Knowledge of Visual Inspection: Camera: High resolution or low resolution? (2)
It is recommended to choose a camera with the appropriate number of pixels for each specific use.
In "(1) High Pixels or Low Pixels," we discussed the advantages of high-pixel cameras in capturing details clearly. Here, I would like to write about the advantages of low-pixel cameras. The advantage of low-pixel cameras can be summed up in one phrase: "processing is faster." There are two reasons for the faster processing. 1. There are fewer pixels to handle as image data. 2. The exposure time can be shorter, resulting in less time needed for shooting. I believe there is no room for doubt regarding point 1. So, why can the exposure time be shorter in point 2? Let me explain. The size of the camera sensor (the square light-receiving part shown in the initial photo) varies, but in industrial cameras, sizes around 5mm square to 7mm square are common (1/3 inch to 1/2 inch). However, as mentioned in "High Pixels or Low Pixels (1)," the variation in pixel counts ranges from about 300,000 pixels to around 14 million pixels. At this time, what differences exist in the size of the pixels?
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Assuming there are two cameras with the same sensor size (6mm wide), one with 300,000 pixels (640 pixels wide) and the other with 14 million pixels (4600 pixels wide). In this case, the pixel size of the 300,000-pixel camera is 6mm/640 = 9.4um/pixel. Similarly, the pixel size of the 14 million-pixel camera is 6mm/4600 = 1.3um/pixel. The exposure time is inversely proportional to the light energy received by the sensor's pixels. Additionally, the light energy received by a pixel is proportional to the pixel's "area," so when comparing the two cameras mentioned earlier, there is a significant difference of 9.4^2 : 1.3^2 = 88 : 2 (in reality, the 300,000-pixel camera typically uses a 1/3 inch sensor, while the 14 million-pixel camera typically uses a 1/2 inch sensor, so the difference is slightly smaller). If we represent this schematically, it would look like the diagrams below. (Figures 2, 3, and 4) Thus, from both the data size and exposure time perspectives, it can be said that low-pixel cameras are more capable of real-time performance. When selecting a camera, it is recommended to choose a camera with an appropriate number of pixels according to the specific application.
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