6.0 FRAME-GRABBING The first step for analysis after filming is transferring the video image into the system for digitizing. Select Grab from the Main APAS Menu to enter the Frame-Grabbing Main Menu.
Frame-Grabbing provides a method of copying the image currently displayed on the video monitor and combining it with the image on the graphic display.
At the top center of the screen is the Image Capacity (images). This is an approximate number of images that the memory can store at this time. If this value is not large enough for the video images then "File Maintenance" must be performed before continuing. The following two lines contain information on the file. When a new file is being created this data will be filled in by the various sub-menus of this module.
The middle window contains the commands that are used to grab or review the images. Each will be explained in the following chapter.
6.1 FILENAME After the VCR is primed and images have been selected, select Filename from the Frame Grabbing Main Menu (Figure 6-1). A small screen will ask whether the file is New or Old. If Old is selected a list of grabbed files available on the current directory is displayed. These may be opened for viewing or editing if necessary. To abort the selection F10 is used to return to the Filename screen.
If New is selected the system asks for the filename that the images will be stored under, but before a file name is give the Compress function should be selected.
6.1.1 F1-Compression Upon pressing F1-Compression, a new screen, the Compression Menu (Figure 6-2), appears. Compression allows the image to be saved with the use of less memory, but at the cost of lower resolution. If the event being filmed doesn't require a detailed picture, then a higher resolution isn't necessary but if the requirement is for a detailed clear picture then the resolution should be at its peak. If the video tape recording is of a high quality, data compression should be used. Data compression produces smaller data files and allows the user to grab more frames. The amount of compression which should be chosen is a function of the quality of the video recording. The poorer the quality of the video recording the higher the resolution is needed thus the lower compression used. There are five choices listed in this screen.
Enter a Filename and press ENTER. The Main Frame Grabbing Menu (Figure 6-1) will reappear and the Filename will be displayed.
It is suggested if more than one camera is used that each of the filenames be either the name of the subject or the event, with a addition of the number of the camera or its position (right, left, side or front). This will help organize the analysis later when digitizing and transforming. For example:
6.2.1 Control Point Selection Select VCR to display the video image of the control points. These are either the cube, tripod or even points in the area, that will help determine the three-dimensional measurement of the field. Control points are discussed in more detail in Chapter 5. Filming and Appendix C, Sample Measurements and Control Points. Pressing F10 will return the screen to the Grab Menu (Figure 6-3).
Select Control from the Grab Menu. The computer will automatically grab and store the image.
6.2.2 Parameter Selection Select VCR again to position the video at the point that is to be the start of the digitizing sequence. Pressing F10 will return the screen to the Grab Menu (Figure 6-3). Select Parms. The Parameter Screen (Figure 6-4) lists the parameters the computer will use to store the images.
Enter each of the fields as follows:
When the Grab Menu reappears notice that the parameters in the upper screen are now displayed with the information entered.
6.2.3 VCR The VCR selection has already been covered in Section 6.5. No matter what menu, FrameGrabbing Main menu (Figure 6-1), Grab Menu (Figure 6-3) or the Review Control Screen, the VCR is accessed from, it will operate the same.
6.2.4 Data Selecting the Data function will grab the images to be stored into memory. If the Toggle_Confirm is "turned on" then each frame will have to be confirmed by pressing the ENTER key. If Toggle_Confirm is "off" then the computer will automatically grab and store the selected images.
6.2.5 Toggle_Confirm Selection Toggle_Confirm allows each frame to be viewed, then either skipped, selected or reselected, before the computer grabs and stores the image. The default setting is "On".
6.3 RESTORE Restores a frame from a video file. The desired frame may be entered or F1 and F2 may used to sequentially view the frames in forward and reverse directions. F3 allows the user to view data from the video tape, thus, for a comparison of the grabbed data with video taped data. F10 is used to finish the sequence.
6.4&bnsp; DELETE The delete function deletes any unwanted file from the current directory. This may be used to remove files if the Image Capacity does not have enough space to store the new file.
Selecting VCR from the main menu at this point will display the VCR Control Screen (Figure 6-5) which allows operation of the VCR from the computer screen using the mouse. When the screen appears the cursor will be flashing in the Play box. Clicking the ENTER button on the mouse will turn on the VCR and start playing the tape. The search button should then be "pressed". The current picture will freeze on the screen and the VCR will be in the Pause mode.
The control bar on the right side of the screen controls the speed of the picture on the VCR. The tape may be forwarded or reversed by placing the cursor above or below the STILL position and clicking the mouse. When the mouse is clicked and the tape is running the cursor will return to the STILL position, therefore, it is not necessary to move the mouse to stop the tape, only to press ENTER.
6.7.1 Enable Enable is selected to activate the Time_Code function. The current status of the Time_Code function is labeled in the upper right corner of the menu box. When the time codes are enabled, advance/reverse commands are controlled by reading information stored on the videotape. CTL30 indicates the VCR being used is capable of 30 Hz analysis while CTL60 indicates 60 Hz capabilities. No indicates the Time_Code function has been turned off.
6.7.2 Disable Disable is selected to turn the timecode function off. The current status of the Time_Code function is labeled in the upper right corner of the menu box. When the Time_Code function is "No", the software controls movement of the tape using frame advance/reverse commands. The tape can still be advanced and reversed, however, this method is more time consuming.
6.8 EXIT The exit command is selected to exit the Grab Module and return to the Main APAS/CES menu. When this option is selected, the Exit Confirmation Screen will appear (Figure 6-8).
6.8.1 Yes Yes is selected to exit the Grab Module and return to the Main APAS/CES menu.
No is selected when you wish to abort the exit command. You will return to the Main Grabbing menu.
A quick sequence of frame grabbing: