[After posting this article, Tom McAvoy was kind enough to respond, twice. His comments are included at the end, [and mine!] so please make sure you read the whole thing to get the full balance of opinion on the subject.]
In a recent paper in Applied Optics,1 Thomas McAvoy has concluded that the intensity of the fluorescence of the Shroud at different places corresponds sufficiently well with Bob Rucker’s calculated intensity of a postulated neutron flux at those places to constitute evidence for a causal relationship. This could be powerful support for Rucker’s hypothesis.
However, the process of determining the relative UV fluorescence across the Shroud is by no means as simple as it might seem, as McAvoy readily acknowledges. The whole area of the cloth was covered by a theoretical 24 photos, in three strips of eight, each of which was individually processed, by a team led by Vernon Miller in 1978, and reported in the Journal of Biological Photography. 2 Unfortunately the original negatives are lost, so analysis has been carried out on the photos posted on the internet at shroudphotos.com by Gilbert Lavoie and Tom d’Muhala, themselves derived from 4 x 5 inch transparencies made from the negatives by Miller. As Miller seems to have made this set of transparencies using colour filters, McAvoy has tried to restore them to their original colour, as best he can, by comparing them to the photos published in Miller’s 1981 paper.
The exact details of McAvoy’s manipulations are less important than what he finally derived and published, namely three strips of eight photos (although three are omitted), shown in Figure 5 (the middle strip), and Figure 8 (the top and bottom strips).
And here they are again, extracted from the paper, with the middle strip between the other two.
With the best will in the world, we can easily see that this collection is far from uniform, both in colour and intensity. The two rows of red circles, and the two rows of green circles, mark exactly the same places on the cloth, but can be seen to be very different in the photos, and there are differences even horizontally across the strips, especially in the two right hand photos of the top and bottom strips, which are successively bluer and then redder than the others of the same strip.
By pushing the contrast and saturation, the differences can be seen more clearly.
Given this wide disparity in colour and intensity, I do not think it possible to conclude that all the photos were similarly processed. In a reply to my comment to that effect in a recent podcast, 3 McAvoy said: “[Hugh] is wrong about the image colour having any significant effect on my results. I have attached a copy of a paper of mine that was published in Applied Optics before the paper I discussed in the podcast. It demonstrates that image intensity contains essentially all the information in the uv images and that colour contains almost no information (see section 3). This paper refutes Hugh’s colour arguments.” I don’t think it does; in fact I think it misses my point. The differences in colour may have no effect on McAvoy’s consideration of the intensity levels, but they do demonstrate that each photo was independently, and slightly differently, processed, such that we cannot be sure that development times and temperatures, and the freshness of the chemicals involved, were the same for all the photos. In fact, we can be sure that they weren’t, since the same place on the Shroud appears quite differently in two different photos.
Thus, for example, We cannot be confident that the middle of the back fluoresced more brightly than the chest, even though the back photo is brighter than the front one, nor that the top strip fluoresced more brightly than the bottom one. Bear in mind that these two illustrations (enlarged from the image above) cover exactly the same area of cloth…
… and have been carefully manipulated to try to make them identical.
McAvoy went on: “Vern Miller, the photographer who took the uv photos of the Shroud, was a professional and it is doubtful that he would have processed each of his photos differently. In the paper that he published with Pellicori in 1981 that shows the uv images, he discusses the difference between the uv Shroud images and visible light images of the Shroud. Had either the uv or Shroud images been taken with variable lighting, or processed differently, as Hugh contends, such a comparison could not have been made. Lighting and processing were almost certainly not variable.”
I have to disagree, although I dare say that every effort was made to keep things the same. Surely McAvoy tacitly acknowledges this in his omitting three photos completely from his investigation, as they are obvious outliers. All 24 areas were photographed. In their paper, Miller and Pellicori discuss seven photos covering the central strip, and a detailed examination of some of the photos published at shroudphotos.com, by Sam Pellicori, includes one of the dorsal thighs, omitted by McAvoy. 4
Nevertheless, assuming his manipulations valid, McAvoy derives three intensity graphs from the these photos, as follows:
These lines are supposed to correlate to Bob Rucker’s predicted estimations of the radiocarbon age at various places over the Shroud, whose details can be found in a paper on academia.edu. 5 Rucker’s hypothesis predicts that close to the shelf-floor and back wall of the sepulchre, radiation effects were increased due the reflection of neutrons off the hard surfaces, so therefore the dorsal image (lying on the floor) would fluoresce more than the ventral image, and that the whole side of the cloth opposite the side-strip (the side against the wall) would fluoresce more than the side-strip side. The fact that he can see two maxima on two of his graphs, and that the top strip is brighter than the bottom strip is sufficient to convince McAvoy of a correlation, but there are a number of serious flaws to this conclusion, which close inspection will make clear. Here are McAvoy’s graphs again, and images of the photos to help the examination.
