In a relatively dark environment to take pictures, clear imaging conditions, is the CMOS chip to obtain enough light. And the methods to obtain enough light are.

Option 1. increase the intensity of light per unit of time (light source, large lens to collect light) 

Program 2. Increase the length of CMOS light-sensitive (extended exposure time) 

Option 3. increase the CMOS light-sensitive area (large target surface, large image elements) 

Trivia: On July 12, the webb telescope's first official photo of the stars with 12.5 hours of exposure time yielded sharper imaging than the Hubble telescope's 10-day exposure time.

The main reason for this is the webb telescope's greater ability to collect light - the lenses are larger.

The following limitations make TDI useful

* Since the photo frequency (line frequency) of the line camera has to be matched with the motion speed, the exposure time cannot be increased at will, and option 2 cannot be used 

* Certain scenes, and can not enhance the light (small space), program 1 can not be used

* with large target CMOS chip, the cost is too high, or the size is too large to install in the field, program 3 can not be used

The essence of TDI

Using different lines of the chip area, the same area of the object photographed, each line by the photon excitation of electrons, are superimposed on the next line, so that the next line indirectly 

obtained the "light" of the previous line, after repeated superposition, the last line of the image is "bright enough", enough clear. clear enough

TDI imaging effect: from the first line to the tenth line, the image gradually becomes brighter and clearer

TDI imaging effect: Case of photovoltaic industry