Point Grey Flea3 USB 3.0 Technical Reference 3 General Camera Operation
Although it is possible to repeatedly transmit the same image, there is no way to access images that are older than the
last image transmitted.
Whether by enabling trigger or disabling isochronous data, switching out of a free running mode leaves the last image
transmitted in an undefined state.
The frame buffer is volatile memory that is erased after power cycling. To store images on the camera after power
cycling, use Non-Volatile Flash Memory on page 38. Accessing flash memory is significantly slower than accessing the
frame buffer, and storage is limited.
3.4.1 IMAGE_RETRANSMIT: 634h
This register provides an interface to the camera’s frame buffer functionality.
Transmitting buffered data is available when continuous shot is disabled. Either One shot or Multi shot can be used to
transmit buffered data when Transfer_Data_Select = 1. Multi shot is used for transmitting one or more (as specified by
Count_Number) buffered images. One shot is used for retransmission of the last image from the retransmit buffer.
Image data is stored in a circular image buffer when Image_Buffer_Ctrl = 1. If the circular buffer overflows, the oldest
image in the buffer is overwritten.
Transmitted data is always stored in the retransmit buffer. If a last or previous image does not exist, (for example, an
image has not been acquired since a video format or mode change), the camera still transmits an image from the
retransmit buffer, but its contents are undefined.
The image buffer is initialized when Image_Buffer_ Ctr is written to ‘1’. Changing the video format, video mode,
image_size, or color_coding causes the image buffer to be initialized and Max_Num_Images to be updated.
Field Bit Description
Image_Buffer_Ctrl [0]
Image Buffer On/Off Control
0: OFF, 1: ON
Transfer_Data_Select [1]
Transfer data path
0: Live data, 1: Buffered image data
Ignored if ISO_EN=1
[2-7] Reserved
Max_Num_Images [8-19]
Maximum number of images that can be stored in the current video format. Must
be greater than zero.
This field is read only.
Number_of_Images [20-31]
The number of images currently in buffer.
This field is read only.
Format:
3.4.2 Example: Retransmitting in Image External Mode Using Registers
There are occasions where it might be beneficial to retransmit an image when in an external trigger mode. Having
configured the camera to be running in an external trigger mode, the user can cause the camera to retransmit an
image by doing the following:
Revised 9/27/2012
Copyright ©2011-2012 Point Grey Research Inc.
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