How can I focus the SPOT RT camera quickly?

Technical Note: 135
Reads: 6815
Creation Date: 14/07/2000
Modification Date: 12/02/2004

Make sure that the SPOT Video and the Video Manager modules are installed in the Openlab Modules folder. Also ensure that the SpotCam.DLL is installed either in the Extensions folder or in the Openlab application folder. The SpotCam.DLL version tested was dated May 02 2000.

Using the Video Manager dialogue select the Image Type, brightfield, fluorescence or darkfield, as this ensures the appropriate calculation is used for the auto-exposure setting, and select the image capture depth.

From the Video Controls palette check the box for color mode or leave unchecked for monochrome. The image frame rate will be faster for monochrome mode, so if speed is important select this mode to focus and then revert to color mode for image capture.

Make sure that the RGB color slider is in the appropriate position for the mode selected. Note that Openlab does not recognise the actual position of the slider but errors are reported in the session log if you try to acquire an image with the slider in the wrong position. While RT Live Focus Mode is inactivated it is still possible to view a very slow Video Preview but if the slider position and palette mode do not match, the screen will display the word Openlab and a flashing cross through the camera. Simply move the slider or change the mode as appropriate until they match and wait, the image will be restored.

To implement the 'live' focus mode check RT Focus Mode box on the Video Manager pallete. The camera now changes mode, you may notice that the Video preview behaves erratically and the image may disappear or appear corrupted for a short time as the camera internally changes mode. Wait and it will return but remember it is a low quality mode. You may also notice that the ‘live’ image appears to be split in half with one side of the image a liitle brighter than the other. This is a feature of the way the SPOT RT camera displays images in real time as the camera uses two separate amplifiers to simultaneously read the two halves of the CCD chip. The ‘split’ real time image is not representative of the final captured image quality.

In RT focus mode the camera performs its own auto-exposure to allow for the real time imaging, thus any exposure times, or gain set for image capture are not honored in the live Video preview. Similarly binning will not visibly increase image brightness.

If you are using the camera in color mode, with dynamic samples you may see image ghosting as the sample moves during the sequential RGB image capture. This effect can be minimised by increasing the binning to 4. This does not increase the intensity of the image but it does increase the data rate such that the image is refreshed much faster and the color ghosting effect is minimised. Making the image document smaller does not improve the image frame rate to reduce the effect of ghosting.

When the sample is correctly positioned and in focus ,clicking on the image capture tool will capture an image with the settings in the Video Manager dialogue or palette that were set prior to switching to RT focus mode. This suggests two possible sequences for working with the RT Focus Mode. White balance and exposure can be set on one part of the specimen, then RT Focus Mode activated and images captured from many different positions (changing focus as necessary), all using the same initial settings. Alternatively, once the sample is positioned and focussed you mayswitch off the RT Focus Mode to check exposure and gain settings before capturing images.