This submenu allows full control of a Panasonic AG-7350 Super VHS video recorder by the DigImage system.
To utilise the ability of DigImage to control the Panasonic AG-7350 Super VHS VTR it is necessary to first connect the computer and VTR together. Details of this process are given in the DigImage installation guide.
Each image captured or processed by DigImage is initially in an interlaced format consisting of two video 'fields'. The first to be transmitted or displayed is the even field which contains the even numbered video lines. The second is the odd field containing the odd numbered lines. Each field takes 1/50s (PAL) or 1/60s (NTSC) to be transmitted or displayed, a complete video frame requiring 1/25s (PAL) or 1/30s (NTSC). DigImage is able to control the VTR to locate an exact frame (in 'pause' mode the SVHS VTR displays only either the even or the odd field; cheap domestic machines generally display both fields), even though most processing is of complete frames and acquisition is always aligned to the even fields. Thus when specifying times, the resolution with which the VTR may be positioned is 0.04s (PAL) or 0.033..s (NTSC).
The distinction between the field rate (1/50s or 1/60s) and the frame rate (1/25s or 1/30s) is important. DigImage generally requires input in terms of fields rather than frames, rounding down to the nearest even field when frame aligned locations are required.
NOTE: The display at the top of the screen gives the current position and state of the VTR. The information on this panel is accurate when the VTR is operated from the computer keyboard. However, if the VTR is operated directly, the limited band width of the serial interface means that DigImage is unable to follow all the changes to the video status and so may loose track of the VTR. Direct manual operation of the VTR from outside this menu will cause DigImage to loose track of the VTR as it is normally unable to tell which direction the tape is moving.
0 Stop video tape - positioning not accurate after this operation has been performed. The errors may be up to 2s.
Use Pause (1) to stop searching. The search speed is set by option 7.
4 Rewind tape - positioning not accurate after this operation has been performed. The errors may be up to 2s.
Equivalent to pressing the PLAY button on the VTR.
6 Fast forward tape - positioning not accurate after this operation has been performed. The errors may be up to 2s.
A value of 1 gives 1/25 normal, up to 8 giving 9x normal.
The search speed is set by option 7.
This option resets the DigImage time and field counter, and the VTR's internal timer, to zero. The 'J' and 'K' jump options use this position as their zero.
The format of the delay time is the normal DigImage minutes:seconds.
Note that the positioning using this option is not able to yield single field accuracy. If greater accuracy is required, utilise the 'O' transition point option. See the VTR users manual for more details on the linear time code.
Images may be grabbed at either a constant time spacing or at specific times. Note that if the specified times are too close for capture 'on the fly', then the tape will be rewound between acquisitions. Further, if the times are more than 20s apart, then the fast search mode will be used to cover the intervening time. The specified times need not be in chronological order. See the help facility within the submenu for more details.
I Initialise VTR; this operation forces DigImage to reinitialise the communications with the VTR. Generally DigImage will perform this initialisation implicitly when needed, but in some circumstances it may be necessary to force the initialisation manually. Note that it is not necessary to reinitialise the VTR (other than through the implicit mechanism) when changing from one DigImage module to another.
The VTR is repositioned so that the DigImage timer takes the specified time value - this is not necessarily equal to the time shown on the VTR's own clock. The DigImage t=0 point is set by the 'C' reset option.
This option provides a convenient way of automatically positioning the VTR at an exact point on the tape. The point is encoded by recording a specific intensity transition (eg. the flash of an LED) at a known point in the image. Executing this option requires the position of the transition and details of the transition (threshold and up/down direction) to be specified. DigImage then plays the video tape until it locates the transition. It records its position and then repositions the tape so that it is at the exact time of the transition. Note that the video tape must be positioned at least one second before the transition is expected.
This option allows a series of buffers to be recorded onto the video tape. The duration of the recording for each buffer may be as little as one complete frame (two fields), thus allowing either time-lapse operation, or the creation of a real-time film of data which requires much longer times to process.
This option allows the video tape to be moved forward or backward by an exact time period. If a negative time is specified, the tape will first be wound back past the required point and then advanced to the required point.
Unfortunately the mechanics of the VTR are not sufficiently reliable to be trusted completely with the timing and positioning of the video tape. Occasionally when changing direction, the VTR may loose a complete frame. While this may be acceptable for most applications of the VTR, it is not acceptable when a time series must be reconstructed exactly in an expanded time frame. This is particularly true with particle tracking. This submenu provides the tools required to encode a signal on one of the audio channels which may then be used as a consistency check, correcting any errors in the VTR's own timing before they have an effect on the remainder of the image processing.
This option allows a command to be sent directly to the VTR using the VTR's own communications protocol.
Q Return to previous menu
W Return to previous menu, pausing the VTR first
This option is identical to Q except that the DigImage routines keeping track of the VTR are disabled. Unless the routines are disabled, it is not possible to use the mouse in the cursor and windows submenus.