McAvoy’s correlations relate to five observations that he lists in his introduction.
1). “Average UV fluorescence is highest in the centre of the dorsal image on the Shroud.” While I agree that after McAvoy’s adjustments, the one photo showing the centre of the dorsal image is brighter than all the others, it is not clear that it truly represents the Shroud’s relative fluorescence. That photo significantly overlaps the one below, so the overlapping areas of both should show the same fluorescence, but this is not the case.
Here are the two relevant photos extracted from above (left), and the colour removed (centre). A small rectangle has then been copied from the top photo to the lower photo, and the lower photo brightened so that the two areas match (right). It is now much less clear that “Average UV fluorescence is highest in the centre of the dorsal image on the Shroud.”
2). “Except for one comparison out of 10, the dorsal side of the Shroud fluoresces more (has higher average intensity) than the frontal side.” Without adjusting the lower band, the dorsal side of the Shroud is represented by seven photos, whose intensities are 46.9, 47.3, 47.9, 48.4, 49.5, 50.7, 55.9, average 49.5. The ventral side is represented by eleven photos, whose intensities are 46.2, 46.4, 46.5, 46.7, 47.1, 47.2, 47.8, 48.8, 49.7, 50.7, 52.6, average 48.2. In this case, the statement is correct. However, if the whole of the lower band is corrected in the same way as the single photo above, the resultant image is on average brighter on the ventral than on the dorsal.
3). “Six out of seven of the top sections of the Shroud fluoresce more than the corresponding bottom sections.” Only if the bottom section is uncorrected, so that where it overlaps the top section, the same place on the Shroud appears darker on the lower strip than it does on the upper. If this anomaly is corrected, so that the same areas have the same intensity, the result looks like this:
Now, as might be expected, we can see that average intensity is much the same all over the Shroud.
4). “Along the centre images, average UV fluorescence intensity goes through two maxima.” This is true, but not saying much. Any random list of six numbers is quite likely to have two maxima, but, assuming that this is not random for a moment, the two maxima are firstly on the middle of the back, as predicted by Rucker’s hypothesis, and secondly between the ventral hips, which is not. We note that the upper strip also has two maxima, between the two heads and between the ventral hips, neither of which concur with Rucker’s hypothesis. The lower strip’s maximum is at the dorsal feet, which again, contradicts Rucker. Of the five maxima, only one is predicted by the neutron radiation hypothesis.
5). “Along the centre images, average UV fluorescent intensity, drops off sharply toward the feet.” The emphasis on the centre images suggests bias, in my opinion. Along both the upper and lower images, average fluorescence intensity actually rises towards the dorsal feet, and at the ventral feet, it may be that the thick strip of non-fluorescent backing material has affected the average UV intensity calculations.
So none of the five observations above can be said to match Rucker’s hypothesis sufficiently well for any conclusions about correlation to be made; and there is another aspect of the photos which also tends to contradict it. For Rucker’s hypothesis to be verified, there should be a variation in fluorescence not only between photos, but also within each one. This is not easy to evaluate, as each one is brighter in the middle and vignetted in the corners, but it can be checked. Take the sequence of three photos of the central series, from the middle of the back to the middle of the chest, which ought to show a drop in intensity from one to the other.
None of the rectangles demarcated on the lower set of photos corresponds to the intensity curve, sketched on the top set, that ought to be present, if McAvoy’s hypothesis of variable fluorescence is viable. The central photo of the ventral shins also shows no sign of the fluorescence dropping off sharply, or, in fact, at all.
For what it’s worth, here are all 24 photos, as I received them, with their filters applied, which I shall comment on beneath.
Bearing in mind that the centre strip overlaps about half of both the top and bottom strips, it is clear that the processing of each strip as a whole, as well as individually along each strip, is individual. It seems to me that photo 1C, 2B and maybe 2G are darker than they should be, and that 2C and perhaps 3D are lighter. We can see this more clearly by making an intensity/height model and looking at the strips sideways on.
If this demonstrates anything, it is that the Shroud fluoresces more or less evenly, and that no correlation between its fluorescence and any predicted neutron irradiation intensity can be shown.
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Thomas McAvoy responds:
Reply to Hugh Farey’s Comments on UV Photos.
