www.qimaging.com
©2017 QImaging. All rights reserved. 58-608-007 REV A00
14
RETIGA ELECTRO
™
USER MANUAL
CHAPTER 4
Intelligent Quantification
Embedded Image Processing Algorithms
The Retiga ELECTRO camera includes user controllable features designed to enhance camera performance and
image quality.
Defective Pixel Correction
QImaging only uses sensor manufacturers with the highest
grade CCD sensors in your Retiga ELECTRO camera. However,
manufacturer’s specifications do not always meet customer
needs for defect free imaging. This is particularly true for
“hot” pixels – pixels that generate dark current at a far higher
rate than average. The converse is also true, e.g. certain pixels
response to light is far lower than average, known as “dark
pixels”. In both cases, suitable threshold can be determined
for defective pixels, and their locations stored in the camera
during manufacture. When Defective Pixel Correction is
enabled, the signal in each defect location is replaced by the
average of the pixel immediately preceding and following the
defect. The Retiga ELECTRO camera can store up to 2048
defects locations.
The factory default method for determining defective “hot”
pixels is to take a pair of 10 minute dark images. After
removing the bias offset, the 1800 “hottest” pixels are
selected as potential defects. A suitable floor is chosen so
that the algorithm does not accidentally catch the tail of the
normal dark current noise distribution. If the same location is
defective in both dark images, its location is programmed into
the camera as a defect.
To determine defective dark pixels, the camera is exposed to
uniform light, filling the pixels to 50% saturation. A median
filter is applied, and the original image is subtracted from the filtered image. Any pixels that have a signal level
of 40% or more of saturation, are deemed defective. Up to 200 dark pixels are stored for correction using this
method.
Defective Pixel Correction: OFF
Defective Pixel Correction: ON