Spectral Instruments Series 800, User Manual, Page: 58 / 70

Spectral Instruments
Pt # 2500- 58
Appendix A
CCD Readout Format
A refresher on row/column terminology. Figure A1., below, shows a single port readout
image. The physical orientation on the page matches the way that SI-Image shows it on
the screen of your computer. Your software may present the image in a different
orientation. The readout proceeds along rows moving from column 0 to column 1 to
column 2 … until column n-1 is read out from row 0. The next row is shifted into the
serial register and columns 0 through n-1 are read out. Columns are the fast-moving
subscript in a two dimensional notation, rows are the slow-moving subscript. The fourth
pixel read from a CCD sensor has the imaging
coordinates of row 0, column 3.
Figure A1. illustrates various components of an image obtained from a CCD with
overscan applied to the readout format. Not all CCDs will look this way - it depends
upon the way the CCD mask set is designed.
Table A1, below, compiles the various image components for several different CCDs
read out with overscan.
To make overscan work the following two steps are required:
1:
Set the parallel readout dimension to be larger than the active imaging pixels -
how large depends upon how much you need to see in the overscan image. Table A1
includes a recommended format for each CCD.
2:
Set the normal pre-scan and post-scan pixel count to 0. These are parameters
that are read into the DSP as readout parameters.
The following notes are possibly useful - going down the letters/numbers in sequence:
A
This sets the total number of readout pixels expected in the parallel direction.
There is not as much interesting information in parallel overscan as there is in serial
overscan but some things do show up right at the end of the active area so read some
extra parallel pixels. Parallel post extension shows the dark signal quite well.
A1
Some CCD manufacturers separate the serial register from the parallel register by
masked pixels.
A2
These are the imaging rows on the sensor.