Hugh Farey has carried out an interesting and detailed study on the Shroud uv photos that I discuss in 3 journal and 1 conference paper. Commenting on the Shroud UV photos Hugh states:
“With the best will in the world, we can easily see that this collection is far from uniform, both in colour and intensity. The two rows of red circles, and the two rows of green circles, mark exactly the same places on the cloth, but can be seen to be very different in the photos, and there are differences even horizontally across the strips, especially in the two right hand photos of the top and bottom strips, which are successively bluer and then redder than the others of the same strip.”
Let me start by stating that I completely agree with Hugh’s points on colour and intensity in this statement. I do, however, disagree with Hugh’s explanation for the differences in intensity and colour and that they might be caused by different processing of the film used to take the photos. Let me start by addressing intensity and then move on to colour and processing.
Intensity
1. How photos were taken: All the Shroud photos, UV, visible light, etc. were taken using the rail system shown below. 2
This rail system was used so that a large number of images could be taken. 6 In this image A designates the 200 watt xenon strobes, B an AC powerpack, C the camera, and D an adjustment rod to keep the distance to the Shroud fixed. The rail was 14 feet long and it allowed the camera to be moved down the length of the Shroud with pictures taken along the length. Having the rail system facilitated taking a large number of photos in a reasonable amount of time. It is my understanding from talking with Barrie Schwortz that for the visible light photos Miller took, an additional lighting source was used and that Barrie used a light meter to check that the Shroud was uniformly lit. For the uv photos the 2 xenon were turned to a 45o angle as shown below. 2
In taking the UV photos, the output from xenon UV sources was filtered to eliminate visible light from the sources and the camera had a UV filter to eliminate reflected UV light. The resulting UV photos would then show the visible light effects produced by exposing the Shroud to the UV sources. When the camera was moved to a new position, the strobe lights would flash and an image would be taken and the camera would be moved down along the Shroud. The UV images that I excluded as outliers were much darker than the others. I asked Barrie Schwortz about this and he said that for these images he felt that the strobe lights probably misfired resulting in the dark images. Given the large number of photos taken, the misfiring was probably not detected when the photo was taken, but after the film was developed.
[HF comments: What do we mean by “misfired”? If the flashes did not go off, then no image would be seen at all. If only one flash went off, some directional information would be visible on the image. If the Italian voltage was variable, then different intensities could be seen all over the Shroud. Perhaps they are.]
2. Effect of non-uniform lighting: For the UV photography supplemental lighting was not used. As a result, there was what I called a hotspot of incident UV light on the Shroud where the beams from the 2 lights converged. I discussed this point in my 2019 Applied Optics paper. 7 The image below is taken from that paper.
This image shows a contour plot of the image intensity for one of Miller’s UV images (image 3d-UV-S1-E-12_0476 on shroudphotos.com). The hot spot is clearly shown in this contour plot. All of the contour plots for Miller’s UV images look like this one. This contour plot demonstrates that unlike the visible light images, the lighting for the UV images was not uniform. This lack of uniform lighting has to be considered in doing any analysis of Miller’s UV photos, and Hugh did not take this into account.
If I take a UV image of the same object using 2 different uv source intensities, I get 2 different intensities for the resulting UV image which is in the visible range. For example, if 1 UV source had twice the intensity of the other, each pixel at identical spots on the object photographed would have an intensity ratio of ½ when comparing one photo to the other. Since the red and green circles in Hugh’s diagram were exposed to different UV source intensities they cannot be compared in terms of their intensities. These circles can only be compared if the UV intensity that they received is known, and it is not. By contrast, since all the UV images except those at the end of the Shroud are the same size and the section of the Shroud photographed was exposed to the same but non-uniform UV light source, it is possible to compare the average intensities of the images to one another. This is exactly what I did, and the patterns I found agree with Bob Rucker’s neutron simulation results. Much of Hugh’s analysis is based on comparing overlapping UV areas to one another but because of the non-uniform UV lighting intensity such comparisons are not valid.
[HF comments: This is an important point, and I most certainly considered it carefully. Consider the pair of photos showing the back of the man on the Shroud. Here are McAvoy’s contour plots (annotated by me).
The first image shows the two plots superimposed, and the overlapping area shown with a black rectangle. The second pair show the individual images. Areas A and B are exactly the same place on the Shroud, but I certainly accept that because A is close the to middle of the photo, and B close to the outside, it is not fair to expect them both to be at similar intensities. However, sites C and D are also exactly the same place on the Shroud, and this time they are also in a very similar place in terms of the the “hot spot” in the centre of each photo. If the circumstances of the production of both photos were really exactly the same, C and D should certainly be the same colour. That they are not is powerful evidence that the circumstances of the production of the photos were not identical.]
