Time Series of Window Means

Time series may be generated, with a sampling rate of even multiples of the field rate (ie. multiples of the frame rate). The mean intensity of one or more windows may be sampled. The maximum number and size of the windows depends on the speed of the PC - if too many are specified, or the windows are too large, then an error message is generated. A maximum of 256K individual readings may be gathered. The time series are optionally available in an INTEGER*1 binary file (which also stores the number of points and the number of samples) and/or displayed on a buffer. The option [P Time series of single point(s)] performs a similar process, but sampling the intensity of a list of individual pixels rather than the mean intensities within a list of windows.

Define sampling windows using which buffer ?

The locations at which the time-series of mean intensities is given is specified interactively using the windows submenu within DigImage. This entry may be used to specify a buffer containing a suitable image to aid the specification process.

Window Selection: Locate window number ##

The window submenu is used to specify the location of each of the windows for which the mean intensity is to be sampled. Control of the window

    specification is in the normal manner with further information available

from [H Help] within the submenu.

Another window ?

DigImage is capable of simultaneously sampling a number of windows, the precise number depending on the size of the windows. The larger the windows, the smaller the number which may be sampled. If a further window is to be added to the sample list, then a response of yes (<Y>) will return to the window submenu. Once all the windows have been specified, <N> will continue with the time series process. Note that if more windows than DigImage is able to sample within one frame period (1/25s or 1/30s) are specified, then an error message will be generated.

Number of samples ?

The number of samples required should be specified. The maximum number depends on the number of windows at which samples are being taken. If the image is being sampled in n windows, then up to INT(262144/n) samples may be taken in each window. Note that the sampling process may be terminated early by pressing <Q> once it has started.

Sample spacing (even number of video fields) ?

This entry specifies how frequently the windows are to be sampled. All the windows are sampled for the same video frame (two video fields) within 1/25s or 1/30s (PAL or NTSC, respectively), but need not be sampled for every frame. A spacing of two video fields means that every video frame will be sampled, four fields for every second frame and so on. If the sampling is not completed within the required time, an error message will be generated.

Manual or Computer control of VTR ?

The VTR may be controlled either manually (<M>), or automatically by the computer (<C>). The latter choice will be required for operation from a command file.

{If computer control}

Start time (offset) ?

The time series will be started at a specified time relative to the current point. The time offset should be specified using the normal DigImage time format of minutes:seconds (see the <shift><f1> general help for more details). A negative time represents offsets to earlier times on the tape.

{If computer control}

On completion Reposition video tape or Leave ?

The answer to this question dictates how the VTR is handled at the end of the time series. If <R> is selected, then the video tape is repositioned to its initial position, while <L> causes the tape to be left where it finished. Once this choice has been made, the computer will take over control of the VTR and process the time series.

Display samples using what buffer (-1 to suppress) ?

As an option, the time series may be written to a frame buffer to create a visual display of the data. This entry specifies the buffer to which the data is written. Note that the data will not be written to the buffer until the time series acquisition is complete. A value of -1 suppresses this display.

{If manual control}

Press any key to start acquisition (<escape> to abort)

Pressing any key will start the acquisition of the time series.

Collecting ## samples for ## points Press <Q> to quit early...

Once the time series sampling has started, it may be terminated early by pressing <Q> or <escape>. The difference lies in that <Q> will still allow the display of the samples and optional saving to a file, while <escape> simply returns control to the previous menu.

Name of file to save data to (blank to suppress) ?

As an option, the time series data may be written to a binary file. The name of the file is specified by this entry; the data is not saved if no file name is given.

Use Formatted or Binary file ?

This entry specifies whether the data is to be written to a formatted or a binary file.

If a formatted file is created, it contains columns for the point number, an index, the time and the intensity. This format may be readily plotted using DigiPlot.

The format of this binary file is as follows:

           nSamples, nPoints,
           iValue(0,0), iValue(1,0), ...
           ... iValue(iPoint,iSample) ...
           ... iValue(nPoints-1,nSamples-1)

where nSamples is INTEGER*4, nPoints is INTEGER*2 and each iValue is unsigned INTEGER*1. The location of each of the points is as specified earlier through the cursor.

Errors, Warnings and Messages

Error Message:
Unable to open output data file

DigImage was unable to open the specified output data file. This may be due to an invalid filename or path, or insufficient disk space.

Error Message: Unable to sample required list

There are either too many windows, or the windows are too large for all the mean intensities to be evaluated within the required time period.

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DigImage User Documentation

Stuart Dalziel, last page update: 19 February 1996