Appendix: Special features for Scion LG-3

This paragraph assume that the reader has read through the "Imaging" part of the TI workbench manual.

Video frame grabbers including Scion LG-3 convert video image frames which are updated 30 times per second. That is, the unit of exposure time is fixed to 1/30 sec and binning operation is not available. These features are different from those of digital CCD cameras: flexible exposure time and variable binning factors. To adapt these characterisics of the frame grabber to the framework of TI Workbench, the parameters of exposure time and binning factors are used differently. These differences and others are described below.

Exposure time:

33 msec is the minimum unit. If exposure time is set to 33 msec, just one video frame image is stored as an 8-bit depth image. If exposure time is multiple of 33 msec (user can not set exposure time other than multiple of 33 msec), image pixels are added for the number of frames. In this case, bit-depth of pixels are expanded to16 bit (unsigned) to avoid data overflow. So the image bit-depth is different between 33 msec exposre and longer exposures. Up to 256 frames (exposure time 7.5 sec), user do not have to worry about data overflow. An alternative way may be averaging the frames instead of summing. I did not take this way because storing 8-bit averaged image could lose a subtle changes. This sum operation is performed digitally AFTER A/D conversion of each video frame, which is different from "analog summention" perfomed on digital CCD chips. The former, "digital summention" is theoretically worse in S/N than the analog summention due to the accumuration of digitizing noise.

Binning factor:

In digital CCD cameras, analog pixel data are added horizontally and/or vertically before A/D conversion. This is called "binning" operation which increases sensitivity and frame rate, and, at the same time, decreases resolution of the image. Frame grabbers have no "analog binning" capability. In TI Workbench, pixel values are added hirizontally and/or vertically AFTER A/D conversion. Once the binning factore is set other than 1x1, bit-depth of the image is expanded to 16 bit due to the same reason explained in the above paragraph. In case for very dimm and noisy situation, this "digital binning" would be a similar effect as spacial filtering. However, the resolution is decreased.

Continuity:

In most of frame-shift type or inter-line type CCD cameras, continuous mode of sequential recording or focusing mode guarantee "continuous" data acquisition. The focusing mode and continuous mode of sequential recording of frame grabbers do not guarantee "continuous" acquisition. Host computer (Macintosh) must catch up every frame update (1/30 sec) to ensure continuous image frames for frame grabbers, and this was not available even for the simplest "33 msec exposure, 1x1 binning" mode (in case for beige Macintosh G3 233 MHz). However, the lapse time stamped to each image frame in sequential recording mode is accurate. So that, the time course plot is also accurate (even after sent to Igor). User need to aware that the continuous mode does not necessarily taking "continuous" image frames or even taking constant interval image frames.

Key operations in focusing mode: (refer to here)

up and down arrow keys to change brightness, and left and right keys for contrast.

TTL output to drive shutter:

TTL output from LG-3 can be used to control TTL-controlable shutter devices. Refer to the wiring section for connection with a Uniblitz shutter.