Tom McAvoy replies:
The colours in this image represent image intensity, and they have nothing to do at all with the colours in the UV images themselves. In the CIE Lab colour space colour is independent from intensity. The colours in the above images show intensities and the intensities are from highest to lowest white-gold-green-blue. As the plot shows there is an enormous difference between the intensities of points A and B, order of a 3 to 4 fold difference. For point C and D the difference is less but probably on the order of 1.5 to 2 fold. The image intensities at these 4 points can easily be calculated in the CIE Lab space to determine the exact differences. Since the points being compared are the same, these intensity differences are caused by the difference in the UV light that each point received. It is not correct to say that the C and D points “are also in a very similar place in terms of the “hot spot” in the centre of each photo.” So, this image reinforces my point about why intensities at the same point on different images cannot be compared. Consider taking an ordinary photo of a scene at mid-day and at dusk with exactly the same camera settings and position. The intensity of the image in these 2 scenes would clearly be different. Comparing the intensities at points A and B and C and D is the same as trying to compare the intensities in the 2 scenes at different times of the day.
[And HF responds: Why does McAvoy disagree that points C and D are in similar places in terms of the “hot spot”? If the lighting conditions were the same for both images, then the intensity of the UV light falling on each image varied exactly similarly from a maximum in the middle to a minimum in the corner, and the fluorescence of a single spot illuminated by light of the same intensity should be the same. But it isn’t. Here are our photos, whose colours, loosely delineated with ‘isochromes,’ indicate the fluorescence intensity. A and B are the same place on the Shroud, but, being illuminated with different intensity, fluoresce with different intensity, and are shown in in different colours, but C and D are not only on the same place on the Shroud, but also within the same isochrome. If the original photos had been taken under the same conditions, C and D should fluoresce with the same intensity, but they don’t.
McAvoy in fact, perhaps unwittingly, seems to agree with me when I say that the film, exposure, or processing must have been different for the two pictures. In his case, he explains that two scenes look different under different lighting conditions (midday and dusk). Exactly. The two ‘scenes’ on the Shroud were also taken at ‘midday’ and ‘dusk’; the right hand one must be lightened – and so must all its fellows on the bottom row of the UV photos, in order to provide a fair comparison.]
Colour
1. Analysis: In section 3 of my 2021 Applied Optics paper, 2 I discuss the use of principal component analysis (PCA) to analyse the information content contained in an image. PCA is a statistical data reduction technique that looks to find combinations of variables that explain decreasing amounts of the variance in a data set. PCA can be used to assess what variables contribute to the information content of an image. In using PCA I first converted Miller’s uv images to the CIE Lab colour space 8 shown below.
In this colour space there are 2 colour dimensions (a,b), shown in the disk, and an intensity dimension (L), shown vertically. L, a, and b are orthogonal and they contain different information about the image being analyzed. The mathematics of using PCA to analyse Miller’s UV images is given in my paper, 1 and I don’t want to repeat it here. What I show is that the intensity variable, L, captures greater than 96% of the information in Miller’s UV photos. The remaining information which is less than 4% is contained in the 2 colour variables, a and b. There are a number of reasons why colour differences could occur in Miller’ UV images, but their information content is very small. For example, Miller’s UV source filter allows light between 400 and 410 nm to pass to the camera. Light in this range is in the blue visible spectrum. In essence PCA shows that colour is essentially unimportant in terms of the information contained in Miller’s UV photos. What is much more important is their image intensity. Differences in the colour of Miller’s UV images are not nearly as significant as differences in their intensity.
[I can’t agree with this at all. The lower series of photos is a different colour from the middle and upper series. There must be a reason for that. Maybe the film was slightly different, or the lighting voltage during exposure was different, or there was something different about the processing, or some other factor. That difference may have made a minor difference to the colour – although the colours are easily distinguished – and it may have also have made a difference to the apparent intensity. As McAvoy says, the two aspects, colour and intensity, are orthogonal and therefore unrelated, so it is not possible to say that because the colour difference is minimal, therefore the intensity change is minimal too. I think that McAvoy’s own contour plots show that the intensity difference is significant.]
Tom McAvoy replies:
Hugh places a great deal of emphasis on the colour of the uv images. What my 2021 paper shows is that colour contributes almost no information in the uv images. One can use principal component reconstruction to demonstrate this point. Consider the figure below.
