The Costella Gap Measurement

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On the right side of the Moorman photograph, Abraham Zapruder is seen standing on a pedestal filming the motorcade. Immediately to the left of the pedestal (Zapruder's right) is a window opening in the back wall of the pergola structure. In taking her famous photo, Mary Moorman happened to position her camera such that the window's bottom right corner almost exactly lines up with the top left corner of the pedestal upon which Zapruder stands. These two points describe a single and very precise line-of-sight (LOS).

White measured the height of this line-of-sight 24 inches southeast of the Elm Street curb. He said in MIDP that it was 44.5 inches above the turf. This is obviously too low for Moorman’s camera position as shown in the Zapruder film. Accordingly, White offered this much-too-low LOS as evidence that the Zapruder film had been altered, that Moorman had actually taken her photo from the street.

Since only the vertical dimension is relevant to White’s argument we can speak of just the window edge (meaning the bottom edge of the window) and the pedestal edge (meaning the top of the pedestal). White’s argument depends on these edges lining up. If they don’t, if there is a significant gap between the pedestal edge and the window edge, then Moorman’s camera was higher and White’s argument fails. This is precisely what critics of White’s claim pointed to. There was a significant gap, they said, between the window edge and the pedestal edge.... so much of a gap that the LOS in the Moorman photo really does match the Zapruder film.

Although White claimed that the edges are exactly aligned, this was clearly not correct. Dr. Costella, however, appeared to save White’s claim by offering a pixel analysis of the Moorman photo showing that the two edges are only slightly separated. By Dr. Costella’s calculations, the gap is only 0.55" at the pedestal and 2.2" at the camera. This measurement of the gap would increase the camera’s height above the ground by an insignificant amount. It would still be much lower that it appears in the Zapruder film.

Dr. Costella worked with a scanned copy of the Moorman Polaroid provided by Josiah Thompson. Dr. Costella rotated the image to bring a vertical edge of the pergola structure behind and to Zapruder's right "to as precise a vertical alignment as one is likely to get for this region of the polaroid. It is only when this is done that horizontal lines on the image correspond to horizontal lines in Dealey plaza." He also magnified the image 3 times larger to facilitate his measurements. Because Mary moved the camera during the exposure, the photo contains some motion blur. As described later, motion blur smears the edges, but with the appropriate calculations, one can locate the original edges within the blur.

That is what Dr. Costella did. His analysis concluded the window edge is only 2.9 pixels higher than the pedestal edge. On the Moorman photo, Dr. Costella also calculated that 2.9 pixels equal 0.55 inches at the pedestal and 2.2 inches at the camera position across Elm Street.

Here is a copy of what Dr. Costella has called his "zoomed" version of the Thompson scan, with his edge positions marked by yellow lines. [These lines were drawn by Joe Durnavich from data sets posted by Dr. Costella.]


Problems with the Costella gap measurement

We had a couple of concerns about Dr. Costella's measurements after an initial analysis of his data. His measurements for the window edge were generally reasonable, but his measurements for the pedestal produce an edge line that runs at an angle to the pedestal edge. Such an angle reduces the size of the calculated gap.

Dr. Costella had the same concerns about the angle of his edge line to the pedestal edge. He writes:

"At this point, I examined the top edge of the pedestal. The natural place to measure this, when one is considering the line of sight debate, is on the left side (as we look at it). However, there are two problems:

(i) The edge looks "soft" in this region.

(ii) The edge seems to slope uphill significantly, from left to right, whereas the actual top of the pedestal does not appear to show this property.

Both of these problems are, most likely, related."

The line-of-sight analysis takes advantage of the fact that the lower right window corner and the upper left pedestal corner are on almost the same line-of-sight from Moorman's camera position, greatly simplifying the analysis. But in the end, Dr. Costella had to ignore his measurements from the left portion of the pedestal edge because of a photographic defect in this area. Instead, he, in effect, treated the window edge and the pedestal edge as two parallel lines and positioned his pedestal edge line on measurements from just the right portion of the pedestal. His final gap size is the distance between these two parallel lines.

We suspected that Dr. Costella's results understates the true size of the gap. We thought it worthwhile to re-measure the gap taking into account the actual angles of the window and pedestal edges. Because of the effect the photographic defect over the left side of the pedestal had on Dr. Costella's results, we made an effort to work with images as close to the original as feasible.

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