Barry Salt: Requiring Split-Second Timing

When I tried out the Cinemetrics software on the first 12 minutes of The World of Suzie Wong, I straightaway put in an extra couple of key presses through trigger-happiness. But more importantly, I was aware that on a couple of occasions my response was delayed, because my attention had been momentarily seized by what was going on across the cut, from the point of view of film editing technique.

This raises an important point about the use of the Cinemetrics recording software. It is founded on the assumption that each user’s reaction time is constant, to within 0.1 second.

Reaction time has been one of the most extensively studied variables in experimental psychology since it was introduced in 1862 by Wundt. The simplest form of test is for the subject to be presented with a series of flashes of light at random intervals, to which he is asked to respond by pressing a button as quickly as possible. Vast numbers of experiments show that the mean value of reaction time

It does not matter for the purposes of Cinemetrics if your mean reaction time is longer or shorter than another person’s reaction time, but it does matter if it is not constant to within 0.1 second.

With this in mind I have checked the recorded Cinemetric results for three films against my frame-accurate measurements. The films analysed were la Signora senza camelie, posted by Yuri Tsivian, Verboten!, posted by John C., and Shadows, posted by Charley Leary. For the first of these I used a rather worn 16 mm. print, which may have some frames missing at the reel changes, and made the measurements on a

The comparison of the sets of results is not as simple as it might seem at first glance, for a number of reasons, First of all, not everyone starts and ends their counts at the same place. My standard procedure for the last thirty years has always been to start the count immediately after the last credit in the main title sequence (usually the director credit), and stop immediately at the

It is not of course possible to determine the mean reaction time for each recorder from their results, but one can get the errors they made in the measurement of the shot lengths.

To give a flavour of this, I quote the differences between my results and those of Yuri Tsivian for the whole 102 shots under consideration in la Signora senza camelie:

0 0 0.1 0.1 0 0.8 1.2 -0.2 -1.7 1.7 0.4 -0 0.2 -0.2 0.2 0.2 -0.1 0 -0.2 0.4 -0.1 0.1 -0.4 0.4 0 -0.7 0.6 0 0 0.2 0.3 0.2 1.7 0.1 0 0.2 -0.3 0.3 -.10 0.2 0 0.4 -0.2 0.2 0 0 0 0 -0.7 -0.4 -0.2 0.1 -0.1 -0.2 0.4 0 0 -0.9 0.6 0 0 0 -0.2 0.6 0 -0.2 1.3 0.4 -0.2 0 -0.1 0 -0.1 -0.2

To get a better sense of this it is best to show the distribution of these errors in a graph:

Figure 1

One would expect the measurement errors to be normally distributed, and indeed the above shows a very rough approximation to a Normal (or Gaussian) distribution. If there were no errors greater than 0.1 second, then there would be just be a single very tall bar straddling the zero point in the above graph, and nothing else. An important variable describing error distributions are their Standard Deviations, which is 0.70 in

The other two films studied have a larger, and more usual, number of shots in them, so I will just illustrate the error graphs for them, starting with Verboten!

Figure 2

The Standard Deviation for the errors about the correct values of the shots lengths in this case is 1.06, which is larger than the previous example.

For Shadows, the results are a lot better.

Figure 3

In this case the Standard Deviation is 0.54, and the error distribution is much more like a Normal distribution.

The general indications are that as long as the Cinemetrics shot length recording system is used, as it is at the moment, for getting general indications of cutting rates throughout a movie, then it is satisfactory. But even with the most accurate Cinemetrics recording so far found by me, which is for Shadows, the errors are still of a size which could make the results noticeably unreliable if they occurred

The alternative method that I have used to get the frame-accurate results for this study does take longer, but in the case of Verboten! and Shadows, it only took me about three hours to mark the cuts on each film.

I think it would be very helpful if in future, as already has been mooted, the people using Cinemetrics would note whether the source they have used is PAL or NTSC, or if the Cinemetrics recording was done during the projection of an actual film. And an indication of the start and end points of the Cinemetrics recording would be helpful as well.

Barry Salt,

January 2008