The image on the left is the original D8 image shown in my 2021 paper. This image has 3 independent variables and therefore principal component analysis of it yields 3 principal components. The image in the middle of the figure shows the results of using only the first principal component (PC1) to reconstruct the original image. As discussed in my 2021 paper, the first principal component is essentially the image intensity. The image on the right shows the results of using the second and third principal components (PC2+PC3) to reconstruct the original image. If all 3 principal components are used together (PC1+PC2+PC3) to reconstruct the D8 image, one gets the original image on the left. The last 2 PC’s essentially contain only colour information. The above figure clearly demonstrates that essentially all the information content in the original D8 image is contained in its intensity, and almost none is contained in its colour dimensions. This same conclusion is also true for all of the UV images. In effect one can consider colour differences in the UV images as being similar noise. Hugh is taking the variable that has by far the smallest effect on image information content and magnifying its importance to being the most important variable. As I stated in my earlier reply, colour contributes less than 4% of the information content in uv Shroud images. Intensity contributes greater than 96 % of the information. Focusing on colour overlooks the important information that is contained in the intensity of the Shroud images. These PC results demonstrate that colour in these images does not provide any “powerful evidence” at all about the images, or their production.
[And HF responds: I disagree completely, although I appreciate McAvoy’s calculations. The fact is that the bottom strip of photos is a different colour from the top strip. Rather than pretend it isn’t, I think it fair to enquire the reason for this. Is it random? I think not. I think the bottom strip was, in some way and at some stage, produced differently from the top strip. And, as the comparison with the middle strip demonstrates, the difference in production, however minor, has made that strip appear to show less fluorescence from the same part of the Shroud than the middle strip.]
Processing of images
1. Discussion: Vern Miller, the photographer who took the UV photos of the Shroud, was a professional and it is doubtful that he would have processed each of his photos differently. Reference 6 discusses how the STuRP photographers went about taking their photos and the detailed preparations that they made. I have had numerous discussions with Gil Lavoie about Miller, whom he knew, and Gill attested to Miller’s professionalism. The paper that Miller published with Pellicori in 1981 2 shows the UV images, and they discuss the difference between the UV Shroud images and visible light images of the Shroud. Had each of the UV or Shroud images been processed differently, as Hugh contends, such a comparison could not have been made. Processing was almost certainly not variable.
[I cannot agree with this. If the films, exposure and processing were all the same, then the colour of overlapping areas would be the same, but it isn’t.]
As Hugh points out Miller’s original UV negatives were lost. What was posted on the web were 4×5 transparencies made from the negatives and these transparencies had a distinctly orange hue. This hue likely resulted from Miller experimenting with different colour filters on his photos, in this case a magenta and yellow filter. However, the orange hue does not affect the PCA analysis which is identical for both the orange hue photos and those in my 2021 paper.
[What I will be happy to concede is that the original negatives may have been much more consistent than the extant reproductions appear to show. I have attributed the differences we see to different conditions before exposure (slightly different film, films of different ages or kept at different temperatures, or even X-rayed as they went through customs), or during exposure (most probably due to variations in the electricity supply to the lights) or after exposure, which I have called “processing.” I would be happy to split that into the actual processing of the film in Turin, and into the “post-processing” processing, resulting in the photos as we have them today. It may be that only the last is actually responsible for the differences.]
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1). ‘Shroud of Turin Ultraviolet Light Images: Colour, and Information Content,’ Thomas McAvoy, Applied Optics, August 2021.
2). ‘Ultraviolet Fluorescence Phototography of the Shroud of Turin,’ Vernon Miller and Sam Pellicori, Journal of Biological Photography, July 1981.
3). ‘Shroud Wars: Re-Evaluating the 1988 Carbon-14 Dating,’ Real Seekers, 12 April 2024.
4). ‘Image Analysis of the Miller & Pellicori UV Fluorescence Images of the Turin Shroud,’ Samuel Pellicori, shroud.com, December 2020.
5). ‘The Carbon Dating Problem for the Shroud of Turin, Part 3: The Neutron Absorption Hypothesis,’ Robert A. Rucker, academia.edu, July 2018.
6). ‘Quantitative photography of the Shroud of Turin’, Donald Devan and Vernon Miller, IEEE 1982 Proceedings of the International Conference on Cybernetics and Society, October 1982
7). ‘Analysis of UV photographs of the Shroud of Turin’, Thomas McAvoy, Applied Optics, September 2019.
8). CIE Lab Color Space, https://en.wikipedia.org/wiki/CIELAB_color_space.