

Sixth, gain.

The so-called gain refers to the process of electronically amplifying the image signal. The CCD used for image processing is equipped with a function that can make it look bright by amplifying the signal when shooting in a dark place. In addition, it is equipped with a gain control function that automatically adjusts according to the brightness of the subject.

▼For example, when shooting at a shutter speed of 1/10000, the comparison before and after increasing the gain is as follows.

Seven, 1D camera (line scan camera)

▼All the CCDs whose pixels are arranged in a matrix we mentioned earlier are area scan cameras that cover 99% of applications in visual inspection.

▼The line scan camera currently has a maximum of 16K pixels in the length direction, but only one pixel in the width direction. Get images by moving.

▼ Compared with flat cameras, the main advantages of line scan cameras are reflected in two aspects.

1. Higher resolution.

2. The image quality is higher. (reflective products, columnar products)

▼In addition, line scan cameras are also very convenient for continuous monitoring of cloth-mounted products.

However, compared with area scan cameras, line scan cameras cost more and are more difficult to install. At the same time, it is necessary to cooperate with the encoder to trigger the camera, and it is necessary to have Know-how in this regard.

▼ Finally, line scan cameras require the use of special lenses and light sources.

Eight, 3D cameras.

At present, 3D cameras on the market are mainly divided into three types according to different imaging principles.

1. Laser

2. Binocular Vision

3, raster class (Strip Pattern)

1. Laser.

▼Mainly through the principle of triangular reflection, the laser generator casts a laser beam on the surface of the object, and the reflected light is accepted by the CCD, and then modeled into a 3D image.

▼ Laser scanning imaging.

2. Binocular category. (Binocular Vision)

Binocular stereo vision refers to the use of two CCD cameras with the same performance and fixed position to obtain two images of the same scene, and to calculate the three-dimensional information of the scene through the two-dimensional images obtained by the two cameras. In principle, it is similar to human binocular vision. Building a complete binocular stereo vision system generally requires steps such as camera calibration, image matching, and depth calculation.

3, the raster class (Strip Pattern).

▼Currently KEYENCE has such mature products, the XR series. The advantage is that no moving mechanism is required, and high-precision imaging is performed at one time (please refer to the historical article).

▼Shooting renderings:

Nine, 2.5D camera.

▼ (For details, please refer to the previous historical article) By controlling the light source to illuminate from different angles, the shadow image generated by the image concave and convex information is obtained, and finally the image of the 3D information is synthesized and calculated (Note: The height "Z" direction cannot be quantitatively measured, so it is called 2.5D).