JAI TM-770, User Manual

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TM-77X Series
38 Functional Options
Figure 35. ALC Advanced Set
•
ALC Window
These parameters define the rectangular Region of Interest (ROI) that will be used to calculate the ALC
exposure level. The user defines the upper left and bottom right corner of the ROI using X & Y coordinates.
The ROI can target the center of the image, or can be set to avoid a certain portion of the image so that its
light value will not affect the ALC function. A window display can be turned on to help the user identify his
ROI, but it should be always set to off during normal operation. The normal default of the ALC window is 90% of
the full frame image.
•
ALC Mode
This allows the user to select the type of algorithm for the ALC function.
Average: The ALC level is based on the calculated average value of the scene.
Peak: The ALC level is based on the calculated peak value of the scene.
Log-Average: The ALC level is based on the calculated average value of the scene, but using a log scale.
• Bright Speed
This selection sets a time value to wait a pre-selected time before the ALC will adjust when the scene is
changing from dark-to-bright. For example, if the average scene level is 50 and it immediately changes to 100,
the camera will verify that the scene has stayed at 100 for the pre-selected time before it will adjust the ALC.
•
Dark Speed
This selection sets a time value to wait a pre-selected time before the ALC will adjust when the scene is
changing from bright-to-dark. For example, if the average scene level is 100 and it immediately changes to 50,
the camera will verify that the scene has stayed at 50 for the pre-selected time before it will adjust the ALC.
•
Weighted Log-Average
This selection adjusts the log curve of the log average algorithm.
•
Impulse Filter
This selection sets a time value to wait a pre-selected time before the ALC will adjust when the scene is
changing. It acts like a hysteresis loop for the system.
•
Electronic Shutter
Setting the ALC Mode to “automatic” in the main control window causes the camera to begin working to
maintain the proper exposure, based on the settings in the ALC Level and AGC Max Gain boxes. When the
Electronic Shutter box is also checked, the Automatic Exposure Control (AEC) function of the ALC mode is
enabled, causing the electronic shutter to work together with auto gain to achieve the optimum ALC level. If
this box is unchecked, only auto gain is used, which may be insufficient to achieve the desired ALC level. This
configuration (ALC on, Electronic Shutter off) is normally used only when an auto-iris lens is connected to the
camera. This allows auto gain and auto iris to control the exposure, while eliminating the chance of any
conflicts between the auto shutter and auto iris actions.