MadSci Network: Engineering

Re: How does the time delay integration camera work?

Date: Sat Dec 30 08:57:55 2000
Posted By: Harry Adam, Research Associate, Research Division, Kodak Limited
Area of science: Engineering
ID: 977234027.Eg

You asked - How does the time delay integration camera work?
This is a technique, which makes use of modern charge-coupled devices 
(CCD’s) – particularly the area array types used in digital cameras. CCD’s 
are simply an array of light sensing elements, which generate electrical 
charge when exposed to light. The charge is read from each sensor at a 
frequency determined by the software and hardware (cpu) used and the 
information about exposure at each sensor is normally recorded as a 
digital value – or a set of digital values which includes information 
about brightness and possibly colour. In certain circumstances – e.g. 
where light levels are very low, or slow changes are taking place, 
repeated readouts provide more information than can be obtained by single 
exposures. By adding up all the separate values, (i.e. integration over 
time) it is possible to detect information which cannot ordinarily be 
seen, either because of very low light levels or because of very slow 
changes. In the latter sense, it is a bit like time-lapsed photography .

CCD’s can be linear arrays (as in scanners) or area arrays (as in 
cameras). Clearly an area array system is more powerful and can collect a 
lot more information in a given time than an area array, but the 
applications of TDI are usually more like scanning than single-image 

The dictionary definition of Time Delay and Integration is - A method of 
scanning in which a frame transfer device produces a continuous video 
image of a moving object by means of a stack of linear arrays aligned with 
and synchronized to the movement of the object to be imaged in such a way 
that, as the image moves from one line to the next, the stored charge 
moves along with it, providing higher resolution at lower light levels 
than is possible with a line-scan camera. 

I’ve found a reference on the web which may be helpful, containing as it 
does, both examples of application as well as a discussion of the 
fundamentals of TDI imaging.

Here it is:

There is also a lot of good information available about CCD’s and how they 
work – for instance, take a look at this tutorial:

There’s a nice pdf file you can download and print of this.

Good luck with your thesis!

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