🚀 go-pugleaf

In article <jecome01.715798061@starbase.spd.louisville.edu>, jecome01@rigel.spd.louisville.edu (Eric Comer) writes:
    	if the lens caps is place on a ccd camera and an image is capture,
    	why aren't all of the pixel values 0 (black)?

Because of the "dark current": charge accumulates on a CCD due
to BOTH light falling on it (zero in your case), and due to thermal
effects. The dark current builds up over time, so you normally
want to keep exposure times short (if you can). If you cannot
(like in astronomy) you can instead reduce the dark current by
cooling the CCD array, charge build-up falls off exponentially
(roughly) with temperature.

Anyway, dark current is quite predictable at constant temperature,
so it can be predicted and subtracted out.

	when the image is
    	normalized it seems like there are faint light diagonal lines
    	throughtout the whole image.  the image acquired was a gray scale
    	image the min value was 0 and the max value was 6.  any ideas?
    
The CCD array is not perfect - meaning that the individual cells
have different response characteristic and different dark current.

When you have subtracted the dark current you also should
calibrate the image, accounting for each pixel's individual
response characteristic. If you use the CCD array as an ordinary
camera the calibration may not be necessary of course.

torbjorn.