Compute average - sequence of frames

Through this option DigImage uses the ALU to produce a weighted average over a specified number of frames for a sequence of buffers. The sequence is defined by offset times and is placed in the specified buffers. The averaging procedure is add the contents of the buffer with the newly digitized image and divide by two. This is repeated until the desired number of video frames has been processed. If the average is to be performed over M frames, then the weightings for each are given by

           Frame           Weighting
           1               1/(2**(M-1))
           2               1/(2**(M-2))
           ...             ...
           M-1             1/4
           M               1/2

Acquire which buffer ?

The user specifies which buffer(s) are to be filled with the average images. Any valid buffer may be used, remembering that buffers in extended memory will be acquired first to buffer 0 and then copied to extended memory.

At what time ?

The time offset at which each buffer is to be acquired must be specified. These time offsets must be specified in ascending order as DigImage does not control the VTR for this facility. The normal time format minutes:seconds is used (see the general help given by <shift><f1> for more details).

Another buffer ?

If another buffer in the sequence is required, then <Y> should be used. If all the buffers required have been specified, then <N> will let DigImage proceed. Up to 32 buffers may be specified in the sequence. Note DigImage does not check to see if a given buffer is specified more than once.

Average over how many frames ?

This specifies the number of frames over which the average is to be computed. A true average is produced only if averaging over two frames. If more than two frames are specified, then they are weighted in favour of the later frames in the manner indicated above.

Base name of file to be saved (no extension). No name => do not save

As an option DigImage can be forced to save all the buffers acquired to a sequence of files if a file name is given (if no name given, then the buffers will not be saved to files). The file names have the form File_Name.001 for buffer 1, File_Name.002 for buffer 2 and so on. The files are in a binary form without any form of encoding or compression. The first two bytes specify the number of rows, while the third and fourth bytes specify the number of columns. The remainder of the file is a byte stream giving the intensity of each pixel and is ordered by column from the top left of the buffer.

Press any key to start

The acquisition process and delay clock are started by pressing any key. Once all the buffers have been acquired, their contents will be written to the specified files (if this was requested) before returning control to the Grab & Display submenu.

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DigImage User Documentation

Stuart Dalziel, last page update: 19 February 1996